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The Cellular Basis Of Working Memory 31 Functional Anatomy of the PFC

The PFC is a collection of distinct architectonic areas. It has traditionally been defined as the region rostral to motor and premotor areas as well as the prominent cortical projection area of the medial dorsal (MD) nucleus of the thalamus (Rose and Woolsey, 1948 Nauta, 1971 Groenewegen et al., 1990 Uylings and van Eden, 1990). The MD projects to the dorsolateral, ventrolateral and ventromedial PFC, and the medial and lateral PFC (Uylings and van Eden, 1990). In the primate, the mid-dorsolateral PFC has received the most attention as a locus for working memory processes, and

Cellular Analyses of Working Memory

The delayed response task has been used extensively to investigate the cellular bases of working memory processes (see Goldman-Rakic 1987, 1990, 1995 for reviews). In the classic delayed response task, monkeys observed an experimenter bait one of two covered food wells. An opaque screen was then lowered to block the monkey's view of the covered food wells. After a delay, the screen was raised and the monkey must choose the previously baited well to obtain the reward. More recently, an oculomotor delayed response task has been used to assess working memory. In this task, First, delay-period activity is not observed on 'mock' trials, when the monkey does not observe a food well being baited (Fuster 1984, 1991). Second, delay-active neurons have 'memory fields' in that individual neurons fire during the delay period of the task, only if a cue was presented previously in a specific spatial location (Funahashi et al., 1989 Goldman-Rakic, 1990). Third, if the activity of these neurons...

DA Modulation of Working Memory Processes Mediated by the PFC

DA strongly modulates both working memory performance and the task-dependent neuronal activity within the PFC. 6-OHDA lesions or microinjection of DA D1 receptor antagonist into the PFC disrupts performance on delayed-response tasks (Brozoski et al., 1979 Sawaguchi et al., 1990b, 1994 Seamans et al., 1998 Zahrt et al., 1997 Aujla and Benninger, 2001). Paradoxically, pharmacologically-induced high rates of DA turnover in the PFC also produce deficits in delayed-tasks (Murphy et al., 1996). Similarly, iontophoresis of either DA or a D1 antagonist at low ejection currents enhance delay period activity, relative to 'background', activity on a delayed response task (Sawaguchi and Matsumura, 1985 Sawaguchi et al. 1986, 1990a,b Sawaguchi, 1987 Williams and Goldman-Rakic, 1995). Thus, the action of DA in the PFC is highly complex, and both increases and decreases in DA activity can enhance or attenuate performance on working memory tasks and task-related neural activity.

Evaluation of Working Memory

Delayed-alternation tasks are widely considered to be particularly sensitive in demonstrating working memory impairment after lesion of the PFC in all species of mammals (Markowitsch and Pritzel, 1977). In rats, this task, usually performed in a T-maze (Moran, 1993 Zahrt et al., 1997), is one of the most common methods for evaluating spatial working memory performance associated with the PFC (Van Haaren et al., 1985). As shown in Figure 1, working memory performance in rats was examined using the T-maze apparatus (Mizoguchi et al., 2000). Briefly, the animals' food allowance was maintained at about 90 of the normal intake until the end of the T-maze test. The rats were initially habituated to the T-maze apparatus dimensions stem arm, 75 length (L) x 13 width (W) x 20 height (H) cm two branch arms, 50 (L) x 13 (W) x 20 (H) cm each for 4 days until

Relationship between Working Memory Impairment and Reduced Dopaminergic Transmission

Although the types of DA receptors, involved in the working memory function in the PFC, remain to be determined, several studies have identified the importance of Di receptors (Sawaguchi and Goldman-Rakic, 1991 Seamans et al., 1995). As shown in Figure 4, the stress-induced working memory impairment was ameliorated by Di receptor stimulation in the PFC with the Di receptor agonist SKF 81297 in a dose-dependent manner, suggesting that this impairment is caused by reduced Di receptor stimulation. The reversal of the SKF 81297 response due to the Di receptor antagonist, SCH 23390, confirms the hypothesis of action at the Di receptor rather than nonspecific drug actions. These results are consistent with the observation that a low dose (e.g. 100 ng kg) of SKF 81297 ameliorates spatial working memory impairment in aged monkeys with naturally occurring DA depletion (Arnsten et al., 1994 Cai and Arnsten, 1997). In addition, the doses of SKF 81297 that had a partial or sufficient ameliorative...

Neuronal Mechanisms For Working Memory Processes

By examining prefrontal task-related activity while monkeys performed various working memory tasks, evidences for neuronal mechanisms related to working memory have been accumulated. For example, delay-period activity has been considered to be a neuronal correlate of the temporary active storage mechanism of information. Delay-period activity has been shown to represent a variety of information including the spatial position, the physical feature of the stimulus, the forthcoming behavioral response, the quality of reward that the subject would receive, the difference of the task, and the rule of the task. Although delay-period activity could represent a variety of information, the information represented by delay-period activity is only the information relevant for the task performance. In Although the evidences for the neuronal mechanisms of short-term storage of information have been accumulated, neuronal mechanisms for processing information is poorly understood. To understand...

Subcomponents Of Working Memory

As we mentioned previously, working memory is thought to contain a number of different storage buffers that mediate the retention of different types of information. The major division proposed by Baddeley (1986) is between verbal and visuo-spatial information, and this idea finds support in the behavioral data. For example, requiring subjects to repeat the the the interferes more with verbal than spatial memory (Baddeley et al., 1984), whereas requiring subjects to trace a moving stimulus with a finger or stylus interferes more with visuo-spatial memory (Baddeley et al., 1975). Thus, primary task performance suffers more when the secondary task is of the same modality than when it is of the other modality, which is commonly taken as evidence of separable pools of cognitive resources.

The Contribution Of The Pfc To Working Memory Not Shortterm Memory

In 1936, Jacobsen first demonstrated that lesions of the PFC of primates impair performance of the delayed-response working memory task and this finding has been replicated by numerous investigators (see Funahashi and Kubota, 1994 for review). However, there has been considerable difficulty in understanding the nature of this deficit. Working memory and short-term memory have been related theoretically, and therefore there has been a lasting tendency to view working memory processes mediated by the PFC simply as short-term memory processes. There is considerable evidence against the idea that the PFC subserves simply short-term memory processing. First, short-term memory loss is generally not a result of selective PFC damage (Petrides, 1996). Patients with PFC damage show no deficits on traditional short-term memory tasks of recognition or recall, and such patients have a normal digit span and are unimpaired in the memory component of intelligence tests (Hebb, 1939, 1977 Stuss and...

Working memory

This scenario illustrates the use of more than one type of memory. Janet stores the locker number and combination in short-term memory (STM), and she maintains the information by rehearsing it. After Janet retrieves the ball and redirects her attention to choosing teams for the football game, she may forget this information. Jacob does not need to rehearse his combination continually to maintain it rather, his frequent use of his combination and the meaningfulness of this information have helped him to store it in long-term memory (LTM). If someone later asks Janet where she got the football, she will retrieve that information from her episodic LTM. Episodic memory holds information about how things appeared and when they occurred it stores things that depend on context. The language comprehension of the children also illustrates another type of LTM. Semantic LTM, or semantic memory, holds all the information they need in order to use language it includes not only words and the...

Working Memory Task

And Genome Sequencing

To examine neuronal mechanisms of working memory processes, singleneuron activities recorded from DLPFC have been analyzed while monkeys performed a variety of working memory tasks. The working memory task often selected for neurophysiological experiments is the delayed-response task, because the delayed-response task requires working memory of spatial position (Goldman-Rakic, 1987 Funahashi and Kubota, 1994 Fuster, 1997) and because delayed-response deficits have been observed by the selective lesion of the cortex within and surrounding the principal sulcus (area 46) (Goldman-Rakic, 1987 Funahashi et al., 1993a Petrides, 1994 Fuster, 1997). Fuster and Alexander (1971) and Kubota and Niki (1971) were the investigators who first examined single-neuron activity in DLPFC while monkeys performed a manual delayed-response or delayed alternation task. Since then, many studies have been performed to examine the characteristics of memory-related activity and other types of activity in the...

The Effect of DA in PFC Enhancing Robustness

When viewed collectively, it is clear that DA has multiple, often contradictory effects on the activity of PFC pyramidal neurons. Durstewitz et al. (2000) and Durstewitz and Seamans (2002) have argued that these diverse actions mediated by DA converge on a single function increasing robustness of working memory representations in PFC networks. Specifically, D1 enhancement of NMDA and persistent inward currents causes strongly activated assemblies of interconnected neurons to exhibit a significant boost in sustained activity levels. Since assemblies of neurons are thought to be regulated by interneuronal activity (Lewis et al., 1999), the increased activation of one assembly may quell activity in nearby competing assemblies. This effect is further enhanced by the D1-mediated increase in widespread (Seamans et al., 2001b) but not cell to cell unitary IPSCs (Gao et al., 2003). Collectively, this leads to the acceleration in the activation of one assembly at the expense of activity in...

The Role of D2 Receptors in PFC Expanding Focus

This hypothesis outlined above is valid only for the case of strong D1 receptor stimuli, which would be a common occurrence, given the disproportionate densities of D1 relative to D2 receptors in the PFC (Vincent et al., 1993 Gaspar et al., 1995). In contrast, conditions favoring strong activation of D2 receptors would actually reduce pyramidal cell excitability (Gulledge and Jaffe, 1998, 2001), NMDA currents (Zheng et al, 1999), and GABAa currents (Seamans et al, 2001b) in pyramidal neurons. Strong D2 activation would therefore have the opposite effect from D1 activation, with assemblies showing spontaneous transitions to persistent activity states (Durstewitz et al., 2000) and multiple assemblies co-activated nearly simultaneously. Under this regime, many items may be encoded in working memory yet none particularly robustly. These ideas are shown graphically in Figure 1.

