Objective: To investigate the neural correlates of postural control in Parkinson’s disease (PD) with and without freezing of gait (FOG) as compared to healthy older adults via motor imagery (MI) of mediolateral weight-shifting during functional MRI (fMRI).

Background: Compromised dynamic weight-shifting contributes to postural instability and falls in people with PD, and in particular those with FOG. MI in combination with fMRI provides a proxy method to unravel the neural mechanisms of postural control, yet balance-related MI has only been studied in young adults.

Method: Twelve freezers, 16 non-freezers and 14 controls performed weight-shifting by moving their center of mass in the mediolateral direction in line with a visual target displayed on a screen. The next day, they imagined themselves executing the same task, as well as a visual imagery (VI) control task, during fMRI in a blocked design with rest intervals. Training and scanning were performed off medication in PD. Preprocessing was done using FMRIPrep and SPM12 was used for the whole-brain analyses (p<0.001, k>20). A predefined region of interest (ROI) analysis was done using MarsBar. The contrast of interest was (MI>REST) > (VI>REST).

Results: Groups were matched for demographic and disease severity measures and had similar imagery ability. Freezers (p=0.001) and non-freezers (p=0.016) scored worse on the Mini-BESTest compared to controls. All groups activated the SMA, inferior parietal lobe, inferior operculum and posterior cerebellum during MI of balance. Whole-brain comparisons revealed lower activations in the pontomedullary junction and bilateral posterior cerebellum in freezers compared to non-freezers. Controls showed higher activation than both PD groups in the parietal and superior temporal lobes. A significant group effect was also found for the MLR (p=0.036), cerebellar vermis (p=0.002) and anterior cerebellum (p=0.022) ROIs with reduced activations in freezers compared to non-freezers, but no differences to controls. Activation in the vermis ROI was, in fact, higher in non-freezers compared to controls (p=0.010).

Conclusion: Reduced activations in brainstem and cerebellar regions might underpin dynamic balance deficits in freezers, with non-freezers potentially displaying compensatory activations in the cerebellar vermis. Together, these explorative findings provide novel insights into the neural correlates of balance deficits in PD and FOG.

References: Notification: A similar abstract containing pilot data of this study has been previously submitted to the 2019 conference of the International Society of Posture & Gait Research (ISPGR)

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-neural-correlates-of-dynamic-balance-control-in-parkinsons-disease-and-freezing-of-gait/