Objective: Motor recovery after stroke depends on the integrity of ipsilesional motor circuits and interactions between the ipsilesional and contralesional hemispheres. In this sham-controlled randomized trial, we investigated whether noninvasive modulation of regional excitability of bilateral motor cortices in combination with physical and occupational therapy improves motor outcome after stroke. Methods:Twenty chronic stroke patients were randomly assigned to receive 5 consecutive sessions of either 1) bihemispheric transcranial direct current stimulation (tDCS) (anodal tDCS to upregulate excitability of ipsilesional motor cortex and cathodal tDCS to downregulate excitability of contralesional motor cortex) with simultaneous physical/occupational therapy or 2) sham stimulation with simultaneous physical/occupational therapy. Changes in motor impairment (Upper Extremity Fugl-Meyer) and motor activity (Wolf Motor Function Test) assessments were outcome measures while functional imaging parameters were used to identify neural correlates of motor improvement.

Objective: Motor impairment after stroke has been related to infarct size, infarct location, and integrity of motor tracts. To determine the value of diffusion tensor imaging (DTI) as a predictor of motor outcome and its role as a structural surrogate marker of impairment in chronic stroke, we tested correlations between motor impairment and DTI-derived measures of motor tract integrity.Methods: Thirty-five chronic stroke patients with varying degrees of recovery underwent DTI and motor impairment assessments. Fibers originating from the precentral gyrus were traced and separated into pyramidal tract (PT) and alternate motor fibers (aMF). Asymmetry indices of fiber number and regional fractional anisotropy (FA) values comparing lesional with nonlesional hemispheres were correlated with motor impairment scores and compared to an age-matched control group.Results: Fiber number and regional FA value asymmetry significantly differed between the groups with lower values in the patients' lesional hemispheres. Both measures significantly predicted motor impairment with stronger predictions when all motor tracts were combined as compared to predictions using only the PT. The pattern of motor tract damage (PT only vs PT and aMF) led to a classification of mild, moderate, or severe impairment with significant between-group differences in motor impairment scores.Conclusions: Diffusion tensor imaging-derived measures are valid structural markers of motor impairment. The integrity of all descending motor tracts, not merely the pyramidal tract, appears to account for stroke recovery. A 3-tier, hierarchical classification of impairment categories based on the pattern of motor tract damage is proposed that might be helpful in predicting recovery potential. Neurology Motor impairment after stroke has been related to lesion site and size, 1,2 amount of previous lesion burden, and other factors like age or comorbidities. 3,4 It has also been shown that the integrity of motor fibers, with the pyramidal tract (PT) as the main descending fiber bundle, but also the cortico-rubro-spinal or cortico-reticulo-spinal systems, 5,6 plays an important role for the degree of motor impairment which can be measured with standardized, reliable, and valid clinical assessments. 7,8 However, mere lesion location may not sufficiently demonstrate the extent to which motor fibers remain intact and a considerable amount of variance remains unexplained.Diffusion tensor imaging (DTI) allows for the visualization and quantitative examination of fiber tracts and their integrity in vivo 9 so that the topographic relation of lesion location and corticospinal fibers can be evaluated [10][11][12][13][14] and fiber degeneration can be revealed.

Electrophysiological and neuroimaging studies suggest that the integrity of ipsilesional and inter-hemispheric motor circuits is important for motor recovery after stroke. However, the extent to which each of these tracts contributes to the variance in outcome remains unclear. We examined whether diffusion tensor imaging (DTI)-derived measures of corticospinal and transcallosal tracts predict motor improvement in an experimental neurorehabilitation trial. 15 chronic stroke patients received bihemispheric transcranial direct current stimulation and simultaneous physical/occupational therapy for five consecutive days. Motor impairment was assessed prior to and after the intervention. At baseline, the patients underwent DTI; probabilistic fiber tracking was used to reconstruct the pyramidal tract (PT), alternate descending motor fibers (aMF) and transcallosal fibers connecting primary motor cortices (M1-M1). Ipsilesional corticospinal tracts (PT, aMF) and M1-M1 showed significantly decreased fractional anisotropy (FA) and increased directional diffusivities when compared to age-matched healthy controls. Partial correlations revealed that greater gains in motor functions were related to higher FA values and lower directional diffusivities of transcallosal and ipsilesional corticospinal tracts. M1-M1 diffusivity had the greatest predictive value. An additional slice-by-slice analysis of FA values along the corticospinal tracts demonstrated that the more the ipsilesional FA profiles of patients resembled those of healthy controls, the greater their functional improvement. In conclusion, our study shows that DTI-derived measures can be used to predict functional potential for subsequent motor recovery in chronic stroke patients. Diffusivity parameters of individual tracts and tract combinations may help in assessing a patient’s individual recovery potential and in determining optimal neurorehabilitative interventions.

Background and Purpose-Previous studies have shown motor impairment after a stroke relates to lesion size and location, but unexplained variability in recovery still exists. In this study, we used lesion-mapping techniques in combination with diffusion tensor imaging to quantitatively test the hypothesis that motor recovery in patients with chronic stroke is inversely related to the proportion of the corticospinal tract (CST) affected by the lesion. Methods-We studied 50 patients with chronic stroke, all of whom presented with moderate to severe motor impairments in the acute stage, using high-resolution anatomic MRI. We evaluated the degree of motor impairment with the Upper Extremity module of the Fugl-Meyer Assessment. To analyze the relationship between CST damage and impairment scores, we calculated a CST-lesion load for each patient by overlaying the patient's lesion map with a probabilistic tract derived from diffusion tensor images of age-matched healthy subjects. Results-CST-lesion load was a significant predictor of motor deficit. Infarct size, despite correlating with motor scores, did not significantly predict impairment. Conclusions-Our results show the degree of functional motor deficit after a stroke is highly dependent on the overlap of the lesion with the CST and not lesion size per se. In the future, automated calculation of CST-lesion load may allow more precise prediction of motor impairment after stroke. (Stroke. 2010;41:910-915.)

