Interlimb Transfer Of Visuomotor Adaptation Research Articles

Facilitative effects of use-dependent learning on interlimb transfer of visuomotor adaptation in a person with congenital mirror movements.

It has been shown that use-dependent learning can facilitate interlimb transfer of motor learning in neurologically intact individuals. However, it is unknown whether it can also facilitate interlimb transfer in individuals with neurological impairment. In this case study, we examined the effect of use-dependent learning on interlimb transfer of visuomotor adaptation in a person with congenital mirror movements, DB, who showed no interlimb transfer in our previous studies (Bao, Morgan, Lei, & Wang, 2020; Javidialsaadi, & Wang, 2021). DB first performed reaching movements with the right arm repeatedly while adapting to a visuomotor rotation condition with the left arm (training session), and then adapted to the same rotation condition with the right arm (transfer session). DB's right arm performance in the transfer session was significantly better than that observed in our previous studies, indicating interlimb transfer of visuomotor adaptation. The percentage of transfer was over 90%, which is similar to that observed in healthy young adults previously. These findings suggest that interlimb transfer of visuomotor adaptation can occur by involving model-based learning, which is effector independent, and/or use-dependent (or model-free) learning, which is effector specific; and also that the relative contribution of use-dependent learning to interlimb transfer of visuomotor adaptation can be as large as that of model-based learning.

Lack of changes in motor function of the brain in healthy older adults after participation in a cognitive walking program.

A walking-based exercise program, called the cognitive walking program (CWP), has been shown to be beneficial for improving cognitive function in healthy older adults. It remains unknown whether it is beneficial for improving motor function of the brain. We investigated the effects of CWP on motor function of the brain by examining changes in interlimb transfer of visuomotor adaptation in older adults. Subjects were divided based on their physical activity level (active vs. sedentary) and participated in CWP. A control group performed normal walking. Fifty-two healthy older adults, 67–78 years old, were studied. All subjects participated in CWP or normal walking for 6 months. To assess brain motor function, all subjects adapted to a rotated visual display during reaching movements with the right arm first, then with the left arm. Interlimb transfer of visuomotor adaptation was assessed at baseline, 3 months, and 6 months after training onset. It was hypothesized that if CWP had beneficial effects, the extent of transfer would change over time. The subject’s physical fitness was also assessed. Significant transfer from the right to the left arm occurred in all subject groups. Improvements in physical fitness were also observed. However, the extent of transfer did not change even after 6 months, with no group difference. Findings suggest that though beneficial for improving cognitive function in older adults, participating in CWP for 6 months is not long enough to improve brain motor function when the motor function is reflected as changes in interlimb transfer of visuomotor adaptation.

Lack of interlimb transfer following visuomotor adaptation in a person with congenital mirror movements despite the awareness of the visuomotor perturbation

There is a controversy regarding whether visuomotor adaptation heavily involves both implicit and explicit learning processes or not. Likewise, another controversy exists regarding whether interlimb transfer of visuomotor adaptation is related to explicit processes or not. To address the latter issue, we examined interlimb transfer of visuomotor adaptation in an individual with congenital mirror movements, ‘DB’. DB has been tested previously using an experimental paradigm in which neurologically intact individuals demonstrated substantial transfer. DB, however, showed no transfer due to impaired interhemispheric communications. In that study, DB was unaware of the visuomotor perturbation. Here, we informed him of the perturbation prior to the experiment to determine whether providing the information would increase interlimb transfer. DB first adapted to a visuomotor rotation with the left arm, then with the right arm during reaching movements. Data from the present study were compared against those from our previous study. Results indicate no transfer across the arms despite the fact that he was aware of the perturbation. Considering overall findings in the literature, we suggest that interlimb transfer does not depend on one’s awareness, although its extent can increase when individuals rely on cognitive strategies to deal with perturbations (c.f., Werner et al., 2019).

A positive association between active lifestyle and hemispheric lateralization for motor control and learning in older adults

Physical activity (PA) is well known to have general health benefits for older adults, but it is unclear whether it can also positively affect brain function involved in motor control and learning. We have previously shown that interlimb transfer of visuomotor adaptation occurs asymmetrically in young adults, while that occurs symmetrically in older adults, which suggests that the lateralized function of each hemisphere during motor tasks is diminished with aging. Here, we investigated the association between the level of PA and hemispheric motor lateralization by comparing the pattern of interlimb transfer following visuomotor adaptation between physically active and inactive older adults. Subjects were divided into two groups based on their PA level (active, inactive). They were further divided into two groups, such that a half of the subjects in each group adapted to a 30° rotation during targeted reaching movements with the left arm first, then with the right arm; and the other half with the right arm first, then with the left arm. Results indicated asymmetrical transfer (from left to right only) in the active subjects, whereas symmetrical transfer (from left to right, and vice versa) was observed in the inactive subjects. These findings suggest that older adults who maintain active lifestyle have a central nervous system that is more intact in terms of its lateralized motor function as compared with those who are inactive.

