Reducing task difficulty during practice improves motor learning in older adults

Self-adaptive over progressive non-adaptive immersive virtual reality serious game to promote motor learning in older adults - A double blind randomized controlled trial

Older adults often experience cognitive and functional decline, which can be mitigated by innovative interventions like immersive virtual reality (iVR). Self-adaptive serious games, which dynamically adjust task difficulty, may provide additional benefits by tailoring challenges to individual performance. However, the comparative effectiveness of self-adaptive versus progressive non-adaptive iVR interventions on motor learning in older adults remains underexplored. This randomized controlled trial primarily aimed to compare the effects of self-adaptive and progressive non-adaptive iVR interventions on motor learning in older adults. A total of 33 older adults were randomly assigned to either a self-adaptive (n = 17) or progressive non-adaptive (n = 16) iVR group. Both interventions involved an iVR serious game requiring unimanual reaching, target selection, and distractor inhibition under increasing difficulty over three days. Performance was evaluated pre- and post-intervention using a standardized iVR task, consisting of hitting a virtual target while ignoring distractors. This task features five levels of difficulty (level 0: no distractors; level 4: 17 low-saliency distractors). Primary outcomes, assessed during the standardized task, included changes in speed-accuracy trade-offs (SAT) and relative response time (RT, compared to level 0). Both participants and assessors were blinded to the intervention. After the intervention, both groups exhibited significant SAT improvements at level 1, 3 and 4 (P < 0.05) and RT gains at level 3 and 4 (P < 0.05). The self-adaptive group demonstrated significantly greater SAT (P = 0.049) and relative RT (P = 0.004) improvements at level 4. Findings suggest that older adults can achieve motor learning in iVR, particularly with self-adaptive serious games, highlighting potential for self-rehabilitation. Clinical trial NCT06141642 approved the 21th November 2023.

Effective Motor Skill Learning Induces Inverted-U Load-Dependent Activation in Contralateral Pre-Motor and Supplementary Motor Area

Motor learning involves complex interactions between the cognitive and sensorimotor systems, which are susceptible to different levels of task load. While the mechanism underlying load-dependent regulations in cognitive functions has been extensively investigated, their influence on downstream execution in motor skill learning remains less understood. The current study extends the understanding of whether and how learning alters the load-dependent activation pattern by a longitudinal functional near-infrared spectroscopy (fNIRS) study in which 30 healthy participants (15 females) engaged in extensive practice on a two-dimensional continuous hand tracking task with varying task difficulty. We proposed the index of difficulty (ID) as a quantitative measure of task difficulty, which was monotonically associated with a psychometric measure of subjective workload. As learning progressed, participants exhibited enhanced behavioral and metacognitive performance. Behavioral improvements were accompanied by plastic changes in the inferior prefrontal cortex, reflecting a shift in control strategy during motor learning. Most importantly, we found robust evidence of the learning-induced alteration in load-dependent cortical activation patterns, indicating that effective motor skill learning may lead to the emergence of an inverted-U relationship between cortical activation and load level in the contralateral pre-motor and supplementary motor areas. Our findings provide new insights into the learning-induced plasticity in brain and behavior, highlighting the load-dependent contributions in motor skill learning.

A Self-Adaptive Serious Game to Improve Motor Learning Among Older Adults in Immersive Virtual Reality: Short-Term Longitudinal Pre-Post Study on Retention and Transfer

BACKGROUND

Despite their potential, the use of serious games within immersive virtual reality (iVR) for enhancing motor skills in older adults remains relatively unexplored. In this study, we developed a self-adaptive serious game in iVR called REAsmash-iVR. This game involves swiftly locating and striking a digital mole presented with various distractors.

OBJECTIVE

This short-term longitudinal pre-post study aims to evaluate REAsmash-iVR's efficacy in promoting motor learning in older adults. Specifically, we seek to determine the transfer and retention of motor learning achieved through REAsmash-iVR to other iVR tasks.

