Electrocorticogram-electromyogram coherence during isometric contraction of hand muscle in human

Objective: To clarify how the primary sensorimotor and supplementary motor areas are involved in the generation of the rhythmicity of electromyogram (EMG) activity during continuous muscle contraction. Method: We analyzed the coherence between subdurally recorded cortical electroencephalograms (EEG) and EMGs of the contralateral wrist extensor muscle during continuous isometric contraction in 8 patients with medically intractable epilepsy. Results: In all subjects, a significant coherence between the primary motor area (M1) and EMG was observed at the peal; frequency of 15 +/- 3 Hz (means +/- SD). In the primary somatosensory area (S1) of 7 subjects and the supplementary motor area proper (SMA proper) of 4 subjects, significant coherence with EMG was observed at 12 +/- 5 and 15 +/- 4 Hz, respectively. The time lags revealed by cross-correlogram were 10 +/- 3, 7 +/- 1 and 22 +/- 8 ms in the M1, S1 and SMA proper, respectively, with the EMG lagging in all areas. Conclusion: These findings suggest that the rhythmic activity in the SMA proper, as well as in the S1 and M1, is related to the generation of the rhythmicity of EMG activity. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.