RESEARCH HIGHLIGHTS MOTOR CONTROL A sense of movement Neuroscience textbooks tell us that with a shorter latency after S1 stimu- whisker protraction, and that M1retract the motor cortex controls move- lation than after M1 stimulation. only induces whisker retraction ment. But now, Carl Petersen and Thus, S1 and M1 are both involved in indirectly, through S1 activation. colleagues show that sensory cortex whisker motor and sensory process- By mapping the neural pathways may have an equally important role ing. The M1 area that induced C2 involved in C2 whisker retraction in motor control. retraction was termed M1retract; a and protraction, the authors found The authors showed that a single, more medial M1 region that induced that M1C2 and S1C2 have reciprocal brief deflection of the C2 whisker C2 protraction under microstimula- connections and project to adjacent induced activity in the correspond- tion was termed M1protract. regions in subcortical areas. In the ing barrel column of the primary The authors next investigated the brain stem, this includes the reticular somatosensory cortex (S1), followed functional relevance of this finding. formation as a projection area of M1, by a response in a small area in the By attaching metal particles to the C2 and the spinal trigeminal nuclei as primary motor cortex (M1). Direct whisker and applying a pulsed mag- a projection area of S1. Both areas microstimulation or optogenetic netic field, the authors could evoke project to the facial nucleus, which stimulation of either area induced C2 whisker deflections. The whisker contains whisker motor neurons. a brief retraction of the C2 whisker, retracted in response to this stimulus, Indeed, direct electrical stimula- and this response was abolished when tion of the reticular formation and S1 was inactivated — but not spinal trigeminal nuclei induced when M1 was inactivated — with whisker protraction and retraction, tetrodoxin (TTX). This suggested respectively. that S1 drives the retraction response. Together, these findings point to These data raised the question of the existence of two parallel pathways whether M1 requires S1 activation for opposing whisker movement. to induce whisker retraction. In fact, Whether sensory cortex drives motor microstimulation or optogenetic responses in other species, including stimulation of M1retract combined with humans, remains to be investigated. S1 inactivation using TTX resulted in Leonie Welberg whisker protraction, and stimulation ORIGINAL RESEARCH PAPER Matyas, F. et al. of M1protract while S1 was inactivated Motor control by sensory cortex. Science 330, enhanced whisker protraction. This 1240–1243 (2010) indicates that M1 primarily drives NATURE REVIEWS | NEUROSCIENCE VOLUME 12 | JANUARY 2011 © 2011 Macmillan Publishers Limited. All rights reserved.