METHODS

A total of 20 older adults participated in the study, engaging with REAsmash-iVR over 7 consecutive days. The evaluation included iVR tests such as KinematicsVR and a VR adaptation of the Box and Block Test (BBT-VR). KinematicsVR tasks included drawing straight lines and circles as fast and as accurately as possible, while BBT-VR required participants to move digital cubes as quickly as possible within 60 seconds. Assessments were conducted before and after the intervention, with a follow-up at 1 week post intervention. The primary outcome focused on evaluating the impact of REAsmash-iVR on speed-accuracy trade-off during KinematicsVR tasks. Secondary outcomes included analyzing movement smoothness, measured by spectral arc length, and BBT-VR scores.

RESULTS

Results revealed significant improvements in speed-accuracy trade-off post intervention compared to that before the intervention, with notable retention of skills for straight lines (t19=5.46; P<.001; Cohen d=1.13) and circle drawing (t19=3.84; P=.001; Cohen d=0.787). Likewise, there was a significant enhancement in spectral arc length, particularly for circle drawing (χ²2=11.2; P=.004; ε2=0.23), but not for straight-line drawing (χ²2=2.1; P=.35; ε2=0.003). Additionally, participants demonstrated transfer with significant improvement (q=5.26; P<.001; Cohen r=0.678) and retention (q=6.82; P<.001; Cohen r=0.880) in BBT-VR skills.

CONCLUSIONS

These findings provide perspectives for the use of iVR to improve motor learning in older adults through delivering self-adaptive serious games targeting motor and cognitive functions.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04694833; https://clinicaltrials.gov/study/NCT04694833.

Cross-Task Differences in Frontocentral Cortical Activations for Dynamic Balance in Neurotypical Adults

Although significant progress has been made in understanding the cortical correlates underlying balance control, these studies focused on a single task, limiting the ability to generalize the findings. Different balance tasks may elicit cortical activations in the same regions but show different levels of activation because of distinct underlying mechanisms. In this study, twenty young, neurotypical adults were instructed to maintain standing balance while the standing support surface was either translated or rotated. The differences in cortical activations in the frontocentral region between these two widely used tasks were examined using electroencephalography (EEG). Additionally, the study investigated whether transcranial magnetic stimulation could modulate these cortical activations during the platform translation task. Higher delta and lower alpha relative power were found over the frontocentral region during the platform translation task when compared to the platform rotation task, suggesting greater engagement of attentional and sensory integration resources for the former. Continuous theta burst stimulation over the supplementary motor area significantly reduced delta activity in the frontocentral region but did not alter alpha activity during the platform translation task. The results provide a direct comparison of neural activations between two commonly used balance tasks and are expected to lay a strong foundation for designing neurointerventions for balance improvements with effects generalizable across multiple balance scenarios.

High-intensity acute exercise impacts motor learning in healthy older adults

Healthy aging is associated with changes in motor sequence learning, with some studies indicating decline in motor skill learning in older age. Acute cardiorespiratory exercise has emerged as a potential intervention to improve motor learning, however research in healthy older adults is limited. The current study investigated the impact of high-intensity interval exercise (HIIT) on a subsequent sequential motor learning task. Twenty-four older adults (aged 55-75 years) completed either 20-minutes of cycling, or an equivalent period of active rest before practicing a sequential force grip task. Skill learning was assessed during acquisition and at a 6-hour retention test. In contrast to expectation, exercise was associated with reduced accuracy during skill acquisition compared to rest, particularly for the oldest participants. However, improvements in motor skill were retained in the exercise condition, while a reduction in skill was observed following rest. Our findings indicate that high-intensity exercise conducted immediately prior to learning a novel motor skill may have a negative impact on motor performance during learning in older adults. We also demonstrated that exercise may facilitate early offline consolidation of a motor skill within this population, which has implications for motor rehabilitation.

Neither Too Easy Nor Too Difficult: Effects of Different Success Criteria on Motor Skill Acquisition in Children

The purpose of this study was to examine the effects of different success criteria on motor learning in children. Forty-eight children threw soft-golf balls toward a circular target using their nondominant arm. On Day 1, they performed six blocks of 12 trials from 5.5 m. On Day 3, they performed a 12-trial retention test followed by a 12-trial transfer test. Participants were randomly assigned to one of four groups: difficult criteria for success, relatively easy criteria for success (RES), easy criteria for success, and control. Results demonstrated that there was a significant difference between the RES and control groups in their throwing accuracy on the retention and transfer tests, and the RES group had the highest score compared with the other two groups. This research suggests that providing relatively easy criteria facilitates motor skill acquisition in children.

