The impact of lesion side on bilateral upper limb coordination after stroke.

BACKGROUND: A stroke frequently results in impaired performance of activities of daily life. Many of these are highly dependent on effective coordination between the two arms. In the context of bimanual movements, cyclic rhythmical bilateral arm coordination patterns can be classified into two fundamental modes: in-phase (bilateral homologous muscles contract simultaneously) and anti-phase (bilateral muscles contract alternately) movements. We aimed to investigate how patients with left (LHS) and right (RHS) hemispheric stroke are differentially affected in both individual-limb control and inter-limb coordination during bilateral movements. METHODS: We used kinematic measurements to assess bilateral coordination abilities of 18 chronic hemiparetic stroke patients (9 LHS; 9 RHS) and 18 age- and sex-matched controls. Using KINARM upper-limb exoskeleton system, we examined individual-limb control by quantifying trajectory variability in each hand and inter-limb coordination by computing the phase synchronization between hands during anti- and in-phase movements. RESULTS: RHS patients exhibited greater impairment in individual- and inter-limb control during anti-phase movements, whilst LHS patients showed greater impairment in individual-limb control during in-phase movements alone. However, LHS patients further showed a swap in hand dominance during in-phase movements. CONCLUSIONS: The current study used individual-limb and inter-limb kinematic profiles and showed that bilateral movements are differently impaired in patients with left vs. right hemispheric strokes. Our results demonstrate that both fundamental bilateral coordination modes are differently controlled in both hemispheres using a lesion model approach. From a clinical perspective, we suggest that lesion side should be taken into account for more individually targeted bilateral coordination training strategies. TRIAL REGISTRATION: the current experiment is not a health care intervention study.

Differential effects of anodal and dual tDCS on sensorimotor functions in chronic hemiparetic stroke patients.

BACKGROUND AND PURPOSE: Previous tDCS studies in chronic stroke patients reported highly inconsistent effects on sensorimotor functions. Underlying reasons could be the selection of different kinematic parameters across studies and for different tDCS setups. We reasoned that tDCS may not simply induce global changes in a beneficial-adverse dichotomy, but rather that different sensorimotor kinematics are differentially affected. Furthermore, the often-postulated higher efficacy of bilateral-dual (bi-tDCS) over unilateral-anodal (ua-tDCS) could not yet be demonstrated consistently either. We investigated the effects of both setups on a wider range of kinematic parameters from standardized robotic tasks in patients with chronic stroke. METHODS: Twenty-four patients with arm hemiparesis received tDCS (20min, 1 mA) concurrent to kinematic assessments in a sham-controlled, cross-over and double-blind clinical trial. Performance was measured on four sensorimotor tasks (reaching, proprioception, cooperative and independent bimanual coordination) from which 30 parameters were extracted. On the group-level, the patterns of changes relative to sham were assessed using paired-samples t-tests and classified as (1) performance increases, (2) decreases and (3) non-significant differences. Correlations between parametric change scores were calculated for each task to assess effects on the individual-level. RESULTS: Both setups induced complex effect patterns with varying proportions of performance increases and decreases. On the group-level, more increases were induced in the reaching and coordination tasks while proprioception and bimanual cooperation were overall negatively affected. Bi-tDCS induced more performance increases and less decreases compared to ua-tDCS. Changes across parameters occurred more homogeneously under bi-tDCS than ua-tDCS, which induced a larger proportion of performance trade-offs. CONCLUSIONS: Our data demonstrate profound tDCS effects on sensorimotor functions post-stroke, lending support for more pronounced and favorable effects of bi-tDCS compared to ua-tDCS. However, no uniformly beneficial pattern was identified. Instead, the modulations varied depending on the task and electrode setup, with increases in certain parameters occurring at the expense of decreases in others.

Alpha and beta neural oscillations differentially reflect age-related differences in bilateral coordination.

