Motor asymmetry reduction in older adults

Upper extremity asymmetry due to nerve injuries or central neurologic conditions: a scoping review

BACKGROUND

Peripheral nerve injuries and central neurologic conditions can result in extensive disabilities. In cases with unilateral impairment, assessing the asymmetry between the upper extremity has been used to assess outcomes of treatment and severity of injury. A wide variety of validated and novel tests and sensors have been utilized to determine the upper extremity asymmetry. The purpose of this article is to review the literature and define the current state of the art for describing upper extremity asymmetry in patients with peripheral nerve injuries or central neurologic conditions.

METHOD

An electronic literature search of PubMed, Scopus, Web of Science, OVID was performed for publications between 2000 to 2022. Eligibility criteria were subjects with neurological conditions/injuries who were analyzed for dissimilarities in use between the upper extremities. Data related to study population, target condition/injury, types of tests performed, sensors used, real-world data collection, outcome measures of interest, and results of the study were extracted. Sackett's Level of Evidence was used to judge the quality of the articles.

RESULTS

Of the 7281 unique articles, 112 articles met the inclusion criteria for the review. Eight target conditions/injuries were identified (Brachial Plexus Injury, Cerebral Palsy, Multiple Sclerosis, Parkinson's Disease, Peripheral Nerve Injury, Spinal Cord Injury, Schizophrenia, and stroke). The tests performed were classified into thirteen categories based on the nature of the test and data collected. The general results related to upper extremity asymmetry were listed for all the reviewed articles. Stroke was the most studied condition, followed by cerebral palsy, with kinematics and strength measurement tests being the most frequently used tests. Studies with a level of evidence level II and III increased between 2000 and 2021. The use of real-world evidence-based data, and objective data collection tests also increased in the same period.

CONCLUSION

Adequately powered randomized controlled trials should be used to study upper extremity asymmetry. Neurological conditions other than stroke should be studied further. Upper extremity asymmetry should be measured using objective outcome measures like motion tracking and activity monitoring in the patient's daily living environment.

Investigating the effects of the aging brain on real tool use performance-an fMRI study

Introduction

Healthy aging affects several domains of cognitive and motor performance and is further associated with multiple structural and functional neural reorganization patterns. However, gap of knowledge exists, referring to the impact of these age-related alterations on the neural basis of tool use-an important, complex action involved in everyday life throughout the entire lifespan. The current fMRI study aims to investigate age-related changes of neural correlates involved in planning and executing a complex object manipulation task, further providing a better understanding of impaired tool use performance in apraxia patients.

Methods

A balanced number of sixteen older and younger healthy adults repeatedly manipulated everyday tools in an event-related Go-No-Go fMRI paradigm.

Results

Our data indicates that the left-lateralized network, including widely distributed frontal, temporal, parietal and occipital regions, involved in tool use performance is not subjected to age-related functional reorganization processes. However, age-related changes regarding the applied strategical procedure can be detected, indicating stronger investment into the planning, preparatory phase of such an action in older participants.

Effects of Short-Term Novice Archery Training on Reaching Movement Performance and Interlimb Asymmetries

Previous studies showed numerous evidence for the interlimb asymmetries in motor performance during arm reaching movements. Furthermore, these interlimb asymmetries have been shown to associate with spatial patterns of hand selection behavior. Importantly, these interlimb asymmetries can be modified systematically by occlusion of visual feedback, or a long-term sports training. In this study, we asked about the effects of a short-term training on interlimb asymmetries. Eighteen healthy young participants underwent a 12-week novice traditional archery training (TAT). Their unimanual dominant and nondominant arm reaching movement performance was assessed before and after TAT. We found that movement accuracy, movement precision, and movement efficiency in the experimental group have all improved significantly as a result of TAT. These improvements were comparable across both arms, thus the interlimb differences in movement performance were not affected by the short-term TAT and remained similar. These results suggest that while short-term training may contribute positively to reaching performance, it is unlikely to have a significant impact on the differences observed between the dominant and nondominant arms. This unique characteristics of dominant and nondominant arm should be taken into consideration when developing targeted sports and rehabilitation programs for athletes or individuals with acute or chronic motor deficits.

Aging reduces manual dexterity and force production asymmetries between the hands

Age-related effects on motor asymmetry provide insight into changes in cortical activation during aging. To investigate potential changes in manual performance associated with aging, we conducted the Jamar hand function test and the Purdue Pegboard test on young and older adults. All tests indicated reduced motor asymmetry in the older group. Further analysis suggested that a significant decline in dominant (right) hand function resulted in less asymmetric performance in older adults. The finding is inconsistent with the application of the HAROLD model in the motor domain, which assumes improved performance in the non-dominant hand, leading to a reduction of motor asymmetry in older adults. Based on the manual performance in young and older adults, it is suggested that aging reduces manual asymmetry in both force production and manual dexterity due to the reduced performance of the dominant hand.

Movement-synchronized cerebellum rhythm coordinates multi-joint movements in young and elderly adults

Rhythmic limb multi-joint movement like locomotion is controlled by intralimb coordination. Intralimb coordination changes entail immediate alterations in movement patterns and be related with cerebellum function. Synchronized cerebellum activity has known to modulate the frequency of walking, but not known the effect of only intralimb coordination. The purpose of this study was to reveal the effect of synchronized and unsynchronized cerebellum activity on the coordination of multi-joint movements of the unilateral leg in young and elderly people. To achieve our purpose, we applied synchronized and unsynchronized cerebellum transcranial alternating current stimulation during cyclic unilateral multi-joint movement by visual tracking task. The results showed that the reduction in comprehensive synchrony between targets and movements through trials had no significant differences under all stimulus conditions in young and elderly people. However, the reduction in variation of synchronization through trials was significantly smaller under the synchronized transcranial alternating current stimulation condition in both young and elderly groups. Variation of synchronization was remarkably reduced under the synchronized transcranial alternating current stimulation condition for the elderly group. This study showed that movement-synchronized cerebellum activity contributes to reducing fluctuations in movement synchrony by coordinating unilateral multi-joint movements. Moreover, this reduction was remarkable in the elderly group.

Laterality in the Damaraland Mole-Rat: Insights from a Eusocial Mammal

Lateralization is the functional control of certain behaviors in the brain being processed by either the left or right hemisphere. Behavioral asymmetries can occur at an individual and population level, although population-level lateralization is less common amongst solitary species, whereas social species can benefit more from aligning and coordinating their activities. We assessed laterality (individual and population) through turning biases in the eusocial Damaraland mole rat, Fukomys damarensis. We considered factors such as breeding status (queen or subordinate), environment (wild-caught or captive), sex (male or female), colony and body mass. All individuals together demonstrated significant left-turning biases, which was also significant at the population level. Wild-caught animals were more strongly lateralized, had a wider spread over a laterality index and lacked the population-level left-turning bias as compared to captive mole rats. Subordinate animals were more lateralized than queens, demonstrating social status differences in turning biases for social mole rats. This emphasizes the importance of animal handling and context when measuring and interpreting behavioral asymmetries.

