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Objectives To investigate the relationship between bimanual performance deficits measured using kinematics and callosum (CC) white matter changes that occur in people with chronic stroke. Design Cross-sectional, observational study of participants with chronic stroke and age-matched controls. Setting Recruitment and assessments occurred at a stroke recovery research center. Behavioral assessments were performed in a controlled laboratory setting. Magnetic resonance imaging scans were performed at the Center for Biomedical Imaging. Participants Individuals were enrolled and completed the study (N=39; 21 participants with chronic stroke; 18 age-matched controls with at least 2 stroke risk factors). Main Outcome Measures Diffusion imaging metrics were obtained for each individual’s CC and corticospinal tract (CST), including mean kurtosis (MK) and fractional anisotropy (FA). A battery of motor assessments, including bimanual kinematics, were collected from individuals while performing bimanual reaching. Results Participants with stroke had lower FA and MK in the CST of the lesioned hemisphere when compared with the non-lesioned hemisphere. The FA and MK values in the CST were correlated with measures of unimanual hand performance. In addition, participants with stroke had significantly lower FA and MK in the CC than matched controls. CC diffusion metrics positively correlated with hand asymmetry and trunk displacement during bimanual performance, even when correcting for age and lesion volume. Conclusions These data confirm previous studies that linked CST integrity to unimanual performance and provide new data demonstrating a link between CC integrity and both bimanual motor deficits and compensatory movements., Highlights • Fractional anisotropy and mean kurtosis in the corpus callosum are lower in participants with stroke. • Hand position symmetry and trunk displacement are disrupted during bimanual tasks. • Corpus callosum white matter correlated with bimanual kinematics in participants with stroke.

Motor function may be enhanced if aerobic exercise is paired with motor training. One potential mechanism is that aerobic exercise increases levels of brain-derived neurotrophic factor (BDNF), which is important in neuroplasticity and involved in motor learning and motor memory consolidation. This study will examine the feasibility of a parallel-group assessor-blinded randomised controlled trial investigating whether task-specific training preceded by aerobic exercise improves upper limb function more than task-specific training alone, and determine the effect size of changes in primary outcome measures. People with upper limb motor dysfunction after stroke will be allocated to either task-specific training or aerobic exercise and consecutive task-specific training. Both groups will perform 60 hours of task-specific training over 10 weeks, comprised of 3 × 1 hour sessions per week with a therapist and 3 × 1 hours of home-based self-practice per week. The combined intervention group will also perform 30 minutes of aerobic exercise (70–85%HRmax) immediately prior to the 1 hour of task-specific training with the therapist. Recruitment, adherence, retention, participant acceptability, and adverse events will be recorded. Clinical outcome measures will be performed pre-randomisation at baseline, at completion of the training program, and at 1 and 6 months follow-up. Primary clinical outcome measures will be the Action Research Arm Test (ARAT) and the Wolf Motor Function Test (WMFT). If aerobic exercise prior to task-specific training is acceptable, and a future phase 3 randomised controlled trial seems feasible, it should be pursued to determine the efficacy of this combined intervention for people after stroke. Keywords: Stroke, Motor function, Aerobic exercise, Task-specific training

Objective: To determine whether chronicity influences outcomes of somatosensory stimulation paired with task-oriented motor training for participants with severe-to-moderate upper extremity hemiparesis. Design: Spearman correlations were used to retrospectively analyze outcomes of a randomized trial. Setting: University research laboratory at a rehabilitation hospital. Participants: Adults, ranging between 3 and 12 months poststroke (N=55). Interventions: About 18 sessions pairing either 2 hours of active (n=33) or sham (n=22) somatosensory stimulation with 4 hours of intensive task-oriented motor training. Main Outcome Measures: The Wolf Motor Function Test (primary), Action Research Arm Test, Stroke Impact Scale, and Fugl-Meyer Assessment were collected as outcome measures. Analyses evaluated whether within-group chronicity correlated with pre-post changes on primary and secondary outcome measures of motor performance. Results: Both groups exhibited improvements on all outcome measures. No significant correlations between chronicity poststroke and the amount of motor recovery were found. Conclusion: Somatosensory stimulation improved motor recovery compared with sham treatment in cases of severe-to-moderate hemiparesis between 3 and 12 months poststroke; and the extent of recovery did not correlate with baseline levels of stroke chronicity. Future studies should investigate a wider period of inclusion, patterns of corticospinal reorganization, differences between cortical and subcortical strokes, and include long-term follow-up periods. Keywords: Humans, Occupational therapy, Rehabilitation, Transcutaneous electric nerve stimulation, Upper extremity

The relationships between impairment, function, arm use and underlying brain structure following stroke remain unclear. Although diffusion weighted imaging is useful in broadly assessing white matter structure, it has limited utility in identifying specific underlying neurobiological components, such as myelin. The purpose of the present study was to explore relationships between myelination and impairment, function and activity in individuals with chronic stroke. Assessments of paretic upper-extremity impairment and function were administered, and 72-hour accelerometer based activity monitoring was conducted on 19 individuals with chronic stroke. Participants completed a magnetic resonance imaging protocol that included a high resolution T1 anatomical scan and a multi-component T2 relaxation imaging scan to quantify myelin water fraction (MWF). MWF was automatically parcellated from pre- and post-central subcortical regions of interest and quantified as an asymmetry ratio (contralesional/ipsilesional). Cluster analysis was used to group more and less impaired individuals based on Fugl-Meyer upper extremity scores. A significantly higher precentral MWF asymmetry ratio was found in the more impaired group compared to the less impaired group (p, Highlights • Identification of neurobiology that contributes to recovery after stroke is critical. • Human post-stroke myelination can be imaged in vivo using T2 relaxation imaging. • Impaired individuals demonstrate precentral myelin asymmetry between hemispheres. • Precentral myelin asymmetry is a predictor of motor function and impairment. • Myelination may be a specific marker of post-stroke neurobiological changes.