Classical Conditioning and Sensitization Share Aspects of the Same Molecular Cascade in Aplysia

Abstract

Since the turn of the century when basic forms of learning were first described by Pavlov and Thorndike, learning has been divided into two discrete, mutually exclusive, categories—nonassociative learning and associative learning (see Hilgard and Marquis 1940; Razran 1971; Kandel 1976). The two categories are distinguished on the basis of whether the learning requires a specific association between two stimuli or between a stimulus and a response. The most common and perhaps most interesting comparison of nonassociative and associative forms of learning derives from studies of sensitization and classical conditioning (see, for example, Grether 1938). Both forms of learning have been shown to involve the effect of one stimulus on the response to another. But classical conditioning requires temporal pairing of the two stimuli whereas sensitization does not. Given the existence of two forms of learning, a central problem in the study of behavior has revolved around the question: How...