Chronic effects of different exercise types on brain activity in healthy older adults and those with Parkinson’s disease: A systematic review

Objective: This study aimed to compare the regulation of brain activity by different kinds of long-term exercises (Tai Chi, treadmill training, and dancing) in healthy older adults and those with PD.

Methods: From January 2000 to October 2021, the electronic databases PubMed, Web of Science, and Scopus were searched. All articles were screened throughout the inclusion and exclusion criteria, which was followed by PICOS criteria. Finally, all articles were systematically reviewed with analyses.

Results: 29 studies were identified for this review, 24 of which were finally included in a group of healthy older adults, and five of which in a group of people with PD. All studies showed that significant changes were showed on people with PD and healthy older adults’ brain activity after three terms of the exercises we chose. An inverse change trend on the functional connectivity in people with PD was observed after treadmill training, whereas increased brain activity, cognitive function, memory, and emotion were noticed in healthy older adults.

Conclusion: Our findings suggest that different patterns of brain activity were also observed between healthy older adults and people with PD after treadmill training. However, more robust evidence and comprehensive studies are needed to determine if there is a difference between healthy older adults and people with PD.

No evidence for a difference in lateralization and distinctiveness level of transcranial magnetic stimulation-derived cortical motor representations over the adult lifespan

This study aimed to investigate the presence and patterns of age-related differences in TMS-based measures of lateralization and distinctiveness of the cortical motor representations of two different hand muscles. In a sample of seventy-three right-handed healthy participants over the adult lifespan, the first dorsal interosseus (FDI) and abductor digiti minimi (ADM) cortical motor representations of both hemispheres were acquired using transcranial magnetic stimulation (TMS). In addition, dexterity and maximum force levels were measured. Lateralization quotients were calculated for homolog behavioral and TMS measures, whereas the distinctiveness between the FDI and ADM representation within one hemisphere was quantified by the center of gravity (CoG) distance and cosine similarity. The presence and patterns of age-related changes were examined using linear, polynomial, and piecewise linear regression. No age-related differences could be identified for the lateralization quotient of behavior or cortical motor representations of both intrinsic hand muscles. Furthermore, no evidence for a change in the distinctiveness of the FDI and ADM representation with advancing age was found. In conclusion this work showed that lateralization and distinctiveness of cortical motor representations, as determined by means of TMS-based measures, remain stable over the adult lifespan.

Determining the Corticospinal Responses and Cross-Transfer of Ballistic Motor Performance in Young and Older Adults: A Systematic Review and Meta-Analysis

Ballistic motor training induces plasticity changes and imparts a cross-transfer effect. However, whether there are age-related differences in these changes remain unclear. Thus, the purpose of this study was to perform a meta-analysis to determine the corticospinal responses and cross-transfer of motor performance following ballistic motor training in young and older adults. Meta-analysis was performed using a random-effects model. A best evidence synthesis was performed for variables that had insufficient data for meta-analysis. There was strong evidence to suggest that young participants exhibited greater cross-transfer of ballistic motor performance than their older counterparts. This meta-analysis showed no significant age-related differences in motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and surface electromyography (sEMG) for both hands following ballistic motor training.

Normal aging affects unconstrained three-dimensional reaching against gravity with reduced vertical precision and increased co-contraction: a pilot study

Reaching for an object in space forms the basis for many activities of daily living and is important in rehabilitation after stroke and in other neurological and orthopedic conditions. It has been the object of motor control and neuroscience research for over a century, but studies often constrain movement to eliminate the effect of gravity or reduce the degrees of freedom. In some studies, aging has been shown to reduce target accuracy, with a mechanism suggested to be impaired corrective movements. We sought to explore how such changes in accuracy relate to changes in finger, shoulder and elbow movements during performance of reaching movements with the normal effects of gravity, unconstrained hand movement, and stable target locations. Three-dimensional kinematic data and electromyography were collected in 14 young (25 ± 6 years) and 10 older adults (68 ± 3 years) during second-long reaches to 3 targets aligned vertically in front of the participants. Older adults took longer to initiate a movement than the young adults and were more variable and inaccurate in their initial and final movements. Target height had greater effect on trajectory curvature variability in older than young adults, with angle variability relative to target position being greater in older adults around the time of peak speed. There were significant age-related differences in use of the multiple degrees of freedom of the upper extremity, with less variability in shoulder abduction in the older group. Muscle activation patterns were similar, except for a higher biceps-triceps co-contraction and tonic levels of some proximal muscle activation. These results show an age-related deficit in the motor planning and online correction of reaching movements against a predictable force (i.e., gravity) when it is not compensated by mechanical support.

Anodal Transcranial Direct Current Stimulation Over Prefrontal Cortex Slows Sequence Learning in Older Adults

Aging is associated with declines in sensorimotor function. Several studies have demonstrated that transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, can be combined with training to mitigate age-related cognitive and motor declines. However, in some cases, the application of tDCS disrupts performance and learning. Here, we applied anodal tDCS either over the left prefrontal cortex (PFC), right PFC, supplementary motor complex (SMC), the left M1, or in a sham condition while older adults (n = 63) practiced a Discrete Sequence Production (DSP), an explicit motor sequence, task across 3 days. We hypothesized that stimulation to either the right or left PFC would enhance motor learning for older adults, based on the extensive literature showing increased prefrontal cortical activity during motor task performance in older adults. Contrary to our predictions, stimulation to the right and left PFC resulted in slowed motor learning, as evidenced by a slower reduction rate of reduction of reaction time and the number of sequence chunks across trials relative to sham in session one and session two, respectively. These findings suggest an integral role of the right PFC early in sequence learning and a role of the left PFC in chunking in older adults, and contribute to mounting evidence of the difficultly of using tDCS in an aging population.

Correlations between Hand Dexterity and Bimanual Coordination on the Activities of Daily Living in Older Adults with Mild Cognitive Impairment

Background/Aims

Many motor impairments are present in older adults with cognitive decline. One of them is the impairment of hand dexterity and bimanual coordination that result in poor functional ability in the activities of daily living (ADL). This study investigated the effects of hand dexterity and bimanual coordination declination on the sub-domains of ADL in older adults with mild cognitive impairment (MCI).

Methods

Thirty-one senior individuals with MCI were recruited in this study. The Purdue Pegboard Test was used to measure hand dexterity, and bimanual coordination was assessed by the continuous circle-drawing task. Their ADL were assessed with the General Activity Daily Living questionnaire.

Results

The correlations analysis showed an association between the dominant hand and bimanual dexterity with the domestic domain of ADL and all conditions of hand dexterity with the complex domain of ADL. Moreover, the multiple regression analysis showed that the predictor of the greatest effect for domestic and complex domains was dominant hand dexterity.

