Age- and task-dependent effects of cerebellar tDCS on manual dexterity and motor learning-A preliminary study.

OBJECTIVES: The role of the cerebellum in motor learning of dexterous control and interaction with aging remains incompletely understood. We compared the effect of age and cerebellar transcranial direct current stimulation (CRB-tDCS) on motor learning in two different manual dexterity tasks, visuomotor force control vs. effector selection (independent finger movements). METHODS: Twenty younger and 20 older adults were randomized (double-blinded) to anodal or sham CRB-tDCS during dexterity training over three consecutive days, and followed-up at day 10. Motor learning was measured as (i) overall learning (across 10 days), (ii) within-day (short-term) learning, (iii) between-day learning (consolidation), and (iv) retention (long-term learning; day 3 to day 10). RESULTS: Younger and older subjects showed significant overall learning in both tasks. Subjects with poor initial performance showed stronger learning. No effects of CRB-tDCS were observed in younger adults. A significant Age*CRB-tDCS interaction showed that CRB-tDCS improved within-day learning in finger independence (improved reaction time in effector selection) in older adults. However, a significant Age*CRB-tDCS interaction showed that CRB-tDCS impacted consolidation negatively in older subjects. No stimulation effects were found on retention. Finally, we found that degree of within-day learning in finger independence (change in reaction times) correlated with baseline (pre-training) reaction times in both young and old subjects. DISCUSSION: The results suggest that CRB-tDCS may improve short-term learning of manual dexterity in older adults in a task-dependent manner, specifically in difficult tasks requiring effector (action) selection. However, cerebellar tDCS stimulation may also interfere with consolidation in older subjects. These results need confirmation in a larger sample.

Recovery and Prediction of Bimanual Hand Use After Stroke.

OBJECTIVE: To determine similarities and differences in key predictors of recovery of bimanual hand use and unimanual motor impairment after stroke. METHOD: In this prospective longitudinal study, 89 patients with first-ever stroke with arm paresis were assessed at 3 weeks and 3 and 6 months after stroke onset. Bimanual activity performance was assessed with the Adult Assisting Hand Assessment Stroke (Ad-AHA), and unimanual motor impairment was assessed with the Fugl-Meyer Assessment (FMA). Candidate predictors included shoulder abduction and finger extension measured by the corresponding FMA items (FMA-SAFE; range 0-4) and sensory and cognitive impairment. MRI was used to measure weighted corticospinal tract lesion load (wCST-LL) and resting-state interhemispheric functional connectivity (FC). RESULTS: Initial Ad-AHA performance was poor but improved over time in all (mild-severe) impairment subgroups. Ad-AHA correlated with FMA at each time point (r > 0.88, p < 0.001), and recovery trajectories were similar. In patients with moderate to severe initial FMA, FMA-SAFE score was the strongest predictor of Ad-AHA outcome (R 2 = 0.81) and degree of recovery (R 2 = 0.64). Two-point discrimination explained additional variance in Ad-AHA outcome (R 2 = 0.05). Repeated analyses without FMA-SAFE score identified wCST-LL and cognitive impairment as additional predictors. A wCST-LL >5.5 cm3 strongly predicted low to minimal FMA/Ad-AHA recovery (≤10 and 20 points respectively, specificity = 0.91). FC explained some additional variance to FMA-SAFE score only in unimanual recovery. CONCLUSION: Although recovery of bimanual activity depends on the extent of corticospinal tract injury and initial sensory and cognitive impairments, FMA-SAFE score captures most of the variance explained by these mechanisms. FMA-SAFE score, a straightforward clinical measure, strongly predicts bimanual recovery. CLINICALTRIALSGOV IDENTIFIER: NCT02878304. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that the FMA-SAFE score predicts bimanual recovery after stroke.

Age effects on voluntary and automatic adjustments in anti-pointing tasks.

We examined the effects of age on automatic and voluntary motor adjustments in pointing tasks. To this end, young (20-25 years) and middle-aged adults (48-62 years) were instructed to point at a target that could unexpectedly change its location (to the left or right) or its color (to green or red) during the movement. In the location change conditions, participants were asked to either adjust their pointing movement toward the new location (i.e., normal pointing) or in the opposite direction (i.e., anti-pointing). In the color change conditions, participants were instructed to adjust their movement to the left or right depending on the change in color. The results showed that in a large proportion of the anti-pointing trials, participants made two adjustments: an early initial automatic adjustment in the direction of the target shift followed by a late voluntary adjustment toward the opposite direction. It was found that the late voluntary adjustments were delayed for the middle-aged participants relative to the young participants. There were no age differences for the fast automatic adjustment in normal pointing, but the early adjustment in anti-pointing tended to be later in the middle-aged adults. Finally, the difference in the onset of early and late adjustments in anti-pointing adjustments was greater among the middle-aged adults. Hence, this study is the first to show that aging slows down voluntary goal-directed movement control processes to greater extent than the automatic stimulus-driven processes.

