What it is
While a learned motor skill is performed, the neurons in layer 2/3 of the primary motor cortex (M1) express a reproducible pattern of activity across space and time, and it has been debated whether M1 actively takes part in generating that pattern and whether the pattern causally drives the learned movement. The authors combined two-photon calcium imaging in living mice with holographic optogenetic stimulation of functionally defined groups of these neurons while the mice performed a skilled lever-pressing task. Brief synchronous stimulation of about 20 neurons whose activity begins before voluntary movement induced movements resembling the learned movement, and produced activity in other M1 neurons resembling the learned activity. Trial-by-trial variability in the triggered population activity correlated with variability in the induced movements, and both were predicted by the initial state of M1 activity before stimulation. In some trials, stimulation induced the learned activity without inducing movements, indicating that the learned activity is not simply a reflection of movement but can arise internally. Stimulation failed to generate movements or learned activity in mice that were not engaged in the task, and stimulating neurons whose activity follows movement onset failed to induce the learned movement in engaged mice. The authors conclude that the learned activity can be generated when M1 is prepared in the optimal initial state and receives precise triggering inputs, supporting an active role for M1 in generating learned activity and learned movements.
Why it matters
Stimulating about 20 mouse motor cortex neurons that fire before movement induced movements resembling a learned lever press, backing the cortex's role in making them. Whether the primary motor cortex generates the reproducible activity seen during a learned skill, or only reflects the movement, has been debated. Here a brief, synchronous stimulus to neurons in layer 2/3 of the primary motor cortex (M1) whose activity normally begins before movement recreated the learned activity in other neurons, sometimes with no movement at all, and only when the mouse was engaged in the task; stimulating neurons that fire after movement onset did not induce the learned movement.
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Filed underMotor Control and Adaptation, Transcranial Magnetic Stimulation Studies, Neuroscience and Neural Engineering