Bilateral in-phase (IP) and anti-phase (AP) movements represent two fundamental modes of bilateral coordination that are essential for daily living. Although previous studies have shown that aging is behaviorally associated with decline in bilateral coordination, especially in AP movements, the underlying neural mechanisms remain unclear. Here, we use kinematic measurements and electroencephalography to compare motor performance of young and older adults executing bilateral IP and AP hand movements. On the behavioral level, inter-limb synchronization was reduced during AP movements compared to IP and this reduction was stronger in the older adults. On the neural level, we found interactions between group and condition for task-related power change in different frequency bands. The interaction was driven by smaller alpha power decreases over the non-dominant cortical motor area in young adults during IP movements and larger beta power decreases over the midline region in older adults during AP movements. In addition, the decrease in inter-limb synchronization during AP movements was predicted by stronger directional connectivity in the beta-band: an effect more pronounced in older adults. Our results therefore show that age-related differences in the two bilateral coordination modes are reflected on the neural level by differences in alpha and beta oscillatory power as well as interhemispheric directional connectivity.

Anodal Transcranial Direct Current Stimulation Over S1 Differentially Modulates Proprioceptive Accuracy in Young and Old Adults.

BACKGROUND: Proprioception is a prerequisite for successful motor control but declines throughout the lifespan. Brain stimulation techniques such as anodal transcranial direct current stimulation (a-tDCS) are capable of enhancing sensorimotor performance across different tasks and age groups. Despite such growing evidence for a restorative potential of tDCS, its impact on proprioceptive accuracy has not been studied in detail yet. OBJECTIVE: This study investigated online effects of a-tDCS over S1 on proprioceptive accuracy in young (YA) and old healthy adults (OA). METHODS: The effect of 15 min of a-tDCS vs. sham on proprioceptive accuracy was assessed in a cross-over, double blind experiment in both age groups. Performance changes were tested using an arm position matching task in a robotic environment. Electrical field (EF) strengths in the target area S1 and control areas were assessed based on individualized simulations. RESULTS: a-tDCS elicited differential changes in proprioceptive accuracy and EF strengths in the two groups: while YA showed a slight improvement, OA exhibited a decrease in performance during a-tDCS. Stronger EF were induced in target S1 and control areas in the YA group. However, no relationship between EF strength and performance change was found. CONCLUSION: a-tDCS over S1 elicits opposing effects on proprioceptive accuracy as a function of age, a result that is important for future studies investigating the restorative potential of a-tDCS in healthy aging and in the rehabilitation of neurological diseases that occur at advanced age. Modeling approaches could help elucidate the relationship between tDCS protocols, brain structure and performance modulation.

Kinematic profiles suggest differential control processes involved in bilateral in-phase and anti-phase movements.

In-phase and anti-phase movements represent two basic coordination modes with different characteristics: during in-phase movements, bilateral homologous muscle groups contract synchronously, whereas during anti-phase movements, they contract in an alternating fashion. Previous studies suggested that in-phase movements represent a more stable and preferential bilateral movement template in humans. The current experiment aims at confirming and extending this notion by introducing new empirical measures of spatiotemporal dynamics during performance of a bilateral circle drawing task in an augmented-reality environment. First, we found that anti-phase compared to in-phase movements were performed with higher radial variability, a result that was mainly driven by the non-dominant hand. Second, the coupling of both limbs was higher during in-phase movements, corroborated by a lower inter-limb phase difference and higher inter-limb synchronization. Importantly, the movement acceleration profile between bilateral hands followed an in-phase relationship during in-phase movements, while no specific relationship was found in anti-phase condition. These spatiotemporal relationships between hands support the hypothesis that differential neural processes govern both bilateral coordination modes and suggest that both limbs are controlled more independently during anti-phase movements, while bilateral in-phase movements are elicited by a common neural generator.

The potential effect of a vibrotactile glove rehabilitation system on motor recovery in chronic post-stroke hemiparesis.

