THEORETICAL CONSIDERATIONS FOR THE ANALYSIS OF POPULATION CODING IN MOTOR CORTEX

Recent evidence of population coding in motor cortex has led some rese archers to claim that certain variables such as hand direction or forc e may be coded within a Cartesian coordinate system with respect to ex trapersonal space. These claims are based on the ability to predict th e rectangular coordinates of hand movement direction using a ''populat ion vector'' computed from multiple cells' firing rates. I show here t hat such a population vector can always be found given a very general set of assumptions. Therefore the existence of a population vector con stitutes only weak support for the explicit use of a particular coordi nate representation by motor cortex.