Modulation of Corticomuscular Coherence by peripheral stimuli
The purpose of this investigation was to examine the effects of peripheral afferent stimuli on the oscillatory linkage between brain and muscle activity as estimated by corticomuscular coherence (CMC). Electroencephalogram (EEG) from sensorimotor cortex and Electromyogram (EMG) from two intrinsic hand muscles were recorded during a key grip motor task. Graded single pulse electrical stimuli, above threshold for perception and activating cutaneous afferents were applied to the dominant or non-dominant index finger and a short-time Fourier Transform was used to estimate dynamic changes in CMC. The level of β-range (14-36Hz) CMC was reduced in a stimulus intensity-dependent fashion for up to 400 ms post-stimulus, then returned with greater magnitude before falling to baseline levels over 2.5 s, outlasting the reflex and evoked changes in EMG and EEG. Subjects showing no baseline β-range CMC nevertheless showed post-stimulus increases in β-range CMC with the same time-course as those with baseline β-range CMC. A pulsed mechanical displacement of the gripped object causing the subject to feel as if the object may be dropped produced similar modulation of β-range CMC. Electrical stimuli to the non-dominant index finger produced no significant changes in β-range CMC. The results suggest that both cutaneous and proprioceptive afferents have access to circuits generating CMC, but that only a functionally relevant stimulus produces significant modulation of the background β-range CMC, suggesting β-range CMC has an important role in sensorimotor integration.