Essential tremor and tremor in Parkinson's disease are associated with distinct 'tremor clusters' in the ventral thalamus.

Different tremor entities such as Essential Tremor (ET) or tremor in Parkinson's disease (PD) can be ameliorated by the implantation of electrodes in the ventral thalamus for Deep Brain Stimulation (DBS). The exact neural mechanisms underlying this treatment, as well as the specific pathophysiology of the tremor in both diseases to date remain elusive. Since tremor-related local field potentials (LFP) have been shown to cluster with a somatotopic representation in the subthalamic nucleus, we here investigated the neurophysiological correlates of tremor in the ventral thalamus in ET and PD using power and coherence analysis. Local field potentials (LFPs) at different recording depths and surface electromyographic signals (EMGs) from the extensor and flexor muscles of the contralateral forearm were recorded simultaneously in twelve ET and five PD patients. Data analysis revealed individual electrophysiological patterns of LFP-EMG coherence at single and double tremor frequency for each patient. Patterns observed varied in their spatial distribution within the Ventral lateral posterior nucleus of the thalamus (VLp), revealing a specific topography of 'tremor clusters' for PD and ET. The data strongly suggest that within VLp individual tremor-related electrophysiological signatures exist in ET and PD tremor.