[The mechanism of action of a reinforcing stimulus]

Experiments on alert non-immobilized rabbits revealed that electrical cutaneous stimulation of a limb, used as a reinforcing agent in elaboration of a conditioned reflex to photic flashes, weakened slow polyrhythmic oscillations of background EEG and late components of evoked potentials in the visual cortex to photic flashes. Against this background, the connection between slow potentials and spike activity in both the visual and sensorimotor cortical areas considerably diminished. During EEG activation, induced by the reinforcing stimulus, inhibitory pauses and post-inhibitory activation in the firing of the neocortical units weakened and protracted, ordered spike activity appeared. The data obtained are in agreement with the hypothesis that weakening of the recurrent inhibition system is one of the basic mechanisms in the action of the reinforcing stimulus in conditioning.