Discussion/Conclusion

These results revealed that dominant hand dexterity strongly affected domestic and complex ADL in older adults with MCI. There were age-related changes regarding lateral asymmetrical motor reduction, especially in cognitive tasks. However, complex tasks involving cognitive function may need dominant, nondominant and bimanual hand dexterity.

Differential Ageing of the Brain Hemispheres: Evidence from a Longitudinal Study of Hand Preferences in Common Marmosets

This paper is concerned with decreasing asymmetry of motor control in ageing. It discusses age-related changes in humans and reports a longitudinal study of hand preferences in common marmosets. An annual assessment of hand preference for holding food was recorded throughout the lifespan of 19 marmosets that lived for at least 9 years, and half of those lived for at least 11 years. Those with a left-hand preference showed a gradual reduction in the strength of their hand preference throughout adult life. No significant change in the strength of hand preference was found in right-handed marmosets. Hence, ageing has a specific effect on motor control by the right hemisphere.

Neural mechanisms mediating cross education: With additional considerations for the ageing brain

CALVERT, G.H.M., and CARSON, R.G. Neural mechanisms mediating cross education: With additional considerations for the ageing brain. NEUROSCI BIOBEHAV REV 21(1) XXX-XXX, 2021. - Cross education (CE) is the process whereby a regimen of unilateral limb training engenders bilateral improvements in motor function. The contralateral gains thus derived may impart therapeutic benefits for patients with unilateral deficits arising from orthopaedic injury or stroke. Despite this prospective therapeutic utility, there is little consensus concerning its mechanistic basis. The precise means through which the neuroanatomical structures and cellular processes that mediate CE may be influenced by age-related neurodegeneration are also almost entirely unknown. Notwithstanding the increased incidence of unilateral impairment in later life, age-related variations in the expression of CE have been examined only infrequently. In this narrative review, we consider several mechanisms which may mediate the expression of CE with specific reference to the ageing CNS. We focus on the adaptive potential of cellular processes that are subserved by a specific set of neuroanatomical pathways including: the corticospinal tract, corticoreticulospinal projections, transcallosal fibres, and thalamocortical radiations. This analysis may inform the development of interventions that exploit the therapeutic utility of CE training in older persons.

Perturbation of cortical activity elicits regional and age-dependent effects on unconstrained reaching behavior: a pilot study

Contributions from premotor and supplementary motor areas to reaching behavior in aging humans are not well understood. The objective of these experiments was to examine effects of perturbations to specific cortical areas on the control of unconstrained reaches against gravity by younger and older adults. Double-pulse transcranial magnetic stimulation (TMS) was applied to scalp locations targeting primary motor cortex (M1), dorsal premotor area (PMA), supplementary motor area (SMA), or dorsolateral prefrontal cortex (DLPFC). Stimulation was intended to perturb ongoing activity in the targeted cortical region before or after a visual cue to initiate moderately paced reaches to one of three vertical target locations. Regional effects were observed in movement amplitude both early and late in the reach. Perturbation of PMA increased reach distance before the time of peak velocity to a greater extent than all other regions. Reaches showed greater deviation from a straight-line path around the time of peak velocity and greater overall curvature with perturbation of PMA and M1 relative to SMA and DLPFC. The perturbation increased positional variability of the reach path at the time of peak velocity and the time elapsing after peak velocity. Although perturbations had stronger effects on reaches by younger subjects, this group exhibited less reach path variability at the time of peak velocity and required less time to adjust the movement trajectory thereafter. These findings support the role of PMA in visually guided reaching and suggest an age-related change in sensorimotor processing, possibly due to a loss of cortical inhibitory control.

Age-related differences in proprioceptive asymmetries

Age-related differences in proprioceptive asymmetries have received little attention. This study aimed to determine differences in asymmetry of the right/left upper limb proprioceptive systems between younger and older adults. Asymmetries were compared in two "eyes closed" experiments involving the same elbow joints. Position sense was tested in two matching conditions: ipsilateral remembered and contralateral concurrent. Movement sense was tested while reproducing with the opposite forearm the illusory movement elicited by distal tendon vibration applied to the reference forearm. Older adults exhibited a larger error when matching with the non-dominant than dominant forearm in the ipsilateral remembered condition and a disparate asymmetry in the contralateral condition when compared to younger adults. In addition, in older adults, the velocity of reproduced illusory movements was slower, and asymmetry in movement perception was not significant. The difference in proprioceptive asymmetry between younger and older adults might be attributed to a significant reduction of the sensory system gain affecting, more particularly, the left non-dominant arm sensory system via several physiological and neurophysiological mechanisms.

How far will you go before switching hands? Handedness on the long pegboard across the lifespan

Handedness is a significant behavioral asymmetry; however, there is debate surrounding the age at which hand preference develops, and little research has been conducted on handedness in older adults. The current study examined performance on the long pegboard, to identify similarities and differences in young children (ages 4-7 years), older children (ages 8-12 years), young adults (ages 18-25 years), and older adults (ages 70+ years). Average time per hole, number of hand switches, and errors were assessed with left- and right-hand starts. A left-right ratio was computed from the long pegboard, along with laterality quotients from the Waterloo Handedness Questionnaire (WHQ). Results revealed faster performance when participants started the task on the right side of the long pegboard with the right-hand, coupled with a later switch to the left-hand. There was a greater number of errors with left-hand starts, and an earlier switch to the right-hand. Age was a significant predictor of the average time per hole and number of errors. Long pegboard ratio and WHQ laterality quotient were only correlated for adults. Together, findings offer insight regarding age-related effects in handedness and support the long pegboard as a useful measure of handedness.

Effect of Age on the Touchscreen Manipulation Ability of Community-Dwelling Adults

Assessment of touchscreen manipulation skills is essential for determining the abilities of older individuals and the extent to which they may benefit from this technology as a means to enhance participation, self-esteem, and quality of life. The aim of this study was to compare the touchscreen manipulation ability between community-dwelling older adults and middle-aged adults using a newly developed Touchscreen Assessment Tool (TATOO) and to determine the usability of this instrument. Convenience samples of two age groups were considered, one including 28 independent community-living older adults aged 81.9 ± 4.2 years with intact or corrected vision and with the abilities to walk independently with or without a walking aid and to understand and follow simple commands, and the other including 25 healthy middle-age adults aged 53.4 ± 5.9 years. The usability assessment was conducted during a single session using the System Usability Scale (SUS). Older adults demonstrated poorer touchscreen skills compared to middle-aged adults. Previous experience in manipulating a smartphone by the older adults did not affect their performance. The SUS results indicated good usability of the TATOO by both age groups. The TATOO shows promise as a user-friendly tool for assessing the specific skills needed to operate touchscreens. The outcomes of this study support the suitability of touchscreen devices and applications as well as the need for adapted accessibility for older adults. Researchers and clinicians will benefit from the availability of a rapid, low-cost, and objective tool to assess the skills required for touchscreen use.

