Objective: To analyze the coupling and causal interplay of motor related brain areas in Parkinson’s patients during the performance of externally and internally paced finger tapping movements in comparison to age-matched healthy controls.

Background: Recent studies suggest that the development of cardinal motor symptoms like bradykinesia, rigidity and tremor are caused by the pathological coupling between motor brain areas and muscles.

Methods: We recorded an EEG with 128 „active“ electrodes together with an EMG of three forearm muscles in Parkinson’s patients (n = 12) and age-matched healthy controls (n= 12). Participants who were all right-handed performed a finger tapping task with the right index finger that consisted of four trials: 1) externally paced condition: the right index finger had to be moved up and down synchronously to an acoustic stimulus that was presented at 2 Hz, 2) internally paced condition: subjects had to reproduce the rhythm before heard, 3) a mixed condition in which ten stimuli were played and then stimuli were switched off while the subjects had to continue tapping and 4) a control condition in which the stimuli were presented, but participants were asked to sit still. Parkinson’s patients performed the behavioral task twice: After overnight withdrawal of the dopaminergic medication and after taking a standardized dose of L-Dopa. Data was analyzed with Dynamic causal modelling (DCM) for quasi stationary responses recorded electrophysiologically.

Results: PD patients performed worse than healthy controls independent of the tapping condition. Analyzing the amount of deviation from the demanded tapping frequency using a mixed design ANOVA, we found an effect of group (F (2.59, 41.50) = 3.30, p = 0.035) that reached statistical significance in the last third (400 s) of the experiment. Preliminary DCM-analysis reflected these differences.

Conclusions: Our results indicate, in line with other studies, the impairment of PD patients in generating and maintaining rhythmic movements, regardless of internal and external pacing. A preliminary connectivity analysis using a DCM of steady-state responses suggests differences in the coupling of motor brain areas between PD patients in the off and on state and healthy controls indicating pathological network connectivity. *Authors FJ and VS co-shared first authorship.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/inferring-the-coupling-of-motor-related-brain-areas-during-paced-finger-tapping-in-parkinsons-patients/