Motor cortex activation is preserved in patients with chronic hemiplegic stroke

Efficacy of transcranial direct current stimulation in patients with dysphagia after stroke: a systematic review

BACKGROUND

Swallowing is a complex function that can be disrupted after stroke. Transcranial Direct Current Stimulation (tDCS) is a non-invasive brain stimulation therapy that recently has been tested to treat stroke-related dysphagia.

METHODS

The authors performed a search in the literature to review the described evidence of the use of tDCS in dysphagia after stroke. Three electronic databases were searched. The risk of bias evaluation was carried out through the RoB-2 tool. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) framework was also implemented.

RESULTS

Of 265 articles, only nine studies were included in this review. The most common location of the tDCS stimulation was the unaffected hemisphere (44%). Regarding the outcome measure, the Dysphagia Outcome and Severity Scale (DOSS) was the most commonly used (55%). However, due to the high heterogeneity of the protocols, and considering the differences between the types of stroke, the authors opted not to perform a metanalysis. Instead, a systematic review with a thorough analysis of each individual study and the impact of the differences to the outcomes was preferred.

CONCLUSIONS

The final considerations are that even though the majority of studies described benefits from tDCS in post-stroke dysphagia, as they present too many methodological differences, it is not possible to compare them. In addition, many articles included patients with less than 6 months after stroke, which is an important bias as the swallowing function can be recovered spontaneously within this period, turning the certainty of the evidence really low.

Effects of transcranial magnetic stimulation on dynamic functional networks in stroke patients as assessed by functional near-infrared spectroscopy: a randomized controlled clinical trial

Studies have shown that there is heterogeneity in the efficacy bewteen the low-frequency (LF) and high-frequency (HF) repetitive transcranial magnetic stimulation (rTMS), but the neural mechanisms underlying the differences in efficacy remain unclear. This study aimed to investigate the specific effects of LF- and HF-rTMS on cortial functional network and the process of neural regulation. A total of sixty-eight patients with hemiplegic motor impairment after stroke were randomly allocated to one of three groups: the LF-rTMS, HF-rTMS, and sham groups. Tissue concentrations of oxyhaemoglobin and deoxyhaemoglobin oscillations in cerebral cortex regions were measured by functional near-infrared spectroscopy (fNIRS) in the resting and rTMS states. Four specific time-windows were divided from the trial duration to observe dynamic changes in cortical haemodynamic responses. Compared with sham, LF-rTMS significantly induced the activation of the contralesional superior frontal cortex and premotor cortex, and continuously regulated ipsilesional hemisphere functional networks in stroke patients. However, HF-rTMS did not induce a significant neurovascular coupling response. Our study provided evidence that LF- and HF-rTMS interventions induced different neurovascular coupling responses and demonstrated the cortical functional network change process of rTMS in specific time-windows. These findings may help to understand the differences in the efficacy of rTMS modalities.

Denoising task-correlated head motion from motor-task fMRI data with multi-echo ICA

Motor-task functional magnetic resonance imaging (fMRI) is crucial in the study of several clinical conditions, including stroke and Parkinson's disease. However, motor-task fMRI is complicated by task-correlated head motion, which can be magnified in clinical populations and confounds motor activation results. One method that may mitigate this issue is multi-echo independent component analysis (ME-ICA), which has been shown to separate the effects of head motion from the desired BOLD signal but has not been tested in motor-task datasets with high amounts of motion. In this study, we collected an fMRI dataset from a healthy population who performed a hand grasp task with and without task-correlated amplified head motion to simulate a motor-impaired population. We analyzed these data using three models: single-echo (SE), multi-echo optimally combined (ME-OC), and ME-ICA. We compared the models' performance in mitigating the effects of head motion on the subject level and group level. On the subject level, ME-ICA better dissociated the effects of head motion from the BOLD signal and reduced noise. Both ME models led to increased t-statistics in brain motor regions. In scans with high levels of motion, ME-ICA additionally mitigated artifacts and increased stability of beta coefficient estimates, compared to SE. On the group level, all three models produced activation clusters in expected motor areas in scans with both low and high motion, indicating that group-level averaging may also sufficiently resolve motion artifacts that vary by subject. These findings demonstrate that ME-ICA is a useful tool for subject-level analysis of motor-task data with high levels of task-correlated head motion. The improvements afforded by ME-ICA are critical to improve reliability of subject-level activation maps for clinical populations in which group-level analysis may not be feasible or appropriate, for example in a chronic stroke cohort with varying stroke location and degree of tissue damage.

Longitudinal optogenetic mapping reveals enhanced motor control by the contralesional cortex after traumatic brain injury in mice

Traumatic brain injury (TBI) is a significant cause of human disability, and understanding its spontaneous recovery pattern after injury is critical for potential treatments. However, studies on the function of the contralesional cortex after TBI have mostly focused on acute-phase changes, and long-term dynamic changes in the control of the affected limb by the contralesional cortex are less understood. To unravel long-term adaptations in the contralesional cortex, we developed a mouse model of TBI and used longitudinal optogenetic motor mapping to observe the function of contralesional corticospinal neurons (CSNs) projecting to the unilateral seventh cervical (C7) segment of the spinal cord. We injected a retrograde adeno-associated virus (AAV) expressing channelrhodopsin-2 to optogenetically stimulate and map the functional connections of the motor-sensory cortex. We validated the effectiveness of transcranial optogenetic stimulation for functional mapping and observed a general increase in the control of the affected limb by the contralesional cortex over time. Using retrograde labeling techniques, we showed that TBI does not affect the distribution of C7-CSNs but alters their function, and the labeled CSNs are concentrated in the caudal and rostral forelimb areas. Our findings provide new insights into harnessing contralesional cortical plasticity to improve treatment for affected limbs. This study sheds light on the long-term adaptations in the contralesional cortex after TBI, paving the way for potential clinical applications of optogenetic stimulation to improve motor control and rehabilitation outcomes.

Effect of High-Frequency rTMS Combined with Bilateral Arm Training on Brain Functional Network in Patients with Chronic Stroke: An fNIRS study

OBJECTIVE

Neurological evidence for the combinational intervention coupling rTMS with motor training for stroke rehabilitation remains limited. This study aimed to investigate the effects of rTMS combined with bilateral arm training (BAT) on the brain functional reorganization in patients with chronic stroke via functional near-infrared spectroscopy (fNIRS).

METHODS

Fifteen stroke patients and fifteen age-matched healthy participants were enrolled and underwent single BAT session (s-BAT) and BAT immediately after 5-Hz rTMS over the ipsilesional M1 (rTMS-BAT), measured cerebral haemodynamics by fNIRS. Functional connectivity (FC), the clustering coefficient (C_coef), and local efficiency (E_loc) were applied to evaluate the functional response to the training paradigms.