Summarizing Hypothesis

Five main points were presented above 1) Working memory within the PFC may be best represented as working with memory to incorporate the online monitoring and manipulation of mnemonic information, 2) Persistent delay-period activity in PFC underlies the ability to work with memories, 3) Persistent activity associated with working memory is affected by behaviorally significant stimuli, 4) DA neurons signal stimuli of behavioral significance, and 5) DA affects working memory performance and the cellular activity encoding working memory information in the PFC. According to our hypothesis (Durstewitz et al., 2000 Durstewitz and Seamans, 2002), if a stimulus of significance is encountered, the increased DA release due to elevated VTA firing enhances the encoding of information in working memory without providing any specific information. Figure 1 Theoretical two state dynamics for working memory buffers in the PFC. State 1 is characterized by low inhibition due to D2 down-regulation of...

DA Modulation of Neural Ensembles and Synaptic Plasticity

The Di facilitation of UP states may contribute to working memory. A membrane depolarization prolonged by Di receptor activation can explain the sustained action potential firing typically observed in PFC neurons during working memory tasks in primates. Indeed, but not receptor blockade disrupts sustained spike firing in PFC neurons and working memory performance (Goldman-Rakic, 1995, 1999).

Alteration of Prefrontal Response to Dopamine in a Developmental Animal Model of Schizophrenia

A neonatal VH lesion in rodents and primates has been proposed as a developmental animal model of schizophrenia. These animals exhibit abnormal behaviors such as exaggerated locomotion in response to DA agonists (Lipska et al., 1993), NMDA antagonists (Al-Amin et al., 2001), or stress (Lipska et al., 1995), but only after puberty. This time course is similar to what is observed in the onset of symptoms in schizophrenia (Weinberger, 1995). In addition, cognitive deficits in working memory (Lipska et al., 2002), latent inhibition (Grecksch et al., 1999), or sensory gating (Lipska et al., 1996), and reduction of social interactions (Sams Dodd et al., 1997) are commonly observed in animals with neonatal VH lesion as well as in schizophrenia patients. Thus, this animal model stresses the link between early-life limbic compromise (Lipska and Weinberger, 2000) and delayed symptom onset in schizophrenia. Because the VH has a massive projection to the PFC (Jay et al., 1989 Jay and Witter,...

Possible Network Mechanism of Prefrontal Dysfunction in Schizophrenia

Hypofrontality is a major component in schizophrenia pathophysiology (Weinberger et al., 1994). It has been linked to the severity of negative symptoms (i.e. social withdrawal and lack of affect) (Wolkin et al., 1992), as well as to a variety of cognitive deficits observed in this disorder (Carter et al., 1998). But what really is hypofrontality Traditionally, it is viewed as lack of PFC activation during tasks that would normally engage this brain region, measured as changes in regional cerebral blood flow (Fig. 5A) (Weinberger et al., 1994 Andreasen et al., 1997). This causes deficits in working memory resembling those seen in PFC lesions (Muller et al., 2002). Our finding of enhanced firing in PFC neurons during VTA-evoked depolarizations in animals with a neonatal VH lesion would suggest that in those animals, the PFC becomes hyper-, but not hypo-, active upon DA activation. Figure 5 Relations between working memory capacity or D, receptor activation and PFC activation. A....

Prelimbic Neuronal Activity during Behavior

The 50 Hz 2 sec conditioning stimuli were used in early studies (Hirsch and Crepel, 1990 Law-Tho et al., 1995). This type of long trains of pulses have been used to induce LTP in many hippocampal studies, since hippocampal neurons can show relatively long high-frequency discharge during, for example, spatial exploration (O'Keefe and Nadel, 1978). Stimulus patterns mimicking theta rhythm are a more adapted version (Larson et al., 1986). Because ventral hippocampus sends monosynaptic projection to the prelimbic area in the rat (Jay and Witter, 1991) and because the hippocampal-prelimbic connection is important for spatial working memory in the rat (Floresco et al., 1997), theta burst-like stimuli (e.g. 4 pulses at 100 Hz, repeated 10 times at 5 Hz) were adopted in prelimbic studies and shown to induce LTP (Vickery et al., 1997 Morris et al., 1999). It is likely that other monosynaptic projection fibers also converge to prelimbic area and convey sensory information (Perez-Jaranay and...

Prefrontal Pathology and LTD

LTD facilitated by dopamine in non-primed naive neurons might best model certain pathological processes (Fig. 6, right). For example, Moghaddam, Adams, and their colleagues (Moghaddam et al., 1997 Adams and Moghaddam, 1998 Moghaddam and Adams, 1998) showed in rats that the injection of phencyclidine (PCP), a psychotomimetic NMDA antagonist that causes schizophrenia-like symptoms in humans, induces some 600 increases of prefrontal dopamine efflux as well as two-fold increases of glutamate (also Suzuki et al., 2002). A pharmacological block of the glutamate increase blocks PCP-induced working memory impairment (Moghaddam and Adams, 1998), suggesting that the coincident efflux of dopamine and glutamate is necessary for the memory impairment. Note that prefrontal LTD appears to require strong dopaminergic input coincident with glutamatergic input and occurs in the presence of a NMDA antagonist (Otani et al., 1998). Human schizophrenia may involve two pathological phases of dopaminergic...

Dopamine Regulates Synaptic Plasticity In The Prefrontal Cortex In Vivo

The mesocortical dopamine system which arises from cell bodies in the ventral tegmental area (VTA) terminates primarily in the PFC and targets the dendritic spines and shafts of layers V-VI pyramidal neurons (Van Eden et al., 1987, Sesack et al., 1995). In view of the role of dopamine in working memory and other aspects of cognitive function, a number of electrophysiological studies have explored the action of dopamine on prefrontal neurons and evoked synaptic responses, but failed to give a consistent picture of dopamine actions. Considering that the dopamine system does not function on its own but rather interacts with afferent projections and modulates their ability to integrate a proper input, we studied the effects of dopamine on hippocampal-prefrontal synaptic plasticity and investigated the role of dopamine receptor subtypes using multiple approaches.

Behavioral Significance of Dopamine Control of LTP

From the data summarized in this chapter, it appears that dopamine is involved in the selective gating of information flow from the hippocampus to the PFC. In both rats and primates, dopamine or the mesocortical dopaminergic system is known to be important for learning in delay-dependent tasks requiring efficient working memory (Brozoski et al., 1979 Simon et al., 1980 Sawaguchi and Goldman-Rakic, 1994). A certain stage of dopamine with an optimal level of receptor activation appears to be essential for the cellular mechanisms of working memory, and interestingly, similar requirements are also true for a proper hippocampal-prefrontal LTP expression (Williams and Goldman-Rakic, 1995 Gurden et al., 2000). The hippocampal input to the PFC could be one important target of dopamine modulation in this process. Indeed, the functional implication of the hippocampal-PFC pathway has been explored in short-term memory processes and the performance in a spatial delay-interposed task (radial maze)...

Impairment Of Ltp In Response To Stress

System, and acute stress is also known to induce a higher glutamate efflux in the PFC. Although a key initial event in stress is long-term changes in multiple neurotransmitter systems, particularly the release of catecholamines (McEwen, 2000 Vermetten and Bremner, 2002), it is only recently that this region has been considered as an important player in the regulation of circulating glucocorticoids by its direct connection with the hypothalamus (Dioro et al., 1993 Sullivan and Gratton, 2002). Chronic stress has also been reported to impair spatial working memory (Mizoguchi et al., 2000 also see Chapter 7 of this volume) and induce atrophy in distal dendrites of cortical neurons (Trentani et al., 2002).

Stress And Prefrontal Cortical Dysfunction In The

Keywords Stress, prefrontal cortex, hippocampus, dopamine, serotonin, acetylcholine, working memory, reference memory, delayed-alternation task, T-maze, rotarod, depression, rat. Abstract Although the mechanism responsible for cognitive deficits or a depressive state in stress-related neuropsychiatry disorders has not been fully elucidated, dopaminergic or serotonergic dysfunction in the prefrontal cortex (PFC) is thought to be involved. In rats, the mesoprefrontal dopaminergic system, in particular, is activated in response to acute stress, whereas chronic stress reduces dopaminergic transmission in the PFC, causing working memory impairment through a Di receptor mechanism. However, chronic stress does not affect reference memory, which is attributed to hyperactivity of hippocampal cholinergic transmission. In addition, chronic stress induces a depressive behavioral state, caused by a reduction in dopaminergic and serotonergic transmission in the PFC. These findings provide important...

Dopaminergic Transmission in the PFC

It has been shown that DA has a beneficial influence on the spatial working memory function of the rat PFC (Simon, 1980 Bubser and Schmidt, 1990). In addition, dopamine release in the PFC shows vulnerability to acute stress (Abercrombie et al., 1989). Considering these findings, it is conceivable that chronic stress may affect dopaminergic transmission in the PFC. Indeed, a microdialysis study revealed that chronic stress greatly decreased the DA release in the PFC (Fig. 3). This finding supports the chronic stress-induced working memory impairment (Fig. 2).