Proactive and retroactive transfer of middle age adults in a sequential motor learning task.

We assessed the effects of aging in the transfer of motor learning in a sequential manual assembly task that is representative for real working conditions. On two different days, young (18-30 years) and middle-aged adults (50-65 years) practiced to build two products that consisted of the same six components but which had to be assembled in a partly different order. Assembly accuracy and movement time during tests, which were performed before and after the practice sessions, were compared to determine proactive and retroactive transfer. The results showed proactive facilitation (i.e., benefits from having learned the first product on learning the second one) in terms of an overall shortening of movement time in both age-groups. In addition, only the middle-aged adults were found to show sequence-specific proactive facilitation, in which the shortening of movement time was limited to components that had the same the order in the two products. Most likely, however, the sequence-specific transfer was an epiphenomenon of the comparatively low rate of learning among the middle-aged adults. The results, however, did reveal genuine differences between the groups for retroactive transfer (i.e., effects from learning the second product on performance of the first). Middle-aged adults tended to show more pronounced retroactive interference in terms of a general decrease in accuracy, while younger adults showed sequence-specific retroactive facilitation (i.e., shortening of movement times for components that had the same order in the two products), but only when they were fully accurate. Together this suggests that in the learning of sequential motor tasks the effects of age are more marked for retroactive transfer than for proactive transfer.

Age and time effects on implicit and explicit learning.

UNLABELLED: BACKGROUND/STUDY CONTEXT: It has been proposed that effects of aging are more pronounced for explicit than for implicit motor learning. The authors evaluated this claim by comparing the efficacy of explicit and implicit learning of a movement sequence in young and older adults, and by testing the resilience against fatigue and secondary tasking after learning. It was also examined whether explicit learning in older adults can be promoted by alleviating time constraints during learning. METHODS: The alternating serial reaction time task (ASRTT) was used. Experiment 1 compared the benefits of receiving full instructions about the stimulus sequence relative to receiving no instructions in young (20-25 years) and older (50-65 years) adults during retention and during transfer to fatigue and secondary task conditions. Experiment 2 alleviated time constraints during the initial bouts of practice with full instructions. RESULTS: Experiment 1 indicated that the older adults learned on the ASRTT and achieved similar performance as young adults when no instructions were given. In contrast to the young adults, learning was not superior in older adults who received full instructions compared with those who did not. Experiment 2 indicated that alleviating time constraints allowed some of the older adults to gain from instruction but only under relatively low time constraints, but there was no retention with rigorous time constraints. CONCLUSION: Explicit learning, but not implicit learning, declines in older adults. This is partly due to older adults difficulties to apply explicit knowledge. Less rigorous time constraints can help to ameliorate some of these difficulties and may induce levels of explicit learning in older adults that will result in superior performance compared with implicit learning. Implicit learning did occur under time constraints that prevented explicit learning.

Optimising assembly learning in older adults through the manipulation of instruction.

The present investigation assessed the putative benefits of reducing instructions for older adults' learning of an assembly task. Young and older adults had to build a product by assembling six components. Two groups practiced following instruction methods that differed in the degree of explicit information they conveyed about the correct assembly order. After practice, retention, consolidation of performance (tested immediately after practice and on a separate day, respectively) and stability of performance (tested by introducing a concurrent second task) were assessed. Younger adults showed similar performance levels for both instruction methods. Older adults, however, showed similar retention but clearly weaker consolidation and stability of performance following less encompassing instructions. Contrary to expectations, enhancing the involvement of explicit processes allowed older adults to gain a more permanent and stable performance improvements. The findings are discussed relative to the characteristics of the assembly task. PRACTITIONER SUMMARY: We addressed how performance and learning of older adults in an assembly task can be optimised through different types of instruction. The findings suggest that increasing awareness of task characteristics enhance not only long-term performance, but also resilience against distraction. Future work must evaluate if these findings generalise to more complex tasks.

Implicit and explicit learning: applications from basic research to sports for individuals with impaired movement dynamics.

PURPOSE: Motor skills can be learned in an explicit or an implicit manner. Explicit learning places high demands on working memory capacity, but engagement of working memory is largely circumvented when skills are learned implicitly. We propose that individuals with impaired movement dynamics may benefit from implicit learning methods when acquiring sports-related motor skills. METHOD: We discuss converging evidence that individuals with cerebral palsy and children born prematurely have compromised working memory capacity. This may in part explain the difficulties they encounter when learning motor and other skills. We also review tentative evidence that older people, whose movement dynamics deteriorate, can implicitly learn sports-related motor skills and that this results in more durable performance gains than explicit learning. RESULTS: Individuals with altered movement dynamics and compromised working memory can benefit from implicit motor learning. CONCLUSION: We conclude with an appeal for more extensive evaluation of the merits of implicit motor learning in individuals with impaired movement dynamics.