[Role of intervals between "conditioned" and "unconditioned" stimuli during elaboration of a cellular analog of a temporary connection].

A cellular model of temporary connection was used to study the effect of intervals between stimulation of ventrobasal thalamic complex (conditioned stimulus) and local activating polarization (unconditioned stimulus) on plastic changes in the neuronal responses of sensorimotor cortex inalert rabbit. It was found that a prolongation of the interval between paired stimuli from 0 to 150 msec. produced a decrease from 60 to 28 per cent in the number of neurones in which after pairings the responses to the conditioned stimulus underwent significant plastic rearrangments. Inspite of the general trend each cell has its own optimal interval between combined stimuli where changes are most pronounced. The fact that rearrangments in cellular responses occur in a time interval corresponding to reinforcement in pairings supports the idea about a selective increase in the efficiency of those excitatory synapses that were activated simultaneously with the cell discharge.