Objective: To identify cortical areas coupled to the ventral intermediate nucleus of the thalamus (VIM) in patients with essential tremor (ET).

Background: ET is a common movement disorder that is characterized by action and postural tremor in the absence of other neurological signs. The VIM is an effective target for deep brain stimulation (DBS) in tremor patients. Despite its therapeutic importance, its functional connectivity has rarely been investigated in humans.

Method: We combined resting-state magnetoencephalography (MEG) with local field potential recordings from the VIM in 19 Essential Tremor patients and from the subthalamic nucleus (STN) in 19 patients with Parkinson’s disease.

Coherence was quantified in different frequency bands (alpha, low-beta, high-beta) and cortical areas coherent with activity in the VIM and STN were localized using a beamformer. Subcortico-cortical coherence was compared across subcortical target structures using a cluster-based permutation test. In addition, we calculated spectral granger causality between cortical areas and subcortical structures.

Results: The topographies of VIM-cortex and STN-cortex coherence were very similar overall, but differed quantitatively. Both nuclei were coupled to ipsilateral sensorimotor cortex in the high-beta band, to sensorimotor cortex, brain stem and cerebellum in the low-beta band and to temporal cortex, brain stem and cerebellum in the alpha band. High-beta coherence to sensorimotor cortex was stronger for the STN (p = 0.003), whereas low-beta connectivity to deeper areas was stronger for the VIM (p = 0.02). While the STN was driven by cortical activity in the high-beta band, no such directionality was observed for VIM-cortex connectivity.

Conclusion: Our findings are evidence for spatially and spectrally organized patterns in thalamo-cortical connectivity. We identified three main areas: temporal cortex, brainstem/cerebellum and motor cortex. We found that thalamo-cortical connectivity is bidirectional and dominated by alpha/low-beta oscillations, unlike the STN, which is driven by motor activity at high-beta frequencies.

The overall similar topographies of VIM-cortex and STN-cortex coherence suggest that functional connections are not necessarily unique to one subcortical nucleus but might reflect larger frequency-specific networks.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-spatial-and-spectral-organization-of-thalamo-cortical-connectivity-in-patients-with-essential-tremor/