Movement Kinematics and Interjoint Coordination Are Influenced by Target Location and Arm in 6-Year-Old Children

Rapid aiming movements are typically used to study upper limb motor control and development. Despite the large corpus of work in this area, few studies have examined kinematic manual asymmetries in children who have just started formal schooling and until now, none have characterized how children coordinate their joints to complete these movements (i.e., interjoint coordination). In the present study, manual asymmetries in kinematics and interjoint coordination in strongly right-handed 6-year-old children were investigated when reaching for ipsilateral and contralateral targets with their dominant right arm and the non-dominant left arm. Overall, manual asymmetries in interjoint coordination are apparent for both 6-year-old children and young adults, although young children completed the task by adopting a different strategy than adults. Also, control strategies employed by 6-year-old children were influenced by both the location of the target as well as the arm used to perform the task. Specifically, compared to all other conditions, children’s trajectories were more curved when performing contralateral movements with the non-dominant left arm, which were driven by smaller shoulder excursions combined with larger elbow excursions for this condition. Based on these results, we argue that the differences in interjoint coordination reflect the stage of development of 6-year-old children, the origin of which derives from maturational (e.g., hand dominance) and environmental factors (e.g., school-based experience).

Food quantity discrimination in puppies (Canis lupus familiaris)

There is considerable evidence that animals are able to discriminate between quantities. Despite the fact that quantitative skills have been extensively studied in adult individuals, research on their development in early life is restricted to a limited number of species. We, therefore, investigated whether 2-month-old puppies could spontaneously discriminate between different quantities of food items. We used a simultaneous two-choice task in which puppies were presented with three numerical combinations of pieces of food (1 vs. 8, 1 vs. 6 and 1 vs. 4), and they were allowed to select only one option. The subjects chose the larger of the two quantities in the 1 vs. 8 and the 1 vs. 6 combinations but not in the 1 vs. 4 combination. Furthermore, the last quantity the puppies looked at before making their choice and the time spent looking at the larger/smaller amounts of food were predictive of the choices they made. Since adult dogs are capable of discriminating between more difficult numerical contrasts when tested with similar tasks, our findings suggest that the capacity to discriminate between quantities is already present at an early age, but that it is limited to very easy discriminations.

Competition for limited neural resources in older adults leads to greater asymmetry of bilateral movements than in young adults

We previously demonstrated that lateralization in the neural control of predictive and impedance mechanisms is reflected by interlimb differences in control of bilateral tasks. Aging has been shown to reduce lateralization during unilateral performance, presumably due to greater recruitment of the ipsilateral hemisphere. We now hypothesize that aging-related reduction in the efficiency of neural resources should produce greater behavioral asymmetry during bilateral actions that require hemispheric specialization for each arm. This is because simultaneous control of dominant and nondominant arm function should induce competition for hemisphere-specific resources. To test this hypothesis, we now examine the effect of aging (young, n = 20; old, n = 20) on performance of a mechanically coupled task, in which one arm reaches toward targets while the other arm stabilizes against a spring that connects the two arms. Results indicate better dominant arm reaching performance and better nondominant arm stabilizing performance for both groups. Most notably, limb and joint compliance was lower in the dominant arm, leading to dominant arm deficits in stabilizing performance. Group analysis indicated that older adults showed substantially greater asymmetry in stabilizing against the spring load than did the younger adults. We propose that competition for limited neural resources in older adults is associated with reduced contributions of right hemisphere mechanisms to right-dominant arm stabilizing performance, and thus to greater asymmetry of performance.NEW & NOTEWORTHY We provide evidence for greater asymmetry of interlimb differences in bilateral coordination for stabilizing and preserved asymmetry of reaching with aging. These results provide the first evidence for increased lateralization with aging within the context of a complementary bilateral task.

Asymmetry in the aging brain: A narrative review of cortical activation patterns and implications for motor function

Age-related changes have been identified in neural and motor level. A prominent change is reduced asymmetry in cortical activation as well as motor performance. Cortical activation models have been established based on cognitive research utilizing neuroimaging techniques to explain age-related effects on neural recruitment and reduced brain asymmetry. Recently, researchers in motor behaviour attempted to apply the models to explain motor pattern changes in aging and proposed compensation as the mechanism of the reduced motor asymmetry in older adults. Age-related alterations in movement patterns and brain activations seem to be correlated. However, based on the literature search result, no direct evidence substantiates the connection between reduced brain asymmetry and motor asymmetry in older adults. Therefore, a theoretical gap was identified. The theoretical gap exists because either neuroimaging studies have not considered motor asymmetry or motor asymmetry studies have not integrated neuroimaging techniques into study designs. Answering the research question can be valuable to both research and clinical practice. With the mechanisms of brain activation patterns during motor tasks in an aging population being better understood, protocols developed upon the new understandings can be applied to current motor interventions and better maintain the longevity of motor function of older adults.

Precision Sensorimotor Control in Aging FMR1 Gene Premutation Carriers

BACKGROUND

Individuals with premutation alleles of the FMR1 gene are at risk of developing fragile X-associated tremor/ataxia syndrome (FXTAS), a neurodegenerative condition affecting sensorimotor function. Information on quantitative symptom traits associated with aging in premutation carriers is needed to clarify neurodegenerative processes contributing to FXTAS.

MATERIALS AND METHODS

26 FMR1 premutation carriers ages 44-77 years and 31 age-matched healthy controls completed rapid (2 s) and sustained (8 s) visually guided precision gripping tasks. Individuals pressed at multiple force levels to determine the impact of increasing the difficulty of sensorimotor actions on precision behavior. During initial pressing, reaction time, the rate at which individuals increased their force, the duration of pressing, and force accuracy were measured. During sustained gripping, the complexity of the force time series, force variability, and mean force were examined. During relaxation, the rate at which individuals decreased their force was measured. We also examined the relationships between visuomotor behavior and cytosine-guanine-guanine (CGG) repeat length and clinically rated FXTAS symptoms.

RESULTS

Relative to controls, premutation carriers showed reduced rates of initial force generation during rapid motor actions and longer durations of their initial pressing with their dominant hand. During sustained force, premutation carriers demonstrated reduced force complexity, though this effect was specific to younger premutation carries during dominant hand pressing and was more severe for younger relative to older premutation carriers at low and medium force levels. Increased reaction time and lower sustained force complexity each were associated with greater CGG repeat length for premutation carriers. Increased reaction time and increased sustained force variability were associated with more severe clinically rated FXTAS symptoms.

CONCLUSION

Overall our findings suggest multiple sensorimotor processes are disrupted in aging premutation carriers, including initial force control guided by feedforward mechanisms and sustained sensorimotor behaviors guided by sensory feedback control processes. Results indicating that sensorimotor issues in aging premutation carriers relate to both greater CGG repeat length and clinically rated FXTAS symptoms suggest that quantitative tests of precision sensorimotor ability may serve as key targets for monitoring FXTAS risk and progression.

