The role of diaschisis in stroke recovery

Acute Combined Cerebrolysin and Nicotinamide Administration Promote Cognitive Recovery Through Neuronal Changes in the Hippocampus of Rats with Permanent Middle Cerebral Artery Occlusion

Stroke is one of the leading causes of disability worldwide, where the Hippocampus (HPC) is affected. HPC organizes memory, which is a cognitive domain compromised after a stroke, where cerebrolysin (CBL) and Nicotinamide (NAM) have been recognized as potentially therapeutic. In this study, we aimed to evaluate the efficacy of a combined administration of CBL and NAM in a rat stroke model. Male Sprague-Dawley rats (n = 36) were divided into four groups: saline (pMCAO - Saline), CBL (pMCAO + CBL), NAM (pMCAO + NAM), and experimental (pMCAO + CBL-NAM) (n = 9 per group). A permanent middle cerebral artery occlusion (pMCAO) was induced through electrocauterization of the middle cerebral artery, followed by the administration of CBL (2.5 ml/kg), NAM (500 mg/kg) or combined immediately after skin suture, as well as at 24, 48, and 72 h post-surgery. The rats were evaluated in the novel object recognition test; hippocampal infarct area measurement; reconstruction of neurons from CA1 for Sholl analysis; and, measurement of brain-derived neurotrophic factor (BDNF) levels near the infarct zone. Our findings revealed that the administration of CBL or NAM induced infarct reduction, improved cognition, and increased BDNF levels. Moreover, a combination of CBL and NAM increased dendritic intersection in CA1 pyramidal neurons. Thus, the combined administration of CBL and NAM can promote cognitive recovery after a stroke, with infarct reduction, cytoarchitectural changes in HPC CA1 neurons, and BDNF increase. Our findings suggest that this combination therapy could be a promising intervention strategy for stroke.

Structural changes of CA1 pyramidal neurons after stroke in the contralesional hippocampus

Significant progress has been made with regard to understanding how the adult brain responds after a stroke. However, a large number of patients continue to suffer lifelong disabilities without adequate treatment. In the present study, we have analyzed possible microanatomical alterations in the contralesional hippocampus from the ischemic stroke mouse model tMCAo 12-14 weeks after transient middle cerebral artery occlusion. After individually injecting Lucifer yellow into pyramidal neurons from the CA1 field of the hippocampus, we performed a detailed three-dimensional analysis of the neuronal complexity, dendritic spine density, and morphology. We found that, in both apical (stratum radiatum) and basal (stratum oriens) arbors, CA1 pyramidal neurons in the contralesional hippocampus of tMCAo mice have a significantly higher neuronal complexity, as well as reduced spine density and alterations in spine volume and spine length. Our results show that when the ipsilateral hippocampus is dramatically damaged, the contralesional hippocampus exhibits several statistically significant selective alterations. However, these alterations are not as significant as expected, which may help to explain the recovery of hippocampal function after stroke. Further anatomical and physiological studies are necessary to better understand the modifications in the "intact" contralesional lesioned brain regions, which are probably fundamental to recover functions after stroke.

Resting state functional connectivity associated with impaired proprioception post-stroke

Deficits in proprioception, the knowledge of limb position and movement in the absence of vision, occur in ~50% of all strokes; however, our lack of knowledge of the neurological mechanisms of these deficits diminishes the effectiveness of rehabilitation and prolongs recovery. We performed resting-state functional magnetic resonance imaging (fMRI) on stroke patients to determine functional brain networks that exhibited changes in connectivity in association with proprioception deficits determined by a Kinarm robotic exoskeleton assessment. Thirty stroke participants were assessed for proprioceptive impairments using a Kinarm robot and underwent resting-state fMRI at 1 month post-stroke. Age-matched healthy control (n = 30) fMRI data were also examined and compared to stroke data in terms of the functional connectivity of brain regions associated with proprioception. Stroke patients exhibited reduced connectivity of the supplementary motor area and the supramarginal gyrus, relative to controls. Functional connectivity of these regions plus primary somatosensory cortex and parietal opercular area was significantly associated with proprioceptive function. The parietal lobe of the lesioned hemisphere is a significant node for proprioception after stroke. Assessment of functional connectivity of this region after stroke may assist with prognostication of recovery. This study also provides potential targets for therapeutic neurostimulation to aid in stroke recovery.

