Cortico-muscular coupling in a human subject with mirror movements--a magnetoencephalographic study.

We studied cortico-muscular coupling in a 15-year-old male suffering from congenital mirror movements (MMs) of hands. Cortex-muscle coherence was analyzed between magnetoencephalographic signals and the electromyograms (EMGs) recorded from both hands and feet during uni- and bilateral isometric contractions. Regardless of the side of the intended contraction, the motor cortex contralateral to the contraction was coupled to the muscles of both hands at 20-25 Hz. No coupling was found from the other, ipsilateral hemisphere. EMGs of the two hands were coupled during both intended uni- and bilateral contractions, but only during unilateral contractions could the coupling solely be explained by cortical activation. We suggest that our subject's MMs result from activation of an ipsilateral corticospinal projection, with involvement of additional synchronizing mechanisms at the subcortical, brainstem, or spinal level during bilateral contraction.