Handedness results from complementary hemispheric dominance, not global hemispheric dominance: evidence from mechanically coupled bilateral movements

Two contrasting views of handedness can be described as 1) complementary dominance, in which each hemisphere is specialized for different aspects of motor control, and 2) global dominance, in which the hemisphere contralateral to the dominant arm is specialized for all aspects of motor control. The present study sought to determine which motor lateralization hypothesis best predicts motor performance during common bilateral task of stabilizing an object (e.g., bread) with one hand while applying forces to the object (e.g., slicing) using the other hand. We designed an experimental equivalent of this task, performed in a virtual environment with the unseen arms supported by frictionless air-sleds. The hands were connected by a spring, and the task was to maintain the position of one hand while moving the other hand to a target. Thus the reaching hand was required to take account of the spring load to make smooth and accurate trajectories, while the stabilizer hand was required to impede the spring load to keep a constant position. Right-handed subjects performed two task sessions (right-hand reach and left-hand stabilize; left-hand reach and right-hand stabilize) with the order of the sessions counterbalanced between groups. Our results indicate a hand by task-component interaction such that the right hand showed straighter reaching performance whereas the left hand showed more stable holding performance. These findings provide support for the complementary dominance hypothesis and suggest that the specializations of each cerebral hemisphere for impedance and dynamic control mechanisms are expressed during bilateral interactive tasks. NEW & NOTEWORTHY We provide evidence for interlimb differences in bilateral coordination of reaching and stabilizing functions, demonstrating an advantage for the dominant and nondominant arms for distinct features of control. These results provide the first evidence for complementary specializations of each limb-hemisphere system for different aspects of control within the context of a complementary bilateral task.

The effect of aging and contextual information on manual asymmetry in tool use

Healthy aging affects manual asymmetries in simple motor tasks, such as unilateral reaching and aiming. The effects of aging on manual asymmetries in the performance of a complex, naturalistic task are unknown, but are relevant for investigating the praxis system. This study examined how aging influences manual asymmetry in different contexts in a tool manipulation task. Fifty healthy, right-hand-dominant young (N = 29; 21.41 ± 2.87 years), and elderly (N = 21; mean: 74.14 ± 6.64 years) participants performed a 'slicing' gesture in response to a verbal command in two contexts: with (tool) and without the tool (pantomime). For interjoint relationships between shoulder plane of elevation and elbow flexion, a HAND × AGE × CONTEXT interaction existed (F_1,43 = 4.746, p = 0.035). In pantomime, interjoint control deviated more in the left (non-dominant) than the right (dominant) limb in the elderly adult group (Wilcoxon, p = 0.010). No such differences existed in the young adult group (Wilcoxon, p = 0.471). Furthermore, contextual information reduced interjoint deviation in young adults when the task was performed with the right (dominant) hand (Wilcoxon, p = 0.001) and in the elderly adults when the task was performed with the left (non-dominant) hand (Wilcoxon, p = 0.012). The presence of the tool did not reduce interjoint deviation for the right hand in the elderly group (Wilcoxon, p = 0.064) or the left hand in the young group (Wilcoxon, p = 0.044). Deviation within trials (i.e., intrasubject deviation) in elbow flexion was higher in the elderly relative to the young adult group (p = 0.003). Finally, resultant peak velocities were smaller (p = 0.002) and cycle duration longer (p < 0.0001) in the elderly adult group. This study provides novel evidence that aging affects manual asymmetries and sensorimotor control in a naturalistic task and warrants that aging research considers the context in which the task is performed.

Age-Related Declines in the Ability to Modulate Common Input to Bilateral and Unilateral Plantar Flexors During Forward Postural Lean

Aging can impair an ability to lean the body forward to the edge of the base of support. Here, we investigated, using a coherence analysis, common inputs to bilateral and unilateral plantar flexor muscles to test a hypothesis that the age-related impairment would be related to strong synchronous bilateral activation and reduced cortical control of these muscles. Healthy young (n = 14) and elderly adults (n = 19), who were all right-foot dominant, performed quiet standing task and tasks that required the subjects to lean their body forward to 35 and 75% of the maximum lean distance. The electromyogram was recorded from the bilateral medial gastrocnemius (MG) and soleus (SL) muscles. We analyzed delta-band coherence, that reflects comodulation of muscle activity, between the bilateral homologous muscles (MG-MG and SL-SL pairs). The origin of this bilateral comodulation is suggested to be the subcortical system. Also, we examined beta-band coherence, that is related to the corticospinal drive, between the unilateral muscles (MG-SL pair) in the right leg. Results indicated that the bilateral delta-band coherence for the MG-MG pair was significantly smaller in the 75% forward lean than quiet standing and 35% forward lean tasks for the young adults (quiet: p = 0.036; 35%: p = 0.0011). The bilateral delta-band coherence for the SL-SL pair was significantly smaller in the 75% forward lean than 35% forward lean task for the young adults (p = 0.027). Furthermore, the unilateral beta-band coherence was larger in the forward lean than quiet standing task for the young adults (35%: p < 0.001; 75%: p = 0.029). Contrarily, the elderly adults did not demonstrate such changes. These findings suggest the importance of decreasing the synchronous bilateral activation and increasing the unilateral cortical control of the plantar flexor muscles for the successful forward postural lean performance, and that aging impairs this modulatory ability.

Manual asymmetry in older adults on a complex coincidence-anticipation task

Age-related asymmetrical functional decline was tested in a sample of 57 right-handed volunteers between 65 and 85 years of age. Participants performed a complex coincidence-anticipation (CA) task with both preferred and non-preferred hands. Results demonstrated that the proficiency of a complex CA task was similar for the 2 age groups, but different for the 2 hands. The non-preferred hand was more proficient for temporal accuracy but not for response timing, which was similar for both hands. Moreover, the lack of interaction between age and hand both in response timing and response accuracy reveal symmetric performance across ages.

The Effects of Tai Chi Intervention on Healthy Elderly by Means of Neuroimaging and EEG: A Systematic Review

Aging is a process associated with a decline in cognitive and motor functions, which can be attributed to neurological changes in the brain. Tai Chi, a multimodal mind-body exercise, can be practiced by people across all ages. Previous research identified effects of Tai Chi practice on delaying cognitive and motor degeneration. Benefits in behavioral performance included improved fine and gross motor skills, postural control, muscle strength, and so forth. Neural plasticity remained in the aging brain implies that Tai Chi-associated benefits may not be limited to the behavioral level. Instead, neurological changes in the human brain play a significant role in corresponding to the behavioral improvement. However, previous studies mainly focused on the effects of behavioral performance, leaving neurological changes largely unknown. This systematic review summarized extant studies that used brain imaging techniques and EEG to examine the effects of Tai Chi on older adults. Eleven articles were eligible for the final review. Three neuroimaging techniques including fMRI (N = 6), EEG (N = 4), and MRI (N = 1), were employed for different study interests. Significant changes were reported on subjects' cortical thickness, functional connectivity and homogeneity of the brain, and executive network neural function after Tai Chi intervention. The findings suggested that Tai Chi intervention give rise to beneficial neurological changes in the human brain. Future research should develop valid and convincing study design by applying neuroimaging techniques to detect effects of Tai Chi intervention on the central nervous system of older adults. By integrating neuroimaging techniques into randomized controlled trials involved with Tai Chi intervention, researchers can extend the current research focus from behavioral domain to neurological level.