RESULTS

The differences in FC responses to the two training paradigms were more pronounced in stroke patients than in healthy controls. In the resting state, stroke patients exhibited significantly lower FC than controls in both hemispheres. rTMS-BAT induced no significant difference in FC between groups. Compared to the resting state, rTMS-BAT induced significant decreases in C_coef and E_loc of the contralesional M1 and significant increases in E_loc of the ipsilesional M1 in stroke patients. Additionally, these above two network metrics of the ipsilesional motor area were significantly positively correlated with the motor function of stroke patients.

CONCLUSIONS

These results suggest that the rTMS-BAT paradigm had additional effects on task-dependent brain functional reorganization. The engagement of the ipsilesional motor area in the functional network was associated with the motor impairment severity of stroke patients. fNIRS-based assessments may provide information about the neural mechanisms underlying combination interventions for stroke rehabilitation.

Sensorimotor Responses in Post-Stroke Hemiplegic Patients Modulated by Acupuncture at Yanglingquan (GB34): A fMRI Study Using Intersubject Functional Correlation (ISFC) Analysis

Motor dysfunction is common in patients with stroke. Acupuncture has become an acceptable alternative method for stroke rehabilitation. Previous studies have shown various functional connectivity changes activated by acupuncture. We introduced intersubject correlation (ISC) and intersubject functional correlation (ISFC) analyses into the functional magnetic resonance imaging (fMRI) for ischemic stroke to seek a common activation and suppression pattern triggered by acupuncture. In this study, 63 ischemic stroke patients with motor dysfunction and 42 normal controls were analyzed. Three functional scans were conducted during the resting state, motor task, and acupuncture at Yanglingquan (GB34) task. Twenty-two sensory, motor, and movement-imagination cortices in the bilateral hemispheres were selected as the region of interest (ROI). We performed ISC and ISFC analyses among these ROIs in three fMRI runs on patients and controls. Subgroup analyses by course or severity were also conducted. The results showed that acupuncture at GB34 triggered ISFC among upper limb motor, upper limb/hand/face, lower limb, tongue/larynx sensory, and movement imagination regions in the patient group. Subgroup ISC and ISFC analyses showed that patients tended to have increasing responses in the early stage of stroke (within 1 month) and decreasing responses afterward (1–3 months). Patients with mild clinical functional damage (NIHSS 2–4) tended to generate more responses via acupuncture than those with moderate damage (NIHSS 5–15). Our findings may help understand the clinical effects and modulatory features of acupuncture based on the group-level post-stroke neuroplasticity.

Effects of Transcranial Direct Durrent Stimulation on Post-stroke Dysphagia: A Systematic Review and Meta-analysis of Randomized Controlled Trials

OBJECTIVE

This review aimed to systematically evaluate the effect of transcranial direct current stimulation (tDCS) on post-stroke dysphagia.

DATA SOURCES

PubMed, Cochrane Library (CENTRAL), Web of Science, VIP, CNKI, and Wanfang databases were systematically searched up to June 2021.

STUDY SELECTION

Randomized controlled trials (RCTs) on the effects of tDCS on post-stroke dysphagia DATA EXTRACTION: The extracted data included the author, country of publication, time of publication, key elements of bias risk assessment (such as randomized controlled trials and blind methods), sample size and basic information (age, course of disease, stroke location), intervention measures, treatment methods of tDCS (stimulation location, intensity, and duration), relevant outcome indicators, and relevant data (standard deviations).The Cochrane Risk of Bias Assessment Tool and PEDro Scale were used to assess the risk of bias.

DATA SYNTHESIS

Sixteen RCTs were included in this meta-analysis. Overall, the results revealed a large and statistically significant pooled effect size (0.80, CI 0.45-1.14; p<0.00001). The subgroup that explored the course of the disease yielded a large and significant effect size for the chronic phase group (0.80, CI 0.43-1.16; p<0.0001). For the stimulation intensity, 1 mA and 1.6 mA showed a moderate and significant effect sizes (0.47, CI 0.13-0.81; p=0.006 vs 1.39, CI 0.69-2.08; p<0.0001). In the subgroup analyses, the affected (0.87, CI 0.26-1.48; p=0.005) vs. unaffected (0.61, CI 0.23-0.99; p=0.002) hemisphere showed a significant result, and stimulation of the affected hemisphere had a more obvious effect. Subgroup analysis of stroke location showed that tDCS was effective for dysphagia after unilateral hemispheric stroke, bulbar paralysis, and brainstem stroke but not for dysphagia after ataxic and basal ganglia stroke. However, the subgroup analysis of stroke location revealed a significant result (0.81, CI 0.44-1.18; p<0.001).

CONCLUSION

This meta-analysis demonstrated the height and significant beneficial effect of tDCS on improving post-stroke dysphagia.

Towards a mechanistic approach for the development of non-invasive brain-computer interfaces for motor rehabilitation

Brain-computer interfaces (BCIs) designed for motor rehabilitation use brain signals associated with motor-processing states to guide neuroplastic changes in a state-dependent manner. These technologies are uniquely positioned to induce targeted and functionally relevant plastic changes in the human motor nervous system. However, while several studies have shown that BCI-based neuromodulation interventions may improve motor function in patients with lesions in the central nervous system, the neurophysiological structures and processes targeted with the BCI interventions have not been identified. In this review, we first summarize current knowledge of the changes in the central nervous system associated with learning new motor skills. Then, we propose a classification of current BCI paradigms for plasticity induction and motor rehabilitation based on the expected neural plastic changes promoted. This classification proposes four paradigms based on two criteria: the plasticity induction methods and the brain states targeted. The existing evidence regarding the brain circuits and processes targeted with these different BCIs is discussed in detail. The proposed classification aims to serve as a starting point for future studies trying to elucidate the underlying plastic changes following BCI interventions.

The Neural Representation of Force across Grasp Types in Motor Cortex of Humans with Tetraplegia

Intracortical brain-computer interfaces (iBCIs) have the potential to restore hand grasping and object interaction to individuals with tetraplegia. Optimal grasping and object interaction require simultaneous production of both force and grasp outputs. However, since overlapping neural populations are modulated by both parameters, grasp type could affect how well forces are decoded from motor cortex in a closed-loop force iBCI. Therefore, this work quantified the neural representation and offline decoding performance of discrete hand grasps and force levels in two human participants with tetraplegia. Participants attempted to produce three discrete forces (light, medium, hard) using up to five hand grasp configurations. A two-way Welch ANOVA was implemented on multiunit neural features to assess their modulation to force and grasp Demixed principal component analysis (dPCA) was used to assess for population-level tuning to force and grasp and to predict these parameters from neural activity. Three major findings emerged from this work: (1) force information was neurally represented and could be decoded across multiple hand grasps (and, in one participant, across attempted elbow extension as well); (2) grasp type affected force representation within multiunit neural features and offline force classification accuracy; and (3) grasp was classified more accurately and had greater population-level representation than force. These findings suggest that force and grasp have both independent and interacting representations within cortex, and that incorporating force control into real-time iBCI systems is feasible across multiple hand grasps if the decoder also accounts for grasp type.

