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Most patients with stroke experience motor deficits, usually referred to collectively as hemiparesis. Although hemiparesis is one of the most common and clinically recognizable motor abnormalities, it remains undercharacterized in terms of its behavioral subcomponents and their interactions. Hemiparesis comprises both negative and positive motor signs. Negative signs consist of weakness and loss of motor control (dexterity), whereas positive signs consist of spasticity, abnormal resting posture, and intrusive movement synergies (abnormal muscle co-activations during voluntary movement). How positive and negative signs interact, and whether a common mechanism generates them, remains poorly understood. Here, we used a planar, arm-supported reaching task to assess poststroke arm dexterity loss, which we compared with the Fugl-Meyer stroke scale; a measure primarily reflecting abnormal synergies. We examined 53 patients with hemiparesis after a first-time ischemic stroke. Reaching kinematics were markedly more impaired in patients with subacute (<3 mo) compared to chronic (>6 mo) stroke even for similar Fugl-Meyer scores. This suggests a dissociation between abnormal synergies (reflected in the Fugl-Meyer scale) and loss of dexterity, which in turn suggests different underlying mechanisms. Moreover, dynamometry suggested that Fugl-Meyer scores capture weakness as well as abnormal synergies, in line with these two deficits sharing a neural substrate. These findings have two important implications: First, clinical studies that test for efficacy of rehabilitation interventions should specify which component of hemiparesis they are targeting and how they propose to measure it. Metrics used widely for this purpose may not always be chosen appropriately. For example, as we show here, the Fugl-Meyer score may capture some hemiparesis components (abnormal synergies and weakness) but not others (loss of dexterity). Second, there may be an opportunity to design rehabilitation interventions to address specific subcomponents of hemiparesis. NEW & NOTEWORTHY Motor impairment is common after stroke and comprises reduced dexterity, weakness, and abnormal muscle synergies. Here we report that, when matched on an established synergy and weakness scale (Fugl-Meyer), patients with subacute stroke have worse reaching dexterity than chronic ones. This result suggests that the components of hemiparesis are dissociable and have separable mechanisms and, thus, may require distinct assessments and treatments.

It has been proposed that a form of cortical reorganization (changes in functional connectivity between brain areas) can be assessed with resting-state (rs) functional MRI (fMRI). Here, we report a longitudinal data set collected from 19 patients with subcortical stroke and 11 controls. Patients were imaged up to five times over 1 year. We found no evidence, using rs-fMRI, for longitudinal poststroke cortical connectivity changes despite substantial behavioral recovery. These results could be construed as questioning the value of resting-state imaging. Here, we argue instead that they are consistent with other emerging reasons to challenge the idea of motor-recovery-related cortical reorganization poststroke when conceived of as changes in connectivity between cortical areas. NEW & NOTEWORTHY We investigated longitudinal changes in functional connectivity after stroke. Despite substantial motor recovery, we found no differences in functional connectivity patterns between patients and controls, nor any changes over time. Assuming that rs-fMRI is an adequate method to capture connectivity changes between cortical regions after brain injury, these results provide reason to doubt that changes in cortico-cortical connectivity are the relevant mechanism for promoting motor recovery.

One-third of stroke survivors worldwide suffer from aphasia. Speech and language therapy (SLT) is considered effective in treating aphasia, but because of time constraints, improvements are often limited. Noninvasive brain stimulation is a promising adjuvant strategy to facilitate SLT. However, stroke might render "classical" language regions ineffective as stimulation sites. Recent work showed the effectiveness of motor cortex stimulation together with intensive naming therapy to improve outcomes in aphasia (Meinzer et al. 2016). Although that study highlights the involvement of the motor cortex, the functional aspects by which it influences language remain unclear. In the present study, we focus on the role of motor cortex in language, investigating its functional involvement in access to specific lexico-semantic (object vs. action relatedness) information in poststroke aphasia. To this end, we tested effects of anodal transcranial direct current stimulation (tDCS) to the left motor cortex on lexical retrieval in 16 patients with poststroke aphasia in a sham-controlled, double-blind study design. Critical stimuli were action and object words, and pseudowords. Participants performed a lexical decision task, deciding whether stimuli were words or pseudowords. Anodal tDCS improved accuracy in lexical decision, especially for words with action-related content and for pseudowords with an "action-like" ending ( t 15  = 2.65, P = 0.036), but not for words with object-related content and pseudowords with "object-like" characteristics. We show as a proof-of-principle that the motor cortex may play a specific role in access to lexico-semantic content. Thus motor-cortex stimulation may strengthen content-specific word-to-semantic concept associations during language treatment in poststroke aphasia. NEW & NOTEWORTHY The role of motor cortex (MC) in language processing has been debated in both health and disease. Recent work has suggested that MC stimulation together with speech and language therapy enhances outcomes in aphasia. We show that MC stimulation has a differential effect on object- and action-word processing in poststroke aphasia. We propose that MC stimulation may specifically strengthen word-to-semantic concept association in aphasia. Our results potentially provide a way to tailor therapies for language rehabilitation.

Impaired hand function after stroke is a major cause of long-term disability. We developed a novel paradigm that quantifies two critical aspects of hand function, strength, and independent control of fingers (individuation), and also removes any obligatory dependence between them. Hand recovery was tracked in 54 patients with hemiparesis over the first year after stroke. Most recovery of strength and individuation occurred within the first 3 mo. A novel time-invariant recovery function was identified: recovery of strength and individuation were tightly correlated up to a strength level of ~60% of estimated premorbid strength; beyond this threshold, strength improvement was not accompanied by further improvement in individuation. Any additional improvement in individuation was attributable instead to a second process that superimposed on the recovery function. We conclude that two separate systems are responsible for poststroke hand recovery: one contributes almost all of strength and some individuation; the other contributes additional individuation. NEW & NOTEWORTHY We tracked recovery of the hand over a 1-yr period after stroke in a large cohort of patients, using a novel paradigm that enabled independent measurement of finger strength and control. Most recovery of strength and control occurs in the first 3 mo after stroke. We found that two separable systems are responsible for motor recovery of hand: one contributes strength and some dexterity, whereas a second contributes additional dexterity., (Copyright © 2017 the American Physiological Society.)