Jeanne Langan

Functional implications of age differences in motor system connectivity

Older adults show less lateralized task-related brain activity than young adults. One potential mechanism of this increased activation is that age-related degeneration of the corpus callosum (CC) may alter the balance of inhibition between the two hemispheres. To determine whether age differences in interhemispheric connectivity affect functional brain activity in older adults, we used magnetic resonance imaging (MRI) to assess resting functional connectivity and functional activation during a simple motor task. We found that older adults had smaller CC area compared to young adults. Older adults exhibited greater recruitment of ipsilateral primary motor cortex (M1), which was associated with longer reaction times. Additionally, recruitment of ipsilateral M1 in older adults was correlated with reduced resting interhemispheric connectivity and a larger CC. We suggest that reduced interhemispheric connectivity reflects a loss of the ability to inhibit the non-dominant hemisphere during motor task performance for older adults, which has a negative impact on performance.

Attentional deficits in concussion

Primary objective: The purpose of the present study was to examine deficits in the alerting, orienting and executive components of attention in individuals who have recently suffered a concussion. Research design: A group design was used in which the performance by individuals with concussion was compared to control subjects matched for age, height, weight and activity level. Methods and procedures: Participants completed the Attentional Network Test (ANT) that breaks down attention into alerting, orienting and executive components. Reaction time and response accuracy were the dependent variables. Main outcomes and results: It was found that only the orienting and executive components of attention were affected by concussion, whereas the alerting component was normal. Furthermore, participants with concussion required a significantly longer time than controls to initiate correct responses. Conclusions: These results suggest that the orienting and executive components of attention are most susceptible to the effects of concussion.

Attentional disengagement dysfunction following mTBI assessed with the gap saccade task

Concussion, or mild traumatic brain injury (mTBI), leads to a number of cognitive, attentional, and sensorimotor deficits that can last a surprisingly long time after the initial injury. We have previously shown that the ability to orient visuospatial attention is deficient in participants with mTBI within 2 days of their injury, but then recovers to normal levels within a week. Orienting attention requires disengagement from the point of fixation, movement of attention to the location of interest, and re-engagement at that location. Deficits in any or all of these processes could lead to the difficulties with orienting attention that we have observed in mTBI. To address this issue, we tested participants with mTBI using a gap saccade task. Because this task manipulates the temporal gap between the offset of the fixation target and the appearance of the peripheral saccade target, it isolates the contribution of the disengagement process to saccadic reaction time. We found that participants with mTBI had significantly longer saccadic reaction times than controls when the temporal gap was short but not when it was long. This gap-dependent difference in saccadic reaction time was present within 2 days of the injury and resolved within 1 week. This pattern of results suggests that as the contribution of the disengagement process is reduced, so too is the extent of the reaction time deficit in the participants with mTBI. Taken together, this is consistent with the idea that the deficits in orienting visuospatial attention in participants with mTBI are fully accounted for by difficulties with the initial disengagement process.

Home-based telerehabilitation shows improved upper limb function in adults with chronic stroke: a pilot study.

OBJECTIVE This pilot study investigates the use of telerehabilitation to improve upper limb performance in chronic stages of stroke recovery. DESIGN Intervention study with pre/post/one month follow-up tests. METHODS Seven adults with chronic stroke participated in the study. Tests consisted of lab-based clinical and kinematic assessments. Participants completed the Upper Limb Training and Assessment (ULTrA) program at home. Training was 5 days/week, 60 min/day for 6 weeks with intermittent supervision of participants. RESULTS Participants showed improvements in the training program tasks as well as clinical and kinematic assessments. Results also suggest there may be auxiliary benefits in cognitive function. CONCLUSIONS A home-based telerehabilitation program is a viable approach to provide rehabilitation in chronic stages of stroke.

Age differences in callosal contributions to cognitive processes

In many cases bilateral cortical activation in older adults has been associated with better task performance, suggesting that a greater reliance on interhemispheric interactions aids performance. Interhemispheric communication is primarily mediated via the corpus callosum (CC), however with advancing age the anterior half of the CC undergoes significant atrophy. Here we determine whether there are age differences in the relationship between cross-sectional area of the CC and performance on cognitive tests of psychomotor processing speed and working memory. We found that older adults had significantly smaller callosal area in the anterior and mid-body of the CC than young adults. Furthermore, older adults with larger size in these callosal areas performed better on assessments of working memory and processing speed. Our results indicate that older adults with larger size of the anterior half of the CC exhibit better cognitive function, although their performance was still poorer than young adults with similar CC size. Thus, while the capability for interhemispheric interactions, as inferred from callosal size, may provide performance benefits for older adults, this capacity alone does not assure protection from general performance decline.

Cancelling planned actions following mild traumatic brain injury

Mild traumatic brain injury (mTBI) leads to a variety of attentional, cognitive, and sensorimotor deficits. An important aspect of behavior that intersects each of these functions is the ability to cancel a planned action. Thus, the purpose of this study was to determine the effects of mTBI on the ability to perform a countermanding saccade task. In this task, participants were asked to generate a saccade to a target appearing in peripheral vision, but to inhibit saccade execution if an auditory stop signal was presented. The delay between the appearance of the peripheral target and the presentation of the auditory stop signal was varied between 0 and 125ms. We found that the change in the probability of cancelling the saccade as a function of this delay was no different between participants with mTBI tested within 2 days of their injury and matched controls. However, saccadic reaction times and the stop signal reaction time were unexpectedly faster in the participants with mTBI and, furthermore, they inaccurately inhibited saccades during 15% of the trials with no stop signal. Taken together, this data suggests that the ability to cancel planned actions is subtly yet adversely affected by mTBI.