A study on how concurrent visual feedback affects motor learning of adjustability of grasping force in younger and older adults

In this study, we investigated the differences of the effectiveness from concurrent visual feedback among younger and older adults in learning tasks that require adjustability of grasping force (AGF), as well as the functions related to AGF in each generation. The younger and older adult groups were evaluated for simple visual reaction time as visual-motor speed (VMS) and a 100 g AGF task that reflected the difference between desired performance and actual performance. The main learning task was then practiced using concurrent visual feedback and tested without feedback. The VMS of older adults was slower than that of the younger, and the error in the 100 g AGF task was larger in older adults than in the younger adults. Performance improved from pre-test to retention test in both groups, but the older adult group failed to reach the level of the younger adult group. The results of this study show that concurrent visual feedback is effective for learning the tasks that require AGF in both groups. Indicatively, improvement in performance during practice is insufficient in older people for whom there is a large difference between desired performance and actual performance, or whose VMS is slow.

Neural Correlates of Motor Skill Learning Are Dependent on Both Age and Task Difficulty

Although a general age-related decline in neural plasticity is evident, the effects of age on neural plasticity after motor practice are inconclusive. Inconsistencies in the literature may be related to between-study differences in task difficulty. Therefore, we aimed to determine the effects of age and task difficulty on motor learning and associated brain activity. We used task-related electroencephalography (EEG) power in the alpha (8–12 Hz) and beta (13–30 Hz) frequency bands to assess neural plasticity before, immediately after, and 24-h after practice of a mirror star tracing task at one of three difficulty levels in healthy younger (19–24 yr) and older (65–86 yr) adults. Results showed an age-related deterioration in motor performance that was more pronounced with increasing task difficulty and was accompanied by a more bilateral activity pattern for older vs. younger adults. Task difficulty affected motor skill retention and neural plasticity specifically in older adults. Older adults that practiced at the low or medium, but not the high, difficulty levels were able to maintain improvements in accuracy at retention and showed modulation of alpha TR-Power after practice. Together, these data indicate that both age and task difficulty affect motor learning, as well as the associated neural plasticity.

Relatively Easy Criteria for Success Enhances Motor Learning by Altering Perceived Competence

The purpose of this study was to examine whether enhancing success expectation by providing relatively easy criteria for success would, in turn, enhance motor learning outcomes. Thirty university student participants threw soft-golf balls towards a circular target, using their non-dominant arm; they performed seven blocks of 12 trials from a distance of 5.5 meters on Day 1, and one block of 12 trials on separate retention and transfer tests on Day 2. After the first block on Day 1, participants were randomly assigned to one of two groups in which they practiced the remaining six blocks of 12 trials: (a) one with relatively easy success (RES) criteria or (b) one with difficult success (DS) criteria. After the practice, we administered a perceived competence scale, a sub-scale of the Intrinsic Motivation Inventory (IMI). On Day 2, participants in the RES group outperformed those in the DS group on both the retention and transfer tests, showing enhanced motor learning. The RES group also self-reported higher perceived competence than the DS group, indicating that the mechanism for benefiting from easier success criteria may have been an alteration in participants' perceived competence.

Potential Motor Benefits of Visual Feedback of Error Reduction for Older Adults

This study investigated how visual feedback of virtual error reduction (ER) modified the visuomotor performance of older adults with limited attentional capacity. Error structures of young and older adults during birhythmic force tracking were contrasted when the visualized error size was exact or half of the actual size. As compared with full-size error feedback, ER feedback improved the force tracking symmetry of older adults, but undermined that of young adults. Extended Poincaré analysis revealed that young adults presented greater short-term error variability (mean value of κ-lagged SD1 of the error signal) with ER feedback, which led to a smaller mean value of κ-lagged SD1 of the error signal for older adults. The ER-related task improvement of the older adults was negatively correlated with the size of the tracking errors with real error feedback and positively correlated with ER-related increases in force spectral symmetry and decreases in the mean value of κ-lagged SD1 of the error signal. ER feedback could advance visuomotor tasks for older adults who perform worse with full-size visual feedback by the enhancement of self-efficacy and stabilization of negative internal feedback.

