[Nonspecific changes in the response of command neurons in Helix leucorum L. to a combination of 2 stimuli]

In a preparation of isolated nervous system of the snail (Helix leucorum L.) an analogue of conditioned food aversion reflex was reproduced using electrical stimulation of the chemoreceptive pathway as conditioned and stimulation of skin innervating nerves as unconditioned stimuli. In 65% of cases, pairing of these stimuli elicited a significant increase of synaptic potential amplitude evoked by the conditioned stimulus in command neurones of avoidance behaviour and/or appearance of action potentials. In 20% of cases in which reinforcement evoked less than 5 spikes, no increase of response to unconditioned stimuli was recorded. In 15% of cases in which no response of command neurones to stimulation of the chemoreceptive pathway was recorded, no changes were observed with any reinforcement. Nonassociative character of responsiveness changes was established in experiments with presentation of conditioned and unconditioned stimuli at random or of isolated unconditioned stimuli: these procedures evoked exactly the same changes as in experiments with temporal pairing of two stimuli.