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E. Carvell, PhD, PT
University of Pittsburgh
WHERE DO VOLUNTARY MOVEMENTS
BEGIN? Who’s On First?
At first blush one might suspect that voluntary movements
begin with activity in the motor cortex. That might seem to be a logical place to set the motor apparatus
into action according to a Jacksonian top-down hierarchical system. W.T. Thach provided early evidence
that subcortical areas may be involved in the earliest aspects of generating voluntary actions. In
addition, he provided evidence that neurons do not all act alike within a distributed motor control system.
About 1/3 of the neurons code for muscle force regardless of joint position (MPAT), 1/3 code for joint
position regardless of force (JPOS), and yet
another 1/3 code for the direction of the upcoming event or motor set (DSET) in over-trained monkeys performing a well rehearsed serial progression of ‘move and hold’ actions.
Who’s On First?
W.T. Thach, Correlation of Neural Discharge with Pattern and
Force of Muscular Activity, Joint Position, and Direction of Intended
Next Move-ment in Motor Cortex and Cerebellum. J Neurophysiol 41: 654-676, 1978.
Fig. 1, p 656
Fig. 16, p
Joint Position Pattern
Motor Set (Predictive) Pattern