Objective: This study aimed at identifying the impact of subcortical stroke on the interaction of cortical motor areas within and across hemispheres during the generation of voluntary hand movements. Methods: Twelve subacute stroke patients with a subcortical ischemic lesion and 12 age-matched control subjects were scanned using 3-Tesla functional magnetic resonance imaging. Subjects performed visually paced hand movements with their left, right, or both hands. Changes of effective connectivity among a bilateral network of core motor regions comprising M1, lateral premotor cortex, and the supplementary motor area (SMA) were assessed using dynamic causal modeling. Results: The data showed significant disturbances in the effective connectivity of motor areas in the patients group: Independently from hand movements, the intrinsic neural coupling between ipsilesional SMA and M1, and the interhemispheric coupling of both SMAs was significantly reduced. Furthermore, movements of the stroke-affected hand showed additional inhibitory influences from contralesional to ipsilesional M1 that correlated with the degree of motor impairment. For bimanual movements, interhemispheric communication between ipsilesional SMA and contralesional M1 was significantly reduced, which also correlated with impaired bimanual performance. Interpretation: The motor deficit of patients with a single subcortical lesion is associated with pathological interhemispheric interactions among key motor areas. The data suggest that a dysfunction between ipsilesional and contralesional M1, and between ipsilesional SMA and contralesional M1 underlies hand motor disability after stroke. Assessing effective connectivity by means of functional magnetic resonance imaging and dynamic causal modeling might be used in the future for the evaluation of interventions promoting recovery of function.

As previous functional neuroimaging studies could not settle the controversy regarding the contribution of dominant and subdominant hemisphere to recovery from poststroke aphasia, language performance was related to H215O‐positron emission tomographic activation patterns in 23 right‐handed aphasic patients 2 and 8 weeks after stroke. In patients classified according to the site of lesion (frontal, n = 7; subcortical, n = 9; temporal, n = 7) and in 11 control subjects, flow changes caused by a word repetition task were calculated in 14 regions representing eloquent and contralateral homotopic areas. These areas were defined on coregistered magnetic resonance imaging scans and tested for significance (Bonferroni corrected t test, α = 0.0036). At baseline, differences in test performance were only found between the subcortical and temporal group. The extent of recovery, however, differed and was reflected in the activation. The subcortical and frontal groups improved substantially; they activated the right inferior frontal gyrus and the right superior temporal gyrus (STG) at baseline and regained left STG activation at follow‐up. The temporal group improved only in word comprehension; it activated the left Broca area and supplementary motor areas at baseline and the precentral gyrus bilaterally as well as the right STG at follow‐up, but could not reactivate the left STG. These differential activation patterns suggest a hierarchy within the language‐related network regarding effectiveness for improvement of aphasia; ie, right hemispheric areas contribute, if left hemispheric regions are destroyed. Efficient restoration of language is usually only achieved if left temporal areas are preserved and can be reintegrated into the functional network. Ann Neurol 1999;45:430–438

Background. Rehabilitation of the severely affected paretic arm after stroke represents a major challenge, especially in the presence of sensory impairment. Objective. To evaluate the effect of a therapy that includes use of a mirror to simulate the affected upper extremity with the unaffected upper extremity early after stroke. Methods. Thirty-six patients with severe hemiparesis because of a first-ever ischemic stroke in the territory of the middle cerebral artery were enrolled, no more than 8 weeks after the stroke. They completed a protocol of 6 weeks of additional therapy (30 minutes a day, 5 days a week), with random assignment to either mirror therapy (MT) or an equivalent control therapy (CT). The main outcome measures were the Fugl-Meyer subscores for the upper extremity, evaluated by independent raters through videotape. Patients also underwent functional and neuropsychological testing. Results. In the subgroup of 25 patients with distal plegia at the beginning of the therapy, MT patients regained more distal function than CT patients. Furthermore, across all patients, MT improved recovery of surface sensibility. Neither of these effects depended on the side of the lesioned hemisphere. MT stimulated recovery from hemineglect. Conclusions. MT early after stroke is a promising method to improve sensory and attentional deficits and to support motor recovery in a distal plegic limb.

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The beneficial effects of 10 Hz rTMS over ipsilesional M1 on motor function of the affected hand depend on the extension of MCA stroke. Neural activity in ipsilesional M1 may serve as a surrogate marker for the effectiveness of facilitatory rTMS.

Transcranial direct current stimulation is a painless, non-invasive brain stimulation technique that allows one to induce polarity-specific excitability changes in the human brain. Here, we investigated, for the first time in a 'proof of principle' study, the behavioural effect of transcranial direct current stimulation on visuospatial attention in both healthy controls and stroke patients suffering from left visuospatial neglect. We applied anodal, cathoP:dal or sham transcranial direct current stimulation (57 microA/cm(2), 10 min) to the left or right posterior parietal cortex. Using a visual detection task in a group of right-handed healthy individuals (n = 20), we observed that transcranial direct current stimulation enhanced or impaired performance depending on stimulation parameters (i.e. current polarity) and stimulated hemisphere. These results are in good accordance with classic models of reciprocal interhemispheric competition ('rivalry'). In a second experiment, we investigated the potential of transcranial direct current stimulation to ameliorate left visuospatial neglect (n = 10). Interestingly, both the inhibitory effect of cathodal transcranial direct current stimulation applied over the unlesioned posterior parietal cortex and the facilitatory effect of anodal transcranial direct current stimulation applied over the lesioned posterior parietal cortex reduced symptoms of visuospatial neglect. Taken together, our findings suggest that transcranial direct current stimulation applied over the posterior parietal cortex can be used to modulate visuospatial processing and that this effect is exerted by influencing interhemispheric reciprocal networks. These novel findings also suggest that a transcranial direct current stimulation-induced modulation of interhemispheric parietal balance may be used clinically to ameliorate visuospatial attention deficits in neglect patients.

No abstract

Dexterity was investigated in right-handed subjects in the subacute phase of a first unilateral subcortical middle cerebral artery stroke affecting the left or right hemisphere and right-handed healthy subjects. Dexterity was quantified at both hands by kinematic recordings of finger and hand tapping, a reach-to-grasp movement, quantitative analysis of grip forces in a grasp-lift task and clinical rating scales. Stroke subjects exhibited significant deficits in timing and coordination of tapping movements at both the contralesional and ipsilesional hands, irrespective of the hemisphere affected. Likely for the reach-to-grasp and grasp-lift movements a bilateral impairment was found in stroke subjects. In particular, slowing of hand transport towards the object, deficient timing and scaling of grasp formation, discoordination between grip and lift forces and inefficient scaling of grip forces were observed. The severity of impairment was independent of the hemisphere affected and evident for both the reach (involving more proximal muscles of the arm) and grasp (involving more distal muscles of the arm and hand) components of the task. Strong correlations were found between clinical scores of hand function and loss of sensibility with the deficits in timing, coordination and efficiency of movement of the contralesional and ipsilesional hand. These data provide evidence that dexterity is impaired at both hands after subcortical middle cerebral artery stroke.