Role of the dorsolateral prefrontal cortex in context-dependent motor performance.

Context-dependent motor performance is a phenomenon in which people perform better in the environmental context where they originally practised a task. Some animal and computer simulation studies have suggested that context-dependent performance may be associated with neural activation of the dorsolateral prefrontal cortex (DLPFC). This study aimed to determine the role of the DLPFC in context-dependent motor performance by perturbing the neural processing of the DLPFC with repetitive transcranial magnetic stimulation (rTMS) in healthy adults. Thirty healthy adults were recruited into the Control, rTMS DLPFC and rTMS Vertex groups. The participants practised three finger sequences associated with a specific incidental context (a coloured circle and a location on the computer screen). One day following practice, the rTMS groups received 1 Hz rTMS prior to the testing conditions in which the sequence-context associations remained the same as practice (SAME) or changed (SWITCH). All three groups improved significantly over practice on day 1. The second day testing results showed that the DLPFC group had a significantly lower decrease in motor performance under the SWITCH condition than the Control and Vertex groups. This finding suggests a specific role of the DLPFC in context-dependent motor performance.

Standardized Measurement of Quality of Upper Limb Movement After Stroke: Consensus-Based Core Recommendations From the Second Stroke Recovery and Rehabilitation Roundtable.

The second Stroke Recovery and Rehabilitation Roundtable "metrics" task force developed consensus around the recognized need to add kinematic and kinetic movement quantification to its core recommendations for standardized measurements of sensorimotor recovery in stroke trials. Specifically, we focused on measurement of the quality of upper limb movement. We agreed that the recommended protocols for measurement should be conceptually rigorous, reliable, valid and responsive to change. The recommended measurement protocols include four performance assays (i.e. 2D planar reaching, finger individuation, grip strength, and precision grip at body function level) and one functional task (3D drinking task at activity level) that address body function and activity respectively. This document describes the criteria for assessment and makes recommendations about the type of technology that should be used for reliable and valid movement capture. Standardization of kinematic measurement protocols will allow pooling of participant data across sites, thereby increasing sample size aiding meta-analyses of published trials, more detailed exploration of recovery profiles, the generation of new research questions with testable hypotheses, and development of new treatment approaches focused on impairment. We urge the clinical and research community to consider adopting these recommendations.

Standardized measurement of quality of upper limb movement after stroke: Consensus-based core recommendations from the Second Stroke Recovery and Rehabilitation Roundtable.

The second Stroke Recovery and Rehabilitation Roundtable "metrics" task force developed consensus around the recognized need to add kinematic and kinetic movement quantification to its core recommendations for standardized measurements of sensorimotor recovery in stroke trials. Specifically, we focused on measurement of the quality of upper limb movement. We agreed that the recommended protocols for measurement should be conceptually rigorous, reliable, valid and responsive to change. The recommended measurement protocols include four performance assays (i.e. 2D planar reaching, finger individuation, grip strength, and precision grip at body function level) and one functional task (3D drinking task at activity level) that address body function and activity respectively. This document describes the criteria for assessment and makes recommendations about the type of technology that should be used for reliable and valid movement capture. Standardization of kinematic measurement protocols will allow pooling of participant data across sites, thereby increasing sample size aiding meta-analyses of published trials, more detailed exploration of recovery profiles, the generation of new research questions with testable hypotheses, and development of new treatment approaches focused on impairment. We urge the clinical and research community to consider adopting these recommendations.

Motor learning after unilateral brain damage.

Forty adults, post-stroke from anterior circulation unilateral cerebrovascular accident (approximately 2 years post onset) and 40 age-matched controls (M = 57 years) practiced a rapid, spatially and temporally constrained programmed action under one of two augmented feedback practice conditions. Participants in the stroke group used the upper limb ipsilateral to the lesion. After an extended practice period (198 trials), acquisition, retention, and reacquisition performance was assessed for accuracy and consistency and compared over trials, between groups and feedback conditions. Both stroke and control groups demonstrated significant improvement in accuracy and consistency over practice with relative persistence of these changes during retention. There were no differences between groups (stroke vs control) in performance patterns across trials for acquisition, retention, or reacquisition phases. In addition, there were no differential effects of the two augmented feedback conditions on performance and no interactions of feedback condition with group. However, independent of feedback condition, the stroke group performed with more error than did the control group during all experimental phases (i.e., acquisition, retention, reacquisition). These results suggest that unilateral stroke-related damage in the sensorimotor areas primarily effects the processes underlying the control and execution of motor skills but not the learning of those skills. Implications of these findings for physical rehabilitation are discussed.

