Is There Task-specificity In Implicit Motor Learning? Comparison Between Individuals With Parkinson's Disease And Controls

Alterations in motor learning are associated with Parkinson’s disease (PD). Possible task-specificity remains unexplored and could have practical implications for testing and rehabilitation. PURPOSE: To investigate the possible task-specificity of implicit motor learning (iML) in three different ecological movements in people with PD vs age-matched healthy controls (C). METHODS: 17 participants with PD (68.6 ± 7.7 yrs, 1.8 ± 0.6 H&Y) and 29 C (69.6 ± 5.3 yrs) performed, on the same day, in random order, the Serial Reaction Time Task (SRTT) in three ecological movement tasks: i) key-press using 4 fingers on a pad; ii) arm-reaching and iii) foot-reaching of 4 targets with arms or feet, respectively. Visual-motor reaction time corrected for errors (cRT) was recorded in response to visual stimuli. A total of 8 trials, each consisting of 4 repetitions of a 12-stimuli sequence, were presented: in trials 1 and 8 sequences had a random order (R1, R8); in trials 2-7 an identical 12-stimuli sequence was repeated (S2-S7) without subjects’ awareness. cRTs in R1 and iML (calculated as % difference between R8 and S7) were compared among groups (PD vs C) and tasks by two-way RM-ANOVA. RESULTS: People with PD had slower cRTs vs C in R1 of arm- (0.59 ± 0.11 vs 0.51 ± 0.07 s respectively, p = 0.02) and foot-reaching movements (0.60 ± 0.09 vs 0.56 ± 0.09 s, p = 0.05) but not of key-press task (0.55 ± 0.13 vs 0.54 ± 0.10 s, p = 0.60). iML was present in both PD and C in all tasks: for arm- and foot-reaching tasks PD and C displayed a similar iML, with no difference between tasks (overall arms 3.71 ± 4.09 vs feet 5.85 ± 4.03%). Vice versa, PD had a smaller iML in key-press task vs C (5.34 ± 8.67 vs 9.99 ± 8.97%, p = 0.01). CONCLUSION: The SRTT paradigm can be effectively applied to the evaluation of iML independently of the movement task. Therefore, the task can be chosen based on movement capabilities and/or the necessity to explore a specific movement. The comparison of cRTs in R1 allows to detect differences in movement planning and execution between C and early-stage PD only when movements that involve either axial control or the lower limb (i.e. arm- and foot-reaching) are used. Finally, the iML of more complex tasks (i.e. the movement of 4 fingers vs that of 2 limbs) appears to highlight better the differences in motor learning between early-stage PD and C. Provincia Autonoma di Bolzano, Ufficio Innovazione e Tecnologia