Objective: The aim of this study was to investigate the influence of dopaminergic cell loss on motor habitual behaviour, by comparison between newly diagnosed Parkinson’s disease (PD) patients and healthy controls participants (HC).

Background: Habits (stimulus-response associations) allows us to perform well-practiced tasks with minimal effort, a function linked to sensorimotor territories of the basal ganglia. In Parkinson´s disease, initial loss of dopamine along the caudal sensorimotor putamen transfers to more rostral regions as disease progresses. Importantly, the role of sensorimotor putamen in habitual control could possibly explain some motor deficits part of everyday-life in PD such as arm swinging, walking and writing.

Method: We hypothesize that everyday-life motor habits (writing) is impaired in automatic conditions associated to reduced striatal activities in PD patients. We developed a handwriting task that differentiates between habitual and goal-directed components. The following psychometric parameters were analyzed: writing duration, horizontal and vertical amplitudes, automatic stroke analysis (number of inversions, mean of jerk). One behavioural (30 PD; 30 HC) and one fMRI (18 PD; 25 HC) sessions were performed. Highly asymmetric and early (less than 2 year since diagnosis) PD patients were tested while off-medicated. All patients were right-handed.

Results: Habitual writing was Impaired in PD compared to controls. This finding was especially true when the most affected side overlapped with hand-dominant side. Neural signals revealed enhanced activity in bilateral posterior putamen in controls in habitual conditions (p<0.05, FPR-corrected). In contrast, in goal-directed conditions, anterior putamen and caudate nucleus showed increased activity. A similar pattern was observed in PD patients, however, showing a reduced posterior putamen activity (p<0.05, FPR-corrected). The decrease of activity was stronger when the affected side coincided with the dominant hand.

Conclusion: Our results suggest that everyday-life motor habits is executed with reduced automatic components in PD patients, accompanied by reduced posterior putamen recruitment in early PD. Our findings demonstrate a functional dysfunction in posterior putamen that plays a fundamental role in the origin of the characteristic habitual motor deficits of PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/decrease-of-striatal-activity-during-the-execution-of-a-everyday-life-motor-habits-in-early-parkinsons-disease/