MRI guided Focused ultrasound (MRgFUS) utilises the destructive thermal heating effects of High Intensity Focused Ultrasound (HIFU) on neural tissue. MRgFUS ablation of the Ventral intermediate (Vim) nucleus of the thalamus is now an established treatment for patient’s with Essential Tremor (ET) who are ineligible for Deep Brain Stimulation (DBS). I will present the results of a prospective study in thirty-eight patients which examined the effects of Thalamotomy on decision making 4-armed bandit reinforcement learning task. We hypothesised that post-operative thalamic oedema extension into Mediodorsal nucleus (MDn) would impair performance and value-based decision making.
Post thalamotomy, patients were less likely to identify the most rewarding bandit. This was explained by an increase in perseverative choices which was independent of the choices value or shift in the explore-exploit trade-off. Between subject variation in perseveration correlated both with the volume of post-operative oedema extension into the MDn, and the functional connectivity of the lesion overlap with this nucleus and the prefrontal cortex.
In the final part of this talk, I will present preliminary results examining the effect of sub-lesional HIFU targeted at MDn on task performance acquired intra-operatively. Using a within subject design, we show that choice perseveration can be induced by HIFU targeted at a caudo-lateral sweet-spot of the MDn identified from the probabilistic lesion-behaviour mapping cohort. This supports the potential feasibility of Thermal Neuromodulation (TN) as a technique, with stereotaxic surgical spatial resolution, to map structure-function relationship’s within individual thalamic nuclei such as the MDn.