Failure to Engage Neural Plasticity through Practice of a High-difficulty Task is Accompanied by Reduced Motor Skill Retention in Older Adults

While the difficulty of a motor task can act as a stimulus for learning in younger adults, it is unknown how task difficulty interacts with age-related reductions in motor performance and altered brain activation. We examined the effects of task difficulty on motor performance and used electroencephalography (EEG) to probe task-related brain activation after acquisition and 24-h retention of a mirror star-tracing skill in healthy older adults (N = 36, 65-86 years). The results showed that the difficulty of the motor skill affected both the magnitude of motor skill learning and the underlying neural mechanisms. Behavioral data revealed that practicing a motor task at a high difficulty level hindered motor skill consolidation. The EEG data indicated that task difficulty modulated changes in brain activation after practice. Specifically, a decrease in task-related alpha power in frontal and parietal electrodes was only present after practice of the skill at the low and medium, but not the high difficulty level. Taken together, our findings show that a failure to engage neural plasticity through practice of a high-difficulty task is accompanied by reduced motor skill retention in older adults. The data help us better understand how older adults learn new motor skills and might have implications for prescribing motor skill practice according to its difficulty in rehabilitation settings.

Force Steadiness During a Cognitively Challenging Motor Task Is Predicted by Executive Function in Older Adults

Motor performance and cognitive function both decline with aging. Older adults for example are usually less steady for a constant-force task than young adults when performing low-intensity contractions with limb muscles. Healthy older adults can also show varying degrees of cognitive decline, particularly in executive function skills. It is not known, however, whether age-related changes in steadiness of low-force tasks and cognitive function are independent of one another. In this study, we determined if executive function skills in aging are associated with the steadiness during a low-force muscle contraction performed with and without the imposition of a cognitive challenge. We recruited 60 older adults (60–85 years old, 34 women, 26 men) and 48 young adults (19–30 years old, 24 women, 24 men) to perform elbow flexor muscle contractions at 5% of maximal voluntary contraction (MVC) force in the presence and absence of a difficult mental-math task (counting backward by 13 from a four-digit number). Force steadiness was quantified as the coefficient of variation (CV) of force and executive function was estimated with the Trail-making Test part A and B. The cognitive challenge increased the CV of force (i.e., decreased force steadiness) with greater changes in older adults than young adults (5.2 vs. 1.3%, respectively, cognitive challenge × age: P < 0.001). Older adults were 35% slower in both parts A and B of the Trail-making Test (P < 0.001), and to eliminate the effects of age and education on this variable, all further analyses were performed with the age-corrected z-scores for each individual using established normative values. Hierarchical regression models indicated that decreased force steadiness during a cognitive challenge trial was in part, explained by the performance in the Trail-making Test part A and B in older (r = 0.53 and 0.50, respectively, P < 0.05), but not in young adults (P > 0.05). Thus, healthy community-dwelling older adults, who have poorer executive function skills, exhibit reduced force steadiness during tasks when also required to perform a high cognitive demand task, and are likely at risk of reduced capacity to perform daily activities that involve cognitively challenging motor tasks.

Remote Limb Ischemic Conditioning and Motor Learning: Evaluation of Factors Influencing Response in Older Adults

Remote limb ischemic conditioning (RLIC) is a clinically feasible method of promoting tissue protection against subsequent ischemic insult. Recent findings from our lab demonstrated that RLIC robustly enhances motor learning in young, healthy humans. The next step is to determine which individuals would receive maximum benefit from RLIC before applying these findings to clinical rehabilitation populations such as stroke. Numerous factors, such as age, sex, body mass index (BMI), and cardiovascular comorbidities may influence the response. Sixty-nine participants aged 40-80 were randomized to receive either RLIC (n = 33) or sham (n = 36) conditioning. Participants underwent seven consecutive sessions consisting of RLIC or sham conditioning with a blood pressure cuff on the upper extremity and motor training on a stability platform balance task, with two follow-up sessions. Balance change (post-test-pre-test) was compared across participants, groups, and the factors of age, sex, BMI, and comorbidities. Participants in both groups improved their performance on the balance task from pre- to post-test. Overall balance change was independently associated with age and BMI. There was no difference in balance change between RLIC and Sham groups. However, RLIC significantly enhanced balance performance in participants with no comorbidities. Compared with our previous study in young adults, middle-aged and older adults demonstrated smaller improvements on the balance task. RLIC enhanced learning in middle-aged and older adults only in the absence of pre-defined comorbidities. RLIC may be a promising tool for enhancing motor recovery, but the accumulation of comorbidity with age may decrease its effectiveness.

