Hans Karbe

Cortical connectivity after subcortical stroke assessed with functional magnetic resonance imaging

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.

Differential capacity of left and right hemispheric areas for compensation of poststroke aphasia.

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

Mirror Therapy Promotes Recovery From Severe Hemiparesis: A Randomized Controlled Trial

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.

Brain plasticity in poststroke aphasia: what is the contribution of the right hemisphere?

The brain may use two strategies to recover from poststroke aphasia: the structural repair of primarily speech-relevant regions or the activation of compensatory areas. We studied the cortical metabolic recovery in aphasic stroke patients with positron emission tomography (PET) at rest and during word repetition. The left supplementary motor area (SMA) showed the most prominent compensatory activation in the subacute state of stroke. The restitution of the left superior temporal cortex determined the long-term prognosis of aphasia. The brain recruited right-hemispheric regions for speech processing, when the left-hemispheric centers were permanently impaired. This strategy, however, was significantly less effective than the repair of the original speech-relevant network.

Effects of Low-Frequency Repetitive Transcranial Magnetic Stimulation of the Contralesional Primary Motor Cortex on Movement Kinematics and Neural Activity in Subcortical Stroke

BACKGROUND Following the concept of interhemispheric competition, downregulation of the contralesional primary motor cortex (M1) may improve the dexterity of the affected hand after stroke. OBJECTIVE To determine the effects of 1-Hz repetitive transcranial magnetic stimulation (rTMS) of the contralesional M1 on movement kinematics and neural activation within the motor system in the subacute phase after subcortical stroke. DESIGN Crossover investigation. SETTING A university hospital. METHODS Fifteen right-handed patients with impaired dexterity due to subcortical middle cerebral artery stroke received 1-Hz rTMS for 10 minutes applied to the vertex (control stimulation) and contralesional M1. For behavioral testing, patients performed finger and grasp movements with both hands at 2 baseline conditions, separated by 1 week, and following each rTMS application. For functional magnetic resonance imaging, patients performed hand grip movements with their affected or unaffected hand before and after each rTMS application. RESULTS Application of rTMS to the contralesional M1 improved the kinematics of finger and grasp movements in the affected hand. At the neural level, rTMS applied to the contralesional M1 reduced overactivity in the contralesional primary and nonprimary motor areas. There was no significant correlation between the rTMS-induced reduction in blood oxygen level-dependent responses within the contralesional M1 and the degree of behavioral improvement of the affected hand. Overactivity of the contralesional dorsal premotor cortex, contralesional parietal operculum, and ipsilesional mesial frontal cortex at baseline predicted improvement of movement kinematics with the affected hand after rTMS of the contralesional M1. CONCLUSION The functional magnetic resonance imaging data suggest that rTMS of the contralesional M1 may normalize neural activation within the cortical motor network after subcortical stroke. Identifying patients suitable for rTMS intervention based on individual patterns of cortical activation may help to implement rTMS in motor rehabilitation after stroke.

Differential effects of high‐frequency repetitive transcranial magnetic stimulation over ipsilesional primary motor cortex in cortical and subcortical middle cerebral artery stroke

Facilitation of cortical excitability of the ipsilesional primary motor cortex (M1) may improve dexterity of the affected hand after stroke. The effects of 10Hz repetitive transcranial magnetic stimulation (rTMS) over ipsilesional M1 on movement kinematics and neural activity were examined in patients with subcortical or cortical stroke.

Piracetam Improves Activated Blood Flow and Facilitates Rehabilitation of Poststroke Aphasic Patients

Background and Purpose In a prospective, double-blind, placebo-controlled study, it was investigated whether piracetam improves language recovery in poststroke aphasia assessed by neuropsychological tests and activation PET measurement of cerebral blood flow. Methods Twenty-four stroke patients with aphasia were randomly allocated to 2 groups: 12 patients received 2400 mg piracetam twice daily, 12 placebo. Before and at the end of the 6-week treatment period in which both groups received intensive speech therapy, the patients were examined neuropsychologically and studied with H215O PET at rest and during activation with a word-repetition task. Blood flow was analyzed in 14 language-activated brain regions defined on reconstructed surface views from MRI coregistered to the PET images. Results Before treatment, both groups were comparable with respect to performance in language tasks and to type and severity of aphasia. In the piracetam group, increase of activation effect was significantly higher (P <0.05) in the left transverse temporal gyrus, left triangular part of inferior frontal gyrus, and left posterior superior temporal gyrus after the treatment period compared with the initial measures. The placebo group showed an increase of activation effect only in the left vocalization area. In the test battery, the piracetam group improved in 6 language functions, the placebo group only in 3 subtests. Conclusions Piracetam as an adjuvant to speech therapy improves recovery of various language functions, and this effect is accompanied by a significant increase of task-related flow activation in eloquent areas of the left hemisphere.

Speech-induced cerebral metabolic activation reflects recovery from aphasia.

Six stroke patients with clinically significant aphasia were studied 4 weeks and again 12-18 months after their first left hemispheric ictus. The regional cerebral metabolic rate of glucose (rCMRglc) was measured repeatedly by PET at rest and during word repetition, and severity of speech impairment was assessed by a neuropsychologic test battery. The patterns of speech-associated activation of glucose metabolism were related to improvement in language performance as measured by the Token test. Three patients experienced significant recovery from aphasia (Token test: 47 to 3, 45 to 12, and 37 to 5 points, respectively), whereas 3 patients had poor outcome (Token test from 48 to 45, and from 47 to 39 and 24, respectively). Good recovery was related to activation of left hemispheric speech areas surrounding the infarct, especially left superior temporal gyrus. In contrast, the 3 patients with persistent aphasia showed rCMRglc recruitment in right hemispheric regions and were unable to activate left hemispheric speech areas on follow-up. These results indicate that favorable outcome is related to partial sparing of speech areas of the dominant hemisphere that can be (re-) activated. Predominant recruitment of contralateral areas is not efficacious for a considerable recovery from aphasia. It rather indicates unspecific involvement of widespread networks in the effort to perform a complex task.

Dexterity is impaired at both hands following unilateral subcortical middle cerebral artery stroke.

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.

Effects of rTMS on grip force control following subcortical stroke

Within the concept of interhemispheric competition we tested the effect of inhibitory 1 Hz repetitive transcranial magnetic stimulation (rTMS), applied over the primary motor cortex of the unaffected hemisphere, upon dexterity of the affected hand in subcortical stroke patients. Subjects grasped, lifted and held an instrumented object between the index finger and thumb with both the affected and unaffected hand prior to (baseline) and following 1 Hz rTMS applied over (i) the vertex (control stimulation) and (ii) the primary motor cortex of the unaffected hemisphere. Compared to baseline, 1 Hz rTMS applied over the unaffected primary motor cortex, but not the vertex, improved the efficiency and timing of grasping and lifting with the affected hand. Our data support the interhemispheric competition concept and furthermore reinforce current efforts to implement rTMS in novel approaches to stroke rehabilitation.