Association of Brain Age, Lesion Volume, and Functional Outcome in Patients With Stroke

BACKGROUND AND OBJECTIVES

Functional outcomes after stroke are strongly related to focal injury measures. However, the role of global brain health is less clear. In this study, we examined the impact of brain age, a measure of neurobiological aging derived from whole-brain structural neuroimaging, on poststroke outcomes, with a focus on sensorimotor performance. We hypothesized that more lesion damage would result in older brain age, which would in turn be associated with poorer outcomes. Related, we expected that brain age would mediate the relationship between lesion damage and outcomes. Finally, we hypothesized that structural brain resilience, which we define in the context of stroke as younger brain age given matched lesion damage, would differentiate people with good vs poor outcomes.

METHODS

We conducted a cross-sectional observational study using a multisite dataset of 3-dimensional brain structural MRIs and clinical measures from the ENIGMA Stroke Recovery. Brain age was calculated from 77 neuroanatomical features using a ridge regression model trained and validated on 4,314 healthy controls. We performed a 3-step mediation analysis with robust mixed-effects linear regression models to examine relationships between brain age, lesion damage, and stroke outcomes. We used propensity score matching and logistic regression to examine whether brain resilience predicts good vs poor outcomes in patients with matched lesion damage.

RESULTS

We examined 963 patients across 38 cohorts. Greater lesion damage was associated with older brain age (β = 0.21; 95% CI 0.04-0.38, p = 0.015), which in turn was associated with poorer outcomes, both in the sensorimotor domain (β = -0.28; 95% CI -0.41 to -0.15, p < 0.001) and across multiple domains of function (β = -0.14; 95% CI -0.22 to -0.06, p < 0.001). Brain age mediated 15% of the impact of lesion damage on sensorimotor performance (95% CI 3%-58%, p = 0.01). Greater brain resilience explained why people have better outcomes, given matched lesion damage (odds ratio 1.04, 95% CI 1.01-1.08, p = 0.004).

DISCUSSION

We provide evidence that younger brain age is associated with superior poststroke outcomes and modifies the impact of focal damage. The inclusion of imaging-based assessments of brain age and brain resilience may improve the prediction of poststroke outcomes compared with focal injury measures alone, opening new possibilities for potential therapeutic targets.

Intestinal epithelial stem cell transplants as a novel therapy for cerebrovascular stroke

Almost 2/3rds of stroke survivors exhibit vascular cognitive impairment and a third of stroke patients will develop dementia 1-3 years after stroke. These dire consequences underscore the need for effective stroke therapies. In addition to its damaging effects on the brain, stroke rapidly dysregulates the intestinal epithelium, resulting in elevated blood levels of inflammatory cytokines and toxic gut metabolites due to a 'leaky' gut. We tested whether repairing the gut via intestinal epithelial stem cell (IESC) transplants would also improve stroke recovery. Organoids containing IESCs derived from young rats transplanted into older rats after stroke were incorporated into the gut, restored stroke-induced gut dysmorphology and decreased gut permeability, and reduced circulating levels of endotoxin LPS and the inflammatory cytokine IL-17A. Remarkably, IESC transplants also improved stroke-induced acute (4d) sensory-motor disability and chronic (30d) cognitive-affective function. Moreover, IESCs from older animals displayed senescent features and were not therapeutic for stroke. These data underscore the gut as a critical therapeutic target for stroke and demonstrate the effectiveness of gut stem cell therapy.

Delayed Infiltration of Peripheral Monocyte Contributes to Phagocytosis and Transneuronal Degeneration in Chronic Stroke

BACKGROUND

Mononuclear phagocytes, including monocyte-derived macrophages (MDMs) and microglia, contribute to infarct development as well as tissue repair in the postischemic brain. Here, we identify the origin and function of MDMs in the brain during poststroke repair processes.

