Nonhuman animals have been used as subjects in memory research since the earliest days of psychology, and much of what is known about the fundamental processes of memory is largely based on work with animals. Rats, mice, pigeons, rabbits, monkeys, sea slugs, flatworms, and fruit flies are among the most commonly used species. The widespread use of animals in memory research can be attributed to the ability systematically to manipulate and control their environments under strict laboratory conditions and to use procedures and invasive techniques, such as surgery and drugs, that cannot ethically be used with humans. A typical research protocol involves training animals on any of a variety of learning paradigms and concurrently measuring or manipulating some aspect of the nervous system to examine its relationship to memory.
Although learning and memory are closely related, a distinction should be drawn between learning and memory. Learning is defined as a relatively permanent change in behavior as a result of experience. Memory is the underlying process by which information is encoded, stored, and retrieved by the nervous system. Modern learning and memory paradigms are based on the principles of classical and operant conditioning first established by the early behaviorists: Ivan Pavlov, Edward L. Thorndike, John B. Watson, and B. F. Skinner. These learning paradigms can be used to examine different types of memory and to explore the underlying brain mechanisms that may mediate them. For classical conditioning, widely used paradigms include eyeblink conditioning, taste aversion learning, and fear conditioning. For operant conditioning, memory for objects, spatial memory, context discrimination, and maze learning are among the most frequently used procedures. Two other very simple forms of learning, habituation (the gradual decrease in response to a stimulus as a result of repeated exposure to it) and sensitization (the gradual increase in response to a stimulus after repeated exposure to it) are both simple forms of nonassociative learning also extensively used in animal memory research.
Researchers have at their disposal a number of techniques that allow them to manipulate the nervous system and assess its functions. Historically, experimental brain damage has been one of the most widely used procedures. This technique involves surgically destroying (known as lesioning) various parts of the brain and assessing the effects of the lesion on memory processes. Pharmacological manipulations are also frequently used and involve administering a drug known to affect a specific neurotransmitter or hormonal system thought to play a role in memory. Functional studies involve measuring brain activity while an animal is actually engaged in learning. Recordings can be made from individual brain cells (neurons), groups of neurons, or entire anatomical regions. Beginning in the late 1990's, genetic engineering began to be applied to the study of animal memory. These procedures involve the direct manipulation of genes that produce proteins suspected to be important for memory.
By combining a wide variety of memory paradigms with an increasing number of ways to manipulate or measure the nervous system, animal research has been extremely useful in addressing several fundamental questions about memory. These issues include the important brain structures involved in memory, the manner in which information is stored in the nervous system, and the causes and potential treatments for human memory disorders.
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