The Cortical Physiology of Ipsilateral Limb Movements

Whereas voluntary movements have long been understood to derive primarily from the cortical hemisphere contralateral to a moving limb, substantial cortical activations also occur in the same-sided, or ipsilateral, cortical hemisphere. These ipsilateral motor activations have recently been shown to be useful to decode specific movement features. Furthermore, in contrast to the classical understanding that unilateral limb movements are solely driven by the contralateral hemisphere, it appears that the ipsilateral hemisphere plays an active and specific role in the planning and execution of voluntary movements. Here we review the movement-related activations observed in the ipsilateral cortical hemisphere, interpret this evidence in light of the potential roles of the ipsilateral hemisphere in the planning and execution of movements, and describe the implications for clinical populations.

Evidence from functional ultrasound imaging of enhanced contralesional microvascular response to somatosensory stimulation in acute middle cerebral artery occlusion/reperfusion in rats: A marker of ultra-early network reorganization?

Following middle cerebral artery (MCA) stroke, enhanced contralesional evoked responses have been consistently reported both in man and rodents as part of plastic processes thought to influence motor recovery. How early this marker of large-scale network reorganization develops has however been little addressed, yet has clinical relevance for rehabilitation strategies targeting plasticity. Previous work in mice has reported enhanced contralesional responses to unaffected-side forepaw stimulation as early as 45 min after MCA small branch occlusion. Using functional ultrasound imaging (fUSi) in anesthetized rats subjected to distal temporary MCA occlusion (MCAo), we assessed here (i) whether enhanced contralesional responses also occurred with unaffected-side whisker pad stimulation, and if so, how early after MCAo; and (ii) the time course of this abnormal response during occlusion and after reperfusion. We replicate in a more proximal MCA occlusion model the earlier findings of ultra-early enhanced contralesional evoked responses. In addition, we document this phenomenon within minutes after MCAo, and its persistence throughout the entire 90-min occlusion as well as 90-min reperfusion periods studied. These findings suggest that plastic processes may start within minutes following MCAo in rodents. If replicated in man, they might have implications regarding how early plasticity-enhancing therapies can be initiated after stroke.

Predicting Gains With Visuospatial Training After Stroke Using an EEG Measure of Frontoparietal Circuit Function

The heterogeneity of stroke prompts the need for predictors of individual treatment response to rehabilitation therapies. We previously studied healthy subjects with EEG and identified a frontoparietal circuit in which activity predicted training-related gains in visuomotor tracking. Here we asked whether activity in this same frontoparietal circuit also predicts training-related gains in visuomotor tracking in patients with chronic hemiparetic stroke. Subjects (n = 12) underwent dense-array EEG recording at rest, then received 8 sessions of visuomotor tracking training delivered via home-based telehealth methods. Subjects showed significant training-related gains in the primary behavioral endpoint, Success Rate score on a standardized test of visuomotor tracking, increasing an average of 24.2 ± 21.9% (p = 0.003). Activity in the circuit of interest, measured as coherence (20–30 Hz) between leads overlying ipsilesional frontal (motor cortex) and parietal lobe, significantly predicted training-related gains in visuomotor tracking change, measured as change in Success Rate score (r = 0.61, p = 0.037), supporting the main study hypothesis. Results were specific to the hypothesized ipsilesional motor-parietal circuit, as coherence within other circuits did not predict training-related gains. Analyses were repeated after removing the four subjects with injury to motor or parietal areas; this increased the strength of the association between activity in the circuit of interest and training-related gains. The current study found that (1) Eight sessions of training can significantly improve performance on a visuomotor task in patients with chronic stroke, (2) this improvement can be realized using home-based telehealth methods, (3) an EEG-based measure of frontoparietal circuit function predicts training-related behavioral gains arising from that circuit, as hypothesized and with specificity, and (4) incorporating measures of both neural function and neural injury improves prediction of stroke rehabilitation therapy effects.

Neural reactivations during sleep determine network credit assignment

A fundamental goal of motor learning is to establish the neural patterns that produce a desired behavioral outcome. It remains unclear how and when the nervous system solves this 'credit assignment' problem. Using neuroprosthetic learning, in which we could control the causal relationship between neurons and behavior, we found that sleep-dependent processing was required for credit assignment and the establishment of task-related functional connectivity reflecting the casual neuron-behavior relationship. Notably, we observed a strong link between the microstructure of sleep reactivations and credit assignment, with downscaling of non-causal activity. Decoupling of spiking to slow oscillations using optogenetic methods eliminated rescaling. Thus, our results suggest that coordinated firing during sleep is essential for establishing sparse activation patterns that reflect the causal neuron-behavior relationship.

MRI Biomarkers for Hand-Motor Outcome Prediction and Therapy Monitoring following Stroke

Several biomarkers have been identified which enable a considerable prediction of hand-motor outcome after cerebral damage already in the subacute stage after stroke. We here review the value of MRI biomarkers in the evaluation of corticospinal integrity and functional recruitment of motor resources. Many of the functional imaging parameters are not feasible early after stroke or for patients with high impairment and low compliance. Whereas functional connectivity parameters have demonstrated varying results on their predictive value for hand-motor outcome, corticospinal integrity evaluation using structural imaging showed robust and high predictive power for patients with different levels of impairment. Although this is indicative of an overall higher value of structural imaging for prediction, we suggest that this variation be explained by structure and function relationships. To gain more insight into the recovering brain, not only one biomarker is needed. We rather argue for a combination of different measures in an algorithm to classify fine-graded subgroups of patients. Approaches to determining biomarkers have to take into account the established markers to provide further information on certain subgroups. Assessing the best therapy approaches for individual patients will become more feasible as these subgroups become specified in more detail. This procedure will help to considerably save resources and optimize neurorehabilitative therapy.

Artistic Skills Recovery and Compensation in Visual Artists after Stroke

Background

Art is a characteristic of mankind, which requires superior central nervous processing and integration of motor functions with visual information. At the present time, a significant amount of information related to neurobiological basis of artistic creation has been derived from neuro-radiological cognitive studies, which have revealed that subsequent to tissue destruction, the artists continue to create art. The current study aims to review the most important cases of visual artists with stroke and to discuss artistic skills recovery and compensation as well as artistic style after stroke.

Methods

The role of various central nervous system regions in artistic creation was reviewed on the basis of previously published functional studies. Our PubMed search (1995–2015) has identified 10 famous artists with right cerebral stroke as well as 5 with left cerebral stroke who survived and continued to create art after stroke. As the artists included in this review lived at various times during the twentieth century and in different countries, clinical information related to their case was limited. However, it appears that artistic skills recovery and compensation appear within days after stroke. Some of the artists would subsequently change their artistic style. All these elements have been evaluated within the context of specific clinical cases.

