Objective: Understanding the pathomechanisms of Essential Tremor (ET) with higher spatial and temporal precision is of important clinical relevance. While the efficiency of Deep Brain Stimulation (DBS) has been extensively demonstrated, side effects may oppose satisfactory tremor relief. A more thorough insight into of the functional anatomy within targets may promote the use of next-generation DBS systems such as directional leads or ultrasound-based thalamotomy. A detailed knowledge of the timing of tremor-related activity could also promote the development of biomarkers to support closed-loop forms of neurostimulation.

Background: DBS surgery enable the delivery of therapeutic interventions to otherwise inaccessible brain areas while, at the same time, offering the unique opportunity to record from these same regions in awake patients. The posterior ventrolateral thalamus (VLp) has become a reliable DBS target for medically-refractory patients suffering from ET. But despite this, the contribution of the thalamus in ET, and even whether VLp is the optimal target, remains a matter of ongoing debate. There are several lines of evidence supporting clusters of activity within the VLp that are important for tremor emergence.

Methods: In this study, we sought to map the functional properties of areas with strong thalamomuscular coherence through microelectrode recordings during DBS surgery. Data were obtained from 10 severely affected ET-patients (12 hemispheres) undergoing DBS surgery.

Results: Our results demonstrate power and coherence maxima located in the inferior VLp and immediate ventral region. Moreover, we identified distinct yet overlapping clusters of efferent and afferent activity, with a preference for more efferent contributors, consistent with a net role in the driving of tremor output. Finally, we demonstrate that resolvable thalamic spiking activity directly relates to background activity, evidence of synchronisation, and that the strength of tremor may be dictated by phase relationships between efferent and afferent pockets in the VLp.

Conclusions: Taken together, these results provide important evidence for the role of the inferior VLp and its border region in ET pathophysiology. Such results progress our mechanistic understanding and promote the adoption of next-generation therapies such as higher resolution DBS electrodes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-functional-micro-electrode-mapping-of-ventral-thalamus-in-essential-tremor/