Oscillatory cortical drive to isometrically contracting muscle in Unverricht-Lundborg type progressive myoclonus epilepsy (ULD).

Abstract

We investigated with whole-scalp magnetoencephalography (MEG) oscillatory cortical drive to isometrically contracting muscle in 8 genetically verified, and thus etiologically homogeneous, Unverricht-Lundborg type progressive myoclonus epilepsy (ULD) patients suffering from cortical myoclonus and generalized tonic-clonic seizures. The results were compared with those of 8 healthy control subjects. Cortical MEG signals were measured simultaneously with surface electromyography (EMG) during isometric contraction of the left and right first dorsal interosseus muscles. Cortex-muscle coherence and cross-correlograms between MEG and EMG signals were calculated as indicators of oscillatory cortical drive to muscle. The cortical areas involved in the maximum cortex-muscle coherence were also identified. In patients, the strengths of the dominant coherent peaks were 2-4 fold compared with the healthy controls. Whereas the coherence was found strictly in the contralateral primary motor cortex in controls, additional coherent activity was observed ipsilaterally in 5 out of 8 patients. The remarkably increased MEG-EMG coherence in ULD patients suggests altered oscillatory cortical drive to the muscle during isometric contraction. We suggest that the enhanced cortex-muscle coherence in ULD patients reflects reduced inhibition in the motor cortex, and may contribute to disturbed voluntary movements.