EMG activity and neuronal activity in the internal globus pallidus (GPi) and their interaction are different between hemiballismus and apomorphine induced dyskinesias of Parkinson's disease (AID).

The nature of electromyogram (EMG) activity and its relationship to neuronal activity in the internal globus pallidus (GPi) have not previously been studied in hyperkinetic movement disorders. We now test the hypothesis that GPi spike trains are cross-correlated with EMG activity during apomorphine-induced dyskinesias of Parkinson's disease (AID), and Hemiballism. We have recorded these two signals during awake stereotactic pallidal surgeries and analyzed them by cross-correlation of the raw signals and of peaks of activity occurring in those signals. EMG signals in Hemiballism usually consist of 'sharp' activity characterized by peaks of activity with low levels of activity between peaks, and by co-contraction between antagonistic muscles. Less commonly, EMG in Hemiballism shows 'non-sharp' EMG activity with substantial EMG activity between peaks; 'non-sharp' EMG activity is more common in AID. Therefore, these hyperkinetic disorders show substantial differences in peripheral (EMG) activity, although both kinds of activity can occur in both disorders. Since GPi spike×EMG spectral and time domain functions demonstrated inconsistent cross-correlation in both disorders, we studied peaks of activity in GPi neuronal and in EMG signals. The peaks of GPi activity commonly show prolonged cross-correlation with peaks of EMG activity, which suggests that GPi peaks are related to the occurrence of EMG peaks, perhaps by transmission of GPi activity to the periphery. In Hemiballism, the presence of direct GPi peak×EMG peak cross-correlations at the site where lesions relieve these disorders is evidence that gradual changes in peak GPi neuronal activity are directly involved in Hemiballism.