Conclusion

The poststroke artistic skills recovery and compensation with development of a new style or the opposite, regaining the previous prestroke style, represents a significant element of clinical importance in medical rehabilitation as well as neuroesthetics, which requires further evaluation. At the present time, the molecular mechanisms of artistic creation are poorly understood, and more standardized clinical and experimental studies are needed.

Brain Reorganization After Stroke

After a stroke, recovery that continues beyond 3 or 4 weeks has been attributed to plasticity, a reorganization of the brain in which functions previously performed by the ischemic area are assumed by other ipsilateral or contralateral brain areas. Neuronal plasticity has been variously attributed to redundancy (parallel distributed pathways), changes in synaptic strength, axonal sprouting with formation of new synapses, assumption of function by contralateral homologous cortex, and substitution of uncrossed pathways. Transcranial magnetic stimulation, positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and 128-electrode high-resolution electroencephalography have been successfully applied to demonstrate cortical reorganization after hemiplegia. Recording the motor potential is a promising noninvasive method for the localization of motor control after hemispheric lesions. Most patients with hemiparetic stroke show some improvement, usually during the first 3 to 6 months after the ictus. Improvement and prognosis depend on a number of variables including volume and location of the infarction, age of the patient, and the elimination of risk factors to avoid future episodes (i.e., dietary control of lipids, the elimination of tobacco, and the control of diabetes and hypertension). Currently, emphasis has been placed on fibrinolytic treatment in the first 3 hours to prevent or minimize neurological deficit. Aside from the above listed factors, improvement after stroke may be due to reorganization of the brain, particularly the cerebral cortex, and repair of damaged tissue and recanalization. It is also important to relate such changes to functional improvement and successful rehabilitation.

Plasticity and Reorganization of the Brain Post Stroke

Reorganization of the cortex post stroke is dependent not only on the lesion site but also on remote brain areas that have structural connections with the area damaged by the stroke. Motor recovery is largely dependent on the intact cortex adjacent to the infarct, which points out the importance of preserving the penumbral areas. There appears to be a priority setting with contralateral and ipsilateral motor pathways, with ipsilateral (unaffected hemisphere) pathways only becoming prominent after more severe strokes where functional contralateral (affected hemisphere) pathways are unable to recover. Ipsilateral or unaffected hemisphere motor pathway activation is therefore associated with a worse prognosis.

The physiology of motor delusions in anosognosia for hemiplegia: implications for current models of motor awareness

Right brain damaged patients sometimes deny that their left arm is paralysed or even claim to have just moved it. This condition is known as anosognosia for hemiplegia (AHP). Here, we used fMRI to study patients with and without AHP during the execution of a motor task. We found that the delusional belief of having moved was preceded by brain activation of the cortical regions that are implicated in motor control in the left intact hemisphere and in the spared motor regions of the right hemisphere; patients without anosognosia did not present with the same degree of activation. We conclude that the false belief of movement is associated with a combination of strategically placed brain lesions and the preceding residual neural activity of the fronto-parietal motor network. These findings provide evidence that the activity of motor cortices contributes to our beliefs about the state of our motor system.

Transcranial Direct Current Stimulation Improves Swallowing Function in Stroke Patients

Background. Poststroke dysphagia can persist, leading to many complications. Objective. We investigated whether noninvasive brain stimulation to the pharyngeal motor cortex combined with intensive swallowing therapy can improve dysphagia. Methods. A total of 20 patients who had dysphagia for at least 1 month after stroke were randomly assigned to receive 10 sessions lasting 20 minutes each of either 1-mA anodal transcranial direct current stimulation (tDCS) or a sham procedure to the ipsilesional pharyngeal motor cortex, along with simultaneous conventional swallowing therapies. We evaluated swallowing function with the Dysphagia Outcome and Severity Scale (DOSS) before, immediately after, and 1 month after the last session. Results. Anodal tDCS resulted in an improvement of 1.4 points in DOSS ( P = .006) immediately after the last session and 2.8 points ( P = .004) 1 month after the last session. The sham tDCS group improved 0.5 points ( P = .059) after the last session and 1.2 points ( P = .026) 1 month after the final session. The improvements in the anodal tDCS group were significantly greater than those in the sham tDCS group ( P = .029 after the last session, and P = .007 1 month after the last session). Conclusions. Anodal tDCS to the ipsilesional hemisphere and simultaneous peripheral sensorimotor activities significantly improved swallowing function as assessed by the DOSS.

Optimizing recovery potential through simultaneous occupational therapy and non-invasive brain-stimulation using tDCS

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.

Using ipsilateral motor signals in the unaffected cerebral hemisphere as a signal platform for brain-computer interfaces in hemiplegic stroke survivors

Brain-computer interface (BCI) systems have emerged as a method to restore function and enhance communication in motor impaired patients. To date, this has been applied primarily to patients who have a compromised motor outflow due to spinal cord dysfunction, but an intact and functioning cerebral cortex. The cortical physiology associated with movement of the contralateral limb has typically been the signal substrate that has been used as a control signal. While this is an ideal control platform in patients with an intact motor cortex, these signals are lost after a hemispheric stroke. Thus, a different control signal is needed that could provide control capability for a patient with a hemiparetic limb. Previous studies have shown that there is a distinct cortical physiology associated with ipsilateral, or same-sided, limb movements. Thus far, it was unknown whether stroke survivors could intentionally and effectively modulate this ipsilateral motor activity from their unaffected hemisphere. Therefore, this study seeks to evaluate whether stroke survivors could effectively utilize ipsilateral motor activity from their unaffected hemisphere to achieve this BCI control. To investigate this possibility, electroencephalographic (EEG) signals were recorded from four chronic hemispheric stroke patients as they performed (or attempted to perform) real and imagined hand tasks using either their affected or unaffected hand. Following performance of the screening task, the ability of patients to utilize a BCI system was investigated during on-line control of a one-dimensional control task. Significant ipsilateral motor signals (associated with movement intentions of the affected hand) in the unaffected hemisphere, which were found to be distinct from rest and contralateral signals, were identified and subsequently used for a simple online BCI control task. We demonstrate here for the first time that EEG signals from the unaffected hemisphere, associated with overt and imagined movements of the affected hand, can enable stroke survivors to control a one-dimensional computer cursor rapidly and accurately. This ipsilateral motor activity enabled users to achieve final target accuracies between 68% and 91% within 15 min. These findings suggest that ipsilateral motor activity from the unaffected hemisphere in stroke survivors could provide a physiological substrate for BCI operation that can be further developed as a long-term assistive device or potentially provide a novel tool for rehabilitation.