Function of the 'direct' and 'indirect' pathways of the basal ganglia motor loop: evidence from reciprocal aiming movements in Parkinson's disease.

The purpose of this study was to test the validity of a neural-network model of the basal ganglia developed by Bischoff and colleagues (A. Bischoff, Modeling the basal ganglia in the control of arm movements (Doctoral dissertation, University of Southern California, 1998). Dissertation Abstr. Int. 59-08B (1998) 3924, 0208; A. Bischoff, M.A. Arbib, Modeling the role of basal ganglia and supplementary motor areas in sequential arm movements, Abstr. Soc. Neurosci. 23 (1997) 466; A. Bischoff, M.A. Arbib, C.J. Winstein, Modeling the role of the basal ganglia in reciprocal aiming task, Proceedings of the Fourth Annual Joint Symposium on Neural Computation, University of Southern California, Los Angeles, 7, 1997, pp. 20-27), and to examine the effects of levodopa on aiming movement performance. Findings confirm the model predictions for repetitive aiming movements. Individuals with late stage Parkinson's disease demonstrated longer movement times and longer pauses between aiming sequences compared to controls. Levodopa only slightly improved bradykinesia but not akinesia in these patients.

Implicit motor-sequence learning in humans following unilateral stroke: the impact of practice and explicit knowledge.

Learning and memory are sub-served by two interrelated systems - explicit and implicit. Explicit memory involves facts, while one form of implicit memory involves perceptual-motor processes. The purpose of this series of experiments was to investigate the ability of individuals with stroke-related brain damage to demonstrate implicit motor-sequence learning and the relative impacts of (1) extended practice, or (2) explicit knowledge prior to practice. Implicit learning was severely impaired without explicit knowledge and even under conditions of extended practice. However, when explicit knowledge was provided prior to practice, participants with stroke demonstrated implicit motor-sequence learning. These data suggest that following unilateral stroke, providing explicit information about the task and sequence can attenuate implicit motor learning deficits.

Knowledge of results and motor learning--implications for physical therapy.

Relevant to this special series on movement science, a brief overview of research in the field of motor learning is provided. A distinction between learning and performance is emphasized with respect to experimental design and the evaluation of laboratory and clinical intervention techniques. Intrinsic and extrinsic feedback are defined. Basic principles of motor learning pertaining to the use of augmented feedback or knowledge of results (KR) are reviewed. Particular emphasis is placed on recent research regarding the effects of selected KR variations (KR relative frequency, bandwidth KR, and KR delay) on motor performance and learning in healthy young adults. Results are discussed in terms of short-lasting temporary performance effects and relatively long-lasting learning effects. Theoretical and practical implications from this research are discussed. It is suggested that it is appropriate to use the principles obtained through laboratory experimentation as guidelines rather than as exact recommendations when applying basic research findings to clinical practice.

Neurogenic dysphagia. Frequency, progression, and outcome in adults following head injury.

A retrospective chart review was conducted to determine the frequency, progression, and outcome of neurogenic dysphagia in head-injured adults admitted to a rehabilitation facility. Approximately 25 percent of the sample demonstrated swallowing or oral motor problems on admission. Ninety-four percent of this group ultimately became successful oral feeders. The majority of these patients participated in a feeding program planned and implemented by the physical therapist. The average time from injury for the nonoral feeders to successful completion of their first oral meal was about three months. A concomitant resolution of cognitive problems, primitive oral motor reflexes, and neurogenic dysphagia occurred.

Learning a partial-weight-bearing skill: effectiveness of two forms of feedback.

BACKGROUND AND PURPOSE: Partial weight bearing (PWB) is a skill commonly taught by physical therapists. This study compared the effects of practice with either augmented feedback provided during the task (concurrent feedback) or augmented feedback provided after the task (postresponse feedback) for the learning of PWB with crutches. SUBJECTS: Sixty young adults without known impairment of the neuromusculoskeletal system volunteered for the study. METHODS: Subjects practiced supporting 30% of body weight while stepping onto a floor scale. Augmented feedback was provided during each trial for the concurrent feedback group and either following each trial or after every five trials for the postresponse feedback groups. Subjects returned 2 days later for a no-feedback retention test. RESULTS: During practice, the concurrent feedback group was more accurate and consistent than either of the postresponse feedback groups. During retention, however, the postresponse feedback groups were the most accurate; all groups were equally consistent during retention. CONCLUSION AND DISCUSSION: These results suggest that practice with concurrent feedback is beneficial for the immediate performance but not for the learning of this sensorimotor skill.

