Evaluation of implicit motor learning across body segments in Parkinson's disease vs. healthy controls

Alterations in motor learning are associated with Parkinson's disease (PD). Possible body segment-specificity remains unexplored and could have practical implications for testing and rehabilitation. Our aim was to investigate sequence-specific implicit motor learning differences in alternative task movements in people with early stages PD vs. age-matched healthy controls (HCs). Thirty participants with PD (67.6 ± 8.0 yrs, 1.9 ± 0.7 H&Y) and 30 HC (69.6 ± 5.2 yrs) performed three Serial Reaction Time Tasks (SRTTs), which differed for the body segment used to perform it: Hands, Arms, and Feet testing. Visual-motor reaction time was recorded in response to visual stimuli. For each task, eight blocks, each consisting of 4 repetitions of a 12-stimuli sequence, were presented: random sequence order was practiced in block one and eight (R1, R8); a fixed 12-stimuli sequence order was performed in blocks from 2 to 7 (S2-S7). Reaction Times were corrected for errors (RT) and reprocessed as percentage values, where the mean RT of R1 represented 100% (RT_R1%). RT at R1 (RT_R1), overall RT (RT_global) and the magnitude of implicit motor learning (_iML, calculated as % difference between R8 and S7) were compared among body segments and PD vs. HCs groups by mixed two-way RM-ANOVA. The learning responses (RT_R1-R8Curve) and the errors curves were compared among body segments, groups and blocks (R1, R8 and S2-S7) by mixed three-way RM-ANOVA. While PD patients showed the characteristic bradykinesia, our data indicate that they are able to gain an identical sequence-specific implicit motor learning magnitude, with a similar timing, compared to HCs. Moreover, the magnitude and timing of the learning response is consistent across different body segments. This suggests that SRTT, conducted with different body segments, could be considered a valuable tool for studying motor learning in PD and HCs in neurorehabilitation.