Tissue Concentration of DA and its Metabolites

Homovanillic acid (HVA), in the PFC during the chronic stress session and the recovery period (Table 1). This neurochemical study revealed that short-term stress (1 week) increased the concentrations of DOPAC and HVA, indicating an increase in DA turnover and thus supporting the concept that a hyperdopaminergic mechanism is responsible for acute stress-induced working memory impairment (Arnsten and Goldman-Rakic, 1998). However, these increases were not observed in the long-term stressed (4 weeks) rats, and the stressed and recovered rats showed a marked decrease in the concentrations of DA, DOPAC, and HVA, supporting the reduced DA release (Fig. 3). Thus, during the chronic stress session and the recovery period, the dopaminergic neurons innervating in the PFC are initially activated, but subsequently inactivated. Also, the chronic stress-induced reduction in DA release (Fig. 3) is thought to be related to a decrease in the DA stored at the synaptosomes. As regards the mechanism of...

Cholinergic Transmission in the Hippocampus

Several reports have shown that the hippocampal cholinergic system is also involved in the formation and maintenance of short-term working memory, or retention and retrieval processes in long-term reference memory (Pope et al., 1987 Murai et al., 1995 Izquierdo et al., 1998). Therefore, we examined the effects of chronic stress on acetylcholine (ACh) release in the rat hippocampus. Consequently, chronic stress increased the hippocampal cholinergic transmission in response to stimuli (Mizoguchi et al., 2001 b), suggesting that hippocampal cholinergic neurons become hypersensitive with chronic stress. Gonzalez and Pazos (1992) have also shown that chronic immobilization stress causes an increase in the density of muscarinic ACh receptors in the hippocampus. Thus, the hippocampal cholinergic system may be activated by chronic stress. As regards the significance of this cholinergic hyperactivity, it is possible that the hyperactivity occurs in compensation for the reduced dopaminergic...

Introduction Pfc Function

And, in general, to learn.' A central position in associational processes and learning is still (or again) considered essential in the PFC function. Later reviewers stressed the importance of PFC in inhibition and short-term memory (Mishkin, 1964 Goldman-Rakic, 1987 see also Roberts, 1998), but Fuster (1997) argued that these functions, together with motor set, underlie the 'superordinate prefrontal function of temporally organizing goal-directed behavior'. The PFC is now thought to form and actively maintain representations of 'goals and the means to achieve them' (Miller, 2000) and to learn and use rules or strategies (Wise et al, 1996). Thus, in the end, it provides the means for cognitive control and flexibility of behavior (Miller and Cohen, 2001). This is relevant in view of the outcome of the pioneer imaging studies performed twenty years ago, which indicated that it participates in any form of structured brain work a subject can do when awake (Roland, 1984). All these reviews...

Components Of The Aretask

A specific retrieval cue was not used in the ARE task (except for the shaping phase) where up to the present no inactivation studies have been carried out. However, retrieval of previously stored task-relevant information may be an important function of the PFC, as a working memory task learned before a PFC-lesion was more affected than the same task acquired after the lesion (Broersen, 2000 see also Becker et al., 1981). It is possible that the late impairment after inactivation of the lateral PFC would fit with these findings (see above), but they obviously need more experimental support.

The Pfc And Its Catecholamine Afferents In Strategy Switching And Reversal Learning

In primates, (dorso)-lateral PFC damage has been associated strongly with deficits in shifting attentional set between, as compared to within, dimensions (Owen et al., 1991 Dias et al., 1996). Tests involving intra- and extra-dimensional shifts using various dimensions have been described (Shepp and Eimas, 1964 Oswald et al., 2001), but only the task recently developed by Birrell and Brown (2000) has been tested in relation to the PFC function in rats. Their results suggest a similar dependence of extradimensional shifts on PFC activity (the medial PFC) as in primates, whereas the emotional shift (or reversal, Dias et al., 1996) depends on the orbital PFC. Neurons in the latter area code the current incentive value of a cue (Schoenbaum and Setlow, 2001). In the terminology of Kesner (2002), they support rules based on reward value or affect. The tripartite memory system of Kesner (2000, 2002) appears to give the most versatile system to probe and explain PFC-dependent functions. Thus,...

Delayperiod Activity As A Neuronal Correlate Of Temporary Information Storage

A majority of neurons exhibited tonic sustained excitation during the delay period, although some prefrontal neurons exhibited a gradual increase or decrease of their discharge rates during the delay period. The duration of delay-period activity depended on the length of the delay period. The duration of delay-period activity was prolonged or shortened, when the length of the delay period increased or decreased, respectively (Fuster, 1973 Funahashi et al., 1989). In addition, delay-period activity was not observed or was truncated when the subject made an error (Fuster, 1973 Funahashi et al., 1989). These results support the notion that delay-period activity is a neuronal correlate of a temporary storage mechanism of working memory. delay period varied monotonically depending upon the stimulus frequency when monkeys performed a tactile frequency discrimination task. They found that the discharge rates during the delay period either increased or decreased monotonically when the...

Dopamine Cognition And Arousal Insights From Experimental Studies From Rats And Monkeys

The first study to implicate DA in prefrontal processing was reported by Brozoski, Rosvold, and Goldman in 1979 (Brozoski et al., 1979). They showed that 6-OHDA infusions into the dorsolateral PFC, which destroyed catecholamine terminals, impaired performance on a spatial delayed alternation task. This impairment was nearly as severe as that induced by surgical ablation of the dorsolateral PFC itself, but unlike surgical ablation, the 6-OHDA lesion-induced impairment could be reversed by treatment with the mixed D1 D2 DA receptor agonist, apomorphine. This study has subsequently been replicated in marmosets (Roberts et al., 1994) and rats (Simon, 1981) with 6-OHDA lesions of the PFC. Consistent with an involvement of DA in spatial working memory, DA levels have been shown to increase in the PFC during working memory performance (Watanabe et al., 1997), and the neuronal 'memory field' activity of PFC neurons is It appears that both excessive as well as insufficient DA receptor...

Cognitive Performance And Its Relationship To Dopamine Levels In Humans

Administration of the D2 DA receptor agonist bromocriptine to young healthy human volunteers was observed to improve performance on a test of executive function in those individuals with an apparently low working memory capacity while impairing performance in those individuals with a high working memory capacity (Kimberg et al., 1997). Similar results were described by Mattay et al. (2000), examining the effects of dextro-amphetamine on performance of an n-back working memory task. To test the hypothesis that such inter-subject variability in cognitive performance and the differential effects of DA-ergic stimulation may be a consequence of underlying differences in baseline DA levels of individual subjects, Egan et al. (2001) exploited the fact that a common functional polymorphism (Val

Functional Neuroimaging And The Prefrontal Cortex Organization By Stimulus Domain

Keywords Prefrontal cortex, spatial memory, object learning, verbal memory, working memory, frontal lobes, human memory, functional MRI, positron emission tomography. Abstract Working memory is the set of cognitive operations that maintains and processes information on-line. It has been characterized both as a mental workspace (Baddeley, 1986) and as a set of operations that allow the efficient allocation of cognitive resources (Carpenter et al., 1990, 1999). Working memory typically is thought to be of limited capacity, between 4-7 items (Miller, 1956 Cowan, 2000), of limited duration, on the order of seconds (Peterson and Peterson, 1959) and as involving a number of separable sub-mechanisms, among these, rehearsal processes, domain-specific storage buffers, and a set of executive processes that are thought to operate on currently active information (Baddeley, 1986 Smith et al., 1996). This chapter focuses on the cognitive operations mediated by the frontal lobes in the service of...

Evidence For Prefrontal Organization By Information Domain

4.1 Verbal versus Visuo-Spatial Working Memory Like verbal processing, spatial processing likely occurs to some degree in both hemispheres, but unlike verbal coding, it is thought to rely disproportionately on the right hemisphere. Split-brain patients can perform visuo-spatial pattern tasks better with their left hands (controlled by the right hemisphere) than with their right (Gazzaniga, 1970 Gazzaninga and LeDoux, 1978). Furthermore, intact subjects also exhibit a left-hemisphere dominance for verbal information and a right-hemisphere dominance for visuo-spatial information (e.g. Kimura, 1973). In light of this verbal-left, spatial-right distinction in hemispheric specialization, researchers have speculated that these divisions might be also hold for working memory. Reuter-Lorenz and Miller (1998) have examined the extent to which split-brain patient V.P. shows laterality effects on spatial and verbal working memory tasks. V.P. was required to attend to a central fixation point and...

Acquisition of New Behaviors and Memory Formation

Measures of large-scale oscillatory brain activity have also been used to describe PFC functioning during target detection tasks. In a series of EEG experiments, Tomberg and Desmedt (1998 also Tomberg, 1999) reported enhancement of frontal gamma phase locking during somatosensory target detection. The timing of this response suggested parieto-frontal interaction, organizing perceptual input and action readiness. Using a similar paradigm in the visual modality, Hermann and collaborators (Hermann et al., 1999) reported evoked (phase-locked) gamma responses at frontal electrode sites, which were greatest when stimulus features were task-relevant. These authors concluded that frontal gamma activity is associated with top-down processes, comparing incoming information with templates in working memory. In line with these results, auditory targets were effective in enhancing phase-locked GBA over frontal leads, when paired with a motor task (Yordanova et al., 2001). In this study,...

