Steina, A. | Search bioRxiv

bioRxiv2025

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

The ventral intermediate nucleus of the thalamus (VIM) is the main thalamic hub for processing cerebellar inputs and the main deep brain stimulation target for the treatment of essential tremor (ET). As such, it presumably plays a critical role in motor control. So far, however, this structure has been rarely investigated in humans, and almost all of the existing studies focus on tremor. Here, we set out to study neural oscillations in the VIM and their coupling to cortical oscillations during voluntary movement. We investigated thalamo-cortical coupling by means of simultaneous recordings of thalamic local field potentials and magnetoencephalography in 10 ET patients with externalized deep brain stimulation electrodes. Brain activity was measured while patients were pressing a button repeatedly in response to a visual cue. In a whole-brain analysis of coherence between VIM and cortex, we contrasted activity around a pre-movement baseline and button pressing. Button pressing was associated with a bilateral decrease of thalamic power in the alpha (8- 12 Hz) and beta (13-21 Hz) band and a contralateral power increase in the gamma (35- 90 Hz) band. Moreover, changes in VIM-cortex coherence were observed. Alpha/low beta (8- 20 Hz) coherence decreased before and during movement, and the effect localized to the supplementary motor area and premotor cortex. A rebound of high beta (21-35 Hz) coherence 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 Parkinsons disease, is transferable to ET.

neuroscience↗

bioRxiv2024

Oscillatory coupling between thalamus, cerebellum and motor cortex in essential tremor

BackgroundEssential tremor is hypothesized to emerge from synchronized oscillatory activity within the cerebello-thalamo-cortical circuit. However, this hypothesis has not yet been tested using local field potentials directly recorded from the thalamus alongside signals from both the cortex and cerebellum, leaving a gap in the understanding of essential tremor. ObjectivesTo clarify the importance of cerebello-thalamo-cortical oscillatory coupling for essential tremor. MethodsWe investigated oscillatory coupling between thalamic local field potentials and simultaneously recorded magnetoencephalography in 19 essential tremor patients with externalized deep brain stimulation electrodes. Brain activity was measured while patients repeatedly adopted a tremor-provoking posture and while pouring rice from one cup to another. In a whole-brain analysis of coherence between the ventral intermediate nucleus of the thalamus and cortex, we contrasted epochs containing tremor and epochs lacking tremor. ResultsBoth postural and kinetic tremor were associated with an increase of thalamic power and thalamo-cortex coherence at individual tremor frequency in the bilateral cerebellum and primary sensorimotor cortex contralateral to tremor. These areas also exhibited an increase in corticomuscular coherence in the presence of tremor. The coupling of motor cortex to both thalamus and muscle correlated with tremor amplitude during postural tremor. ConclusionsThese results demonstrate that essential tremor is indeed associated with increased oscillatory coupling at tremor frequency within a cerebello-thalamo-cortical network, with coupling strength directly reflecting tremor severity.

neuroscience↗