Movement-associated cortical potentials with unilateral and bilateral simultaneous hand movement.

Cortical potentials associated with unilateral and bilateral simultaneous thumb opposition were studied in 9 healthy subjects. The P1 component, "pre-motion positivity", was recognized in 5 out of 9 subjects on unilateral thumb movement. In all subjects in whom P1 was recognized, P1 was dominant over the cerebral hemisphere ipsilateral to the contracting muscles. On bilateral simultaneous thumb movement, however, P1 was not discerned in any subject. This is compatible with the assumption that P1 is related to an inhibition of imitative movement of the opposite hand (mirror movement). The N2 component had its onset after the start of muscle contraction in most cases, suggesting that N2 might not reflect activation of the corticospinal pathways.