Reinforcement concept in investigations on simple nervous systems.

An analysis of the applicability of the concept of reinforcement to the studies of learning in simple nervous systems of invertebrates is made. Analysis of the literature data and my own results suggests that reinforcement cannot be regarded as an independent behavioral phenomenon. A description of reinforcement as a state of the nervous system which precedes long-term changes of behavior is given. Using the example of aversive conditioning to food in gastropod snails it is shown that a state of the network that can be correlated with the state of reinforcement can be elicited in the simple nervous system by activation of serotonergic pedal cells modulating avoidance behavior of the animal. The conclusion is made that with certain limitations the reinforcement concept can be used in studies on simple nervous systems.