The Overdose Hypothesis In Parkinsons Disease Its Relevance To Cognition And The Inverted Ushaped Dopamine Function

Is cell loss in the substantia nigra leading to severe DA loss in the dorsal parts of the striatum as well as additional DA loss in the PFC. Although the disease is mainly a movement disorder, patients also exhibit significant cognitive deficits, even in the earliest stages of the disease. Given strong connections between the dorsal parts of striatum and the dorsal parts of the PFC (Alexander et al., 1986), it is not surprising that the pattern of cognitive deficits resembles that seen in patients with dorsal frontal lobe damage (Owen et al., 1992). Thus, like frontal lobe patients, mild PD patients exhibit significant impairment on tests of attentional set shifting (Downes et al., 1989 Owen et al., 1992), task-set switching (Hayes et al., 1998 Cools et al., 2001a), planning and spatial working memory (Owen et al., 1992, 1995). These deficits are sometimes remediated following administration of L-DOPA medication (Lange et al., 1992), a precursor affecting primarily levels of DA in the...

Tms Studies On Episodic Longterm Memory

Despite the increasing interest in TMS as one of the most attractive tools for neuroscientists (Chicurel, 2002), its application to the investigation of episodic long-term memory is still limited. A Medline search in the first week of the year 2003, using TMS rTMS, prefrontal cortex, and memory as keywords, detected the articles most of which deal with verbal visual working memory (n 5) and saccadic eye movements (n 3). Among remaining papers, only four articles (one of which is a review) fully matched our request and dealt with episodic memory. These relevant papers will be reviewed here. In addition, we will discuss some recent works from our research team, which are in press (Sandrini et al., 2003) or have been published only in abstract form (Rossi et al., 2003). Episodic memory is a neurocognitive system that enables human beings to form a permanent record of everyday events, and is therefore essential for daily life (Tulving, 2002 for an exhaustive review). The ability to...

Whither The Prefrontal Cortex Of The

It is less obvious just what the class-common functions of the frontal cortex might be, but we would anticipate that if the frontal cortex of mammals developed because all mammals face common functional problems, then we should be able to identify class-common functions of the frontal cortex. One place to begin searching for class-common frontal functions is to consider what animals use sensory inputs for. The most obvious function is to guide behavior on line, such as in the visuomotor control of movements in space or the identification of food items using visual, tactile, and olfactory information. But the sensory world has far more information available than the brain can handle at one time so there must be some system to select information as well as to focus and maintain attention. Similarly, although behavior can be directed to sensory stimuli on-line, it can also be related to information that is stored or expected. Stored information may be in a type of scratch-pad memory...

Cholinergic and Monoaminergic Gating Systems

The cholinergic and monoaminergic inputs are presumed to modulate whatever functions are ongoing in the prefrontal areas. In recent years, there has been an attempt to demonstrate how these inputs contribute to working memory and attention, in particular (e.g. Sagawachi and Goldman-Rakic, 1994 Ragozzino, 2000). In addition, various lines of work suggest that there are dynamic changes in dopamine release in the mPFC when there are changes in the environmental demands on animals, especially under

Effects of Lesions to the mPFC

It was demonstrated in the early 1970s that lesions to the mPFC and OFC in rats produced very different behavioral syndromes, and that these behavioral changes were strikingly similar to those observed in primates with lesions to the dorsolateral and OFC regions, respectively (Table 1 for reviews see Kolb, 1984, 1990). For example, damage to the mPFC area produces severe deficits in acquisition and retention of working memory tasks such as delayed response (Kolb et al., 1974), delayed alternation (Wikmark et al., 1973), different types of delayed nonmatching-to-sample tasks (e.g. Dunnett, 1990 Otto and Eichenbaum, 1992 Kolb et al., 1994a), and related tasks (e.g. Kesner and Holbrook, 1987). More recently, deficits have been shown in various types of attentional tasks (e.g. Muir et al., 1996) and in a task requiring a shift of attention from one set of cues to another (Birrel and Brown, 2000). Medial frontal lesions also produce disruptions to the production of various motor and...

Effects of Lesions to the OFC

There is much more parsimony in reviews comparing the effects of OFC lesions in rodents and primates (e.g. Schoenbaum and Setlow, 2002). The OFC receives significant olfactory and taste input, and although OFC lesions do not produce deficits in olfactory or taste discriminations, they do produce deficits in tasks requiring working memory for odor or taste information (e.g. Otto and Eichenbaum, 1992 DeCoteau et al., 1997 Ragozzino and Kesner, taxa, and certainly between rodents and primates, there are relatively discrete regions across both orders that are involved in higher order cognitive functions (e.g. working memory, directed attention) as well as social and affective behavior and motor programming. As we look for models of prefrontal plasticity, it thus appears that the rat is an excellent model for understanding prefrontal function and plasticity in primates. We now turn our attention to the nature of prefrontal plasticity in rodents.

Frontal Lobe Plasticity in the Injured Brain

But what happens if there is cerebral injury during development Recall that Hebb (1949) emphasized that the development of the PFC is especially important to problem solving in adulthood. We could predict that early injury to regions with intimate connections with the frontal lobe could disrupt normal frontal lobe development. This idea has not been well studied, with the exception of Weinberger and his colleagues who have studied the effects of neonatal injury to the ventral hippocampus (e.g. Raedler et al., 1998). In adulthood, these animals show various symptoms characteristic of rats with prefrontal injuries, such as hyperactivity and deficits in social behavior and working memory (e.g. Sams-Dodd et al., 1997). These functional deficits are ameliorated by antipsychotic drugs and are associated with a decrease in the metabolites of dopamine in the medial frontal region, which has led the

Conclusion

Working memory buffers in PFC do not simply hold memory information transiently but rather work with memories to guide action in a dynamic fashion according to internal and external stimuli. In conditions where highly important stimuli are encountered, PFC networks may establish a limited number of goal states perhaps via predominant activation of D1 receptors, at the expense of all competing information and goal states. In less stressful situations, PFC networks may deal flexibly with mnemonic information to guide forthcoming actions in manner that is less dire and more exploratory, perhaps via predominant activation of D2 receptors. The goal of future research will be to determine what types of stimuli and DA release events activate D1 versus D2 classes of DA receptors in PFC, and whether this varies on an individual or context dependent basis. Such information may provide a novel way to look at working memory processes in the PFC under normal and pathological conditions.

General Conclusion

The potential to modify prefrontal synapses by hippocampal stimulation and the significant contribution of the mesoprefrontal dopamine circuit in these changes illustrate how synaptic plasticity, at least in the PFC, may be differentially regulated according to the animal's or human's behavioral state. Mesoprefrontal dopamine activity is known to affect behavioral performance in both humans and animals on tasks dependent on PFC function that implicate the planning of behaviors in appropriate sequences. The hippocampal-PFC communication can be considered as an important network for the transfer of spatial information (context) that is used to execute prospective strategies for action. The conclusion emerging from these data is that the hippocampus, the PFC, and the mesoprefrontal dopamine system are in a cooperative relationship with respect to working memory. Whether these cortical networks subserve different sub-functions in the overall cognitive operation when information needs to...

Clinical Relevance

Are associated with profound hypometabolism, involving the medial PFC in particular. Similarly, it has been reported that both bipolar and unipolar depressives are characterized by decreases in cerebral blood flow and the rate of glucose metabolism in the PFC (Drevets et al., 1997). Furthermore, agents such as bupropion that enhance DA transmission have been successfully used as antidepressants (Calabrese and Markovitz, 1991). Various other serotonergic antidepressants, such as fluoxetine, clomipramine, and imipramine, also increase the release of DA as well as 5-HT in the rat PFC (Tanda et al., 1994), indicating that the PFC is a target site of antidepressants. These findings implicate a reduction in dopaminergic and serotonergic transmission in the PFC in the pathogenesis of depression. A similar association has been suggested in patients with Parkinson's disease who suffer from depression (Cummings, 1992 Deutch, 1993). Depression occurs in large populations of patients with...

Concluding Remarks

In this chapter, I have described the evidence that exposure to chronic stress in rats is sufficient to produce PFC dysfunction. Thus, dopaminergic and serotonergic neurons in the PFC show vulnerability to chronic stress, which causes working memory impairment or a depressive state, whereas cholinergic neurons in the hippocampus show resistance to this stress, which may be involved in the maintenance of reference memory (Fig. 9). These findings will lead to a deeper understanding of the mechanisms underlying the pathogenesis of stress-related neuropsychiatric disorders.

Conclusions

The evidence found in the neuroimaging literature seems to support a division of PFC that is consistent with a loose organization based on stimulus modality. This evidence is not entirely consistent, but the general trend across studies seems to favor three principles. The first is that verbal working memory relies on left-hemisphere mechanisms, whereas spatial working memory relies on right-hemisphere mechanisms. The second is that object working memory is less lateralized than either spatial working memory or verbal working memory. This may be because objects occupy a representational middle-ground, or because subjects simply use a mixture of strategies to maintain them in memory. The third principle is that working memory for objects is mediated by more left ventral PFC regions and spatial information is mediated by more dorsal regions, especially on the right. These findings imply that the what and where processing division extends into PFC. One important question is why our...

Kuei Yuan TSENG

On one hand, we have accumulated knowledge on the properties of neurons and synapses in the prefrontal cortex as well as the actions of critical neuromodulators such as dopamine. On the other hand, behavioral and cognitive neurosciences have begun to reveal the fascinating role of the prefrontal cortex in such mental processes as working memory, attention switching and rule following, and long-term memory. Needless to say, our ultimate goal as neurobiologists is to know what relationship there is between these cellular and cognitive processes. This volume is meant to serve as a comprehensive introduction towards that goal. Readers will be informed, for example, of how plasticity of prefrontal neurons is regulated, how it is involved in certain cognitive processes in rodents, and how the rodent models can apply to the primates. Equally, the prefrontal cortex-dependent cognitive processes in human and non-human primates are themselves analyzed in detail, which will invite the readers to...

