Reply to 'One motor cortex, two different views'

The article by Todorov1 and associated letters illustrate clear opinion differences regarding the function of motor cortex during goal-directed arm movements. This controversy is partially generated by the different experimental protocols used to examine motor cortex function in non-human primates. The first, introduced by Evarts, examines single-joint movements and relates neural activity to muscle-based or joint-based variables15. The second, introduced by Georgopoulos, examines whole-arm movements and relates neural activity to hand-based variables16. Practitioners of the former find correlates of muscle-based or joint-based variables; practitioners of the latter find correlates of hand-based variables.

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