Model investigation of neuronal mechanisms of discrimination between two tactile stimuli in snails

Abstract

Synaptic and spike responses of neurons were studied in a two-layered model based on a study of the structure of the neuronal net of the defensive reflex in snails [4], using a technique of simultaneous application of two equal stimuli. When the points of application of the two stimuli were brought closer together the bimodal distribution of synaptic and spike responses of the efferent neurons of the model gradually changed into unimodal. The character of quantitative changes in synaptic and spike responses of neurons of the model, as the points of application of the two stimuli move closer together, reflects well the character of changes in effector responses of the snail's foot under experimental conditions as the distance between the two simultaneously acting tactile stimuli is reduced. After removal of the CNS, responses of contraction of the foot muscles of the snail become less accurate (they have a more diffuse maximum). It is suggested that the difference between functions of the central and peripheral nerve nets in molluscs lies in differences in the degree of accuracy of performance of the reflex response.