Memory and Unconscious

The emotions can be seen as being part of an adaptive process in relation to the cognitive system and the asymmetrical hemispheric functions (Gainotti, Chap. 5, this volume). It is the right hemisphere that seems to be delegated to organizing the lower level of emotions and integrating it with their higher level. Recent observations suggest that the right hemisphere is involved in the various forms of unconscious emotional memories those produced by emotional conditioning and those represented by the various dimensions of the implicit memory. This latter function is of particular interest for psychoanalysis since it links the emotional memory to the unconscious and gives the right hemisphere the important role in the organization of this last function of the mind. The discovery of the dual memory system 7, 32-34 -the explicit or declarative memory that is conscious, can be verbalized and recalled, and is essential to our identity and our autobiography, and the implicit memory, that is...

Information Processing and Memory

The mediation school of thought suggests theoretical mechanisms of encoding, retention, and retrieval to explain memory functioning. Consequently, concerted efforts have been made to attribute memory changes across the life span to the specific deterioration of such mechanisms. Researchers continue to debate the importance, even existence, of such constructs. Similarly, the dichotomy of long-term versus short-term memory continues to be debated. In order to test the empirical validity of such theories, constructs must be able to be disproved if false, and these metaphorical constructs have proved difficult or impossible to test because of their abstract nature.

Studies in Age Related Cognition

Psychologists who studied memory change identified diminished memory capacity in the elderly as attributable to a number of processes, such as slowed semantic access and a reduced ability to make categoricaljudgments. Other researchers concluded that older subjects were slower in mental operations but were not less accurate. Some researchers hypothesized that slower speed tied up processing functions, resulting in apparent memory impairment. Still others hypothesized that older adults have more trouble with active memory tasks because of increased competition for a share of memory processing resources, whereas others linked the aged's poor performance on working memory tasks to an actual deficiency in processing resources. Finally, some researchers concluded that older adults might simply have less mental energy to perform memory tasks. These studies accept gradual memory decline, or a slowing of processing, as a normal by-product of aging.

Evidence For The Component Processes

In all of the experiments described here, a prospective memory task was embedded in an ongoing short-term memory task and a concurrent four-choice reaction time task. For the short-term memory task, five words appeared in a row in the center of the computer screen for a short period of time, and participants recalled the words when they disappeared. Performance was scored as the number of words that were recalled correctly on each trial. In all cases these trials were arranged into six-trial sets and each set was followed by a 10-second rest break. For the reaction time task, asterisks appeared in one of four horizontal positions on the computer screen, and participants pressed one of four keys that corresponded to the asterisk location. The task was continuous and concurrent with the short-term memory task. Whenever a participant pressed a key, asterisks immediately appeared in another location, and this continued while the words were studied and recalled. Performance was scored as...

TABLE 32 Target Checking and Retrieval Mode Predictions for Performance in the Ongoing Tasks

Accordingly, in a subsequent experiment, different manipulations were used to explore each component process (Guynn, 2005). To investigate target checking, participants performed one block of 24 control trials and two blocks of 24 experimental trials (the order of the three blocks was counterbalanced across participants). The critical manipulation was that participants were given information about the possible locations of the prospective memory targets (i.e., the fruits). On one block of experimental trials, participants were informed that the fruits could appear as any one of the five words in a short-term memory trial, and on one block of experimental trials participants were informed that the fruits could appear as just the first word in a short-term memory trial.

TABLE 34 Retrieval Mode Predictions for Performance on the Ongoing Tasks Control Trials

A final experiment was conducted to rule out the possibility that this latter cost actually reflected target checking (i.e., participants checking for the targets during the control trials after having been instructed about the prospective memory task). In this experiment, all participants were instructed about the prospective memory task before they performed the control trials the number and the order of the control and experimental trials were the same as in the prior experiment. However, one group was informed that the fruits in the later experimental trials could appear as any one of the five words, and one group was informed that the fruits could appear as just the first word, in a short-term memory trial (see Table 3.5 for predictions).

Neural Implementation of Memory as a Dynamic Constructive Process

12 From this theoretical perspective it is therefore problematic to postulate that the different memory systems are separated from each other in an absolute way the postulate of different memory systems is mostly based on findings made by the so-called neuroa-natomic research method (e.g., the finding that patients with lesions in the hippocampus lose their procedural memory) 2, 4,10 . However, as we have discussed elsewhere in detail, the conclusion that these findings can be interpreted as localizing the different memory systems in a particular region of the brain may be too simplistic 27 .

Memory and the Neurosciences

The short-term memory, also called the operative memory, holds information that is only needed for a few minutes. The long-term memory is where we file information for life. The two are, of course, related. According to Atkinson and Shiffrin 1 , information has anyway to pass through the short-term-operative-memory, where it is selected for eventual storage in the long-term memory. The two are therefore in line. Other models, however, view them more as in parallel, long-term information being filed directly without necessarily passing through the operative memory 2 . The long-term memory comprises an explicit or declarative memory and an implicit, nondeclarative one 3,4 . The explicit memory can be recalled consciously, and rendered verbally. It may be selective and episodic, dealing with the person's autobiographic experiences as regards certain specific events, or else it may be semantic, dealing with facts and knowledge, giving meaning to the oldest recollections. The explicit...

Knowledge from Neuropsychology

This century offers numerous clinical examples of disorders of the short-and long-term memory. Studies in humans with brain damage have provided much useful information on the memory. A typical memory problem arises with Alzheimer's disease, when patients are no longer able to store new information, but persist in harking back to experience dating from before the onset of the illness. These patients also show abnormalities of the semantic memory which gives meaning to recent events on the basis of past experiences. Bioimaging techniques indicate that patients with Alzheimer's disease suffer a loss of function of the hippocampal neurons, bilaterally, of the cingulate cortex and the basal frontal areas. This implies that medial temporal lobe (MTL) structures-particularly the hippocampus-and frontal areas are needed to select and store information in the long-term memory. Another cause of memory loss in man is Korsakov's syndrome patients with this syndrome too can dig out recollections...

Interactions Between Emotion and Attention

Selective attention, by exerting top-down modulation in sensory areas (for a review, see 69 ). These regions include the superior parietal lobule, the frontal eye fields, and the anterior cingulate cortex. Interestingly, largely overlapping networks appear to be involved in different types of selective attention, such as spatial-based attention, object-based attention, feature-based attention, as well as working memory.

Interactions Between Memory and Emotion

A large number of studies have consistently shown that emotionally arousing, particularly negative, stimuli-such as stories 92, 93 , pictures 94 , and words 95 -are better remembered than similar material without emotional value. Based on the fear-conditioning animal literature, it has been assumed that the amygdala plays a role in the enhancement of memory by emotion. Lesion studies with patients with unilateral temporal lobectomy (surgical treatment for intractable epilepsy) or selective bilateral lesions of the amygdala (Urbach-Wiethe disease or herpes simplex encephalitis) have largely confirmed this hypothesis. One of the first studies was performed by Markowitsch and colleagues with two patients, known as B.P. and C.P.,with Urbach-Wiethe disease 96 , presenting bilateral mineralization of the amygdala and deficits in emotional memory (B.P. less impaired than C.P.). Specifically, B.P. failed to show any memory enhancement for emotional words, whereas C.P. had a superior memory...

Introductory Comments

By definition, in essence, prospective memory is remembering to perform an intended act at an appropriate time and place when enactment must be delayed. The different chapters in this section all accept, in principle, that there are multiple stages of processing required in situations demanding prospective remembering, including the creation of an intention to act, along with conditions for enactment, maintenance of that intention over some delay period, retrieval of the intention at a time and place appropriate for action, and then action. All the authors are essentially in agreement that the plan of action, as Smith calls it, is not actively held in working memory during the delay interval between the formation of the intention to act and the opportunity for enactment. Instead, typically, attention is occupied with other events and planned actions during the delay. The chapters differ in some important respects about the mechanisms underlying processing at different stages, however,...

Artificial Neural Network Theory And Function

During training, cases with known output values are presented to the ANN sequentially and repeatedly. Each complete cycle in which all the training cases are presented to the ANN is known as a training epoch or iteration. The training algorithm will adjust the weights incrementally and, over time, a matrix of weights emerges that produces outputs for the training set that approach the lowest global error. It is important to emphasize that the training algorithm produces a set of weights that 'fit' the training data, which does not necessarily mean that the ANN model will generalize to new data. It is possible for an ANN to 'over-fit' or 'memorize' the training set. This phenomenon, also known as overtraining, can limit the ability of an ANN model to generalize and, therefore, limit its usefulness.

Unconscious Emotional Experiences and the Right Hemisphere

Emotional conditioning, however, is not the only component of emotional memory that could be mainly linked to the right hemisphere. The long-term memory system, whose structure is schematically reported in Fig. 1, is indeed a complex system, which consists both of conscious (explicit declarative) and of nonconscious (implicit nondeclarative) subsystems. Spontaneous emotions are, indeed, accompanied by bodily changes, whose importance has been rightly stressed by Damasio 86 , and produce motor habits and postures that can be considered as part of the pre-verbal implicit memory system, whose importance as a nonrepressed unconscious nucleus of the self has been recently proposed by Mancia 87 . This preverbal implicit memory system could also be preferentially linked to the right hemisphere, because, according to Damasio 86 ,body-related information elicited by positive and negative emotional experiences is linked to a few critical brain structures amygdala, ventro-medial frontal areas,...

