Download Re-examining the debate about the functional role of motor cortex

Re-examining the debate about the functional role of motor cortex
Robert Ajemian
Brain and Cognitive Sciences, MIT
It is now quite common knowledge that Georgopoulos' pioneering work on the tuning of
motor cortical neurons to movement direction precipitated a protracted debate on the
function of motor cortex. The success of the population vector approach led some to
speculate that high level kinematic details of movement are represented by the firing
rates of these neurons. Others more firmly rooted in the neurophysiological tradition of
Evarts
maintained
that
correlations
to
high-level
movement
parameters
emerge artifactually, and in predictable patterns, from the biomechanical properties of
the periphery. Peter Strick has colorfully referred to this controversy as a "muscles vs.
movements" debate. Through a series of experimental and theoretical studies, my
colleagues and I re-examine this debate in the context of neuralprosthetics. In
particular, since all decoding algorithms use a state space description of the endeffector to represent movement and since these devices work pretty well, then does that
not provide strong evidence for a Cartesian goal-oriented view of the
motor
cortex? We show that this is not the case and that, in fact, in many common
experimental contexts the question of representation is ill-posed.