A BS TRACT: Background: Action observation training and motor imagery may improve motor learning in Parkinson's disease (PD). Objectives: The objectives of this study were to assess mobility and balance (performing motor and dual tasks) and brain functional reorganization following 6 weeks of action observation training and motor imagery associated with dual-task gait/balance exercises in PD patients with postural instability and gait disorders relative to dual-task training alone. Methods: Twenty-five PD-postural instability and gait disorder patients were randomized into 2 groups: the DUAL-TASK+AOT-MI group performed a 6-week gait/balance training consisting of action observation training-motor imagery combined with practicing the observed-imagined exercises; the DUAL-TASK group performed the same exercises combined with watching landscape videos. Exercises were increasingly difficult to include the dual task. At baseline and at 6 weeks, patients underwent: mobility, gait, and balance evaluations (also repeated 2 months after training), cognitive assessment, and functional MRI, including motor and dual tasks. Results: Dual-task gait/balance training enhanced mobility, during both single-and dual-task conditions, and executive functions in PD-postural instability and gait disorders, with a long-lasting effect at 14 weeks. When exercises were preceded by action observation trainingmotor imagery, PD-postural instability and gait disorders showed greater improvement of balance and gait velocity both with and without the dual task, particularly during the turning phase. After training, the DUAL-TASK+AOT-MI group showed reduced recruitment of frontal areas and increased activity of cerebellum during functional-MRI motor and dual task, correlating with balance/turning velocity and executive improvements, respectively. The DUAL-TASK group showed reduced activity of supplementary motor area and increased recruitment of temporo-parietal areas during the dual task and decreased cerebellar activity during the motor task correlating with faster turning velocity. Functional MRI results were not corrected for multiple comparisons and should be interpreted carefully. Conclusions: Adding action observation training-motor imagery to dual-task gait/balance training promotes specific functional reorganization of brain areas involved in motor control and executive-attentive abilities and more long-lasting effects on dual-task mobility and balance in PD-postural instability and gait disorders.

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Highlights Cortical and subcortical atrophy is accelerated early after the onset of PD. Brain atrophy in PD progressed with cognitive, non-motor and mood deficits. Structural MRI may be useful for predicting disease progression in PD.

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