METHODS

Adult mice were subjected to transient middle cerebral artery occlusion. Longitudinal brain atrophy and secondary degeneration were evaluated during acute to recovery phases of stroke. Adoptive transfer of GFP+ splenocytes into asplenic mice was used to distinguish MDMs from resident microglia. Fluorescence beads were injected into stroked animals to examine phagocytic function.

RESULTS

Progressive atrophy and neuronal degeneration in remote regions were observed in chronic stroke, which also was accompanied by MDM infiltration into the ipsilateral hemisphere. Compared with microglia, MDMs had significantly higher phagocytic activity. MDM trafficking and phagocytosis was spatiotemporally regulated with acute and prolonged infiltration into infarcted tissue, as well as delayed entry in remote areas such as the thalamus and substantia nigra.

CONCLUSIONS

The stepwise and long-lasting involvement of MDMs at multiple poststroke stages shows that MDMs have a role in progressive stroke-induced injury and repair processes. These findings suggest that manipulating monocyte entry at different stroke stages may be an effective immune-based strategy to limit injury propagation in chronic stroke.

Changes in Bihemispheric Structural Connectivity Following Middle Cerebral Artery Infarction

This study investigated the changes in the structural connectivity of the bilateral hemispheres over time following a middle cerebral artery infarction. Eighteen patients in the subacute group and nine patients in the chronic group with mild upper extremity motor impairment (Fugl-Meyer motor assessment score for the upper limb > 43) following middle cerebral artery infarction were retrospectively evaluated in this study. All the patients underwent T1-weighted and diffusion tensor imaging. Tract-based statistical analyses of fractional anisotropy were used to compare the changes in the bilateral structural connectivity with those of age-matched normal controls. The corticospinal tract pathway of the affected hemisphere, corpus callosum, and corona radiata of the unaffected hemisphere had decreased structural connectivity in the subacute group, while the motor association area and anterior corpus callosum in the bilateral frontal lobes had increased structural connectivity in the chronic group. The bilateral hemispheres were influenced even in patients with mild motor impairment following middle cerebral artery infarction, and the structural connectivity of the bilateral hemispheres changed according to the time following the stroke.

Excessive Astrocytic GABA Causes Cortical Hypometabolism and Impedes Functional Recovery after Subcortical Stroke

Glucose hypometabolism in cortical structures after functional disconnection is frequently reported in patients with white matter diseases such as subcortical stroke. However, the molecular and cellular mechanisms have been poorly elucidated. Here we show, in an animal model of internal capsular infarct, that GABA-synthesizing reactive astrocytes in distant cortical areas cause glucose hypometabolism via tonic inhibition of neighboring neurons. We find that reversal of aberrant astrocytic GABA synthesis, by pharmacological inhibition and astrocyte-specific gene silencing of MAO-B, reverses the reduction in cortical glucose metabolism. Moreover, induction of aberrant astrocytic GABA synthesis by cortical injection of putrescine or adenovirus recapitulates cortical hypometabolism. Furthermore, MAO-B inhibition causes a remarkable recovery from post-stroke motor deficits when combined with a rehabilitation regimen. Collectively, our data indicate that cortical glucose hypometabolism in subcortical stroke is caused by aberrant astrocytic GABA and MAO-B inhibition and that attenuating cortical hypometabolism can be a therapeutic approach in subcortical stroke.

Multi-scale image analysis and prediction of visual field defects after selective amygdalohippocampectomy

