MOVEMENT-RELATED CORTICAL POTENTIALS IN PERSISTENT MIRROR MOVEMENTS

Mirror movements (MMs) are involuntary movements executed on one side of the body during voluntary movements of the contralateral homologous body parts which may abnormally persist into adulthood. In 6 subjects affected by persistent MM with autosomal dominant inheritance, moveme nt-related cortical potentials (MRCPs) during self-paced, voluntary ex tensions of either the left or right middle finger were recorded from 30 EEG electrodes simultaneously with the electromyogram (EMG) of both extensor digitorum communis muscles. The negative potentials before a nd during EMG onset were evaluated statistically for the two electrode s next to the cortical hand areas. A comparison with 7 normal subjects revealed no marked differences for the Bereitschaftspotential (BP) an d the negative slope (NS'). Only in the periods around EMG onset (from -50 to +50 msec) a significant difference between both groups was fou nd. The MM subjects showed fairly symmetric potentials over the right and left hemispheres, whereas the potentials of the control subjects w ere lateralized to the hemisphere contralateral to the intended moveme nt. No difference was found for the amplitude of the maximum negative peak of MRCP following EMG onset. Our data showed no evidence for a di fferent type of movement preparation in MM subjects as compared to nor mals. We propose that the additional ipsilateral cortical activation a round movement onset may be the cortical mechanism, which compensates for abnormal ipsilateral corticospinal pathways in subjects with persi stent MM.