Testing Multiple Coordination Constraints with a Novel Bimanual Visuomotor Task

The acquisition of a new bimanual skill depends on several motor coordination constraints. To date, coordination constraints have often been tested relatively independently of one another, particularly with respect to isofrequency and multifrequency rhythms. Here, we used a new paradigm to test the interaction of multiple coordination constraints. Coordination constraints that were tested included temporal complexity, directionality, muscle grouping, and hand dominance. Twenty-two healthy young adults performed a bimanual dial rotation task that required left and right hand coordination to track a moving target on a computer monitor. Two groups were compared, either with or without four days of practice with augmented visual feedback. Four directional patterns were tested such that both hands moved either rightward (clockwise), leftward (counterclockwise), inward or outward relative to each other. Seven frequency ratios (3∶1, 2∶1, 3∶2, 1∶1, 2∶3. 1∶2, 1∶3) between the left and right hand were introduced. As expected, isofrequency patterns (1∶1) were performed more successfully than multifrequency patterns (non 1∶1). In addition, performance was more accurate when participants were required to move faster with the dominant right hand (1∶3, 1∶2 and 2∶3) than with the non-dominant left hand (3∶1, 2∶1, 3∶2). Interestingly, performance deteriorated as the relative angular velocity between the two hands increased, regardless of whether the required frequency ratio was an integer or non-integer. This contrasted with previous finger tapping research where the integer ratios generally led to less error than the non-integer ratios. We suggest that this is due to the different movement topologies that are required of each paradigm. Overall, we found that this visuomotor task was useful for testing the interaction of multiple coordination constraints as well as the release from these constraints with practice in the presence of augmented visual feedback

Bimanuele Coördinatie en Switching Gedrag: de rol van veranderingen inhersenstructuur in achteruitgang van prestatie bij veroudering

Aging of the world population is a fact. Consequently, there is an increasing number of relatively healthy older adults that may need help during the execution of their daily tasks because of a loss of motor as well as cognitive skills. These older adults have partly lost their functional independence which can lead to a decreased quality of life. In the current thesis, it is investigated how alterations in brain structure with increasing age contribute to declines in specific skills. Brain structure was investigated using specific MRI (magnetic resonance imaging) and analysis techniques. The first part focuses on the relations between brain structure and performance on a motor oriented skill, namely bimanual coordination. The second part focuses on a cognitively oriented skill, namely switching between different tasks. Both skills are essential for many daily life activities. For example, imagine a typical morning: combing your hairs; buttoning your clothes; preparing your sandwiches. Besides, these bimanual skills are often interrupted by answering your phone or answering some questions of your relatives, thus requiring switching between tasks. The first part of this thesis comprises two experimental studies in which the associations between brain structure and bimanual coordination performance were investigated. The apparent simplicity of bimanual tasks masks their underlying complexity. Because of this complexity, declines in bimanual coordination are often observed in older adults. Accordingly, they often show slower and less accurate performance. During bimanual tasks, the coordination between the hands in the brain mainly occurs via the corpus callosum. This is a large bundle of white matter tracts that enables the connections between both hemispheres. In the first study, the microstructural organization of 7 subregions of the corpus callosum was investigated and related to performance on different bimanual tasks with specific task characteristics in a group of young and older adults. Accordingly, diffusion tensor imaging (DTI) was used to divide the corpus callosum into these subregions, based on connectivity with specific cortical regions. Results indicated that declines in microstructural organization in specific subregions of the corpus callosum were related to deterioration of bimanual performance on different tasks within the older adults. In a second study, it was investigated whether age-related atrophy in a selection of subcortical structures also contributes to deterioration of bimanual performance with aging. This was achieved by collecting structural scans from participants between 20 and 79 years old. Results of this study indicated that age-related atrophy of specific thalamic subregions contributed to bimanual performance declines. Interestingly, these thalamic subregions subserve connectivity with some key cortical regions in bimanual coordination, i.e., the premotor, the primary motor and the somatosensory cortical regions. Also task switching performance, i.e., the ability to switch between different tasks, has been shown to deteriorate with increasing age, thereby affecting daily functioning. In the second part of this thesis, the associations between white matter structural properties and task switching performance were investigated by means of an extensive literature overview and a third experimental study. To start, the associations between microstructural properties of different white matter connections and task switching performance as reported in different age and patient groups were discussed in the literature overview. Also the third (experimental) study was included in this overview. In this study, it was investigated how white matter structural alterations contribute to the slowing of switching performance with increasing age. In this regard, two white matter measures were selected that have been proposed to be related to myelin. The first measure was a radial diffusivity measure obtained using DTI, for which higher values could be indicative of less myelin content. The second measure was a magnetization transfer ratio measure obtained using MTI (magnetization transfer imaging), for which lower values could be indicative of less myelin content. From this study it was concluded that lower magnetization transfer ratio values in the superior corona radiata, a white matter tract that connects frontal and subcortical areas, partly explained the observed slowing of switching performance in older adults. In conclusion, in this thesis it was investigated how alterations in brain structure contribute to deterioration of performance with increasing age. It was found that both microstructural changes in the corpus callosum (white matter) and local atrophy in subcortical regions (gray matter) are related to deterioration of bimanual performance in older adults. Additionally, it was found that mainly structural alterations in a specific white matter tract, i.e., the superior corona radiata, seem to contribute to slowing of task switching performance in older adults. We express our hope that this thesis will contribute to a greater understanding of the aging process, with the ultimate aim of promoting prolonged independent functioning of older adults.status: publishe

