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J Neurophysiol (September 27, 2006). doi:10.1152/jn.00808.2006
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Submitted on August 3, 2006
Accepted on September 16, 2006

Delay of movement caused by disruption of cortical preparatory activity

Mark M Churchland1 and Krishna V Shenoy1*

1 Electrical Engineering & Neurosciences Program, Stanford University, Stanford, California, United States

* To whom correspondence should be addressed. E-mail: shenoy{at}stanford.edu.

We tested the hypothesis that delay-period activity in premotor cortex is essential to movement preparation. During a delayed-reach task, we used sub-threshold intra-cortical microstimulation to disrupt putative 'preparatory' activity. Microstimulation led to a highly-specific increase in reach reaction time. Effects were largest when activity was disrupted around the time of the go cue. Earlier disruptions, which presumably allowed movement preparation time to recover, had only a weak impact. Furthermore, saccadic reaction time showed little or no increase. Finally, microstimulation of nearby primary motor cortex, even when slightly supra-threshold, had little effect on reach reaction time. These findings provide the first evidence, of a causal and temporally-specific nature, that activity in premotor cortex is fundamental to movement preparation. Furthermore, although reaction times were increased, the movements themselves were essentially unperturbed. This supports the suggestion that movement preparation is an active and actively-monitored process, and that movement can be delayed until inaccuracies are repaired. These results are readily interpreted in the context of the recently-developed optimal-subspace hypothesis.




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