The use of non-invasive brain stimulation techniques to facilitate recovery from post-stroke aphasia

Aphasia is a common symptom after left hemispheric stroke. Neuroimaging techniques over the last 10-15 years have described two general trends: Patients with small left hemisphere strokes tend to recruit perilesional areas, while patients with large left hemisphere lesions recruit mainly homotopic regions in the right hemisphere. Non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) have been employed to facilitate recovery by stimulating lesional and contralesional regions. The majority of these brain stimulation studies have attempted to block homotopic regions in the right posterior inferior frontal gyrus (IFG) to affect a presumed disinhibited right IFG (triangular portion). Other studies have used anodal or excitatory tDCS to stimulate the contralesional (right) fronto-temporal region or parts of the intact left IFG and perilesional regions to improve speech-motor output. It remains unclear whether the interhemispheric disinhibition model, which is the basis for motor cortex stimulation studies, also applies to the language system. Future studies could address a number of issues, including: the effect of lesion location on current density distribution, timing of the intervention with regard to stroke onset, whether brain stimulation should be combined with behavioral therapy, and whether multiple brain sites should be stimulated. A better understanding of the predictors of recovery from natural outcome studies would also help to inform study design, and the selection of clinically meaningful outcome measures in future studies.

Bihemispheric brain stimulation facilitates motor recovery in chronic stroke patients

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.

RESULTS

The improvement of motor function was significantly greater in the real stimulation group (20.7% in Fugl-Meyer and 19.1% in Wolf Motor Function Test scores) when compared to the sham group (3.2% in Fugl-Meyer and 6.0% in Wolf Motor Function Test scores). The effects outlasted the stimulation by at least 1 week. In the real-stimulation group, stronger activation of intact ipsilesional motor regions during paced movements of the affected limb were found postintervention whereas no significant activation changes were seen in the control group.

CONCLUSIONS

The combination of bihemispheric tDCS and peripheral sensorimotor activities improved motor functions in chronic stroke patients that outlasted the intervention period. This novel approach may potentiate cerebral adaptive processes that facilitate motor recovery after stroke.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that for adult patients with ischemic stroke treated at least 5 months after their first and only stroke, bihemispheric tDCS and simultaneous physical/occupational therapy given over 5 consecutive sessions significantly improves motor function as measured by the Upper Extremity Fugl-Meyer assessment (raw change treated 6.1 ± 3.4, sham 1.2 ± 1.0).

The corticospinal system and transcranial magnetic stimulation in stroke

During the last decades, transcranial magnetic stimulation (TMS) has been used as a noninvasive method to investigate motor cortical reorganization and neuroplasticity in humans after stroke. An increasing number of studies in the field of motor control have used TMS to gain an understanding of the different aspects of stroke cortical physiology and motor recovery. This review addresses the effects of corticospinal tract (CST) lesions in humans and nonhuman primates on the functional organization of the motor system. We review information on the physiological mechanisms by which the CST contributes to normal motor control and to central nervous system reorganization following stroke when the CST is injured as measured using TMS. Insight into these physiological mechanisms has led to the development of scientifically sound interventional proposals in the field of neurorehabilitation.

What Do Motor “Recovery” and “Compensation” Mean in Patients Following Stroke?

There is a lack of consistency among researchers and clinicians in the use of terminology that describes changes in motor ability following neurological injury. Specifically, the terms and definitions of motor compensation and motor recovery have been used in different ways, which is a potential barrier to interdisciplinary communication. This Point of View describes the problem and offers a solution in the form of definitions of compensation and recovery at the neuronal, motor performance, and functional levels within the framework of the International Classification of Functioning model.

Repairing the human brain after stroke. II. Restorative therapies

Spontaneous behavioral recovery is usually limited after stroke, making stroke a leading source of disability. A number of therapies in development aim to improve patient outcomes not by acutely salvaging threatened tissue, but instead by promoting repair and restoration of function in the subacute or chronic phase after stroke. Examples include small molecules, growth factors, cell-based therapies, electromagnetic stimulation, device-based strategies, and task-oriented and repetitive training-based interventions. Stage of development across therapies varies widely, from preclinical to late-phase clinical trials. The optimal methods to prescribe such therapies require further studies, for example, to best identify appropriate patients or to guide features of dosing. Likely, anatomic, functional, and behavioral measures of brain state, as well as measures of injury, will each be useful in this regard. Considerations for clinical trials of restorative therapies are provided, emphasizing both similarities and points of divergence with acute stroke clinical trial design.

Bimanual passive movement: functional activation and inter-regional coupling

The aim of this study was to investigate intra-regional activation and inter-regional connectivity during passive movement. During fMRI, a mechanic device was used to move the subject's index and middle fingers. We assessed four movement conditions (unimanual left/right, bimanual symmetric/asymmetric), plus Rest. A conventional intra-regional analysis identified the passive stimulation network, including motor cortex, primary and secondary somatosensory cortex, plus the cerebellum. The posterior (sensory) part of the sensory-motor activation around the central sulcus showed a significant modulation according to the symmetry of the bimanual movement, with greater activation for asymmetric compared to symmetric movements. A second set of fMRI analyses assessed condition-dependent changes of coupling between sensory-motor regions around the superior central sulcus and the rest of the brain. These analyses showed a high inter-regional covariation within the entire network activated by passive movement. However, the specific experimental conditions modulated these patterns of connectivity. Highest coupling was observed during the Rest condition, and the coupling between homologous sensory-motor regions around the left and right central sulcus was higher in bimanual than unimanual conditions. These findings demonstrate that passive movement can affect the connectivity within the sensory-motor network. We conclude that implicit detection of asymmetry during bimanual movement relies on associative somatosensory region in post-central areas, and that passive stimulation reduces the functional connectivity within the passive movement network. Our findings open the possibility to combine passive movement and inter-regional connectivity as a tool to investigate the functionality of the sensory-motor system in patients with very poor mobility.

Neural Correlates of Proprioceptive Integration in the Contralesional Hemisphere of Very Impaired Patients Shortly After a Subcortical Stroke: An fMRI Study

Background. The effects of physiotherapy are difficult to assess in very impaired early stroke patients. Objective. The aim of the study was to characterize the impact of 4 weeks of passive proprioceptive training of the wrist on brain sensorimotor activation after stroke. Methods. Patients with a subcortical ischemic lesion of the pyramidal tract were randomly assigned to a control or a wrist-training group. All patients had a single pure motor hemiplegia with severe motor deficit. The control group (6 patients) underwent standard Bobath rehabilitation. The second, “trained,” group (7 patients) received Bobath rehabilitation plus 4 weeks of proprioceptive training with daily passive calibrated wrist extension. Before and after the training period, patients were examined with validated clinical scales and functional MRI (fMRI) while executing a passive movement versus rest. The effect of standard rehabilitation on sensorimotor activation was assessed in the control group on the wrist, and the effect of standard rehabilitation plus proprioceptive training was assessed in the trained group. The effect of 4-week proprioceptive training alone was statistically evaluated by difference between groups. Results. Standard rehabilitation along with natural recovery mainly led to increases in ipsilesional activation and decreases in contralesional activation. On the contrary, standard rehabilitation and paretic wrist proprioceptive training increased contralesional activation. Proprioceptive training produced change in the supplementary motor area (SMA), prefrontal cortex, and a contralesional network including inferior parietal cortex (lower part of BA 40), secondary sensory cortex, and ventral premotor cortex (PMv). Conclusion. We have demonstrated that purely passive proprioceptive training applied for 4 weeks is able to modify brain sensorimotor activity after a stroke. This training revealed fMRI change in the ventral premotor and parietal cortices of the contralesional hemisphere, which are secondary sensorimotor areas. Recent studies have demonstrated the crucial role of these areas in severely impaired patients. We propose that increased contralesional activity in secondary sensorimotor areas likely facilitates control of recovered motor function by simple proprioceptive integration in those patients with poor recovery.

