Reflexes have been widely studied by psychologists and biologists interested in learning and memory. Russian physiologists Ivan Sechenov and Ivan Pavlov have generally been credited with the first attempts to study systematically how reflexes could be used to examine relationships between behavior and physiology. Pavlov in particular had a huge influence on the study of behavior. Most students are familiar with the story of Pavlov and his successful demonstration of conditioned salivation in dogs produced by pairing a bell with meat powder. Over the years, the Pavlovian conditioning procedure (also known as classical conditioning) has often been used to study the behavioral principles and neural substrates of learning. The conditioning of a variety of reflexes has been observed, including skeletal muscle responses such as forelimb flexion, hindlimb flexion, and eyelid closure as well as auto-nomic responses such as respiration, heart rate, and sweat gland activity.
One of the most widely studied classical conditioning procedures is classical eyelid conditioning. This reflex conditioning procedure has been studied in a variety of species, including rabbits, rats, cats, dogs, and humans. Mostly because of the research efforts of Isadore Gormezano and his colleagues, which began in the early 1960's, much is known about behavioral aspects of classical eyelid conditioning in rabbits. In this paradigm, a mild electric shock or air puff is presented to elicit reliably a reflexive blink from the rabbit. The blink is typically measured by means of devices that are at tached to the nictitating membrane, a third eyelid that is present in a variety of species, including the rabbit. During training sessions, a neutral stimulus such as a tone or light is delivered 0.3 to 1.0 second prior to the air puff. After about one hundred of these tone and air-puff pairings, the rabbit learns to blink when the tone or light is presented (the rabbit begins to interpret the tone as a signal of the impending air-puff presentation).
This preparation has yielded a wealth of data concerning the parameters of behavioral training that produce the fastest or slowest learning rates (such as stimuli intensities, time between stimuli, and number of trials per day). Furthermore, this simple reflexive learning situation has been used to study how the brain codes simple forms of learning and memory. A number of researchers (most notably Richard F. Thompson) have studied the activity of a variety of brain structures during learning and performance of the classically conditioned eyelid response. These studies have shown that discrete brain regions such as the cerebellum and hippocampus alter their activity to generate or modify the conditioned response. In brief, these researchers have used the conditioning of a very simple reflex to advance the understanding of how the brain might code more complex learning and memory processes.
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