[Principle of neuronal organization of defensive reflexes in mollusks]

Spontaneous and evoked synaptic activity of the command neurons of the snail defensive reaction were studied by means of simultaneous intracellular recording. The spontaneous synaptic potentials and monosynaptic EPSP evoked by stimulation of presynaptic neurons were investigated. A mathematical model of a two-layered neuronal net of the defensive reaction was developed and constructed on the basis of the neurophysiological data. In this model the neurons of the afferent layer have local but overlapping receptive fields. Each afferent neuron is monosynaptically connected with all efferent neurons but the efficiency of the connections is different (each efferent neuron has the most effective connection with one afferent neuron only). The number of spikes of each afferent neuron appearing after stimulation of different points of its receptive field as well as efficiency of synaptic connections of each afferent neuron with efferent neurons are described by the normal low. Such neuronal net acquires the following principal property: different stimuli result in different one-model "excitation profiles" of efferent neurons.