Learning new gait patterns: Age-related differences in skill acquisition and interlimb transfer

Evidence from upper-extremity literature suggests that the normal ageing process affects an individual's ability to learn and retain a motor skill, but spares their ability to transfer the skill to the untrained, opposite limb. While this phenomenon has been well-studied in the upper-extremity, evidence in the lower-extremity is limited. Further, it is unclear to what extent age-related differences in motor learning and transfer are dependent on visual feedback of the motor task. Therefore, the purpose of this study was to examine the effects of ageing on motor learning, retention, and interlimb transfer during walking with and without visual feedback. Forty-four subjects (24 young; 20 older adults) were tested on a treadmill over two consecutive days. On day 1, subjects learned a new gait pattern by performing a foot-trajectory tracking task that necessitated greater hip and knee flexion during the swing phase of the gait. On day 2, subjects repeated the task with their training leg to test retention, then with their untrained leg to test interlimb transfer. Trials without visual feedback were also collected on both days. Results indicated that older adults had reduced ability to learn the task, and also exhibited lower retention and inter-limb transfer. However, these differences were dependent on visual feedback as the groups performed similarly when feedback was removed. The findings provide novel evidence indicating that ageing impairs learning, retention, and transfer of motor skills in the lower-extremity during walking, which may have implications for gait therapy after stroke and other geriatric conditions.

Mild cognitive impairment affects motor control and skill learning

Mild cognitive impairment (MCI) is a transitional phase between normal cognitive aging and dementia. As the world population is aging rapidly, more MCI patients will be identified, posing significant problems to society. Normal aging is associated with cognitive and motor decline, and MCI brings additional impairments. Compared to healthy older adults, MCI patients show poorer motor control in a variety of tasks. Efficient motor control and skill learning are essential for occupational and leisure purposes; degradation of motor behaviors in MCI patients often adversely affects their health and quality of life. In this article, we first define MCI and describe its pathology and neural correlates. After this, we review cognitive changes and motor control and skill learning in normal aging. This section is followed by a discussion of MCI-related degradation of motor behaviors. Finally, we propose that multicomponent interventions targeting both cognitive and motor domains can improve MCI patients’ motor functions. Future research directions are also raised.

Rapid Responsiveness to Practice Predicts Longer-Term Retention of Upper Extremity Motor Skill in Non-Demented Older Adults

Skill acquisition is a form of motor learning that may provide key insights into the aging brain. Although previous work suggests that older adults learn novel motor tasks slower and to a lesser extent than younger adults, we have recently demonstrated no significant effect of chronological age on the rates and amounts of skill acquisition, nor on its long-term retention, in adults over the age of 65. To better understand predictors of skill acquisition in non-demented older adults, we now explore the relationship between early improvements in motor performance due to practice (i.e., rapid responsiveness) and longer-term retention of an upper extremity motor skill, and whether the extent of rapid responsiveness was associated with global cognitive status. Results showed significant improvements in motor performance within the first five (of 150) trials, and that this “rapid responsiveness” was predictive of skill retention 1 month later. Notably, the extent of rapid responsiveness was not dependent on global cognitive status, as measured by the Montreal Cognitive Assessment (MoCA). Thus, rapid responsiveness appears to be an important variable in longer-term neurorehabilitative efforts with older adults, regardless of their cognitive status.

