Neuronal reactions in the reticular nucleus of the thalamus upon realization of conditioned placing and its differential inhibition

Abstract

Cats were trained to perform conditioned forepaw placing (CFP) using food reinforcement. Reactions of 33 neurons were recorded extracellularly in the reticular nucleus (RN) of the thalamus; among these neurons, 24 units were localized in the sensorimotor part of the nucleus. We used short acoustic signals as conditioning positive and differential (negative) stimuli (PS and DS, respectively). When CFP was realized, 21 neurons of the RN sensorimotor part generated late long-lasting activating or inhibitory spike reactions (durations up to 6 sec and 2 sec, respectively); in 3 neurons there were no reactions. Under conditions of differential inhibition, such reactions were not observed, while the background impulse activity became clearly suppressed. In two-thirds of the neurons under study, alternating PS and DS presentations led to suppression of the reactions to PS presentation. We suppose that differential inhibition-related suppression of the background activity and of the spike reactions related to CFP realization result from restriction of the input synaptic volleys to the RN neurons.