Selective amygdalohippocampectomy is an effective treatment for patients with therapy-refractory temporal lobe epilepsy but may cause visual field defect (VFD). Here, we aimed to describe tissue-specific pre- and postoperative imaging correlates of the VFD severity using whole-brain analyses from voxel- to network-level. Twenty-eight patients with temporal lobe epilepsy underwent pre- and postoperative MRI (T1-MPRAGE and Diffusion Tensor Imaging) as well as kinetic perimetry according to Goldmann standard. We probed for whole-brain gray matter (GM) and white matter (WM) correlates of VFD using voxel-based morphometry and tract-based spatial statistics, respectively. We furthermore reconstructed individual structural connectomes and conducted local and global network analyses. Two clusters in the bihemispheric middle temporal gyri indicated a postsurgical GM volume decrease with increasing VFD severity (FWE-corrected p < 0.05). A single WM cluster showed a fractional anisotropy decrease with increasing severity of VFD in the ipsilesional optic radiation (FWE-corrected p < 0.05). Furthermore, patients with (vs. without) VFD showed a higher number of postoperative local connectivity changes. Neither in the GM, WM, nor in network metrics we found preoperative correlates of VFD severity. Still, in an explorative analysis, an artificial neural network meta-classifier could predict the occurrence of VFD based on presurgical connectomes above chance level.

Unique Subtype of Microglia in Degenerative Thalamus After Cortical Stroke

BACKGROUND AND PURPOSE

Stroke disrupts neuronal functions in both local and remotely connected regions, leading to network-wide deficits that can hinder recovery. The thalamus is particularly affected, with progressive development of neurodegeneration accompanied by inflammatory responses. However, the complexity of the involved inflammatory responses is poorly understood. Herein we investigated the spatiotemporal changes in the secondary degenerative thalamus after cortical stroke, using targeted transcriptome approach in conjunction with histology and flow cytometry.

METHODS

Cortical ischemic stroke was generated by permanent occlusion of the left middle cerebral artery in male C57BL6J mice. Neurodegeneration, neuroinflammatory responses, and microglial activation were examined in naive and stroke mice at from poststroke days (PD) 1 to 84, in both ipsilesional somatosensory cortex and ipsilesional thalamus. NanoString neuropathology panel (780 genes) was used to examine transcriptome changes at PD7 and PD28. Fluorescence activated cell sorting was used to collect CD11c⁺ microglia from ipsilesional thalamus, and gene expressions were validated by quantitative real-time polymerase chain reaction.

RESULTS

Neurodegeneration in the thalamus was detected at PD7 and progressively worsened by PD28. This was accompanied by rapid microglial activation detected as early as PD1, which preceded the neurodegenerative changes. Transcriptome analysis showed higher number of differentially expressed genes in ipsilesional thalamus at PD28. Notably, neuroinflammation was the top activated pathway, and microglia was the most enriched cell type. Itgax (CD11c) was the most significantly increased gene, and its expression was highly detected in microglia. Flow-sorted CD11c⁺ microglia from degenerative thalamus indicated molecular signatures similar to neurodegenerative disease-associated microglia; these included downregulated Tmem119 and CX3CR1 and upregulated ApoE, Axl, LpL, CSF1, and Cst7.

CONCLUSIONS

Our findings demonstrate the dynamic changes of microglia after stroke and highlight the importance of investigating stroke network-wide deficits. Importantly, we report the existence of a unique subtype of microglia (CD11c⁺) with neurodegenerative disease-associated microglia features in the degenerative thalamus after stroke.

The neuroanatomical-functional paradox in spinal cord injury

Although lesion size is widely considered to be the most reliable predictor of outcome after CNS injury, lesions of comparable size can produce vastly different magnitudes of functional impairment and subsequent recovery. This neuroanatomical-functional paradox is likely to contribute to the many failed attempts to independently replicate findings from animal models of neurotrauma. In humans, the analogous clinical-radiological paradox could explain why individuals with similar injuries can respond differently to rehabilitation. We describe the neuroanatomical-functional paradox in the context of traumatic spinal cord injury (SCI) and discuss the underlying mechanisms of the paradox, including the concepts of lesion-affected and recovery-related networks. We also consider the various secondary complications that further limit the accuracy of outcome prediction in SCI and provide suggestions for how to increase the predictive, translational value of preclinical SCI models.