Kinematic Outcome Measures using Target-Reaching Arm Movement in Stroke

This study aimed to quantitatively investigate upper extremity motor performance and disclose the abnormality of motor control induced by stroke. Ten patients and ten healthy subjects were instructed to perform target-reaching tasks at nine difficulty levels, and coordinates of the shoulder, elbow and tip of the index finger were recorded. Age-matched control performed significantly better than patients, as indicated by lower movement time (MT) and normalized jerk score (NJS) and higher peak velocity (V _peak), percentage time to peak velocity (PTPV), fuzzy approximate entropy (fApEn) and relative joint angles correlation (RJAC); also, significant effects of difficulty on all parameters except RJAC and fApEn, were observed in two groups. There were significant correlations between PTPV and Fugl-Meyer assessment for upper extremity (FMA-UE) and between RJAC and FMA-UE at certain difficulty levels. The stroke-related differences could be explained by the increase in intrinsic neuromotor noise, and the difficulty-related differences may be related to extrinsic neuromotor noise. The increase in either noises could result in a degradation in motor control. The significant linear relationships between some kinematic parameters and the clinical score suggested that the kinematic parameters could be applied as quantitative outcome measures in the clinic in the future.

Long-interval intracortical inhibition is asymmetric in young but not older adults

Aging is typically accompanied by a decline in manual dexterity and handedness; the dominant hand executes tasks of manual dexterity more quickly and accurately than the nondominant hand in younger adults, but this advantage typically declines with age. Age-related changes in intracortical inhibitory processes might play a role in the age-related decline in manual dexterity. Long-interval intracortical inhibition (LICI) is asymmetric in young adults, with more sensitive and more powerful LICI circuits in the dominant hemisphere than in the nondominant hemisphere. Here we investigated whether the hemispheric asymmetry in LICI in younger adults persists in healthy older adults. Paired-pulse transcranial magnetic stimulation was used to measure LICI in the dominant and nondominant hemispheres of younger and older adults; LICI stimulus-response curves were obtained by varying conditioning stimulus intensity at two different interstimulus intervals [100 ms (LICI₁₀₀) and 150 ms]. We have replicated the finding that LICI₁₀₀ circuits are more sensitive and more powerful in the dominant than the nondominant hemisphere of young adults and extend this finding to show that the hemispheric asymmetry in LICI₁₀₀ is lost with age. In the context of behavioral observations showing that dominant hand movements in younger adults are more fluent than nondominant hand movements in younger adults and dominant hand movements in older adults, we speculate a role of LICI₁₀₀ in the age-related decline in manual dexterity.NEW & NOTEWORTHY In younger adults, more sensitive and more powerful long-interval intracortical inhibitory circuits are evident in the hemisphere controlling the more dexterous hand; this is not the case in older adults, for whom long-interval intracortical inhibitory circuits are symmetric and more variable than in younger adults. We speculate that the highly sensitive and powerful long-interval intracortical inhibition circuits in the dominant hemisphere play a role in manual dexterity.

Age-related changes in hand dominance and functional asymmetry in older adults

The aim of the study was to investigate fine motor performance and ascertain age-related changes in laterality between the dominant and non-dominant hand. A representative sample of 635 adults (144 males and 491 females) aged 50 years and over completed a test battery MLS (Motor Performance Series) to assess a broad range of hand functions. Functional asymmetry was observed in all four motor tests (postural tremor, aiming, tapping, and inserting long pins). Significant differences between the dominant and non-dominant hand were obtained in both sexes across all age groups, except in the oldest female group (age >70) for the aiming (number of hits and errors) and postural tremor (number of errors) tasks. These differences in age-related changes may be attributed to hemispheric asymmetry, environmental factors, or use-dependent plasticity. Conflicting evidence in the literature warrants additional research to better explain age-related alterations of hand dominance and manual performance in old age.

Both hands at work: the effect of aging on upper-limb kinematics in a multi-step activity of daily living

The kinematic performance of basic motor tasks shows a clear decrease with advancing age. This study examined if the rules known from such tasks can be generalized to activities of daily living. We examined the end-effector kinematics of 13 young and 13 elderly participants in the multi-step activity of daily living of tea-making. Furthermore, we analyzed bimanual behavior and hand dominance in the task using different conditions of execution. The elderly sample took substantially longer to complete the activity (almost 50%) with longer trajectories compared with the young sample. Models of multiple linear regression revealed that the longer trajectories prolonged the trial duration in both groups, and while movement speed influenced the trial duration of young participants, phases of inactivity negatively affected how long the activity took the elderly subjects. No differences were found regarding bimanual performance or hand dominance. We assume that in self-paced activities of daily living, the age-dependent differences in the kinematics are more likely to be based on the higher cognitive demands of the task rather than on pure motor capability. Furthermore, it seems that not all of the rules known from basic motor tasks can be generalized to activities of daily living.

Age-related changes in bilateral upper extremity coordination

Although evidence exists that changes in sensorimotor function occur with aging, changes in the bilateral coordination of the upper extremities is less understood. Here, we review the behavioral and neural evidence of declines in bilateral coordination as well as the implications these deficits have on function and physical rehabilitation. We begin with an introduction to the two major forms of bilateral coordination, symmetric and non-symmetric and their sub-groupings. After discussing the motor performance changes with age in symmetric tasks, we address age-related changes in motor lateralization that may affect the bilateral coordination of non-symmetric coordination. This is followed by a discussion of the contributions of cognitive, sensory, and cortical changes with age that influence and underlie bilateral motor performance. Finally, age-related changes in motor learning of bilateral movements are also considered. In general, most age related changes are found in complex symmetric movements but, surprisingly, there is a dearth of information about changes in the more challenging and ubiquitous non-symmetric bilateral movements. Future investigations should focus on broadening the understanding of age-related changes in complex, functionally relevant bilateral movements, such that the real-world implications of these changes may be derived.