The locus of age-related movement slowing: sensory processing in continuous goal-directed aiming.

Prolonged movement times in elderly persons have been well documented; however, the locus of this slowing is uncertain. Kinematic analysis of discrete aiming has revealed deficits primarily in the target approach phase, suggesting inefficient feedback processing. This study investigated age-related movement slowing in a continuous aiming task, for which movements are mediated by feedforward and on-line sensory processes. Two-dimensional video-recordings were made of young and elderly adults performing reciprocal tapping using the right and left hands under three different accuracy conditions. The elderly subjects exhibited more discrete adjustments in the trajectories coupled with longer times in this period. Further, the elderly spent more time reversing direction between target hits, especially in the high accuracy condition. Longer time on target was seen in the left-hand performance of the elderly. Results suggest that the locus of age-related slowing in the performance of continuous aiming may reflect a greater dependence on slower feedback processes instead of rapid, on-line, and feedforward sensory processes. Age-related differences in hand performance may provide further insight into central processing deficits.

Sensory-motor control in the ipsilesional upper extremity after stroke.

There is substantial evidence to indicate that sensory-motor control of the ipsilesional upper extremity (UE) in adults after unilateral stroke is abnormal. Some of the sensory-motor deficits differ as a function of the side of the cerebral lesion. Rapid movements of the ipsilesional UE that require precise timing and sequencing are more affected in individuals with lesions in the left hemisphere. In contrast, ipsilesional movements that have constrained spatial requirements are more affected in those with lesions in the right hemisphere. Ipsilesional UE coordination of discrete tasks may be normal, but the coordination of continuous tasks is affected in adults with left stroke. Sensation in the ipsilesional UE appears to be unaffected, or minimally affected after stroke. Strength deficits have been demonstrated in the ipsilesional UE, but primarily in those with right sided lesions. Ipsilesional performance deficits are revealed in clinical tests of function that use time to completion as the measure of success. Ipsilesional performance deficits may reflect motor control deficits that are masked on the contralateral side by hemiplegia and hemisensory loss. Interventions that focus on specific motor control deficits, such as speed of sensory-motor processing, through practice with the ipsilesional UE, may result in functional improvements in both limbs.

Qualitative dynamics of disordered human locomotion: a preliminary investigation.

A qualitative approach to the evaluation of disordered locomotion is introduced within the framework of dynamical systems theory. Exemplar phase plane and angle-angle plots of knee and ankle movements were constructed from limb trajectories of neurologically impaired individuals and qualitatively compared with similar plots, reflecting normal locomotion. In phase plane trajectories of normal locomotion, characteristics of spring-like dynamics dominated the loading and unloading phases whereas those of ballistic pendular dynamics were seen during swing. The overall squareness of the normal phase plane trajectories suggested precisely timed and narrowly focused controls. in contrast, phase plane records from hemiparetic subjects had markedly reduced segmental velocities, pronounced velocity reversals in both stance and swing, and a loss of overall squareness. Knee-ankle plots of normal locomotion revealed important features of intersegmental coordination such as coupled out-of-phase coordination in loading and unloading, a decoupled phase offset in early swing, and a kind of active partitioning in late swing in which one segment moved while the other remained constant. These intersegmental relations were absent or distorted in the hemiparetic angle-angle plots. It is suggested that this qualitative approach, together with electromyography and force dynamics, may allow the characterization of the movement disorders associated with given neuropathologies.

The potential of virtual reality and gaming to assist successful aging with disability.

Using the advances in computing power, software and hardware technologies, virtual reality (VR), and gaming applications have the potential to address clinical challenges for a range of disabilities. VR-based games can potentially provide the ability to assess and augment cognitive and motor rehabilitation under a range of stimulus conditions that are not easily controllable and quantifiable in the real world. This article discusses an approach for maximizing function and participation for those aging with and into a disability by combining task-specific training with advances in VR and gaming technologies to enable positive behavioral modifications for independence in the home and community. There is potential for the use of VR and game applications for rehabilitating, maintaining, and enhancing those processes that are affected by aging with and into disability, particularly the need to attain a balance in the interplay between sensorimotor function and cognitive demands and to reap the benefits of task-specific training and regular physical activity and exercise.