Prolonged training does not result in a greater extent of interlimb transfer following visuomotor adaptation

Learning a visumotor adaptation task with one arm typically facilitates subsequent performance with the other. The extent of transfer across the arms, however, is generally much smaller than that across different conditions within the same arm. This may be attributed to a possibility that intralimb transfer involves both algorithmic and instance–reliant learning, whereas interlimb transfer only involves algorithmic learning. Here, we investigated whether prolonged training with one arm could facilitate subsequent performance with the other arm to a greater extent, by examining the effect of varying lengths of practice trials on the extent of interlimb transfer. We had 18 subjects adapt to a 30° visuomotor rotation with the left arm first (training), then with the right arm (transfer). During the training session, the subjects reached toward multiple targets for 160, 320 or 400 trials; during the transfer session, all subjects performed the same task for 160 trials. Our results revealed substantial initial transfer from the left to the right arm in all three conditions. However, neither the amount of initial transfer nor the rate of adaptation during the transfer session was significantly different across the conditions, indicating that the extent of transfer was similar regardless of the length of initial training. Our findings suggest that interlimb transfer of visuomotor adaptation may only occur through algorithmic learning, which is effector independent, and that prolonged training may only have beneficial effects when instance–reliant learning, which is effector dependent, is also involved in the learning process.

The extent of interlimb transfer following adaptation to a novel visuomotor condition does not depend on awareness of the condition

There is a controversy in the literature as to whether transfer of motor learning across the arms occurs because of an individual's cognitive awareness of the learned condition. The purpose of this study was to test whether the extent of interlimb transfer following adaptation to a novel visuomotor rotation with one arm, as well as the rate of learning acquired by the other arm, would vary depending on the subjects' awareness of the rotation condition. Awareness of the condition was varied by employing three experimental conditions. In one condition, visual rotation of the display up to 32° was gradually introduced to minimize the subjects' awareness of the rotation during targeted reaching movement. In another condition, the 32° rotation was abruptly introduced from the beginning of the adaptation session. Finally, the subjects were informed regarding the rotation prior to the adaptation session. After adaptation with the left arm under the three conditions, subjects performed reaching movement with the right arm under the same 32° rotation condition. Our results showed that the amount of initial transfer, and also the changes in performance with the right arm, did not vary significantly across the three conditions. This finding suggests that interlimb transfer of visuomotor adaptation does not occur based on an individual's awareness of the manipulation, but rather as a result of implicit generalization of the obtained visuomotor transformation across the arms.

Aging reduces asymmetries in interlimb transfer of visuomotor adaptation

Hemispheric asymmetry reduction in older adults (HAROLD) has been reported in previous imaging studies that employed not only cognitive, but also motor tasks. However, whether age-related reductions in asymmetry of hemispheric activations affect the symmetry of motor behavior in older adults remains largely untested. We now examine the effect of aging on lateralization of motor adaptation and transfer by investigating adaptation to novel visuomotor transformations in both old and young age groups. We have previously reported substantial asymmetries in interlimb transfer of learning these transformations in young adults, and attributed these asymmetries in transfer to hemispheric lateralization for motor control, as detailed by our dynamic dominance hypothesis. Based on the HAROLD model, we reasoned that older adults should recruit more symmetrical hemispheric activity, and thus show more symmetrical transfer of adaptation across the arms. Half of the subjects in each age group first adapted to a rotated visual display with the left arm, then with the right arm; and the other half in the reversed order. Naïve performance with one arm and the same-arm performance following opposite arm adaptation were compared to determine the extent of transfer in each age group. Our results showed that interlimb transfer of initial direction information only occurred from the nondominant to dominant arm in young adults, whereas it occurred in both directions in older adults. Our findings clearly indicate substantially reduced asymmetry in visuomotor adaptation in older adults, and suggest that this reduced motor asymmetry might be related to diminished hemispheric lateralization for motor control.

Limitations in interlimb transfer of visuomotor rotations.

It has been shown that learning visuomotor rotations with multiple target directions, compared with a single target direction, leads to greater generalization to untrained targets within the same limb. This implies that multiple direction learning results in a more complete internal model of the visuomotor transform. It has also been documented that the extent of transfer of movement information regarding visuomotor adaptations between the limbs is limited, relative to that between different configurations of the same limb. The present study thus investigated the origin of this restriction in interlimb transfer, by comparing the effects of eight-direction and one-direction training conditions with one arm on the subsequent performance with the other arm. It was hypothesized that if multiple direction learning leads to a more complete model of the novel visuomotor transform, interlimb transfer should be enhanced relative to that following single direction training. However, if no differences are observed between single and multiple direction training conditions, this would suggest that such learning is effector dependent. We also tested the hypothesis that interlimb transfer of visuomotor adaptation is not obligatory, by examining the effects of visual rotation direction (same or oppositely directed visuomotor rotations for the two arms). All subjects first adapted to a 30 degrees rotation, either clockwise or counterclockwise, in the visual display during reaching movements. Following this, they adapted to a 30 degrees rotation in either the same or opposing direction with the other arm. Results showed that initial training with the non-dominant arm facilitated subsequent performance with the dominant arm in terms of initial direction control, but only under the same rotation condition. Both single and eight direction training conditions led to substantial transfer in subsequent performance with the other arm, but multiple direction training was no more beneficial than single direction training. This finding suggests that the previously reported intralimb advantages of multiple direction learning are effector specific. Our findings are discussed in the context of hierarchical models of motor control to explain the intralimb advantages of multiple direction training.