Answering the call: the influence of neuroimaging and electrophysiological evidence on rehabilitation

Functional recovery after brain damage or disease is dependent on the neuroplastic capability of the cortex and the nonaffected brain. Following cortical injury in the motor and sensory regions, the adjacent spared neural tissues and related areas undergo modifications that are required in order to drive more normal motor control. Current rehabilitation models seek to stimulate functional recovery by capitalizing on the inherent potential of the brain for positive reorganization after neurological injury or disease. This article discusses how neuroimaging and electrophysiological data can inform clinical practice; representative data from the modalities of functional magnetic resonance imaging, diffusion tensor imaging, magnetoencephalography, electroencephalography, and positron emission tomography are cited. Data from a variety of central nervous system disease and damage models are presented to illustrate how rehabilitation practices are beginning to be shaped and informed by neuroimaging and electrophysiological data.

fMRI-vs-MEG evaluation of post-stroke interhemispheric asymmetries in primary sensorimotor hand areas

Growing evidence emphasizes a positive role of brain ipsilesional (IL) reorganization in stroke patients with partial recovery. Ten patients affected by a monohemispheric stroke in the middle cerebral artery territory underwent functional magnetic resonance (fMRI) and magnetoencephalography (MEG) evaluation of the primary sensory (S1) activation via the same paradigm (median nerve galvanic stimulation). Four patients did not present S1 fMRI activation [Rossini, P.M., Altamura, C., Ferretti, A., Vernieri, F., Zappasodi, F., Caulo, M., Pizzella, V., Del Gratta, C., Romani, G.L., Tecchio, F., 2004. Does cerebrovascular disease affect the coupling between neuronal activity and local haemodynamics? Brain 127, 99-110], although inclusion criteria required bilateral identifiable MEG responses. Mean Euclidean distance between fMRI and MEG S1 activation Talairach coordinates was 10.1+/-2.9 mm, with a 3D intra-class correlation (ICC) coefficient of 0.986. Interhemispheric asymmetries, evaluated by an MEG procedure independent of Talairach transformation, were outside or at the boundaries of reference ranges in 6 patients. In 3 of them, the IL activation presented medial or lateral shift with respect to the omega-shaped post-rolandic area while in the other 3, IL areas were outside the peri-rolandic region. In conclusion, despite dissociated intensity, the MEG and fMRI activations displayed good spatial consistency in stroke patients, thus confirming excessive interhemispheric asymmetries as a suitable indicator of unusual recruitments in the ipsilesional hemisphere, within or outside the peri-rolandic region.

Progress in clinical neurosciences: stroke recovery and rehabilitation

BACKGROUND

Recent literature has provided new insights into the role of rehabilitation in neurological recovery post-stroke. The present review combines results of animal and clinical research to provide a summary of published information regarding the mechanisms of neural recovery and impact of rehabilitation.

METHODS

Plasticity of the uninjured and post-stroke brain is examined to provide a background for the examination of brain reorganization and recovery following stroke.

SUMMARY AND CONCLUSIONS

Recent research has confirmed many of the basic underpinnings of rehabilitation and provided new insight into the role of rehabilitation in neurological recovery. Recovery post stroke is dependent upon cortical reorganization, and therefore, upon the presence of intact cortex, especially in areas adjacent to the infarct. Exposure to stimulating and complex environments and involvement in tasks or activities that are meaningful to the individual with stroke serves to increase cortical reorganization and enhance functional recovery. Additional factors associated with neurological recovery include size of stroke lesion, and the timing and intensity of therapy.

Functional Imaging of Intervention Effects in Stroke Motor Rehabilitation

OBJECTIVE

To assess intervention-specific effects on cortical reorganization after stroke as shown by available functional neuroimaging studies.

DATA SOURCES

We searched Medline for clinical trials that contained the terms stroke, reorganization, and recovery, as well as either positron-emission tomography and PET, near-infrared spectroscopy and NIRS, single-photon emission tomography and SPECT, or functional magnetic resonance imaging and functional MRI; we reviewed primary and secondary references.

STUDY SELECTION

Articles that reported neuroimaging findings as a result of a specific treatment involving more than 1 subject were included.

DATA EXTRACTION

We included clinical trials that contained the terms stroke, reorganization, and recovery, as well as functional neuroimaging data findings as a result of a specific treatment involving more than 1 subject.

DATA SYNTHESIS

Included studies differed clearly from one another with regard to patient characteristics, intervention protocol, and outcome measures. Most studies used functional magnetic resonance imaging and a motor paradigm. Studies were limited in size.

CONCLUSIONS

Despite the methodologic differences, several common features can be identified based on the reviewed studies. Clinical improvements occurred even late after injury, after subjects were deemed to have reached a recovery plateau. This clinical improvement was accompanied by cortical reorganization that depended on the type of intervention as well as other factors. This review also suggests direction for future research studies.

Imaging correlates of motor recovery from cerebral infarction and their physiological significance in well-recovered patients

We studied motor representation in well-recovered stroke patients. Eighteen right-handed stroke patients and eleven age-matched control subjects underwent functional Magnetic Resonance Imaging (fMRI) while performing unimanual index finger (abduction-adduction) and wrist movements (flexion-extension) using their recovered and non-affected hand. A subset of these patients underwent Transcranial Magnetic Stimulation (TMS) to elicit motor evoked potentials (MEP) in the first dorsal interosseous muscle of both hands. Imaging results suggest that good recovery utilizes both ipsi- and contralesional resources, although results differ for wrist and index finger movements. Wrist movements of the recovered arm resulted in significantly greater activation of the contralateral (lesional) and ipsilateral (contralesional) primary sensorimotor cortex (SM1), while comparing patients to control subjects performing the same task. In contrast, recovered index finger movements recruited a larger motor network, including the contralateral SM1, Supplementary Motor Area (SMA) and cerebellum when patients were compared to control subjects. TMS of the lesional hemisphere but not of the contralesional hemisphere induced MEPs in the recovered hand. TMS parameters also revealed greater transcallosal inhibition, from the contralesional to the lesional hemisphere than in the reverse direction. Disinhibition of the contralesional hemisphere observed in a subgroup of our patients suggests persistent alterations in intracortical and transcallosal (interhemispheric) interactions, despite complete functional recovery.

