Objective: To evaluate entrainment of MEG-recorded brain oscillations induced by a rhythmic task structure in patients with Parkinson’s disease (PD).

Background: PD patients do not generally report difficulty in perceiving a regular beat, but existing evidence from slow brain potentials and beta oscillatory activity suggests that PD patients have a reduced tendency to entrain to regular environmental patterns. Here we investigate whether reduced entrainment in patients concerns a generalized deficit or is confined to movement-related activity, leaving sensory entrainment intact.

Methods: MEG was recorded during a rhythmic auditory target detection task, in a group of 14 PD patients and 14 control subjects. Participants were instructed to press a button when hearing a target tone amidst a sequence of isochronous tones. Standard tones differed in pitch, indicating the next tone to be the target tone with different probabilities (10, 30 and 50%). In addition, targets were occasionally omitted to evaluate phase entrainment uncontaminated by stimulus effects.

Results: Reaction times were identical between groups, and both groups benefited equally from the predictive value of the standard tones. Analyses of event-related fields (ERFs) over auditory cortices showed no differences between groups. By contrast, ERFs over motor areas revealed marked differences between groups. PD patients showed a general reduction in neural activity over motor areas, and a significantly reduced effect of target probability, not explained by failure to attend or discriminate the cues. After tone omissions, both groups showed an omission response in the ERFs over sensory areas, but this omission response was significantly reduced over central-parietal areas in patients. Analyses of oscillatory beta power over motor areas showed an attenuated modulation in patients, consistent with the ERF effects.

Conclusions: Together, these results show entrainment of neural activity over sensory areas in controls and patients alike. However, patients are deficient in translating this adjustment to the task rhythm to central motor areas. The results are relevant to the neurophysiology of rhythmic cueing in PD, and suggest that reduced entrainment in PD is specific to the motor system.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/sensory-and-motor-aspects-of-rhythmic-entrainment-in-parkinsons-disease/