Primary motor cortex (M1) activity exhibits synchronous waves of oscillations with frequency around 20Hz. These are strongest during periods of steady contraction or at rest, but abolished during active movement. These oscillations propagate down the corticospinal tract to motoneurons, and thence to muscle, producing corticomuscular coherence in this band. In addition, our recent work demonstrates that oscillations are sensed by muscle spindle afferents, and are thereby transmitted back to the cortex via cuneate nucleus and thalamus. Using directed coherence (Granger causality) analysis, we have shown bidirectional interactions between cortex and the periphery, in support of this idea. Oscillations at ~20Hz are also present in somatosensory cortex, and indeed have a larger amplitude than in M1. Finally, we have shown that the power of oscillations in both cortical local field potential activity and single unit spiking carries information about digit position. We speculate that this system is used to achieve some form of sensorimotor recalibration after a movement, by measuring the response to a known oscillatory probe signal.
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