BACKGROUND: Poor fine motor skills are common among chronic stroke patients. Conventional rehabilitation programs only emphasize intensive and repeated exercises that do not motivate patients to continue rehabilitation. Using a vibrotactile glove rehabilitation system with a human-computer interaction interface can therefore resolve this issue. OBJECTIVE: The objective of this study was to examine the potential benefits of this vibrotactile glove rehabilitation system for chronic stroke patients who have already reached the recovery plateau. METHODS: Two interesting computer games were designed to coordinate with the vibrotactile gloves in patient training. The training sessions lasted for about 30 minutes twice a week for five consecutive weeks. We compared finger ROM, grip strength, pinch strength, NHPT, and MHQ results before and after the intervention and surveyed subject satisfaction afterwards. RESULTS: The subjects showed slight improvements in muscle strength and hand after five weeks. The patients reported progress, but the differences did not reach statistical significance. In the satisfaction questionnaire, the subjects gave positive ratings. CONCLUSIONS: This vibrotactile glove rehabilitation system has the potential to help chronic stroke patients who have reached their recovery plateau to make progress and is clinically quite effective in increasing their motivation.

Development of a novel haptic glove for improving finger dexterity in poststroke rehabilitation.

Almost all stroke patients experience a certain degree of fine motor impairment, and impeded finger movement may limit activities in daily life. Thus, to improve the quality of life of stroke patients, designing an efficient training device for fine motor rehabilitation is crucial. This study aimed to develop a novel fine motor training glove that integrates a virtual-reality based interactive environment with vibrotactile feedback for more effective post stroke hand rehabilitation. The proposed haptic rehabilitation device is equipped with small DC vibration motors for vibrotactile feedback stimulation and piezoresistive thin-film force sensors for motor function evaluation. Two virtual-reality based games ``gopher hitting'' and ``musical note hitting'' were developed as a haptic interface. According to the designed rehabilitation program, patients intuitively push and practice their fingers to improve the finger isolation function. Preliminary tests were conducted to assess the feasibility of the developed haptic rehabilitation system and to identify design concerns regarding the practical use in future clinical testing.

Effects of exercise intensity on spatial memory performance and hippocampal synaptic plasticity in transient brain ischemic rats.

Memory impairment is commonly noted in stroke survivors, and can lead to delay of functional recovery. Exercise has been proved to improve memory in adult healthy subjects. Such beneficial effects are often suggested to relate to hippocampal synaptic plasticity, which is important for memory processing. Previous evidence showed that in normal rats, low intensity exercise can improve synaptic plasticity better than high intensity exercise. However, the effects of exercise intensities on hippocampal synaptic plasticity and spatial memory after brain ischemia remain unclear. In this study, we investigated such effects in brain ischemic rats. The middle cerebral artery occlusion (MCAO) procedure was used to induce brain ischemia. After the MCAO procedure, rats were randomly assigned to sedentary (Sed), low-intensity exercise (Low-Ex), or high-intensity exercise (High-Ex) group. Treadmill training began from the second day post MCAO procedure, 30 min/day for 14 consecutive days for the exercise groups. The Low-Ex group was trained at the speed of 8 m/min, while the High-Ex group at the speed of 20 m/min. The spatial memory, hippocampal brain-derived neurotrophic factor (BDNF), synapsin-I, postsynaptic density protein 95 (PSD-95), and dendritic structures were examined to document the effects. Serum corticosterone level was also quantified as stress marker. Our results showed the Low-Ex group, but not the High-Ex group, demonstrated better spatial memory performance than the Sed group. Dendritic complexity and the levels of BDNF and PSD-95 increased significantly only in the Low-Ex group as compared with the Sed group in bilateral hippocampus. Notably, increased level of corticosterone was found in the High-Ex group, implicating higher stress response. In conclusion, after brain ischemia, low intensity exercise may result in better synaptic plasticity and spatial memory performance than high intensity exercise; therefore, the intensity is suggested to be considered during exercise training.