Discussion And Conclusions

The third critical finding concerns the absence of age differences when the ongoing task did not encourage focal processing of the target event (i.e., the target event of a face with glasses during the ongoing task of naming the occupations of the people pictured the target event of a particular syllable during the ongoing task of deciding whether the word was a category coordinate). With such nonfocal targets, we (McDaniel & Einstein, 2000) have argued that successful prospective memory retrieval is more dependent on strategic processes that monitor environmental events for the target (see also Guynn, 2003 Smith, 2003). This strategic monitoring is thought to invoke attentional or working memory resources, and given that the ongoing task requires attentional resources as well, then performance theoretically will be characterized by the person's resource allocation policy to the two demanding activities (Navon & Gopher, 1979). From previous work (Einstein et al., 2005 Guynn,...

Recollections and Forecasts

The normal form of fear can thus develop into survival anxiety, in the face of the danger of attack from outside, or of a separation, or of bodily malfunctioning. The emotive brain develops before the cognitive one, and fears learned and archived early in the procedural memory tend to persist over the years, even if development of the cortical functions inhibits their manifestation to outsiders 4 . We also know that our brain tends to anticipate events, in order to be ready to assess and respond to a danger it does this by drawing on an outline of previous experience as applicable to current perception of the situation, without waiting to specifically assess the These findings seem closely compatible with the idea of an inner world and with the transference in psychoanalysis. The inner world is not only made up of sensory perceptions from outside. We know that the processes of perception, especially the top-down (descending) ones, are heavily influenced by early experiences stored in...

Prediction and Habitual or Routine Behavior

Prefrontal cortex and basal ganglia circuits typically work in tandem in relation to behavior 9,48 . Prefrontal cortex is generally involved in consciously acquiring new motor skills. When a new behavior is repeated over and over, it becomes automatic or habitual, and activity shifts to subcortical structures such as the cerebellum and basal ganglia, where it is stored as procedural memory of the behavior 9,49-52 . Most of the time, we are not aware of the nature of the knowledge and do not even remember when or how we have learned the skill. Procedural memory is what we use when we learn how to play a musical instrument, how to dance, how to play a sport, or how to speak native language. Grigsby 53 , who studies personality, and Beebe 25 , who studies mother-infant interaction, suggest that this memory is also the basis for learning social interaction patterns. Basal ganglia can activate these kinds of behaviors noncon-sciously, leaving the prefrontal cortex and consciousness system...

Preimplantation Genetic Diagnosis For Single Gene Disorders

In the patient was done because of the early-onset AD in her sister, who carried this mutation and developed symptoms of AD at age 38 56 . This sister is still alive, but her cognitive problems progressed to the point that she was placed in an assisted living facility. Her father had died at age 42 and also had a history of psychological difficulties and marked memory problems. V717L mutation was also detected in one of her brothers, who experienced mild short-term memory problems as early as age 35, with a moderate decline in memory, new learning, and sequential tracking in the next 2-3 years. The other family members, including one brother and two sisters were asymptomatic, although predictive testing was done only in the sisters, who appeared to be free from mutation in APP gene (Figure 3.28).

The Biopsychosocial Development of Individuals

Thus, developmental changes in the brain's functional state as manifested in the EEG during wakefulness reflect the level of attained complexity of the neuronal representations of the autobiographical memory contents. However, this developmental increase in individual knowledge is linked with the phenomenon of childhood amnesia (i.e., the finding that it is very difficult for people to remember events that occurred before they were 4 years old). Childhood amnesia, together with dreaming and dream recall, are of basic importance in psychoanalytic theory and practice. In order to discuss the nature and functional significance of these phenomena within the framework of our working model, we now introduce its central concept. This is the concept of multifactorially defined and EEG-manifested functional states of the brain. It implies memory-driven information-processing operations with EEG-state-dependent accessibility of knowledge. More precisely, the multifactorially defined and...

Aging Pm In The Laboratory

Preliminary evidence from young adults in the laboratory comes from a study by Maylor (1996d) in which 94 undergraduate students were tested either in the morning or in the afternoon. The ongoing task was either to name famous people from their photographs or to provide their occupations (half assigned to each condition) and the PM task was to indicate those wearing glasses (cf. Maylor, 1996a, 1998). Figure 10.2 shows correct performance on the ongoing and PM tasks (name and occupation data were combined) as a function of time of day. There was no overall effect of time of day but there was a significant interaction with task (p < .05), indicating that PM performance was relatively better in the morning and ongoing performance was relatively better in the afternoon. The reason for this is unclear one possibility is that there are differential and independent effects of time of day on retrieval from semantic memory (ongoing task) and PM another possibility is that participants adopt...

Lessons Learned Issues Related To Experimental Design In Erp And Functional Imaging Studies

Three salient issues have emerged from our studies using ERPs to examine the neural correlates of prospective memory. The first of these is related to the relative frequency with which one can present prospective cues. The conceptual issue is focused on this question At what point does a task move from being a prospective memory task to being a dual or working memory task, wherein individuals adopt the strategy of continuously rehearsing the prospective cues In our research we have utilized several strategies that we hope discourage active rehearsal. First, we hold the frequency of prospective cues to between 5 and 10 of the total trials (West et al., 2001 West & Krompinger, 2005) and try to maintain a minimum of five trials between prospective cues in tasks where multiple cues can appear within a single block (West et al., 2006 West & Ross-Munroe, 2002). Second, in studies where a single prospective cue is presented within each block of trials, care is taken to present the cues...

Prospective Memory in Parkinsons Disease

(see earlier chapter 9) to examine the locus of the particular deficits associated with Parkinson's disease. Relative to healthy controls, the patients were found to be impaired in the intention formation phase in terms of developing less complex plans. Regarding intention initiation, patients also showed a trend toward diminished performance. By contrast, no group differences were found in retrospective memory for the self-generated plans and in the actual execution of the intention. It was thus concluded that Parkinson's disease might be associated with a relatively specific deficit in the ability to execute intended activities, namely with a poor ability to adequately plan the execution of an intention. Moreover, for these patients prospective memory deficits do not seem to result from failures in retrospective memory for the content of an intention but rather from a disruption of the prospective component. With regard to potential mechanisms underlying these deficits, Kliegel,...

Sources for Further Study

Human Memory Theory and Practice. Rev. ed. Boston Allyn and Bacon, 1998. Updated edition of a classic text. The original emphasis on history of memory research continues, along with experimental views of consciousness and implicit memory. Collins, Alan, ed. Theories of Memory. Mahwah, N.J. Lawrence Erlbaum, 1993. Emphasis of the book is on research into theories of memory, particularly that of a cognitive approach. Various explanations are presented. Hunt, R. Reed, and Henry Ellis. Fundamentals of Cognitive Psychology. 6th ed. Boston McGraw-Hill, 1999. The authors approach the role of cognitive psychology in memory using an experimental problem-solving approach. Updated theories explaining both long-term and short-term memory, as well as retrieval, are included. Kandel, Eric. The Molecular Biology of Memory Storage A Dialogue Between Genes and Synapses. Science294 (2001) 1030-1038. A summary of the Nobel Prize-winning research into the physiological basis of memory....

Prospective Memory in Schizophrenia

Overview Schizophrenia is a psychopathological disorder that is associated with neuropsychological dysfunctions in the areas of attention, retrospective memory, working memory, and executive functioning (Aleman, Hijman, de Haan, & Kahn, 1999 Egeland et al., 2003 Hoff & Kremen, 2003 Kremen, Seidman, Faraone, & Tsuang, 2001 Meissner, Hacker, & Heilemann, 2001), possibly due to subtle damage of the medial temporal lobes and prefrontal cortex. On the basis of these impairments, it was expected that schizophrenia patients would also exhibit substantial problems in performing prospective memory tasks (Shum, Leung, Ungvari, & Tang, 2001).

The Anatomy of Memory

One area of the cortex that has been shown to be involved in memory is the prefrontal cortex. This area has been implicated in short-term memory, which is the ability to hold temporarily a mental representation of an object or event. Monkeys and rats that received lesions to the prefrontal cortex were impaired in learning tasks that required them to remember briefly the location of an object or to learn tasks that require them to switch back and forth between strategies for solving the task. Studies involving the measurement of brain function have also demonstrated that this area of the brain is active during periods when animals are thought to be holding information in short-term memory.

The Molecules of Memory

Strengthening of connections between neurons as a result of their repeated activation during learning. With the Aplysia, it is possible indirectly to observe and manipulate the connections between neurons while learning is taking place. Eric Kandel of Columbia University has used the Aplysia as a model system to study the molecular biology of memory for more than thirty years. He demonstrated that when a short-term memory is formed in the Aplysia, the connections between the neurons involved in the learning process are strengthened by gradually coming to release more neuro-transmitters, particularly serotonin. When long-term memories are formed, new connections between nerve cells actually grow. With repeated disuse, these processes appear to reverse themselves. Kandel's work has suggested that memory (what Lashley referred to as the engram) is represented in the nervous system in the form of a chemical or structural change, depending on the nature and duration of the memory itself....

Themes 2 And 3 Components Of Prospective Memory And Their Neural Correlates And Substrates

Given the variety of components that contribute to prospective memory, I was relieved to discover that it is possible to distinguish them from those implicated in some tests of free recall, cued recall and recognition, working memory, vigilance, and divided attention in elegant experiments either conducted by the authors of these chapters or reported by them (see especially West, chap. 12, this volume). What seems to make prospective memory different from all these is the requirement to act on delayed intentions. A crucial region is the rostral prefrontal cortex, or area 10, with the lateral aspect acting in conjunction with the medial aspect, to maintain intentions and shift attention from internal thoughts or intentions to external stimuli, as Burgess et al.'s (chap. 11, this volume) gateway theory posits.

