Direct Cortical Control of Muscle
Activation in Voluntary Arm Movements: A Model
Emanuel Todorov
Gatsby Computational Neuroscience Unit
University College London
Nature Neuroscience . volume 3 no 4 . April 2000
What neural activity in motor cortex represents and how it controls
ongoing movement remain unclear. Suggestions that cortex generates low-level muscle
control are discredited by correlations with higher-level parameters of hand movement, but
no coherent alternative exists. I argue that the view of low-level control is in principle
correct, and that seeming contradictions result from overlooking known properties of the
motor periphery. Assuming direct motor cortical activation of muscle groups and taking
into account the state dependence of muscle-force production and multi-joint mechanics, I
show that cortical population output must correlate with hand kinematics in quan-titative
agreement with experimental observations. The model reinterprets the "neural
population vector" to afford unified control of posture, movement and force
production.
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