Objective: To investigate the interplay between subthalamic nucleus (STN) activity and striatal dopamine deficiency in the production of arm movements in subjects with Parkinson’s disease (PD).

Background: In PD, there is a modulation of β-activity (13-30 Hz) at cortical and subcortical level during passive and active movements. Still, the contribution of the two hemispheres and the cortical-subcortical interplay to the production of such movements remain unclear.

Methods: In 5 subjects with PD, we recorded high density EEG (BrainAmp) activity and Local Field Potentials (LFPs) of the STN by means of Activa PC+S (Medtronic). Striatal dopaminergic innervation was measured with FP-CIT and SPECT. STN were distinguished in STN- and +, according to the lower/higher striatal-specific binding ratio of the two hemispheres. All subjects moved a cursor on a digitizing tablet and performed out-and-back movements toward one of 8 targets presented on the computer screen every 3 seconds. An opaque panel prevented the arm vision. We used two tasks: a baseline motor task, in which the cursor position on the screen and the hand position on the tablet corresponded; and a visuomotor adaptation task, in which the cursor position was rotated 30° counterclockwise to the actual hand movement. Recordings were performed twice in two consecutive days in stimulation-off (60 min) and medication-off state (overnight withdrawal of all dopaminergic drugs). On each day, subjects performed a total of 48 baseline movements with both hands and 96 rotated movements with the dominant hand only (the right one in all patients). We measured several characteristics of the motor performance, including reaction time, movement speed and spatial errors.

Results: The main finding was a similar modulation of β-amplitude over the left and right sensori-motor cortices, independently of the arm performing the movement. On the contrary, β-modulation was larger in the STN- compared to STN+, irrespective of moving hand, and STN+ showed high significant correlations of β-activity with all behavioural data.

Conclusions: Despite the limited number of subjects, our data showed a direct and selective involvement of dopamine in processing motor commands at sub-cortical level; thus suggesting a differential involvement of cortical and subcortical β-activity in the production of upper limb movements in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cortical-and-subcortical-contribution-in-the-production-of-reaching-movements-in-parkinsons-disease/