The Dream in Psychoanalysis Today

The discovery of the implicit memory and the unrepressed early unconscious 4,5,20 and their connections with the experiences of early infan-cy-sometimes traumatic-has given the dream another, particularly valuable, dimension in theory and clinical practice. Here we must look at the child's earliest relations with its mother and the environment where it grows up 21 . From late in pregnancy the fetus is in direct contact with its mother's rhythms-her heartbeat and breathing-and her voice 22 , After the voice, the child's body is an important area of interaction with the mother. How she contains, touches, watches, and speaks to the baby, and her capacity for r verie, are basic vehicles of affects in this early relation. This presymbolic and preverbal experience, and the affects, fantasies, and emotions they evoke in the newborn, are all filed in the implicit memory, where they help build up the main structures of an unrepressed, unconscious nucleus of the self. They cannot be repressed...

Introduction aims of the study

According to Mountcastle (1992, 1998), the paradigm change introduced by using brain oscillations became one of the most important conceptual and analytic tools for the understanding of cognitive processes. Mountcastle further stated that a major task for neuroscience is to devise ways to study and to analyze the activity of distributed systems in waking brains, including particularly human brains. According to Luria (1966) mental functions too are similar to vegetative functions, a product of complex systems, and a component part, which may be distributed through the structures of the brain. The task of neuroscience is, therefore. not to localize centers, but rather, to identify the components of the various complex systems that interact to generate the mental functions. Luria called this task dynamic localization.'' A recent study tested the possible interplay between the working and long-term memory systems and indicated the relevance of this dynamic localization (Sauseng et al.,...

Synthesis in the Functional Significance of Dreams

It is generally believed that non-REM sleep is needed for metabolic activity, homeostasis, and thermoregulation, while REM sleep-which interests us more here in relation to mental activity-is required to elaborate and memorize information the brain has received during waking hours. During development, starting with the fetus, REM sleep acts as an endogenous stimulus to synaptogenesis and maturation, particularly of the neocortex. It is also necessary for restoration of the catecholaminergic system. This is interesting, since the catecholamines help regulate mood. Both REM and non-REM sleep can stimulate the synaptic structures that are inadequately activated during waking 76 . A structural hypothesis suggests that REM sleep may function as an information processor, particularly for the right-hand hemisphere, which is considered the seat of the emotions 77 and is more involved than the left hemisphere in dream organization 47 . In addition, REM sleep is believed to permit recurrent,...

Properties of Retrieval Induced Forgetting

Taken together, the foregoing properties indicate that the impairment underlying retrieval-induced forgetting is unlikely to be produced by traditional associative interference mechanisms. Rather, it is likely to reflect the action of an inhibitory control process acting to override unwanted retrievals of competitors in memory, helping to achieve selective memory retrieval. This supports the view that selective memory retrieval may be regarded as a special case of response override arising in long-term memory retrieval.

Unconscious Influence and Recoverability as Necessary Features of Repression

Although it is true that unconscious influences and memory recovery have not been demonstrated for suppressed items in the think no-think paradigm, these are not good reasons to conclude that this phenomenon is unrelated to repression. They are, at worst, reasons to defer judgment. Empirical work must be conducted to evaluate these possibilities, and this work is quite tractable with the methods we have developed. In fact, memory inhibition is very likely to exhibit these attributes. First, the fact that these effects are linked to modulation of hippocampal activation indicates that suppression is affecting declarative memory for the suppressed events. If the effect primarily occurs in declarative memory, we might see preserved implicit memory for nondeclarative aspects of the suppressed experiences, including perceptual priming, and even affective learning, given a suitable adaptation of the think no-think procedure. Second, other related inhibition effects (e.g., retrieval-induced...

Bivariate Decision Processes

Models are developed for decision making where a system's evolution is described by a general stochastic process. The general structure of the problem includes many statistical tests such as treatment comparisons, regression models and likelihood ratio tests. The process is monitored and decisions are made in response to the observed system state. The decision process is simplified by using an associated process as well as the underlying state as decision variables in many situations a functional of the underlying process defines a statistic. The approach is motivated by the idea of a performance metric based on the system state. The bivariate approach allows a wide class of models to be considered and can incorporate long term memory within a simple probability structure. The decisions in this study are based on an average cost and a life-cycle cost. The approach can deal with decisions that entail restarting the process as new or continuing the process after an intervention...

Behavioral and Social Emotional Problems

Behavior and social-emotional problems are more difficult to define clinically, and most of these data are elicited from surveys of parents and teachers. Symptoms suggestive of ADHD occur two to six times more frequently in children born preterm with birth weights of less than 1,000 grams, less than 1,500 grams, and less than 2,000 grams than in controls born full term (9 to 15 percent diagnosed with ADHD compared with 2 percent of controls born full term) (Aylward, 2002 Bhutta et al., 2002 Breslau, 1995 Levy, 1994 Pharoah et al., 1994 Saigal et al., 2001 Stjernqvist and Svenningsen, 1995 Szatmari et al., 1990 Taylor et al., 1998). Refinement of descriptions of impairments of attention and behavior provides further insight into the problems children born preterm and their families face. In a study of 8-year-old children born at less than 28 weeks of gestation or with birth weights of less than 1,000 grams, the preterm children had significantly lower scores for processing speed,...

Memory Acquisition Retention and Recall Changes in Old

While disorders of memory may occur at all ages, they occur with increasing frequency in old age. As mentioned earlier, there are various types of memory. Their characteristics and underlying mechanisms are still being elucidated (65,66). The long-held idea that information storage was widely and equally distributed throughout large brain regions has been displaced by the view indicating that memory is localized in specific areas of the brain. Actually, current theories hold that memory is localized in discrete brain areas involved in specific aspects of short-term memory as well as being widespread, with many areas communicating to form long-term memory. Among the primary areas involved are the limbic system (especially the hippocampus), the thalamus, the cerebral cortex (temporal, prefrontal, and frontal lobes), and the cerebellum. faster than 1 sec Short term memory or minutes Long-term memory or secondary memory May need hours or days to develop but lasts a lifetime...

Cognitive Aspects of Medical Adherence

(c) remembering the plan, and (d) remembering to execute the plan. The comprehension and integration of the plan relies primarily on working memory, remembering the plan relies on retrospective memory (Einstein, Holland, McDaniel, & Guynn, 1992) and executing the plan relies on prospective memory. It is our contention in this chapter that the cognitive components of adherence differ in their importance and relative contribution to adherence in adults of different ages. We present evidence that suggests that much of the problem in medical adherence in older adults involves the first three components of cognition (comprehension, working memory, and retrospective memory) and that prospective memory for taking medications is actually quite good in older adults. We also present evidence suggesting that prospective memory is a pressing problem for young and middle-aged adults in adhering to a medication regimen, and that this difficulty in prospective memory is related to age differences...

Cognitive Vulnerability Increases with

There is convincing evidence that as people age, there are declines in speed of information processing, working memory, and long-term memory (Park et al., 2002 Park et al., 1996). At the same time that basic cognitive processes decrease with age, there is also evidence that world knowledge remains intact (Park et al., 2002 Park et al., 1996). Thus, although cognitive processes operate less efficiently, knowledge the product of experience is preserved. Figure 18.1 displays this relationship. With respect to prospective memory, there is evidence that when participants are provided with a cue for prospective memory (event-based memory), age differences are small or nonexistent (Einstein, McDaniel, Richardson, Guynn, & Cunfer, 1995 Park, Hertzog, Kidder, Morrell, & Mayhorn, 1997). However, when an individual must remember to perform an action in the absence of a cue at FIGURE 18.1 A composite view of life-span performance on measures of processing (working memory, short-term memory,...

Role of Neuropeptides Hormones and Metabolites

Impaired memory learning in adulthood and old age Decreased protein synthesis due to blocking of protein kinase activity responsible for amino acid phosphorylation in the absence of protein phosphorylation failure of cAMP response element to bind to the CREB protein that promotes transcription decreased synaptic synthesis impairs of long-term memory by preventing synaptic potentiation of repetitive presynaptic stimuli Changes in posttranslational modification at the synapse may be responsible for impairment of short-term memory in old age Decreased cortical activation, as measured by brain-imaging techniques, has been recorded in old individuals in some brain area (frontal, temporal), whereas, in others (frontal), activation is increased. It is unclear whether increased activation represents recruitment of neurons to compensate for difficulty of task or diffuse, nondifferentiated activity A number of studies have tested the effects of stimulating or inhibiting neuronal protein...

Comprehension and Memory for Medical Information

In an initial study, Morrell, Park, and Poon (1989) studied comprehension and memory for a fictitious medical regimen in old and young adults. They reported that older adults showed poorer memory than young adults for the adherence instructions associated with the medications. The deficits persisted even when the older adults were able to have these written instructions available to them while they planned their medication schedules, as well as when the older adults had unlimited time to encode the information. These data are suggestive of comprehension, working memory, and long-term (retrospective) memory difficulties in planning and remembering a medical regimen. The working memory difficulties were manifested by older adults' difficulty in integrating an accurate adherence schedule across the multiple medications, even when the medications were available to them. The increased deficits observed when older adults were required to In an effort to relieve the working memory and...