Physical activity predicts performance in an unpracticed bimanual coordination task

Practice of a given physical activity is known to improve the motor skills related to this activity. However, whether unrelated skills are also improved is still unclear. To test the impact of physical activity on an unpracticed motor task, 26 young adults completed the international physical activity questionnaire and performed a bimanual coordination task they had never practiced before. Results showed that higher total physical activity predicted higher performance in the bimanual task, controlling for multiple factors such as age, physical inactivity, music practice, and computer games practice. Linear mixed models allowed this effect of physical activity to be generalized to a large population of bimanual coordination conditions. This finding runs counter to the notion that generalized motor abilities do not exist and supports the existence of a "learning to learn" skill that could be improved through physical activity and that impacts performance in tasks that are not necessarily related to the practiced activity.status: publishe

Aging effects on the resting state motor network and interlimb coordination

Both increases and decreases in resting state functional connectivity have been previously observed within the motor network during aging. Moreover, the relationship between altered functional connectivity and age-related declines in bimanual coordination remains unclear. Here, we explored the developmental dynamics of the resting brain within a task-specific motor network in a sample of 128 healthy participants, aged 18-80 years. We found that age-related increases in functional connectivity between interhemispheric dorsal and ventral premotor areas were associated with poorer performance on a novel bimanual visuomotor task. Additionally, a control analysis performed on the default mode network confirmed that our age-related increases in functional connectivity were specific to the motor system. Our findings suggest that increases in functional connectivity within the resting state motor network with aging reflect a loss of functional specialization that may not only occur in the active brain but also in the resting brain. Hum Brain Mapp, 2014. © 2014 Wiley Periodicals, Inc.status: publishe

Cortical grey matter content is associated with both age and bimanual performance, but is not observed to mediate age-related behavioural decline

Declines in both cortical grey matter and bimanual coordination performance are evident in healthy ageing. However, the relationship between ageing, bimanual performance, and grey matter loss remains unclear, particularly across the whole adult lifespan. Therefore, participants (N = 93, range 20-80 years) performed a complex Bimanual Tracking Task, and structural brain images were obtained using magnetic resonance imaging. Analyses revealed that age correlated negatively with task performance. Voxel-based morphometry analysis revealed that age was associated with grey matter declines in task-relevant cortical areas and that grey matter in these areas was negatively associated with task performance. However, no evidence for a mediating effect of grey matter in age-related bimanual performance decline was observed. We propose a new hypothesis that functional compensation may account for the observed absence of mediation, which is in line with the observed pattern of increased inter-individual variance in performance with age

Bimanual motor deficits in elderly predicted by Diffusion Tensor Imaging of corpus callosum subregions

status: publishe

Bimanual motor deficits in older adults predicted by diffusion tensor imaging metrics of corpus callosum subregions

Age-related changes in the microstructural organization of the corpus callosum (CC) may explain declines in bimanual motor performance associated with normal aging. We used diffusion tensor imaging in young (n = 33) and older (n = 33) adults to investigate the microstructural organization of seven specific CC subregions (prefrontal, premotor, primary motor, primary sensory, parietal, temporal and occipital). A set of bimanual tasks was used to assess various aspects of bimanual motor functioning: the Purdue Pegboard test, simultaneous and alternating finger tapping, a choice reaction time test and a complex visuomotor tracking task. The older adults showed age-related deficits on all measures of bimanual motor performance. Correlation analyses within the older group showed that white matter fractional anisotropy of the CC occipital region was associated with bimanual fine manipulation skills (Purdue Pegboard test), whereas better performance on the other bimanual tasks was related to higher fractional anisotropy in the more anterior premotor, primary motor and primary sensory CC subregions. Such associations were less prominent in the younger group. Our findings suggest that structural alterations of subregional callosal fibers may account for bimanual motor declines in normal aging.status: publishe

Microstructural organization of corpus callosum projections to prefrontal cortex predicts bimanual motor learning

The corpus callosum (CC) is the largest white matter tract in the brain. It enables interhemispheric communication, particularly with respect to bimanual coordination. Here, we use diffusion tensor imaging (DTI) in healthy humans to determine the extent to which structural organization of subregions within the CC would predict how well subjects learn a novel bimanual task. A single DTI scan was taken prior to training. Participants then practiced a bimanual visuomotor task over the course of 2 wk, consisting of multiple coordination patterns. Findings revealed that the predictive power of fractional anisotropy (FA) was a function of CC subregion and practice. That is, FA of the anterior CC, which projects to the prefrontal cortex, predicted bimanual learning rather than the middle CC regions, which connect primary motor cortex. This correlation was specific in that FA correlated significantly with performance of the most difficult frequency ratios tested and not the innately preferred, isochronous frequency ratio. Moreover, the effect was only evident after training and not at initiation of practice. This is the first DTI study in healthy adults which demonstrates that white matter organization of the interhemispheric connections between the prefrontal structures is strongly correlated with motor learning capability