Ultrastructural Dendritic Changes Underlying Diaschisis After Capsular Infarct

Diaschisis has been described as functional depression distant to the lesion. A variety of neuroscientific approaches have been used to investigate the mechanisms underlying diaschisis. However, few studies have examined the pathological changes in diaschisis at ultrastructural level. Here, we used a rat model of capsular infarct that consistently produces diaschisis in ipsilesional and contralesional motor and sensory cortices. To verify the occurrence of diaschisis and monitor time-dependent changes in diaschisis, we performed longitudinal 2-deoxy-2-[18F]-fluoro-d-glucose microPET (FDG-microPET) study. We also used light and electron microscopy to identify the microscopic and ultrastructural changes at the diaschisis site at 7, 14, and 21 days after capsular infarct modeling (CIM). FDG-microPET showed the occurrence of diaschisis after CIM. Light microscopic examinations revealed no significant histopathological changes at the diaschisis site except a mild degree of reactive astrogliosis. However, electron microscopy revealed swollen, hydropic degeneration of axial dendrites and axodendritic synapses, although the neuronal soma (including nuclear chromatin and cytoplasmic organelles) and myelinated axons were relatively well preserved up to 21 days after injury. Furthermore, number of axodendritic synapses was significantly decreased after CIM. These data indicate that a circumscribed subcortical white-matter lesion produces ultrastructural pathological changes related to the pathogenesis of diaschisis.

Impact of unilateral stroke on right hemisphere superiority in executive control

In our previous study, we have demonstrated a right hemisphere superiority in executive control of attention, with the right hemisphere being more efficient in dealing with conflict for stimuli presented in the left visual field. However, the unique and synergetic contribution of the two hemispheres to this superiority effect is still elusive. Here, using the lateralized attention network test, we compared the flanker conflict effect for stimuli presented in the left and right visual fields in patients with an ischemic stroke in the right or left hemisphere as the unilateral lesion groups and in patients with a transient ischemic attack without an acute infarction as the control group. In contrast to the transient ischemic attack group, which demonstrated a right hemisphere superiority in conflict processing, there was no evidence for such an effect in both unilateral stroke groups. These results can be explained by our model proposing that there is bilateral hemispheric involvement for conflict processing for information received from the left visual field and unilateral hemispheric involvement for conflict processing for information received from the right visual field, resulting in more efficient processing for the left visual field, i.e., the right hemisphere superiority effect. When there is damage to either hemisphere, the responsibility of conflict processing will largely fall on the intact hemisphere, eliminating the right hemisphere superiority effect.

Multimodal magnetic resonance imaging correlates of motor outcome after stroke using machine learning

This study applied machine learning regression to predict motor function after stroke based on multimodal magnetic resonance imaging. Fifty-four stroke patients, who underwent T1 weighted, diffusion tensor, and resting state functional magnetic resonance imaging were retrospectively included. The kernel rigid regression machine algorithm was applied to gray and white matter maps in T1 weighted, fractional anisotropy and mean diffusivity maps in diffusion tensor, and two motor-related independent component analysis maps in resting state functional magnetic resonance imaging to predict Fugl-Meyer motor assessment scores with the covariate as the onset duration after stroke. The results were validated using the leave-one-subject-out cross-validation method. This study is the first to apply machine learning in this area using multimodal magnetic resonance imaging data, which constitutes the main novelty. Multimodal magnetic resonance imaging correctly predicted the Fugl-Meyer motor assessment score in 72 % of cases with a normalized mean squared error of 5.93 (p value = 0.0020). The ipsilesional premotor, periventricular, and contralesional cerebellar areas were shown to be of relatively high importance in the prediction. Machine learning using multimodal magnetic resonance imaging data after a stroke may predict motor outcome.

