Sequential movement representations based on correlated neuronal activity.

We tested the hypothesis that sequential movements are represented in the correlated activity of motor cortical neurons. We simultaneously recorded multiple single neurons in the motor cortex while monkeys performed a two-segment movement sequence. Before any movement began the correlated spike firing between pairs of neurons differed when these sequences were planned as whole (planned) as compared to when they were planned one segment at a time (unplanned) even when the firing rates of these neurons did not distinguish between the two conditions. Moreover, the correlation strength was significantly larger when the directional preferences of the neurons matched the direction of the final segment of the sequence. Our results suggest that spatially distributed groups of MI neurons form dynamic correlation structures that distinguish different forms of sequential action.