Cross-correlation analysis of interneuronal connectivity in the motor cortex of the monkey.

Pairs of neurones were recorded within the hand region of the precentral motor cortex of monkeys trained to squeeze a force transducer between the thumb and index finger. Neuronal discharges of a pair of cells, recorded through the same electrode, were first examined for their co-variation with force. The discharges of those pairs with a consistent co-variation were cross-correlated during periods of constant isometric force. Cross-correlograms in the majority of cases had either a sharp peak or trough at latencies suggesting monosynaptic causal relations between the cell discharges. A peak was associated with pairs of cells whose discharges co-varied similarly with force and when a trough was observed, the cell discharges of the pair generally differed in their force co-variation. It is concluded that the action of motor cortical neurones is linked by common and recurrent collateral inputs during isometric co-contraction of finger muscles.