The posterior ventrolateral thalamus (VLp) plays a crucial role in Parkinson's
tremor and in
essential tremor:
deep brain stimulation (DBS) of the VLp effectively diminishes both
tremor types. Previous research has shown
tremor oscillations in the VLp, but the spatial extent and somatotopy of these oscillations remained unclear. In this issue of Experimental Neurology, Pedrosa and colleagues measured neuro-muscular coherence at multiple sites in the VLp of patients with
essential tremor and
Parkinson's disease using implanted DBS
electrodes (Pedrosa et al., 2012). They found multiple
tremor clusters within the VLp, with spatially distinct
tremor clusters for antagonistic muscles, and in many patients also multiple distinct
tremor clusters for a single muscle. Interestingly, this group previously showed similar effects for the STN in tremulous
Parkinson's disease (Reck et al., 2009, 2010). Together, these studies suggest that the distribution of
tremor clusters is a general organizational principle of
tremor, being present in two different
tremor pathologies, and in two different nodes of the motor system. The presence of multiple
tremor clusters also fits with the distributed somatotopy of the healthy motor system. Therefore, a further conclusion of this study could be that
tremor is caused by aberrant synchronization within an otherwise healthy network, brought about by different pathophysiological neural triggers.