Correlation analysis of neuronal interaction in the motor cortex of rats during performance of a discrete instrumental reaction.

Unit activity was recorded in 7 rats trained to reach into a narrow feeder for food. Capillary microelectrodes were inserted with a head-mounted microdrive into the motor cortex contralateral to the preferred forepaw. Recordings of pairs of identifiable units were processed with the LINC 8 computer programmed for detection and classification of spikes, compilation of perireach histograms (+/- 512 ms) and construction of auto- (64 ms) and crosscorrelation (+/- 32 ms) histograms. Perireach histograms revealed activity changes (mostly of the excitatory type) in 82% of examined neurons (n = 28). Significant crosscorrelation was found in 8 of 14 pairs of neurons recorded for about 1 h. Most crosscorrelograms showed symmetric inhibitory troughs, lasting for 6 to 15 ms and better expressed in the +/- 512 ms perireach interval than during periods of spontaneous activity. Whereas symmetric crosscorrelograms (n = 6) indicate a shared inhibitory input, asymmetric crosscorrelograms (n = 2) suggest more direct interaction between the recorded neurons. Significant crosscorrelations were found more frequently when both neurons of the pair displayed significant perireach reactions. It is concluded that reaching is accompanied not only by characteristic excitatory and inhibitory reactions of individual neurons but also by modified neural coordination probably due to shared cerebellar and basal ganglia inputs.