Abstract
Parkinson's disease (PD) is a neurodegenerative illness often characterized by asymmetrical symptoms. However, the reason for this asymmetry and the cerebral correlates underlying symptom asymmetry are still not well understood. Furthermore, the effects of levodopa on the cerebral correlates of disease asymmetry have not been investigated. In this study, right-handed PD patients performed self-initiated, externally triggered and repetitive control finger movements with both their right and left hands during functional magnetic resonance imaging (fMRI) to investigate asymmetrical effects of levodopa on the hemodynamic correlates of finger movements. Patients completed two experimental sessions OFF and ON medication after a minimum of 12 hours medication withdrawal. We compared the effect of levodopa on the neural activation patterns underlying the execution of both the more affected and less affected hand for self-initiated and externally triggered movements. Our results show that levodopa led to larger differences in cerebral activity for movements of the more affected, left side: there were significant differences in activity after levodopa administration in regions of the motor cortico-striatal network when patients performed self-initiated and externally triggered movements with their left hand. By contrast, when patients used their right hand, levodopa led to differences in cerebellar activity only. As our patients were affected more severely on their left side, we propose that levodopa may help provide additional dopaminergic input, improving movements for the more severely affected side. These results suggest that the impact of reduced dopamine in the cortico-striatal system and the action of levodopa is not symmetrical.
Highlights
Parkinson’s disease (PD) is a neurodegenerative disease whose cardinal symptoms are rigidity, tremor and bradykinesia
We suggested that the gradual involvement of the putamen during right hand movements is masked by the lack of proficiency of the non-dominant hand [10]
There were no significant correlations between Montreal Cognitive Assessment (MoCA) or Beck Depression Inventory II (BDI-II) scores and behavioral performance during the finger-movement tasks
Summary
Parkinson’s disease (PD) is a neurodegenerative disease whose cardinal symptoms are rigidity, tremor and bradykinesia. Patients with PD can reach movement automaticity, they show greater increases in cortical and cerebellar activity than healthy controls when doing so [9]. In young healthy adults, we have shown that activity of the putamen increases during repetitive control, ET and SI movements performed with the right hand. We suggested that the gradual involvement of the putamen during right hand movements is masked by the lack of proficiency of the non-dominant hand [10]. It remains to be investigated whether symptom asymmetry may impact task-related cerebral activation, and the response in the affected regions to dopamine therapy
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