Oscillatory interactions between sensorimotor cortex and the periphery

Abstract

Field potential recordings from motor cortex show oscillations in the beta-band (approximately 20 Hz), which are coherent with similar oscillations in the activity of contralateral contracting muscles. Recent findings have revised concepts of how this activity might be generated in the cortex, suggesting it could achieve useful computation. Other evidence shows that these oscillations engage not just motor structures, but also return from muscle to the central nervous system via feedback afferent pathways. Somatosensory cortex has strong beta-band oscillations, which are synchronised with those in motor cortex, allowing oscillatory sensory reafference to be interpreted in the context of the oscillatory motor command which produced it.

Figure 1

(a) Example descending (red) and ascending (blue) pathways which could mediate corticomuscular coherence. (b) Task-dependence of corticomuscular coherence. Coherence is shown as a function of frequency (y-axis) and time during task performance (x-axis), whilst a human subject moved the levers of a precision grip manipulandum according to the displacement target shown schematically above the colour map. Coherence only appears during steady holding phases, and is larger following large movements than small ones. The colour scale has been thresholded so that non-significant coherence appears black. (c) The phase of coherence between EEG from sensorimotor cortex and hand muscle EMG in a human subject during steady contraction. Phase is only plotted for frequencies with significant corticomuscular coherence. The red line shows the best-fit straight line to frequencies around the beta-band; the slope of this line was not significantly different from zero. (d) Average coherence between forearm EMG and the discharge of seven single afferent units recorded in an awake behaving monkey. Units were putatively identified as muscle spindle primary afferents. Coherence in the beta-band was above significance (red line). (e) Comparison of the power of beta-band oscillations in local field potential recorded from different monkey cortical areas. Although oscillations can be seen in all areas illustrated, they are stronger in S1 (area 3a and 2) and posterior parietal cortex (area 5) than in M1 (area 4). (b) redrawn from [1^•]; (c) redrawn from [21^••]; (d) redrawn from [24^••]; (e) redrawn from [13^••].