Objective: To investigate whether cortical oscillations involved in sensorimotor processes might predict motor symptom response to dopaminergic treatment (MSRD) in Parkinson’s disease (PD).

Background: MSRD is an important diagnostic and prognostic indicator in PD. It is unclear why MSRD varies as PD progresses. Yet, cortical processes may be intrinsically involved in the physiology of MSRD.

Method: We recorded whole-head EEG in 10 patients [2 women; median age 65 years, range 60-79; median PD duration 8 years, range 2-20; median levodopa equivalent daily dose 763 mg, range 325-1880]. Median motor UPDRS ON medication was 29 (range 13-37) and 33 OFF medication (range 24-43). Patients were assessed while ON dopaminergic medication and, on a separate day, after 12-hour medication withdrawal. While seated, patients manipulated foot pedals to walk in a virtual environment. To progress, patients had to depress the right toe-left heel together and then left toe-right heel together. Initially, patients practiced with a metronome to complete two phases per second. They then maintained the pace while we recorded EEG. Time-frequency data was time-warped to individual rates. High beta (21-35 Hz) power was averaged over right toe-left heel phase and left toe-right heel phase. We took the absolute difference in high beta power between the two phases to assess high beta fluctuation. Large fluctuation meant that high beta power varied considerably between phases, and small fluctuation meant that high beta power plateaued. All data was analyzed in predetermined premotor/frontal, motor and parietal EEG clusters. Since movement alone can change high beta power, we included only trials that involved >60% of the full movement range and we compared the amplitude of movement ON and OFF medication.

Results: High beta fluctuations were significantly larger in the ON medication state compared to the OFF medication state in all cortical areas assessed. MSRD correlated to high beta fluctuation such that patients with less motor improvement had larger fluctuation while ON medication. Movement amplitude did not differ between ON and OFF medication.

Conclusion: Cortical oscillations are involved in the physiology of MSRD in PD. Impaired MSRD and large fluctuations in high beta power during movement could result from cortical neurodegeneration or altered thalamocortical projections as PD worsens. These findings may be useful as a marker of PD severity.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-cortical-signature-of-motor-response-to-dopaminergic-therapy-in-parkinsons-disease/