Switching between hands in a serial reaction time task: a comparison between young and old adults

Healthy aging is associated with a variety of functional and structural brain alterations. These age-related brain alterations have been assumed to negatively impact cognitive and motor performance. Especially important for the execution of everyday activities in older adults (OA) is the ability to perform movements that depend on both hands working together. However, bimanual coordination is typically deteriorated with increasing age. Hence, a deeper understanding of such age-related brain-behavior alterations might offer the opportunity to design future interventional studies in order to delay or even prevent the decline in cognitive and/or motor performance over the lifespan. Here, we examined to what extent the capability to acquire and maintain a novel bimanual motor skill is still preserved in healthy OA as compared to their younger peers (YA). For this purpose, we investigated performance of OA (n = 26) and YA (n = 26) in a bimanual serial reaction time task (B-SRTT), on two experimental sessions, separated by 1 week. We found that even though OA were generally slower in global response times, they showed preserved learning capabilities in the B-SRTT. However, sequence specific learning was more pronounced in YA as compared to OA. Furthermore, we found that switching between hands during B-SRTT learning trials resulted in increased response times (hand switch costs), a phenomenon that was more pronounced in OA. These hand switch costs were reduced in both groups over the time course of learning. More interestingly, there were no group differences in hand switch costs on the second training session. These results provide novel evidence that bimanual motor skill learning is capable of reducing age-related deficits in hand switch costs, a finding that might have important implications to prevent the age-related decline in sensorimotor function.

Augmenting mirror visual feedback-induced performance improvements in older adults

Previous studies have indicated that age-related behavioral alterations are not irreversible but are subject to amelioration through specific training interventions. Both training paradigms and non-invasive brain stimulation (NIBS) can be used to modulate age-related brain alterations and thereby influence behavior. It has been shown that mirror visual feedback (MVF) during motor skill training improves performance of the trained and untrained hands in young adults. The question remains of whether MVF also improves motor performance in older adults and how performance improvements can be optimised via NIBS. Here, we sought to determine whether anodal transcranial direct current stimulation (a-tDCS) can be used to augment MVF-induced performance improvements in manual dexterity. We found that older adults receiving a-tDCS over the right primary motor cortex (M1) during MVF showed superior performance improvements of the (left) untrained hand relative to sham stimulation. An additional control experiment in participants receiving a-tDCS over the right M1 only (without MVF/motor training of the right hand) revealed no significant behavioral gains in the left (untrained) hand. On the basis of these findings, we propose that combining a-tDCS with MVF might be relevant for future clinical studies that aim to optimise the outcome of neurorehabilitation.

Task complexity and maximal isometric strength gains through motor learning

This study compared the effects of a simple versus complex contraction pattern on the acquisition, retention, and transfer of maximal isometric strength gains and reductions in force variability. A control group (N = 12) performed simple isometric contractions of the wrist flexors. An experimental group (N = 12) performed complex proprioceptive neuromuscular facilitation (PNF) contractions consisting of maximal isometric wrist extension immediately reversing force direction to wrist flexion within a single trial. Ten contractions were completed on three consecutive days with a retention and transfer test 2‐weeks later. For the retention test, the groups performed their assigned contraction pattern followed by a transfer test that consisted of the other contraction pattern for a cross‐over design. Both groups exhibited comparable increases in strength (20.2%, P < 0.01) and reductions in mean torque variability (26.2%, P < 0.01), which were retained and transferred. There was a decrease in the coactivation ratio (antagonist/agonist muscle activity) for both groups, which was retained and transferred (35.2%, P < 0.01). The experimental group exhibited a linear decrease in variability of the torque‐ and sEMG‐time curves, indicating transfer to the simple contraction pattern (P < 0.01). The control group underwent a decrease in variability of the torque‐ and sEMG‐time curves from the first day of training to retention, but participants returned to baseline levels during the transfer condition (P < 0.01). However, the difference between torque RMS error versus the variability in torque‐ and sEMG‐time curves suggests the demands of the complex task were transferred, but could not be achieved in a reproducible way.

This study examines the effect of task complexity on the acquisition, retention, and transfer of increases in maximal strength and decreases in force variability, which is novel. Simple agonist‐only contractions are compared to a more complex reversal contraction pattern as used during proprioceptive neuromuscular facilitation (PNF). The goal was to determine if the more complex contraction pattern interferes with the strength gains and reduced variability by impeding the development of agonist‐antagonist coordination.