Investigation of changes in the choice reaction time with levodopa in patients with Parkinson's disease.

Objective: To investigate the alterations in the choice reaction time (RT) with levodopa in Parkinson's disease (PD) patients. Via concurrent clinical assessments, we aimed to provide perspectives regarding the clinical significance of these alterations and responsible pathophysiology.

Methods: Participants were recruited from consecutive PD patients who applied to our Movement Disorders Polyclinics between September/2024 October/2024. Demographic, clinical features, and the MDS-UPDRS-3 scale (-on and -off) were evaluated. The Blazepod technology was used to measure choice RT.

Results: We included 25 PD patients with a mean age of 65.7 ± 9.0 y (F/M = 9/16). The comparative analyses between medication-off and -on states revealed that the MDS-UPDRS-3 scores decreased significantly during the medication-on states (p < 0.001, d = 1.09). Besides, all the parameters related to reaction time including RT, number of hits, and errors improved during medication-on state (d = 0.71, d = 0.88, d = 0.72, respectively). The RT-off showed moderate positive correlations with the UPDRS-3 scores (CC:0.416, p = 0.039). The left side RT-off and also the right-side RT-off showed moderate positive correlations with the left-side UPDRS-3-'off' scores (CC:0.499, p = 0.011, CC:0.440, p = 0.028, respectively).

Conclusion: In conclusion, we found significant improvements in all the measures of choice RT after levodopa intake which reached moderate-large effects sizes. Our findings suggest that RT impairment in PD may involve shared neural mechanisms, with possible lateralized contributions that require further investigation. The RT measures may also constitute an alternative method for measuring LR and needs to be tested in the distinct clinical scenarios in future-related studies.