Age differences in spatial working memory contributions to visuomotor adaptation and transfer

Throughout our life span we encounter challenges that require us to adapt to the demands of our changing environment; this entails learning new skills. Two primary components of motor skill learning are motor acquisition, the initial process of learning the skill, and motor transfer, when learning a new skill is benefitted by the overlap with a previously learned one. Older adults typically exhibit declines in motor acquisition compared to young adults, but remarkably, do not demonstrate deficits in motor transfer [10]. Our recent work demonstrates that a failure to engage spatial working memory (SWM) is associated with skill learning deficits in older adults [16]. Here, we investigate the role that SWM plays in both motor learning and transfer in young and older adults. Both age groups exhibited performance savings, or positive transfer, at transfer of learning for some performance variables. Measures of spatial working memory performance and reaction time correlated with both motor learning and transfer for young adults. Young adults recruited overlapping brain regions in prefrontal, premotor, parietal and occipital cortex for performance of a SWM and a visuomotor adaptation task, most notably during motor learning, replicating our prior findings [12]. Neural overlap between the SWM task and visuomotor adaptation for the older adults was limited to parietal cortex, with minimal changes from motor learning to transfer. Combined, these results suggest that age differences in engagement of cognitive strategies have a differential impact on motor learning and transfer.

The influence of hand dominance on the response to a constraint-induced therapy program following stroke.

Background. Following stroke it is common to exhibit deficits in mobility of the upper extremity. Constraint-induced therapy (CIT) is a rehabilitation technique used to promote use of the more affected hand via constraint of the less affected hand. One factor that could impact the outcome following CIT is hand dominance. Years of preferred use of one hand may give individuals with the dominant hand affected by stroke an advantage in improving the mobility of the more affected hand compared to those individuals with the nondominant hand affected by stroke. In addition, the diminished use of the less affected hand during CIT may also create changes. Objective. Our goal was to better understand how hand dominance may influence the response to a CIT program both cortically and behaviorally in both the more affected hand and less affected constrained hand. Methods. A repeated measures design with a double baseline was used to assess changes in clinical tests and functional magnetic resonance imaging (fMRI) in individuals with their dominant or nondominant hand affected by stroke involved in a CIT program. Results. No significant differences were found between groups in their responses to CIT. Overall subjects demonstrated behavioral and cortical changes with the more affected hand and the less affected constrained hand did not significantly change. Conclusion. CIT promotes improvement of the more affected hand particularly on complex tests without decrements to the less affected constrained hand. Cortically, statistically significant changes in activation were noted after the intervention for the more affected hand; no changes were noted with the less affected constrained hand.

Influence of Task on Interlimb Coordination in Adults With Cerebral Palsy

OBJECTIVE To examine movement time and kinematic properties of unilateral and bilateral reaching movements in adults with cerebral palsy (CP), focusing on how different types of bilateral movements, simultaneous or sequential, may influence interlimb coordination. DESIGN Quantitative study using between-group repeated-measures analyses. SETTING Motor control laboratory at a research university. PARTICIPANTS Adults with hemiplegic CP (n=11; mean age ± SD, 33±10y; 4 men) and age-matched controls (mean age ± SD, 32±9y; 4 men). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Movement time (MT), maximum deviation from a straight trajectory to the target, and peak speed. RESULTS Although adults with hemiplegic CP showed strong unilateral deficits, bilateral simultaneous reaching movements were temporally and spatially coupled. Movement of the less affected arm slowed to match the movement of the more affected arm. In contrast, bilateral sequential movements improved MTs of the less affected and more affected arms. CONCLUSIONS Bilateral sequential movements were conducive to faster MT compared with unilateral or bilateral simultaneous movements. Training that includes bilateral sequential movements may be beneficial to adults with hemiplegic CP. Upper-limb movements are coordinated in a variety of ways to perform routine bilateral tasks. Some bilateral tasks, such as stacking boxes, require more symmetric movements of the upper limbs. Other bilateral tasks, such as opening the refrigerator with 1 hand while placing an item on the shelf with the other hand, emphasize coordinated sequential action between upper limbs. Despite the prevalence of integrative upper-limb use, the control of different forms of bilateral movement is not well understood. A more comprehensive knowledge of upper-limb bilateral movements may hold important implications for developing more effective upper-limb movement therapies.

Cognitive Neuroscience of Skill Acquisition

Publisher Summary This chapter provides an overview of present research on the cognitive neuroscience of human motor skill learning. Skill acquisition has been defined as “a set of processes associated with practice or experience leading to relatively permanent changes in the capability for responding”. Researchers studying skill acquisition have classified learning into at least two broad categories, including sensorimotor adaptation and sequence learning. In sensorimotor adaptation paradigms, participants modify movements to adjust to changes in either sensory input or motor output characteristics. Sensorimotor adaptation tasks are used to gain insight into how humans represent their environment, the mechanics of the body, and interactions between the two during movement planning and production. These tasks can be described as either (1) dynamic paradigms, which alter anticipated proprioception by having participants move the limb through an opposing force field or (2) kinematic paradigms, which disrupt visual feedback of movements through the use of displacing wedge prisms or altered visual feedback on a computer screen For sequence learning, individuals learn to combine isolated movements into one smooth, coherent action. The chapter reviews some of the major current theories on the cognitive neuroscience of skill learning, and draws attention to the overlap and differences among these theories.