EEG-EMG coherence changes in postural tasks

Purpose: Recent studies have investigated the possible function of synchronous oscillatory activity within the sensorimotor cortex of monkeys and humans that is thought to arise from synchronous discharge of large numbers of cortical neurons. There has been found clear task-dependent changes in 15-30 Hz oscillations. In leg muscles, coherence also occurs in the same frequency band during voluntary static contraction. Therefore we investigated changes in coherence in leg muscles during several postural tasks. Methods: We examined the coherence between EEGs and soleus EMGs during voluntary contraction and in various postural tasks. Results: There was a significant coherence during voluntary static contraction, but not during standing, forward bending, or standing on one foot; whereas, there was significant coherence during stamping the ground. Conclusion: These results suggest that the coherence at 15-30 Hz originates from the motor cortex during voluntary contraction, not when doing postural tasks. Coherence analysis indicates that during postural tasks the motor cortex would not produce the synchronous discharge of large numbers of cortical neurons or might not induce soleus EMG activity.