# Modulations of thalamo-cortical coupling during voluntary movement in patients with essential tremor

## TL;DR

The study shows how brain connections between the thalamus and motor areas change during voluntary movement in people with essential tremor.

## Contribution

The study reveals distinct modulations of low- and high-beta band oscillatory activity during movement in essential tremor patients.

## Key findings

- Voluntary movement is associated with decreased alpha/low-beta coherence in the supplementary motor area and premotor cortex.
- Pre-movement low-beta thalamo-cortical coupling correlates with reaction time in essential tremor patients.
- High-beta coherence increases during movement but is more localized than low-beta suppression.

## Abstract

•Thalamo-cortical coupling is modulated during voluntary movement.•Strongest modulations in thalamic coupling to premotor/supplementary motor cortex.•Distinct modulations of oscillatory activity in low- and high-beta band.•Pre-movement thalamo-cortical low-beta coupling correlates with reaction time.

Thalamo-cortical coupling is modulated during voluntary movement.

Strongest modulations in thalamic coupling to premotor/supplementary motor cortex.

Distinct modulations of oscillatory activity in low- and high-beta band.

Pre-movement thalamo-cortical low-beta coupling correlates with reaction time.

The ventral intermediate nucleus of the thalamus (VIM) is the main thalamic hub for cerebellar inputs and the primary deep brain stimulation target in essential tremor (ET). As such, it presumably plays a critical role in motor control. However, this structure is rarely studied in humans, and existing studies mostly focus on tremor. Here, we studied neural oscillations in the VIM and their coupling to cortical oscillations during voluntary movement.

We investigated thalamo-cortical coupling, combining recordings of thalamic local field potentials and magnetoencephalography, in 10 ET patients with externalized deep brain stimulation electrodes. During the recording, patients repeatedly pressed a button in response to a visual cue. In a whole-brain analysis of VIM-cortex coherence, we contrasted activity during pre-movement baseline and button pressing.

Button pressing was associated with a bilateral decrease of thalamic alpha (8–12 Hz) and beta (13–21 Hz) power and a contralateral gamma (35–90 Hz) power increase. Alpha/low-beta (8–20 Hz) coherence decreased during movement. This effect localized to the supplementary motor area and premotor cortex. A high-beta (21–35 Hz) coherence increase occurred in the same region but was more focal than the suppression. Pre-movement levels of thalamo-cortex low-beta coherence correlated with reaction time.

Our results demonstrate that voluntary movement is associated with modulations of behaviourally relevant thalamic coupling, primarily to premotor areas. We observed a clear distinction between low- and high-beta frequencies and our results suggest that the concept of “antikinetic” beta oscillations, originating from research on Parkinson’s disease, is transferable to ET.