The Prospective Aspect of Prospective Memory

Another aspect of prospective memory relates to the ability to remember to execute the prospective task. Sometimes an individual may encounter an external cue that successfully catches his or her attention to remind him or her to perform a prospective action, but the cue occurs at a time or in a context where it is inconvenient or impossible to act on the individual's intention (e.g., one's medication bottle is at home while one is at the grocery store). To address this issue, Einstein et al. (1998) gave people an overt experimental task and within this task also presented cues that needed to be acted on only after the participants had waited 30 seconds from the onset of the cue's appearance. Some participants were also asked to complete a distracter task simulating the busyness of multitasking in daily life. Einstein et al. found that older adults had a harder time responding accurately to the cues than did younger adults, and at the beginning of the experiment these differences were...

Enhancing Medical Adherence with Implementation Intentions

Levels of accessibility of intention words were positively associated with achievement of the intended goals (Aarts, Dijksterhuis, & Midden, 1999). Chasteen, Park, and Schwarz (2001) also showed that implementation intentions can increase desired behaviors in experimental situations. In Chasteen et al.'s experiment, older adults completed a working memory task and were also asked to complete two prospective memory tasks responding with a certain key press whenever a specific series of numbers was presented on screen during the cover task (which occurred randomly within 2-minute intervals), and writing the current day of the week on worksheets that were completed during a later portion of the experiment. Before engaging in the working memory task, participants formed implementation intentions about either the number sequence and its subsequent desired key press or the worksheets and the desired act of writing the current weekday. Creating an implementation intention about pressing a...

Techniques For Behavioral Measurement

Simultaneous and continuous focal sampling of all individuals in a group might be the most accurate and informative combination of sampling and recording, but circumstances may render this combination unattainable. Technology is at hand to help. Computer-based event-recording software provides an automated string of actor, behavior (time), and modifiers (such as recipient of interaction and quality of interaction). Currently, memorizing the keyboard is the way to avoid taking one's eyes off the subjects, but voice recognition software may soon allow input of data spoken in the correct syntax. Various software packages already assist behavioral recording, and the most sophisticated, such as Noldus Observer, offer a variety of tools for manipulation and basic statistical analysis of the data and an easy Windows interface (Albonetti et al. 1992 Noldus Information Technology 1995). Noldus also performs sequential and nested analysis and allows simultaneous input from an alternative...

Application Of Neuropsychological Methods To Research And Clinical Practice

Neuropsychological deficits are now recognized to be a common and significant feature of depressive disorder, resembling the profile of cognitive deficiencies seen in traumatic brain injury 16 . Attentional, executive and secondary memory functioning are the areas principally affected 17-21 . Two different patterns of attentional deficit have been described in depression distractor inhibition, and deficits in the processing of resources, that is, the central executive component of working memory 22 . Memory disorder in depression is principally due to a retrieval rather than encoding deficit 23 , but has not been consistently reported, perhaps because testing is often limited to verbal or visual stimuli, and there is some evidence to suggest the deficit may in some cases be related to dysfunction in a single hemisphere 17,24 . The neuropsychological disturbances of OCD are principally characterized by a frontal lobe syndrome with accompanying difficulties in motor initiation, shifting...

Results and Discussion

Research into the influence of Mexidol on short-term memory during short-term adaptation was done on the 3rd day of stay in mountains in the same dosage and on the same models of amnesia. Preservation of the antiamnestic effect of the preparation has been shown in cases of short-term adaptation to natural high altitude conditions. The comparative analysis of efficiency has shown that the antiamnestic activity of the preparation was more expressed in shock amnesia, than the scopalaminic one.

Brain Imaging Studies

A focus on function in the middle frontal cortex in schizophrenia developed early from one of the first observations using a functional imaging methodology. Ingvar and Franzen 97 measured neuronal activity in this region and found it to be reduced. Others followed up on this observation and reported reduced frontal activity, particularly during task performance 98-102 . The abnormality in working memory in schizophrenia and the elegant work of Goldman-Rakic in non-human primates, tying working memory performance to this region of frontal cortex, both gave these early findings considerable credibility 103 .

Recent Studies on Hearing Loss and Speech Recognition

According to Pichora-Fuller et al. (165), reallocatable processing resources are used to aid in auditory processing when listening becomes difficult due to noise- or age-related auditory deterioration. Thus, fewer resources are available for storage and retrieval aspects of working memory therefore, upstream processing of auditory information is negatively impacted (165).

Animal Investigations Behavioural Paradigms

Working Memory and Prefrontal Cortex Cognitive psychologists and theorists recognize a type of memory that is active and relevant for very short periods of time 213 . Complex paradigms, such as the delayed response tasks (DRT), involve working memory, and their counterpart, the Wisconsin Card Sort Test (WCST), can be applied to human subjects. Subjects with prefrontal lesions and schizophrenia 99 show pronounced deficits in their ability to perform this task. Accordingly, schizophrenia has been postulated to involve a defect in the processing of information in the dorsolateral prefrontal cortex 213 . This model is consistent with various abnormalities, such as a decreased amount of neuropil 214 and GABAergic dysfunction 96,138 , that recent post-mortem studies have observed in schizophrenia.

Childhood Amnesia Dreams Dream Content and the Fragility of Dream Recall

We have seen that psychosocial development goes parallel with EEG changes from slower to faster wave frequencies. They reflect the increasing complexity and quantity of the autobiographical memory contents. We now see that sleep shows EEG changes from faster to slower EEG wave frequencies. Thus, there are reverse relationships between developmental EEG changes during wakefulness and vigilance changes from wakefulness to sleep. What is the functional significance of these EEG findings for childhood amnesia and for dream content and dream recall within the framework of our model

Two Clinical Vignettes

I suspected that most of the transference references were for the years from 5 onwards when his autobiographical memory was firmly established and deference for others and concealing painful feelings had become ego-syntonic. Intrapsychically he had to find a way of getting at these earlier feelings which had no autobiographical content . . . As with repressed contents so with implicit memory, it cannot directly be brought into consciousness. There were many more sensations and phantasies in the sessions after his accident and they revealed a complex bridging system between implicit and explicit memory, the concrete experiences of Klein's internal I believe that in Peter's case his autobiographical memory was nonexistent at the level we are discussing, but his unconscious emotional memory with later priming (worse things at sea, etc.) found discharge by pro-jective identification in the way suggested by the authors and in the way experienced by me. Of the third device, his brother's...

Intestinal Nematodes and Cognitive Function

The mechanisms whereby cognitive impairment may occur have been suggested to be nutritional deficiency. Iron deficiency has a strong association with impaired school performance and is common in children with high-intensity hookworm infections. Lower height for age (stunting) has also been associated with detriments in cognitive function, mental development, behaviour and educational achievement, and these are complications of heavy intestinal nematode infection (see above). This suggests that the nutritional consequences of intestinal helminth infection impair the ability of children to perform well at school. Another possible mechanism is that the subclinical symptoms of heavy intestinal infection reduce attention at school. Further support for the idea that intestinal nematodes impair cognitive function has been provided by intervention studies, where various measures of cognitive function have been measured before and after intestinal nematode treatment. Various tests have been...

Interleaving Tasks and Monitoring

In a flight simulation study, pilots' scanning outside the cockpit increased substantially when potentially conflicting airplanes started appearing, but returned to near baseline levels minutes after the last airplane appeared (Colvin, Dodhia, & Dismukes, 2005). We speculate that it is difficult to maintain the monitoring task goal in working memory when the result of each inspection of the monitored scene reveals that no event has occurred. In this sense the monitoring aspect of the pilots' dual tasks somewhat resembles vigilance tasks (Parasuraman, 1986). Apparently humans are wired to allocate attention heavily toward sources of high information content, and thus have difficulty maintaining monitoring for low-probability events, even when those events may have high consequences (see Wickens, Goh, Helleberg, Horrey, & Talleur, 2003, for a model of attention allocation among tasks). However, this sort of monitoring differs from traditionally studied vigilance tasks in that the...

Prospective Memory in Developmental Disorders

Overview There is currently little research on prospective memory in childhood and adolescence, and even fewer studies have investigated whether the development of prospective memory skills is negatively affected by psychopa-thologies such as autism or Attention Deficit Hyperactivity Disorder (ADHD). In individuals with autism (Ozonoff & Jensen, 1999 Ozonoff & McEvoy, 1994 Prior & Hoffmann, 1990 Rumsey & Hamburger, 1988) and in those with ADHD (Willcutt, Doyle, Nigg, Faraone, & Pennington, 2005) executive dysfunctions are well documented. Hence, given the assumed involvement of executive functions in prospective memory, it was expected that children with autism or ADHD would be impaired in carrying out intended actions.

Substance Abuse and Dependence

In returning to the self-medication hypothesis, research has shown that in the comorbid population, the development of PTSD typically precedes Substance Abuse or Dependence. Some research has shown that PTSD sufferers who have high levels of anxiety sensitivity (i.e., are very sensitive to low levels of anxiety) and who catastrophize about the consequences of their anxiety are more likely to cope with drugs that reduce arousal, such as central nervous system suppressants (Stewart & Conrod, 2003). This suggests that hyperarousal symptoms may be the link for the self-medication hypothesis. Alcohol and certain drugs that are particularly effective at inhibiting activity in anxiety-related brain circuitry have been found effective at reducing the startle response. Alcohol, for example, has been shown to reduce the startle response and has particular effects on the amygdala and the prefrontal cortex (for more on the biological underpinnings of PTSD, see Chapter 6). Although substances...

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