RECURRENT COLLATERAL INHIBITION IN PYRAMIDAL TRACT NEURONS

Abstract

Intra-cellular and extracellular microelectrode studies of recurrent axon collateral inhibition have been carried out in pyramidal tract neurons of the cat. Repeated vollies of antidromic impulses were found to produce a graded increase in membrane polarization proportional to the intensity of the stimulus and number of impulses in the train. Parallel with the polarization antidromic impulses were blocked at or near the axon hillock and an arrest of spontaneous firing and of orthodromic synaptic excitation. Inhibition reached a maximum in about 20 msec. and lasted for 80-100 or more msec. This powerful inhibition is probably mediated over cortical interneurons and acts to suppress surrounding "fringe" neurons thus improving motor "contrast" in the integration of precise finely controlled voluntary movements.