Contralateral cerebellar damage impairs imperative planning but not updating of aimed arm movements in humans.

The specific motor control processes supported by the cerebellum and impaired with cerebellar damage remain unclear. The cerebellum has been implicated in both planning and updating of accurate movements. Previously, we used a statistical model to parcel aiming performance that was constrained by a timed-response paradigm into contributions attributed to a specified plan and feedforward updating. Here, we apply this procedure to determine the putative role of the cerebellum in planning and updating goal-directed aiming by comparing the performance of subjects with unilateral cerebellar stroke to controls. Subjects rapidly moved to targets in predictable or unpredictable conditions and cerebellar subjects used the contralesional limb to control for ipsilesional motor execution deficits. Displacement-derived movement velocity was used in the statistical model to determine the effect of planning and updating on accuracy. Compared to controls, the cerebellar group demonstrated errors in final position that were primarily determined by planning deficits. This finding is manifest in four ways: Cerebellar subjects (1) were less accurate than controls in both predictable and unpredictable conditions; (2) they showed minimal benefit from increased preparation time for target amplitude specification; (3) with ample time to plan direction, wrong direction response frequency was greater; and (4) final position was minimally determined by the plan. Because these deficits were found contralesional to the moving limb, the cerebellum's role in planning is not lateralized to one hemisphere but rather our findings suggest that cerebellar output affects motor planning for both upper limbs. Indeed, a lesion analysis showed that the dentate nucleus, an area implicated in planning motor strategies and the primary cerebellar output nucleus, was the only common region affected by our patient group with contralateral cerebellar strokes.

The co-ordination of bimanual rapid aiming movements following stroke.

OBJECTIVE: To determine the role of anticipatory and movement control processes for the coordination of bimanual target aiming in individuals post stroke. SUBJECTS: Thirty adults with chronic stroke and 30 individuals without stroke history. DESIGN: A two-group (stroke, control) by two-aiming type (unimanual, bimanual) by two-limb (paretic, nonparetic; left, right for controls) design with repeated measures on the last two factors. OUTCOME MEASURES: Kinematic analyses of performance and psychometric measures of reaction time, movement time, peak resultant velocity, time to and after peak resultant velocity and interlimb timing for movement initiation and target impact. RESULTS: Compared with unimanual aiming, the nonparetic limb exhibited a prolonged movement time in the bimanual condition; the locus for prolongation was primarily in the deceleration phase. This adaptive response allowed for a nearly simultaneous (both limbs) target impact in 81% of trials. Compared with the unimanual condition, the nonparetic limb exhibited a lower peak velocity (10%) in the bimanual condition. Conversely, compared with the unimanual condition, the paretic limb exhibited a higher peak velocity (4%) in the bimanual condition. This disociation between limb and condition was observed for the stroke group but not the control group. CONCLUSIONS: The interlimb coordination that emerged for the stroke group revealed a complex and asymmetric contribution from each limb mediated through anticipatory and motor control processes. We suggest that this coordination may be harnessed for future bimanual intervention approaches to rehabilitation of upper limb function after stroke.

Practice effects on the less-affected upper extremity after stroke.

OBJECTIVE: To test the hypotheses that (1) adults who have had a stroke, using the less affected upper extremity (UE), improve performance of an aiming task with practice, and (2) compared with control subjects, stroke patients show less improvement in a complex condition. DESIGN: Movement time (MT) and kinematic data were collected over practice. Comparisons were made between the less-affected UE of stroke patients and the same hand of controls. SETTING: A human performance laboratory. PARTICIPANTS: A matched sample of right-handed adults, 10 with unilateral stroke and 10 nondisabled controls. INTERVENTION: Practice of an aiming task in an easy and complex condition as defined by target width and distance between two targets. MAIN OUTCOME MEASURES: MT, peak velocity, and temporal phases of the trajectory. RESULTS: Adults who had experienced a stroke had persistently longer MTs than control subjects; however, all participants achieved faster MTs with practice in both conditions. The absolute amount of time in each temporal phase decreased without a change in the relative times. Peak velocity increased only in the easy condition. CONCLUSIONS: Adults with stroke damage can improve motor performance of the less-affected UE with practice. Further study is needed to see if practice effects are permanent and generalizable.

Effects of unilateral brain damage on the control of goal-directed hand movements.

