[Formation of the defensive response to the time in snails during rhythmic stimulation of an individual command neuron]

A defensive reaction of closing the pneumostome was rhythmically induced (with 2 or 3 min intervals) in a semi-intact preparation of Helix locorum by activation of a burst of action potentials in the command neurone with a suprathreshold depolarizing current (lasting 2 to 5 s). After 10 to 30 stimulations of the command neurone, defensive reactions of closing pneumostome appeared preceding the next stimulus and setting in after an omission of the stimulus. During this period, spike reactions to time appeared in non-stimulated neurones (the command neurone and neurones of the visceral ganglion) and sometimes in the stimulated command neurone. Their appearance was preceded by augmentation of synaptic activity. Since most of the synaptic inputs on the command neurone are sensory, it may be assumed that the leading role in the formation of reaction to time belongs to changes in the afferent link of the unconditioned reflex.