Stem Cell Repair of the Microvascular Damage in Stroke

Stroke is a life-threatening disease that leads to mortality, with survivors subjected to long-term disability. Microvascular damage is implicated as a key pathological feature, as well as a therapeutic target for stroke. In this review, we present evidence detailing subacute diaschisis in a focal ischemic stroke rat model with a focus on blood–brain barrier (BBB) integrity and related pathogenic processes in contralateral brain areas. Additionally, we discuss BBB competence in chronic diaschisis in a similar rat stroke model, highlighting the pathological changes in contralateral brain areas that indicate progressive morphological brain disturbances overtime after stroke onset. With diaschisis closely approximating stroke onset and progression, it stands as a treatment of interest for stroke. Indeed, the use of stem cell transplantation for the repair of microvascular damage has been investigated, demonstrating that bone marrow stem cells intravenously transplanted into rats 48 h post-stroke survive and integrate into the microvasculature. Ultrastructural analysis of transplanted stroke brains reveals that microvessels display a near-normal morphology of endothelial cells and their mitochondria. Cell-based therapeutics represent a new mechanism in BBB and microvascular repair for stroke.

Contralesional White Matter Alterations in Patients After Hemispherotomy

Cerebral lesions may cause degeneration and neuroplastic reorganization in both the ipsi- and the contralesional hemisphere, presumably creating an imbalance of primarily inhibitory interhemispheric influences produced via transcallosal pathways. The two hemispheres are thought to mutually hamper neuroplastic reorganization of the other hemisphere. The results of preceding degeneration and neuroplastic reorganization of white matter may be reflected by Diffusion Tensor Imaging-derived diffusivity parameters such as fractional anisotropy (FA). In this study, we applied Diffusion Tensor Imaging (DTI) to contrast the white matter status of the contralesional hemisphere of young lesioned brains with and without contralateral influences by comparing patients after hemispherotomy to those who had not undergone neurosurgery. DTI was applied to 43 healthy controls (26 females, mean age ± SD: 25.07 ± 11.33 years) and two groups of in total 51 epilepsy patients with comparable juvenile brain lesions (32 females, mean age ± SD: 25.69 ± 12.77 years) either after hemispherotomy (30 of 51 patients) or without neurosurgery (21 of 51 patients), respectively. FA values were compared between these groups using the unbiased tract-based spatial statistics approach. A voxel-wise ANCOVA controlling for age at scan yielded significant group differences in FA. A post hoc t-test between hemispherotomy patients and healthy controls revealed widespread supra-threshold voxels in the contralesional hemisphere of hemispherotomy patients indicating comparatively higher FA values (p < 0.05, FWE-corrected). The non-surgery group, in contrast, showed extensive supra-threshold voxels indicating lower FA values in the contralesional hemisphere as compared to healthy controls (p < 0.05, FWE-corrected). Whereas lower FA values are suggestive of pronounced contralesional degeneration in the non-surgery group, higher FA values in the hemispherotomy group may be interpreted as a result of preceding plastic remodeling. We conclude that, whether juvenile brain lesions are associated with contralesional degeneration or reorganization partly depends on the ipsilesional hemisphere. Contralesional reorganization as observed in hemispherotomy patients was most likely enabled by the complete neurosurgical deafferentation of the ipsilesional hemisphere and, thereby, the disinhibition of the neuroplastic potential of the contralesional hemisphere. The main argument of this study is that hemispherotomy may be seen as a major plastic stimulus and as a prerequisite for contralesional neuroplastic remodeling in patients with juvenile brain lesions.

Errors in proprioceptive matching post-stroke are associated with impaired recruitment of parietal, supplementary motor, and temporal cortices

Deficits in proprioception, the ability to discriminate the relative position and movement of our limbs, affect ~50% of stroke patients and reduce functional outcomes. Our lack of knowledge of the anatomical correlates of proprioceptive processing limits our understanding of the impact that such deficits have on recovery. This research investigated the relationship between functional impairment in brain activity and proprioception post-stroke. We developed a novel device and task for arm position matching during functional MRI (fMRI), and investigated 16 subjects with recent stroke and nine healthy age-matched controls. The stroke-affected arm was moved by an experimenter (passive arm), and subjects were required to match the position of this limb with the opposite arm (active arm). Brain activity during passive and active arm movements was determined, as well as activity in association with performance error. Passive arm movement in healthy controls was associated with activity in contralateral primary somatosensory (SI) and motor cortices (MI), bilateral parietal cortex, supplementary (SMA) and premotor cortices, secondary somatosensory cortices (SII), and putamen. Active arm matching was associated with activity in contralateral SI, MI, bilateral SMA, premotor cortex, putamen, and ipsilateral cerebellum. In subjects with stroke, similar patterns of activity were observed. However, in stroke subjects, greater proprioceptive error was associated with less activity in ipsilesional supramarginal and superior temporal gyri, and lateral thalamus. During active arm movement, greater proprioceptive error was associated with less activity in bilateral SMA and ipsilesional premotor cortex. Our results enhance our understanding of the correlates of proprioception within the temporal parietal cortex and supplementary/premotor cortices. These findings also offer potential targets for therapeutic intervention to improve proprioception in recovering stroke patients and thus improve functional outcome.