Insight into the functional neural substrates associated with the control of goal-directed purposive movements can be obtained through the study of the performance of individuals with brain damage. The control of rapid reciprocal aiming was investigated by comparing ipsilateral limb performance of subjects with unilateral brain damage to that of controls performing with the same limb. Thirty right-hand-dominant individuals, ten with right hemisphere stroke, ten with left hemisphere stroke, and ten age-matched controls performed unconstrained alternating tapping movements under three conditions of task complexity. The path of the stylus was recorded by video using two-dimensional kinematic techniques. Key kinematic features of the vertical and horizontal components of the trajectories were analyzed using both quantitative and qualitative methods. All subjects with brain damage showed prolonged movement times; however, the locus of the slowing depended on lesion side. Specifically, subjects with left stroke showed deficits in the open-loop component of the movement across all three conditions of task complexity, and a prolonged reversal phase surrounding target impact, particularly in the most complex condition. In contrast, subjects with right stroke showed deficits in the closed-loop phase of the movement prior to target impact, particularly in the most complex condition when visual information was necessary for accuracy. Together, these results suggest that for the control of rapid goal-directed aiming movements, the left hemisphere is dominant for task-relevant aspects of processing associated with the ballistic component and the timing or triggering of sequential movements. In contrast, the right hemisphere is dominant for processing associated with rapid, on-line visual information even when target location is known and direction is certain.

Motor task difficulty and brain activity: investigation of goal-directed reciprocal aiming using positron emission tomography.

Differences in the kinematics and pattern of relative regional cerebral blood flow (rCBF) during goal-directed arm aiming were investigated with the use of a Fitts continuous aiming paradigm with three difficulty conditions (index of difficulty, ID) and two aiming types (transport vs. targeting) in six healthy right-handed young participants with the use of video-based movement trajectory analysis and positron emission tomography. Movement time and kinematic characteristics were analyzed together with the magnitude of cerebral blood flow to identify areas of brain activity proportionate to task and movement variables. Significant differences in rCBF between task conditions were determined by analysis of variance with planned comparisons of means with the use of group mean weighted linear contrasts. Data were first analyzed for the group. Then individual subject differences for the movement versus no movement and task difficulty comparisons were related to each individual subjects' anatomy by magnetic resonance imaging. Significant differences in rCBF during reciprocal aiming compared with no-movement conditions were found in a mosaic of well-known cortical and subcortical areas associated with the planning and execution of goal-directed movements. These included cortical areas in the left sensorimotor, dorsal premotor, and ventral premotor cortices, caudal supplementary motor area (SMA) proper, and parietal cortex, and subcortical areas in the left putamen, globus pallidus, red nucleus, thalamus, and anterior cerebellum. As aiming task difficulty (ID) increased, rCBF increased in areas associated with the planning of more complex movements requiring greater visuomotor processing. These included bilateral occipital, left inferior parietal, and left dorsal cingulate cortices--caudal SMA proper and right dorsal premotor area. These same areas showed significant increases or decreases, respectively, when contrast means were compared with the use of movement time or relative acceleration time, respectively, as the weighting factor. Analysis of individual subject differences revealed a correspondence between the spatial extent of rCBF changes as a function of task ID and the individuals' movement times. As task ID decreased, significant increases in rCBF were evident in the right anterior cerebellum, left middle occipital gyrus, and right ventral premotor area. Functionally, these areas are associated with aiming conditions in which the motor execution demands are high (i.e., coordination of rapid reversals) and precise trajectory planning is minimal. These same areas showed significant increases or decreases, respectively, when contrast means were compared with the use of movement time or relative acceleration time, respectively, as the weighting factor. A functional dissociation resulted from the weighted linear contrasts between larger (limb transport) or smaller (endpoint targeting) type amplitude/target width aiming conditions. Areas with significantly greater rCBF for targeting were the left motor cortex, left intraparietal sulcus, and left caudate. In contrast, those areas with greater rCBF associated with limb transport included bilateral occipital lingual gyri and the right anterior cerebellum. Various theoretical explanations for the speed/accuracy tradeoffs of rapid aiming movements have been proposed since the original information theory hypothesis of Fitts. This is the first report to relate the predictable variations in motor control under changing task constraints with the functional anatomy of these rapid goal-directed aiming movements. Differences in unimanual aiming task difficulty lead to dissociable activation of cortical-subcortical networks. Further, these data suggest that when more precise targeting is required, independent of task difficulty, a cortical-subcortical loop composed of the contralateral motor cortex, intraparietal sulcus, and caudate is activated. This is consistent with the role of motor cortex