Introduction: Essential tremor (ET) is the most common movement disorder. Drug-resistant ET can benefit from standard procedures (deep brain stimulation, thalamotomy) or minimally invasive high-intensity focused ultrasound (HIFU) or stereotactic radiosurgical thalamotomy (SRS-T). Resting state fMRI (rs-fMRI) is a non-invasive imaging method acquired in absence of a task. We examined whether rs-fMRI correlates with tremor score on the treated hand (TSTH) improvement 1 year after SRS-T.

Methods: We included 17 consecutive patients treated with left unilateral SRS-T in Marseille, France. Tremor score evaluation and rs-fMRI were acquired at baseline and 1 year after SRS-T. Resting-state data (34 scans) were analyzed without a priori hypothesis, in Lausanne, Switzerland. Based on degree of improvement in TSTH, to consider SRS-T at least as effective as medication, we separated two groups: 1, <= 50% (n=6, 35.3%); 2, > 50% (n=11, 64.7%). They did not differ statistically by age (p=0.86), duration of symptoms (p=0.41) or lesion volume at 1 year (p=0.06).

Results: We report TSTH improvement correlated with interconnectivity strength between salience network with left claustrum and putamen, as well as between bilateral motor cortices with right visual association area (the former also with lesion volume). Longitudinal changes showed additional associations in inter-connectivity strength between right dorsal attention network with ventro-lateral prefrontal cortex and salience network with fusiform gyrus.

Conclusions: Brain functional connectivity measured by resting-state fMRI relates to clinical response after SRS-T. Relevant networks are visual, motor and attention. Inter-connectivity between visual and motor areas is a novel finding, revealing implication in movement sensory guidance.

Patient Care: We aimed at a better understanding of the radiobiology of radiosurgery of the Vim for essential tremor. We report that a focal Vim lesion, produced by SRS-T, is correlated with a distinct functional connectivity pattern, implying changes not only within parts of the pure widely known motor loop, but also on remote areas, including primarily motor (claustrum, putamen; interconnected with salience network) and visual (occipital association cortex; interconnected with bilateral motor cortex) area. Using longitudinal data, at baseline and one year after SRS-T, we suggest that rs-fMRI relates to clinical response. The main areas involved include motor and visual networks, but also cognitive regions, mainly involved in attention (e.g., salience, dorsal attention), suggesting the connection between the former in sensory guidance of movements of hands and fingers.

Learning Objectives: By the conclusion of this session, participants should be able to: 1- understand the role of resting-state fMRI, as an advanced neuroimaging tool for understanding normal and pathological states, including the use in movement disorders 2- have a basic understanding of the statistical approach used for fMRI data analysis 3- have a basic understanding on the role of each surgical treatment for tremor (inclduign non invasive, such as radiosurgery and HIFU)

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