Inflammatory Responses in the Secondary Thalamic Injury After Cortical Ischemic Stroke

Stroke is one of the major causes of chronic disability worldwide and increasing efforts have focused on studying brain repair and recovery after stroke. Following stroke, the primary injury site can disrupt functional connections in nearby and remotely connected brain regions, resulting in the development of secondary injuries that may impede long-term functional recovery. In particular, secondary degenerative injury occurs in the connected ipsilesional thalamus following a cortical stroke. Although secondary thalamic injury was first described decades ago, the underlying mechanisms still remain unclear. We performed a systematic literature review using the NCBI PubMed database for studies that focused on the secondary thalamic degeneration after cortical ischemic stroke. In this review, we discussed emerging studies that characterized the pathological changes in the secondary degenerative thalamus after stroke; these included excitotoxicity, apoptosis, amyloid beta protein accumulation, blood-brain-barrier breakdown, and inflammatory responses. In particular, we highlighted key findings of the dynamic inflammatory responses in the secondary thalamic injury and discussed the involvement of several cell types in this process. We also discussed studies that investigated the effects of blocking secondary thalamic injury on inflammatory responses and stroke outcome. Targeting secondary injuries after stroke may alleviate network-wide deficits, and ultimately promote stroke recovery.

Quantifying the Impact of Chronic Ischemic Injury on Clinical Outcomes in Acute Stroke With Machine Learning

Acute stroke is often superimposed on chronic damage from previous cerebrovascular events. This background will inevitably modulate the impact of acute injury on clinical outcomes to an extent that will depend on the precise anatomical pattern of damage. Previous attempts to quantify such modulation have employed only reductive models that ignore anatomical detail. The combination of automated image processing, large-scale data, and machine learning now enables us to quantify the impact of this with high-dimensional multivariate models sensitive to individual variations in the detailed anatomical pattern. We introduce and validate a new automated chronic lesion segmentation routine for use with non-contrast CT brain scans, combining non-parametric outlier-detection score, Zeta, with an unsupervised 3-dimensional maximum-flow, minimum-cut algorithm. The routine was then applied to a dataset of 1,704 stroke patient scans, obtained at their presentation to a hyper-acute stroke unit (St George's Hospital, London, UK), and used to train a support vector machine (SVM) model to predict between low (0-2) and high (3-6) pre-admission and discharge modified Rankin Scale (mRS) scores, quantifying performance by the area under the receiver operating curve (AUROC). In this single center retrospective observational study, our SVM models were able to differentiate between low (0-2) and high (3-6) pre-admission and discharge mRS scores with an AUROC of 0.77 (95% confidence interval of 0.74-0.79), and 0.76 (0.74-0.78), respectively. The chronic lesion segmentation routine achieved a mean (standard deviation) sensitivity, specificity and Dice similarity coefficient of 0.746 (0.069), 0.999 (0.001), and 0.717 (0.091), respectively. We have demonstrated that machine learning models capable of capturing the high-dimensional features of chronic injuries are able to stratify patients-at the time of presentation-by pre-admission and discharge mRS scores. Our fully automated chronic stroke lesion segmentation routine simplifies this process, and utilizes routinely collected CT head scans, thereby facilitating future large-scale studies to develop supportive clinical decision tools.