Measuring the hemodynamic response in chronic hypoperfusion

Although structural brain scans help assess brain injury in stroke, they cannot identify regions that are functionally disabled due to disrupted perfusion. Perfusion and functional MRI have the potential for determining the functional consequences of stroke. Here we examine the effectiveness of functional MRI to measure brain function in a single patient (LB) with chronic hypoperfusion. When LB made sustained hand movements we observed a sustained decrease in the fMRI signal, while normal individuals exhibit a sustained increase in signal while conducting this task. This work has clear implications for understanding stroke using functional MRI.

Stroke recovery and its imaging

Functional imaging of stroke recovery is a unique source of information that might be useful in the development of restorative treatments. Several features of brain function change spontaneously after stroke. Current studies define many of the most common events. Key challenges for the future are to develop standardized approaches to help address certain questions, determine the psychometric qualities of these measures, and define the clinical usefulness of these methods.

Brain motor system function after chronic, complete spinal cord injury

Most therapies under development to restore motor function after spinal cord injury (SCI) assume intact brain motor functions. To examine this assumption, 12 patients with chronic, complete SCI and 12 controls underwent functional MRI during attempted, and during imagined, right foot movement, each at two force levels. In patients with SCI, many features of normal motor system function were preserved, however, several departures from normal were apparent: (i) volume of activation was generally much reduced, e.g. 4-8% of normal in primary sensorimotor cortex, in the setting of twice normal variance in signal change; (ii) abnormal activation patterns were present, e.g. increased pallido-thalamocortical loop activity during attempted movement and abnormal processing in primary sensorimotor cortex during imagined movement; and (iii) modulation of function with change in task or in force level did not conform to patterns seen in controls, e.g. in controls, attempted movement activated more than imagined movement did within left primary sensorimotor cortex and right dorsal cerebellum, while imagined movement activated more than attempted movement did in dorsolateral prefrontal cortex and right precentral gyrus. These modulations were absent in patients with SCI. Many features of brain motor system function during foot movement persist after chronic complete SCI. However, substantial derangements of brain activation, poor modulation of function with change in task demands and emergence of pathological brain events were present in patients. Because brain function is central to voluntary movement, interventions that aim to improve motor function after chronic SCI likely also need to attend to these abnormalities of brain function.

Intrinsic factors influencing post stroke brain reorganization

Reorganization of the brain, specifically the motor cortex surrounding the stroke, accounts for much of the observed neurological recovery following stroke. Not surprisingly, size of the stroke lesion has the greatest impact on neurological recovery in both animal and clinical research studies. Spontaneous recovery of lost function is possible after a cortical lesion, particularly if the lesion is small. Age correlates negatively with recovery; older individuals generally demonstrate slower and less complete recovery. However, age by itself is a poor predictor of functional recovery.

Somatotopy and movement representation sites following cortical stroke

Stroke has been associated with many changes in motor system function, but there has been limited study of changes in somatotopic organization. This was examined in a group of patients with cortical stroke affecting primary sensorimotor cortex. In 17 patients with good outcome after cortical stroke involving precentral and/or postcentral gyri, plus 14 controls, four functional MRI evaluations of brain activity were obtained: finger, shoulder, and face motor tasks plus a sensory task, passive finger motion. For each, coordinates for contralateral primary sensorimotor cortex activation site were determined, as was a measure of inter-hemispheric balance. The normal motor somatotopy measured in controls was largely preserved after stroke. The main difference found between controls and patients was that the face was lateral to finger motor activation in all controls, but face was centered medial to finger in 43% of patients. Among patients, smaller infarct volume was associated with more ventral, and larger infarct with more dorsal, contralateral primary sensorimotor cortex activation. On the other hand, better behavioral outcome was associated with a more posterior, and poorer outcome with more anterior, activation. Larger infarct and poorer behavioral outcome were each associated with a change in inter-hemispheric balance towards the non-stroke hemisphere. Shifts in contralateral movement representation site did not correlate with changes in inter-hemispheric balance. Motor somatotopy is generally preserved after injury to primary sensorimotor cortex. Greater injury and larger behavioral deficits are associated with distinct effects on movement representation sites. Changes in motor organization within and between hemispheres arise independently after stroke.

Impairment–oriented training and adaptive motor cortex reorganisation after stroke: a fTMS study

In a sample of 28 subacute anterior circulation ischemic stroke patients with severe arm paresis, reduced motor cortex excitability (increased motor thresholds, reduced MEP amplitudes, reduced number of active points) and a reduced conduction velocity in the corticospinal system were found in the affected hemisphere. At the same time motor cortex topology for the abductor pollicis brevis (APB) representation was comparable for the affected and non-affected hemisphere. Considerable arm motor recovery (Fugl-Meyer test) was observed when assessed four weeks later after a period of rehabilitation intervention. Motor cortex excitability and conduction velocity in the corticospinal system improved in the affected hemisphere. In addition, APB representation showed a medial shift in patients with such a representation at pre test (n=14). Multiple stepwise regression indicated that of all transcranial magnetic stimulation (TMS) parameters only the medial shift of the motor cortex map predicted motor recovery. Assessing the effect of training time (non-intensified vs. intensified therapy) and type of arm training (Bobath approach vs. Arm BASIS training) with a randomised controlled design revealed that the impairment-oriented Arm BASIS training improved motor control more than the control conditions. In addition, patients of the group receiving the Arm BASIS training with an APB representation at pre test showed a medial shift of the motor cortex map and improved conduction times. In conclusion, changes in motor cortex topology were likely to be relevant for motor recovery and might have been induced by the impairment-oriented training.

Prospective demonstration of short-term motor plasticity following acquired central pareses

The effect of newly acquired central pareses on functional MRI (fMRI) signal pattern is not known, since up to now all investigated patients were examined while they already experienced the motor weakness. We describe the first prospective and controlled study demonstrating the impact of new, acquired central pareses on fMRI motor activation pattern. Six patients suffering from a new central paresis after resection of a brain tumor infiltrating the central region were prospectively compared with a control group of five patients without postoperative paresis and a group of six healthy, age-matched controls who were investigated at two time points. fMRI signal was postoperatively analyzed during the performance of hand motor tasks and compared to the preoperative fMRI results. The relative signal change between rest and activation was evaluated for five cortical regions: the primary motor cortex (M1) and the ipsilateral primary motor cortex (M1i), the supplementary motor area (SMA), the premotor area (PMA), and the superior parietal lobule (SPL). In the patients with new postoperative central pareses, significant (P = 0.0313) decreases in fMRI activation were found in M1, whereas significant (P = 0.0313) increases were found in SMA and PMA. For M1i and SPL, there was a signal increase on average as well, but it failed to reach significance (P = 0.1250). In both control groups, no significant changes between both examinations were seen. Even though the number of investigated patients is too small to draw definite conclusions, our results support the concept of short-term motor plasticity being mediated by redundant systems that may take over function after damage of the primary motor cortex. The findings potentially also reflect increased functional demands imposed upon the motor network subsequent to a loss of dexterity.