Peripheral neuropathy reduces asymmetries in inter-limb transfer in a visuo-motor task

Asymmetry of inter-limb transfer has been associated with the specialization of the dominant and non-dominant motor system. Reductions of asymmetry have been interpreted as behavioural evidence showing a decline of hemispheric lateralization. A previous study showed that ageing did not qualitatively change the inter-limb transfer asymmetry of a visuo-motor task. The current study elaborates on these findings; it examines whether diminished somatosensory information as a result of peripheral neuropathy (PN) adversely affects inter-limb transfer asymmetry. Twenty individuals affected by PN and 20 older controls were recruited and divided equally across two groups. One group trained a visuo-motor task with the right hand while the other group trained it with the left hand. Performance (initial direction error) of the untrained hand before and after training was collected to determine learning effects from inter-limb transfer. Similar to previous studies, the current study showed asymmetric inter-limb transfer in older controls. In contrast, PN showed inter-limb transfer in both directions indicating that PN reduces inter-limb transfer asymmetry. Increased bilateral hemispheric recruitment is suggested to be responsible for this reduced asymmetry which may compensate for deteriorated tactile and/or proprioceptive inputs in PN. Two possible hypotheses are discussed explaining the relationship between declined somatosensory information and increases in bilateral hemispheric recruitment.

Evaluation of the effects of the Arm Light Exoskeleton on movement execution and muscle activities: a pilot study on healthy subjects

Background

Exoskeletons for lower and upper extremities have been introduced in neurorehabilitation because they can guide the patient’s limb following its anatomy, covering many degrees of freedom and most of its natural workspace, and allowing the control of the articular joints. The aims of this study were to evaluate the possible use of a novel exoskeleton, the Arm Light Exoskeleton (ALEx), for robot-aided neurorehabilitation and to investigate the effects of some rehabilitative strategies adopted in robot-assisted training.

Methods

We studied movement execution and muscle activities of 16 upper limb muscles in six healthy subjects, focusing on end-effector and joint kinematics, muscle synergies, and spinal maps. The subjects performed three dimensional point-to-point reaching movements, without and with the exoskeleton in different assistive modalities and control strategies.

Results

The results showed that ALEx supported the upper limb in all modalities and control strategies: it reduced the muscular activity of the shoulder’s abductors and it increased the activity of the elbow flexors. The different assistive modalities favored kinematics and muscle coordination similar to natural movements, but the muscle activity during the movements assisted by the exoskeleton was reduced with respect to the movements actively performed by the subjects. Moreover, natural trajectories recorded from the movements actively performed by the subjects seemed to promote an activity of muscles and spinal circuitries more similar to the natural one.

Conclusions

The preliminary analysis on healthy subjects supported the use of ALEx for post-stroke upper limb robotic assisted rehabilitation, and it provided clues on the effects of different rehabilitative strategies on movement and muscle coordination.

The 'Goldilocks Zone': getting the measure of manual asymmetries

Some studies have shown that manual asymmetries decrease in older age. These results have often been explained with reference to models of reduced hemispheric specialisation. An alternative explanation, however, is that hand differences are subtle, and capturing them requires tasks that yield optimal performance with both hands. Whereas the hemispheric specialisation account implies that reduced manual asymmetries should be reliably observed in older adults, the ‘measurement difficulty’ account suggests that manual asymmetries will be hard to detect unless a task has just the right level of difficulty—i.e. within the ‘Goldilocks Zone’, where it is not too easy or too hard, but just right. Experiment One tested this hypothesis and found that manual asymmetries were only detected when participants performed in this zone; specifically, performance on a tracing task was only superior in the preferred hand when task constraints were high (i.e. fast speed tracing). Experiment Two used three different tasks to examine age differences in manual asymmetries; one task produced no asymmetries, whilst two tasks revealed asymmetries in both younger and older groups (with poorer overall performance in the old group across all tasks). Experiment Three revealed task-dependent asymmetries in both age groups, but highlighted further detection difficulties linked with the metric of performance and compensatory strategies used by participants. Results are discussed with reference to structural learning theory, whereby we suggest that the processes of inter-manual transfer lead to relatively small performance differences between the hands (despite a strong phenomenological sense of performance disparities).

Arm dominance affects feedforward strategy more than feedback sensitivity during a postural task

Handedness is a feature of human motor control that is still not fully understood. Recent work has demonstrated that the dominant and nondominant arm each excel at different behaviors and has proposed that this behavioral asymmetry arises from lateralization in the cerebral cortex: the dominant side specializes in predictive trajectory control, while the nondominant side is specialized for impedance control. Long-latency stretch reflexes are an automatic mechanism for regulating posture and have been shown to contribute to limb impedance. To determine whether long-latency reflexes also contribute to asymmetric motor behavior in the upper limbs, we investigated the effect of arm dominance on stretch reflexes during a postural task that required varying degrees of impedance control. Our results demonstrated slightly but significantly larger reflex responses in the biarticular muscles of the nondominant arm, as would be consistent with increased impedance control. These differences were attributed solely to higher levels of voluntary background activity in the nondominant biarticular muscles, indicating that feedforward strategies for postural stability may differ between arms. Reflex sensitivity, which was defined as the magnitude of the reflex response for matched levels of background activity, was not significantly different between arms for a broad subject population ranging from 23 to 51 years of age. These results indicate that inter-arm differences in feedforward strategies are more influential during posture than differences in feedback sensitivity, in a broad subject population. Interestingly, restricting our analysis to subjects under 40 years of age revealed a small increase in long-latency reflex sensitivity in the nondominant arm relative to the dominant arm. Though our subject numbers were small for this secondary analysis, it suggests that further studies may be required to assess the influence of reflex lateralization throughout development.

Age and practice effects on inter-manual performance asymmetry

Manual dexterity declines with increasing age, however, the way in which inter-manual asymmetry responds to aging is unclear. Our purpose was to determine the effect of age and practice on inter-manual performance asymmetry in an isometric force pinch line tracing task that varied in difficulty within segments. Thirty right-handed participants, five males and five females in each of three age groups, young (Y20), young–old (O70), and old–old (O80), practiced an isometric force pinch task for 10 trials with each hand on each of five consecutive days. Inter-manual performance asymmetry of the right and left hands was analyzed with a repeated measures analysis of variance (ANOVA) of asymmetry with age groups, practice, task difficulty, and hand as factors. The within-individual magnitude of asymmetry was also analyzed with a repeated measures ANOVA of manual asymmetry calculated as an asymmetry index (AI). Post hoc pair-wise comparisons were performed when significance was found. We observed no inter-manual performance asymmetry on this isometric tracing task among any of the age groups, either in the hand performance differences or in the magnitude of the AI. Age and practice interacted in terms of manual performance: the Y20 and O70 group improved accuracy and task time across the 5 days of practice but the O80 group did not. However, practice did not differentially affect the AI for accuracy or task time for any group. Accuracy of performance of the two hands was differentially affected by practice. All age groups exhibited poorer performance and larger AIs on the most difficult segments of the task (3 and 6) and this did not change with practice.

