Objective: This study aims to evaluate the functional correlates of Parkinson’s disease (PD) dysgraphia from coupled fMRI and kinematic recordings.

Background: Beyond the abnormal reduction in writing size, known as micrographia, PD dysgraphia is characterized by a significant decrease in the velocity and fluency of handwriting movements. While behavioural studies help to better characterise PD dysgraphia, none have examined the possible relationship between its behavioural features and specificities in the neural network involved in handwriting. To tackle this issue, we combined simultaneous recording of handwriting movement and brain activity of individuals with and without PD. More precisely, we dissociated the sequential component of handwriting, characterized by the succession of strokes to form letters, from the motor adaptation component involved in the visuo-spatial control of pen movements to respect the spatial constraints of handwriting.

Method: In all, 20 participants with PD and 20 age- and gender-matched control participants will be included in this fMRI experiment. Two independent factors were manipulated: For the ‘Sequence’ factor, three items were selected: i) a sequence of four downward loops; ii) the pseudo-cursive word “mune”; and iii) the participant’s own signature. These items differ in the size of the memorised motor sequences, ranging from simple strokes (loop) to the letter (pseudoword) to the whole item (signature). For the ‘Adaptation’ factor, participants perform the items either without any constraint or between two parallel lines.

Results: Inclusion is still ongoing. In control group, we expect to observe an increase in the velocity and fluency of handwriting with increasing size of the memorised motor sequences, associated with higher activations in regions of the cortico-striatal loop (SMA, putamen). In contrast, the spatial constraint will disturb handwriting and increase activation in brain regions associated with the cortico-cerebellar loop (cerebellum, SPL). In PD group, we expect to observe that, contrary to the control group, spatial constraint will improve the performance while complexification at the sequential level will disturb writing and will be accompanied by modulations in both cortico-striatal and cortico-cerebellar loops.

Conclusion: If confirmed, this study will shed light on the neural basis of parkinsonian dysgraphia and will provide further evidence that PD dysgraphia may have its own pathophysiology.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/neural-correlates-of-parkinsons-disease-dysgraphia/