The effect of carbamazepine on human corticomuscular coherence

EEG recordings from motor cortex show oscillations at approximately 10 and 20 Hz. The 20-Hz oscillations are coherent with contralateral EMG; in most studies those at 10 Hz are not. However, significant 10-Hz coherence has recently been reported in a group of epileptic patients, all of whom were taking the anticonvulsant drug carbamazepine (CBZ). In a double blind study, we investigated the effects of CBZ on corticomuscular coherence in eight healthy human subjects (all male). Subjects performed a precision grip task against an auxotonic load, whilst left sensorimotor EEG and EMGs from five muscles in the right hand and forearm were recorded. CBZ (100 mg) or a placebo was then given orally, and 6 h later subjects were re-tested. One week separated CBZ and placebo experiments in each subject. Coherence averaged across subjects and muscles during the hold phase of the task was maximal at 21 Hz; it increased significantly (P < 0.05, Z-test) by 89% after CBZ administration. This was significantly greater than a much smaller increase following placebo, which itself may reflect an effect of the time of day when experiments were performed. There was no significant approximately 10-Hz coherence either before or after CBZ administration. CBZ did not significantly alter EEG power at either 10 or 20 Hz. Recently, we showed that diazepam markedly increases the power of approximately 20-Hz motor cortical oscillations with little effect on coherence. We show here that CBZ raises coherence without altering EEG power. This pharmacological dissociation may indicate an important role for corticomuscular coherence in motor control.