Handedness throughout the lifespan: cross-sectional view on sex differences as asymmetries change

Manual asymmetries has been studied by many researchers, however contradictory findings still exist as to whether preferred manual asymmetries increases with age or do we become more ambidextrous. Recently it was shown that perhaps there is a third option, that there is no increase or decrease in laterality but rather preferred manual asymmetries remains consistent throughout adulthood. Another related finding is that females appear to have an advantage in some handedness tasks, such as the Grooved Pegboard. When a larger pegboard is used, sex differences may reverse as males may perform better when larger pegs and a larger trajectory are required. However, it is not fully understood if these sex differences arise from an early age and continue throughout life. Therefore, we sought to explore sex differences in preferred hand dominance throughout the lifespan. In order to explore preferred hand dominance during the lifespan we examined 76 children (19.4–5 year olds, 12 female, M_age = 4.73; 34.6–8 year olds, 12 female, M_age = 6.97; 23.9–12 year olds, 14 female, M_age = 10.83) in Experiment 1 and 35 healthy young right-handed adults (15 female, M_age = 20.91) and 37 healthy older right-handed adults (20 female, M_age = 72.3) in Experiment 2. Individuals were tested using a standard size (small) and modified Grooved Pegboard (larger pegboard). Our study demonstrates that hand asymmetries are present early in life (children 4–5 years old) at that these differences attenuate as a function of age until adulthood (Experiment 1). Furthermore, our results demonstrate that as we age (Experiment 2), asymmetries may increase (small and large pegboards), decrease (Annett), or stay the same (finger tapping). As well we demonstrated that the sex differences could not be entirely accounted for by hand size. Therefore, asymmetries as regard to the aging process, seems to be task specific which may account for the conflicting findings in research.

Motor asymmetry in elite fencers

The authors previously reported that asymmetrical patterns of hand preference are updated and modified by present sensorimotor conditions. They examined whether participation in long-term training in the upper extremity sport fencing might modify arm selection and performance asymmetries. Eight fencers and eight nonfencers performed reaching movements under 3 experimental conditions: (a) nonchoice right, (b) nonchoice left, and (c) choice, either right or left arm as selected by subject. The nonchoice conditions allowed assessment of potential interlimb differences in movement performance, while the choice condition allowed assessment of the frequency and pattern of arm selection across subject groups. Our findings showed that the athlete group showed substantially greater symmetry in the performance and selection measures. These findings suggest that arm selection and performance asymmetries can be altered by intense long-term practice.

Motor Asymmetry Attenuation in Older Adults during Imagined Arm Movements

Laterality is an important feature of motor behavior. Several studies have shown that lateralization in right-handed young adults (i.e., right versus left arm superiority) emerges also during imagined actions, that is when an action is internally simulated without any motor output. Such information, however, is lacking for elderly people and it could be valuable to further comprehend the evolution of mental states of action in normal aging. Here, we evaluated the influence of age on motor laterality during mental actions. Twenty-four young (mean age: 24.7 ± 4.4 years) and 24 elderly (mean age: 72.4 ± 3.6 years) participants mentally simulated and actually executed pointing movements with either their dominant-right or non-dominant-left arm in the horizontal plane. We recorded and analyzed the time of actual and mental movements and looked for differences between groups and arms. In addition, electromyographic activity from arm muscle was recorded to quantify any enhancement in muscle activation during mental actions. Our findings indicated that both groups mentally simulated arm movements without activating the muscles of the right or the left arm above the baseline level. This finding suggests that young and, notably, elderly adults are able to generate covert actions without any motor output. We found that manual asymmetries (i.e., faster movements with the right arm) were preserved in young adults for both actual and mental movements. In elderly adults, manual asymmetries were observed for actual but not for mental movements (i.e., equal movement times for both arms). These findings clearly indicate an age-related reduction of motor laterality during mental actions.

Contralesional Arm Preference Depends on Hemisphere of Damage and Target Location in Unilateral Stroke Patients

Background Previous research has shown that during simulated activities of daily living, right-handed stroke patients use their contralesional arm more after left- than right-hemisphere stroke. These findings were attributed to a hand preference effect. However, these decisions about when to use the contralesional arm may be modulated by where in the work space the task is performed, a factor that could be used in physical rehabilitation to influence recovery by decreasing learned nonuse. Objective To examine how target location and side of stroke influences arm selection choices for simple reaching movements. Methods A total of 14 right-handed stroke patients (7 with left-hemisphere and 7 with right-hemisphere damage [RHD]), with similar degrees of hemiparesis (Fugl-Meyer motor score), and 16 right-handed controls participated in this experiment. In a pseudorandom fashion, 32 targets were presented throughout the reachable horizontal plane work space, and the participants were asked to select 1 hand to reach the target on each trial. Results The group with left-hemisphere damage chose their contralesional arm significantly more often than the group with RHD. Patients with RHD also chose their left (contralesional) arm significantly less often than the control group. However, these patterns of choice were most pronounced in the center of the workspace. Conclusion Both the side of hemisphere damage and work space location played a significant role in the choice of whether to use the contralesional arm for reaching. These findings have implications for structuring rehabilitation for unilateral stroke patients.

Age-related differences in proprioceptive and visuo-proprioceptive function in relation to fine motor behaviour

Leversen et al. (PLoS One 7(6):e38830, 2012) emphasise the importance of understanding the principles of life-long development. In their study of motor control, they found a common tendency towards improved motor performance from childhood to adulthood and a subsequent deterioration. The aim of our study was to examine this issue further by investigating fine motor behaviour (tracing a model line) in 196 participants (age range 12-95 years old) in two sensory conditions-proprioceptive + visual (PV) and proprioceptive only-in both hands and in two types of movement, frontal and transversal. Regression analyses of line length and task performance speed in relation to age were conducted for the different test conditions. The best performance was found in middle age, and a quadratic function provided the best fit for most of the test conditions. The corresponding inflection points (the age at which graphical analysis showed a change in performance as a peak of maturation before decline due to ageing) showed earlier ages in the proprioceptive condition. For most types of movement analysed, performance speed was slower under the PV condition. Paired correlation analysis showed that the symmetry of precision performance between hands became stronger with age. The results provide information on age-dependent differences in proprioception based on fine motor performance. They may be of use in the design of preventive strategies for preserving proprioceptive function by reducing the risk of falls and accidents or diseases such as Parkinson's.

Representational pseudoneglect: a review

Pseudoneglect, the tendency to be biased towards the left-hand side of space, is a robust and consistent behavioural observation best demonstrated on the task of visuospatial line bisection, where participants are asked to centrally bisect visually presented horizontal lines at the perceived centre. A number of studies have revealed that a representational form of pseudoneglect exists, occurring when participants are asked to either mentally represent a stimulus or explore a stimulus using touch in the complete absence of direct visuospatial processing. Despite the growing number of studies that have demonstrated representational pseudoneglect there exists no current and comprehensive review of these findings and no discussion of a theoretical framework into which these findings may fall. An important gap in the current representational pseudoneglect literature is a discussion of the developmental trajectory of the bias. The focus of the current review is to outline studies that have observed representational pseudoneglect in healthy participants, consider a theoretical framework for these observations, and address the impact of lifespan factors such as cognitive ageing on the phenomenon.