[Dynamics of hippocampal neuronal activity during formation of conditioned avoidance reflexes]

Activity of 72 neurones of the dorsal hippocampus was studied in unrestrained rabbits during avoidance conditioning. In the process of conditioning, associative reorganization of neuronal activity were found, which were of a dynamic nature and depended on the stage of reflex stabilization. The initial stage of elaboration was characterized by a change in background activity between pairings in 87.5% of the hippocampal neurons, recorded in that period. Phasic associative reorganization recorded in 53.1% of neurons in response to a signal stimulus before the appearance of conditioned movements, reflected the orienting component of the conditioned reaction, reaction to time during the period of action of associated stimuli and a change in the level of neurons activity resulting from association of conditioned and unconditioned stimuli. The nature of response was changing in the most of the neurones at the appearance of the conditioned motor reaction. Stabilization of the level of background activity and of phasic responses of neurones to signal stimulus were observed at the stage of stable conditioned reflex. Phasic responses had several modifications which reflected a level of neuronal activity specific for the conditioned reflex, and they were also linked to signal involvement of the system providing for the movement. The data obtained show that participation of regulatory tonic mechanisms is an essential condition of the formation and manifestation of the temporary connection.