Background and Purpose Previous studies have suggested that patients’ potential for post-stroke language recovery is related to lesion size; however, lesion location may also be of importance, particularly when fiber tracts that are critical to the sensorimotor mapping of sounds for articulation (e.g. the arcuate fasciculus [AF]) have been damaged. In this study, we tested the hypothesis that lesion loads of the AF (i.e. volume of AF that is affected by a patient’s lesion) and of two other tracts involved in language processing (the extreme capsule [EmC] and the uncinate fasciculus [UF]) are inversely related to the severity of speech production impairments in stroke patients with aphasia. Methods Thirty chronic stroke patients with residual impairments in speech production underwent high-resolution anatomical MR imaging and a battery of cognitive and language tests. Impairment was assessed using three functional measures of spontaneous speech (e.g. rate, informativeness, and overall efficiency) as well as naming ability. To quantitatively analyze the relationship between impairment scores and lesion-load along the three fiber tracts, we calculated tract–lesion overlap volumes for each patient using probabilistic maps of the tracts derived from diffusion tensor images of ten age-matched healthy subjects. Results Regression analyses showed that AF-lesion load, but not EmC- or UF-lesion load or lesion size, significantly predicted rate, informativeness, and overall efficiency of speech, as well as naming ability. Conclusions A new variable, AF-lesion load, complements established voxel-based lesion-mapping techniques and, in the future, may potentially be used to estimate impairment and recovery potential after stroke and refine inclusion criteria for experimental rehabilitation programs.

Background and purpose Treatment options for stroke related dysphagia are currently limited. In this study we investigated whether non-invasive brain stimulation in combination with swallowing maneuvers facilitates swallowing recovery in dysphagic stroke patients during early stroke convalescence. Methods Fourteen patients with subacute unilateral hemispheric infarction were randomized to anodal transcranial direct current stimulation (tDCS) versus sham stimulation to the sensorimotor cortical representation of swallowing in the unaffected hemisphere over 5 consecutive days with concurrent standardized swallowing maneuvers. Severity of dysphagia was measured using a validated swallowing scale, Dysphagia Outcome and Severity Scale (DOSS), before the first and after the last session of tDCS or sham. The effect of tDCS was analyzed in a multivariate linear regression model using changes in DOSS as the outcome variable, after adjusting for the effects of other potential confounding variables such as the NIH Stroke Scale (NIHSS) and DOSS scores at baseline, acute ischemic lesion volumes, patient’s age and time from stroke onset to stimulation. Results Patients who received anodal tDCS gained 2.60 points improvement in DOSS scores compared to patients in the sham stimulation group who showed an improvement of 1.25 points (P=0.019) after controlling for the effects of other aforementioned variables. 6 out 7 (86%) patients in tDCS stimulation group gained at least 2 points improvement compared with 3 out 7 (43%) patients in sham group (P=0.107). Conclusion Since brainstem swallowing centers have bilateral cortical innervations, measures that enhance cortical input and sensorimotor control of brainstem swallowing may be beneficial for dysphagia recovery.

As the main interhemispheric fiber tract, the corpus callosum (CC) is of particular importance for musicians who simultaneously engage parts of both hemispheres to process and play music. Professional musicians who began music training before the age of 7 years have larger anterior CC areas than do nonmusicians, which suggests that plasticity due to music training may occur in the CC during early childhood. However, no study has yet demonstrated that the increased CC area found in musicians is due to music training rather than to preexisting differences. We tested the hypothesis that approximately 29 months of instrumental music training would cause a significant increase in the size of particular subareas of the CC known to have fibers that connect motorrelated areas of both hemispheres. On the basis of total weekly practice time, a sample of 31 children aged 5-7 was divided into three groups: high-practicing, low-practicing, and controls. No CC size differences were seen at base line, but differences emerged after an average of 29 months of observation in the high-practicing group in the anterior midbody of the CC (which connects premotor and supplementary motor areas of the two hemispheres). Total weekly music exposure predicted degree of change in this subregion of the CC as well as improvement on a motorsequencing task. Our results show that it is intense musical experience/practice, not preexisting differences, that is responsible for the larger anterior CC area found in professional adult musicians.

Purpose It is thought that following a stroke the contralesional motor region exerts an undue inhibitory influence on the lesional motor region which might limit recovery. Pilot studies have shown that suppressing the contralesional motor region with cathodal transcranial Direct Current Stimulation (tDCS) can induce a short lasting functional benefit; greater and longer lasting effects might be achieved with combining tDCS with simultaneous occupational therapy (OT) and applying this intervention for multiple sessions. Methods We carried out a randomized, double blind, sham controlled study of chronic stroke patients receiving either 5 consecutive days of cathodal tDCS (for 30 minutes) applied to the contralesional motor region and simultaneous OT, or sham tDCS+OT. Results We showed that cathodal tDCS+OT resulted in significantly more improvement in Range-Of-Motion in multiple joints of the paretic upper extremity and in the Upper-Extremity Fugl-Meyer scores than sham tDCS+OT, and that the effects lasted at least one week post-stimulation. Improvement in motor outcome scores was correlated with decrease in fMRI activation in the contralesional motor region exposed to cathodal stimulation. Conclusions This suggests that cathodal tDCS combined with OT leads to significant motor improvement after stroke due to a decrease in the inhibitory effect that the contralesional hemisphere exerts onto the lesional hemisphere.