ABSTRACT
In recent years, a major focus of research in the area of learning and memory has been to describe the neuronal pathways involved in the integration and expression of simple learned responses. In this type of work, it is necessary to develop a paradigm that allows the investigator to have precise control over the stimuli, and that elicits a simple and clear form of associative learning (Thompson et al., 1984). Furthermore, the model system used should allow neuronal analyses (Cohen, 1974) and the neuronal activity should be related to a significant behavior (Kandel & Spencer, 1968). Thompson and colleagues (Thompson et al., 1984) have pointed out that, once a suitable preparation has been established, the first issue that must be addressed is to identify the neural structures and pathways involved in the model of learning. Using lesion, electrophysiological, and neuroanatomical techniques, it is possible to trace CNS circuitry that links sensory information, in the form of conditioned and unconditioned stimuli (CSs & USs), with motor outflow, in the form of conditioned and unconditioned responses (CRs & URs). Certainly, the CNS circuitry involved in any learned behavior is quite complex; however, through careful and systematic studies the essential neuronal pathways for a relatively simple CR may be elucidated. Once the neuronal circuitry has been identified, electrophysiological and biochemical analyses of cellular activity in the various pathways can provide further information regarding the neural substrates of learning.
