Neural coding of finger and wrist movements

Previous work (Schieber and Hibbard, 1993) has shown that single motor cort ical neurons do not discharge specifically for a particular flexion-extensi on finger movement but instead are active with movements of different finge rs. In addition, neuronal populations active with movements of different fi ngers overlap extensively in their spatial locations in the motor cortex. T hese data suggested that control of any finger movement utilizes a distribu ted population of neurons. In this study we applied the neuronal population vector analysis (Georgopoulos et al., 1983) to these same data to determin e (1) whether single cells are tuned in an abstract, three-dimensional (3D) instructed finger and wrist movement space with hand-like geometry and (2) whether the neuronal population encodes specific finger movements. We foun d that the activity of 132/176 (75%) motor cortical neurons related to fing er movements was indeed tuned in this space. Moreover, the population vecto r computed in this space predicted well the instructed finger movement. Thu s, although single neurons may be related to several disparate finger movem ents, and neurons related to different finger movements are intermingled th roughout the hand area of the motor cortex, the neuronal population activit y does specify particular finger movements.