ABSTRACT
There is a simple organism, Aplysia californica, a sea snail that wades in the waters of California, to which we owe a great deal with regard to the understanding of the molecular mechanisms of synaptic plasticity linked with the processes of memory and learning. The animal has learned to associate an unconditional stimulus (US), that is, a stimulus (the presentation of food) that triggers a response (salivation) without conditioning, with a conditional stimulus (CS), that is, a stimulus (the sound of a bell) that triggers a response (salivation) after conditioning, hence an act of learning. This chapter focuses on a form of synaptic plasticity in a neuronal circuit involved in behaviors even closer to what can be observed in man. A type of behavioral experiment in the laboratory rat helps to make a connection with what we have seen by way of associative learning in Aplysia. The rat has learned that the sound predicts the emergence of a disagreeable sensation.
