in the premotor cortex

Abstract Recently, we compared the encoding of movement direction in primary motor cortex (MI) under three coordinate systems, an extrinsic cartesian (CA), an intrinsic joint angle (JA), and an intermediate shoulder-centered (SC) and found that no single coor-dinate system was uniquely represented in MI. Here we extend this investigation to the premotor area which is regarded as a major source of input to the MI. Multiple single units were simultaneously recorded from the caudal portions of dorsal premotor (PMd) and ventral premotor (PMv) cortices as a behaving monkey moved its hand over the horizontal work space. We compared the mutual information between the neuronal Wring rate of each unit and hand move-ment direction under each of the three coordinate sys-tems. As in the MI study, the results showed that there was no evidence for a unique coordinate system repre-sentation. There was a bias towards the SC system in PMd, albeit weaker than the SC bias observed in MI. In PMv, there was a strong bias for both SC and JA coordinate systems as compared to a CA coordinate system. These results provided further evidence against a unique coordinate system for movement direction within the motor cortex. However, the direc-tional information within both PMd and PMv was sig-niWcantly less than that of MI suggesting that factors other than the detailed motion of the arm account for much of the variance of activity within the premotor cortex