Finger and face representations in the ipsilateral precentral motor areas in humans

Several human neuroimaging studies have reported activity in the precentral gyrus (PcG) ipsilateral to the side of hand movements. This activity has been interpreted as the part of the primary motor cortex (M1) that controls bilateral or ipsilateral hand movements. To better understand hand ipsilateral-PcG activity, we performed a functional MRI experiment in eight healthy right-handed adults. Behavioral tasks involved hand or lower face movements on each side or motor imagery of the same movements. Consistent with the known M1 organization, the hand contralateral-PcG activity was centered at the "hand-knob" portion of the PcG; face contralateral-PcG activity was localized ventrolateral to it. Hand ipsilateral-PcG activity was identified in most subjects. However, converging results indicated that this ipsilateral PcG activity was situated in Brodmann's area 6 in both hemispheres. The hand ipsilateral-PcG zones were active not only during hand movements but also face movements. Moreover, the hand ipsilateral-PcG zones revealed substantial imagery-related activity, which also failed to differentiate the hand and face. Statistical analyses confirmed poor effector selectivity of the hand ipsilateral PcG activity during both movement and imagery tasks. From these results, we conclude that the hand ipsilateral-PcG activity in healthy adults probably corresponds to a part of the ventral premotor cortex. In contrast, available evidence suggests that M1 contributes to controlling the ipsilateral hand in children and patients after stroke recovery. It appears that within the human PcG, there are two parallel systems potentially capable of controlling ipsilateral hand movements: ventral premotor cortex and M1. These two systems may be differentially influenced by developmental or pathologic changes.

Functional Imaging in Stroke Recovery

Assessing neurobiology of brain systems can provide information not available from anatomic or behavioral assessment. Such information may be of value in understanding, defining, and prescribing potential therapeutic interventions that target restorative brain events after stroke. A number of methods have been used to study stroke recovery, each with its relative merits and limitations. Several studies suggest that greater injury is associated with reduced laterality of brain activity. This might be in relation to changes in interhemispheric inhibition and is a phenomenon that is likely useful for functional gains in some patients. Many other features of brain activity change in the months after a stroke, including the site and size of activation in relevant brain network nodes. While there is incomplete agreement regarding which features of altered brain activity predict and parallel better behavioral outcome, studies converge on the conclusion that best outcome is achieved by activating the brain in a pattern that most resembles the normal state.

Brain function early after stroke in relation to subsequent recovery

This study aimed to characterize brain activation and perfusion early after stroke within cortical regions that would later change activation during recovery. Patients were studied serially after stroke (mean t1, = 16 days after stroke, t2 = 3.5 months later) using perfusion-weighted imaging and functional magnetic resonance imaging during finger movement. Controls (n = 7) showed no significant change in regional activation volumes over time. Among stroke patients (n = 8), however, recovery was accompanied by several patterns of functional magnetic resonance imaging change, with increased activation volumes over time in five patients and decreased in two. Most regions increasing activation over time were in the stroke hemisphere. Of the five patients showing increased activation over time, specific activation foci enlarged at t2 were already activated at t1 in four patients, and at least one focus growing from t1 to t2 was in a different arterial distribution from the infarct in all five patients. Perfusion of sensorimotor cortex at t1 was generally not reduced in the stroke hemisphere (94% of noninfarcted hemisphere). Improved clinical outcome was related to increased activation within sensory cortices of both brain sides, including bilateral secondary somatosensory areas. Early after stroke, cortical activation that will later increase in parallel with recovery is often already identifiable, can be remote from the vascular territory of the infarct, and is not likely hindered by reduced perfusion. The findings may be useful for restorative interventions introduced during the weeks after a stroke.

Reduced muscle selectivity during individuated finger movements in humans after damage to the motor cortex or corticospinal tract

We investigated how damage to the motor cortex or corticospinal tract affects the selective activation of finger muscles in humans. We hypothesized that damage relatively restricted to the motor cortex or corticospinal tract would result in unselective muscle activations during an individuated finger movement task. People with pure motor hemiparesis attributed to ischemic cerebrovascular accident were tested. Pure motor hemiparetic and control subjects were studied making flexion/extension and then abduction/adduction finger movements. During the abduction/adduction movements, we recorded muscle activity from 3 intrinsic finger muscles: the abductor pollicis brevis, the first dorsal interosseus, and the abductor digit quinti. Each of these muscles acts as an agonist for only one of the abduction/adduction movements and might therefore be expected to be active in a highly selective manner. Motor cortex or corticospinal tract damage in people with pure motor hemiparesis reduced the selectivity of finger muscle activation during individuated abduction/adduction finger movements, resulting in reduced independence of these movements. Abduction/adduction movements showed a nonsignificant trend toward being less independent than flexion/extension movements in the affected hands of hemiparetic subjects. These changes in the selectivity of muscle activation and the consequent decrease in individuation of movement were correlated with decreased hand function. Our findings imply that, in humans, spared cerebral motor areas and descending pathways that remain might activate finger muscles, but cannot fully compensate for the highly selective control provided by the primary motor cortex and the crossed corticospinal system.

Impaired Motor Speed, Visuospatial Episodic Memory and Verbal Fluency Characterize Cognition in Long-Term Stroke Survivors: The Tromsø Study

The cognitive function after stroke is examined in acute and subacute phase, but poorly characterized in long-term stroke survivors. This paper discusses cognitive function among long-term stroke survivors, with matched stroke-free subjects, based on a population survey. General cognition, verbal, executive and visuospatial function, memory, attention, and motor speed were tested as well as motor function in upper extremities. Stroke survivors and controls were most effectively discriminated by means of motor speed, followed by visuospatial episodic memory and verbal fluency. This pattern of cognitive disturbances may be a consequence of cerebral lesions in frontal subcortical areas, and is different from Alzheimer's disease.

Differential impairment of individuated finger movements in humans after damage to the motor cortex or the corticospinal tract

The purpose of this study was to quantify the long-term loss of independent finger movements in humans with lesions relatively restricted to motor cortex or corticospinal tract. We questioned whether damage to the motor cortex or corticospinal tract would permanently affect the ability to move each finger to the same degree or would affect some fingers more than others. People with pure motor hemiparesis due to ischemic cerebrovascular accident were used as our experimental sample. Pure motor hemiparetic and control subjects were tested for their ability to make cyclic flexion/extension movements of each finger independently. We recorded their finger joint motion using an instrumented glove. The fingers of control subjects and of the unaffected hands (ipsilateral to the lesion) of hemiparetic subjects moved relatively independently. The fingers of the affected hands (contralateral to the lesion) of hemiparetic subjects were differentially impaired in their ability to make independent finger movements. The independence of the thumb was normal; the independence of the index finger was slightly impaired, while the independence of the middle, ring, and little fingers was substantially impaired. The differential long-term effects of motor cortical or corticospinal damage on finger independence may result from rehabilitative training emphasizing tasks requiring independent thumb and index movements, and from a greater ability of the spared components of the neuromuscular system to control the thumb independently compared with the other four fingers.