Synchronized brain network associated with essential tremor as revealed by magnetoencephalography.

Despite the fact that essential tremor (ET) is the most prevalent movement disorder, the underlying pathological mechanisms are not fully understood. There is accumulating evidence that this specific type of tremor is mainly of central origin, in particular involving inferior olive, cerebellum, thalamus, and primary motor cortex. We studied 8 patients with ET recording simultaneously neural activity with a whole-scalp neuromagnetometer and tremor activity with surface electromyography (EMG). Subjects performed an isometric contraction of the left forearm. Tremor frequency of 5 to 7 Hz and its first harmonic were clearly evident in power spectra of EMG recordings. We used the localization technique dynamic imaging of coherent sources (DICS) to identify cerebral areas coherent to the EMG signal at tremor frequency and its first harmonic. All subjects showed coherence to the contralateral primary motor cortex. In a further step, DICS was used to identify areas of significant cerebro-cerebral coherence. The analysis revealed a network of areas consisting of contralateral primary motor cortex, premotor cortex, thalamus, brainstem, and ipsilateral cerebellum. These results are consistent with the view that in ET, a network of cerebral areas including brainstem shows oscillatory interactions, which lead to a rhythmic modulation of muscle activity becoming apparent as tremor.