Cross-correlation reveals facilitation of single motor units in thenar muscles by single corticospinal neurones in the conscious monkey.

The functional connections between corticospinal neurones and motor units of the monkey's hand muscles were investigated by constructing cross-correlograms of activity recorded from pyramidal tract neurones and from single motor units in the contralateral thenar muscles during performance of a precision grip between thumb and index finger. Only those neurones which produced postspike facilitation of the surface-recorded electromyogram (EMG) of these muscles were selected for analysis. Positive correlations were observed for 11/15 selected neurones, and the form of the correlation was suggestive of monosynaptic action. Corticospinal cells which produced a correlation peak often did so with all concurrently-sampled motor units.