THE INFLECTION OF BETA POWER IN THE VENTRAL INTERMEDIATENUCLEUS THROUGHOUT INVERTED CENTRE-OUT MOVEMENTS IN PATIENTS

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Dr. Muhammad Mansoor Jaffar 1 , Dr. Hassan Javed 2 , Dr. Muhammad Aizaz Mazari 3

Abstract— Beta oscillations in sensorimotor structures contribute to the planning, sequencing and stopping of movements, functions that are typically associated with the role the basal ganglia. The observation of beta oscillations in the cerebellar territory of the thalamus (Vim) indicates that this rhythm may also be involved in cerebellar functions such as motor learning and visuomotor adaptation. In order to test whether Vim beta oscillations are involved in such cerebellar tasks, we devised a visuomotor learning paradigm whereby ET and PD patients performed a centre-out movement in an inverted computer display. Recordings from the Vim of 10 ET patients were obtained using microelectrodes during electrophysiological mapping procedures in DBS surgery. For comparison, recordings from the STN of 10 PD patients who performed the same task were also obtained. The results show that, in ET, Vim beta oscillations of the LFP were suppressed during the performance of the inverted centre-out task (compared to normal orientation, ANOVA, p<0.05). Interestingly, firing rates increased significantly during periods of low beta power, particularly on approach to the peripheral target (ANOVA, p<0.05). In contrast, beta power in the STN of PD patients did not differ significantly between the deinverted and the normal orientation of the centre-out task. The findings confirm the hypothesis that beta oscillations of the Vim are modulated by novel visuomotor tasks. The inverse relationship between the power of Vim-LFP beta oscillations and Vim firing ratessuggest that the suppression of beta oscillations may facilitate information throughput to the thalamocortical circuit by modulation of Vim firing rates.

Keywords: Beta oscillations, thalamocortical circuit, sensorimotor structures