Objective: To investigate cortical activity of doorway-provoked motor blocks (MB) during pedalling in Parkinson’s disease (PD).

Background: Freezing of gait (FOG) is common in PD and is resistant to current treatments. Passing through doorways is a known trigger for FOG. The neural correlates of doorway-provoked FOG are poorly understood. A neuroimaging study found that doorway-provoked motor blocks (MB) are related to supplementary motor area (SMA) hypoactivation. Further, FOG is linked to elevated cortical beta synchronization in frontoparietal regions.  We aim to examine cortical beta activity (13-30 Hz) during doorway-provoked MB in PD.

Method: 19 PD participants (OFF and ON medications) and 20 age-matched healthy controls (HC) were tested. While seated, participants navigated through a virtual hall displayed on a computer screen with a series of doors using bilateral pedalling. Cortical activity was assessed using 64-channel EEG. MB were defined as periods in which step latency exceeded 2 times the z-score of the square root transformed step latency. MB durations were expressed as percentage of the time spent in doors and in halls. MB severity was characterized by speed and area under the curve (AUC) of the foot pedal waveform during MB periods. A mixed ANOVA was used to compare group (HC vs. OFF vs. ON) and location (door vs. hall). EEG current density were processed and analyzed using statistical non-parametric mapping with sLORETA to compare between groups and location (door vs. hall).

Results: Both location (p = 0.016) and group (p < 0.001) had a significant effect on MB duration. While all groups spent a larger percent time in MB in doors than in halls, PD OFF had the highest percent of time frozen in doors (OFF: 15.0 ± 12.0%; ON: 10.9 ± 6.5%; HC: 7.6 ± 2.4%). HC showed more effective pedalling than PD during MB (p < 0.001), measured by AUC, and was faster than PD-OFF during MB (p = 0.004). Compared to MB in HC, MB in PD patients were associated with significantly higher beta power in the parahippocampal gyrus, dorsal lateral prefrontal cortex and SMA, regardless of doors or halls. Medication had no significant effect on the duration and severity of MB or EEG beta power in PD.

Conclusion: PD participants had increased doorway-provoked MB compared to HC. In line with previous work, lower limb MB were related to elevated frontal EEG beta power. Targeting frontal beta oscillations may be a potential therapy for FOG.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cortical-beta-activity-in-doorway-provoked-motor-blocks-in-parkinsons-disease/