Introduction: To evaluate functional connectivity (FC) of the ventro-lateral thalamus, a common target for drug-resistant essential tremor (ET), resting-state data were analyzed before and 1 year after stereotactic radiosurgical thalamotomy (SRS-T), and compared against healthy controls (HC).

Methods: 17 consecutive patients and 10 HC were enrolled. Tremor network was investigated using ventro-lateral ventral (VLV) nucleus as region-of-interest (ROI), extracted using automated segmentation from pretherapeutic diffusion MRI. Temporal correlations of VLV at whole brain level were evaluated by comparing drug-naïve ET with HC, and longitudinally, 1 year after SRS-T. Thalamotomy volume was always located inside VLV, and did not correlate with any of FC measures (p>0.05). This suggested presence of longitudinal changes in VLV FC independently of thalamotomy volume.

Results: Pretherapeutic ET displayed altered VLV FC with left primary sensory-motor cortex, pedunculopontine nucleus, dorsal anterior cingulate, left visual association and left superior parietal areas. Pretherapeutic negative FC with primary somatosensory cortex and pedunculopontine nucleus correlated with poorer baseline tremor scores (Spearmann=0.04 and 0.01). Longitudinal study displayed changes within right dorsal attention (frontal eye-fields and posterior parietal) and salience (anterior insula) networks, as well as areas involved in hand movement planning or language production.

Conclusions: Our results demonstrated that ET and HC differ in their VLV FC to primary somatosensory and supplementary motor, visual association, or brainstem areas (pedunculopontine nucleus). Longitudinal changes display reorganization of dorsal attention and salience networks after thalamotomy. Beside attentional gateway, they are also known for their major role in facilitating a rapid access to the motor system.

Patient Care: A better understanding of radiobiology of SRS-T for tremor could further aim at a targeting refinement and better clinical results.

Learning Objectives: By the conclusion of this session, participants should be able to: 0- How functional MRI and diffusion weighted imaging could be useful in stereotactic and functional neurosurgery 1- Understand how differs functional connectivity (FC) of the ventro-lateral thalamus (a common target for drug-resistant ET), as depicted from resting-state data, in HC as compared with pretherapeutic ET? 2- What are the statistically significant FC changes between pretherapeutic state and 1 year after SRT? 3- How could this contribute to a better understanding of the radiobiology of stereotactic radiosurgical thalamotomy for tremor?

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