Structural brain networks and functional motor outcome after stroke-a prospective cohort study

The time course of topological reorganization that occurs in the structural connectome after an ischaemic stroke is currently not well understood. We aimed to determine the evolution of structural brain networks in stroke patients with motor deficits and relate changes in their global topology to residual symptom burden and functional impairment. In this prospective cohort study, ischaemic stroke patients with supratentorial infarcts and motor symptoms were assessed longitudinally by advanced diffusion MRI and detailed clinical testing of upper extremity motor function at four time points from the acute to the chronic stage. For each time point, structural connectomes were reconstructed, and whole-hemisphere global network topology was quantified in terms of integration and segregation parameters. Using non-linear joint mixed-effects regression modelling, network evolution was related to lesion volume and clinical outcome. Thirty patients were included for analysis. Graph-theoretical analysis demonstrated that, over time, brain networks became less integrated and more segregated with decreasing global efficiency and increasing modularity. Changes occurred in both stroke and intact hemispheres and, in the latter, were positively associated with lesion volume. Greater change in topology was associated with larger residual symptom burden and greater motor impairment 1, 3 and 12 months after stroke. After ischaemic stroke, brain networks underwent characteristic changes in both ipsi- and contralesional hemispheres. Topological network changes reflect the severity of damage to the structural network and are associated with functional outcome beyond the impact of lesion volume.

Diffusion Imaging of Cerebral Diaschisis in Neonatal Arterial Ischemic Stroke

BACKGROUND

Neonatal arterial ischemic stroke is a leading cause of cerebral palsy and lifelong disability. Diffusion-weighted imaging has revolutionized diagnosis and facilitated outcome prognostication in acute neonatal arterial ischemic stroke. Diaschisis refers to changes in brain areas functionally connected but structurally remote from primary injury. We hypothesized that acute diffusion-weighted imaging can quantify cerebral diaschisis and is associated with outcome from neonatal arterial ischemic stroke.

METHODS

Subjects were identified from a prospective, population-based research cohort (Alberta Perinatal Stroke Project). Inclusion criteria were unilateral middle cerebral artery neonatal arterial ischemic stroke, diffusion-weighted magnetic resonance imaging within 10 days of birth, and more than 12-months follow-up (pediatric stroke outcome measure). Diaschisis was characterized and quantified using a validated software method (ImageJ). Volumetric analysis assessed atrophy of affected structures. Diaschisis scores were corrected for infarct size and compared with outcomes (Mann-Whitney).

RESULTS

From 20 eligible neonatal arterial ischemic strokes, two were excluded for poor image quality. Of 18 remaining (61% male, median age 3.2 days), 16 (89%) demonstrated diaschisis. Thalamus (88%) was the most common location in addition to corpus callosum (50%). Age at imaging was not associated with diaschisis. Affected structures demonstrated atrophy on imaging. Long-term outcomes available in 81% (median age 7.5 years) were not associated with diaschisis scores.

CONCLUSIONS

Cerebral diaschisis occurs in neonatal arterial ischemic stroke and can be quantified with diffusion-weighted imaging. Occurrence is common and should not be mistaken for additional infarction. Determining clinical significance will require larger samples with well-characterized long-term outcomes.

Proprioception and motor performance after stroke: An examination of diffusion properties in sensory and motor pathways

Proprioceptive and motor impairments commonly occur after stroke. Relationships between corticospinal tract (CST) fractional anisotropy (FA) and motor recovery have been identified. However, the relationship between sensory tract microstructure and proprioceptive recovery remains unexplored. Using probabilistic tractography, we examined the relationship between diffusion metrics in three tracts known to contain proprioceptive information (a) dorsal-column medial-lemniscal (DCML), (b) postcentral gyrus to supramarginal gyrus (POCG-SMG), (c) postcentral gyrus to Heschl's gyrus (POCG-HG) and proprioception at 1 (n = 26) and 6 months (n = 19) poststroke. Proprioception was assessed using two robotic tasks. Motor performance was also assessed robotically and compared to CST diffusion metrics. At 1-month poststroke, a nonsignificant relationship (r = -0.43, p = 0.05) was observed between DCML-FA and proprioceptive impairment. A moderate relationship was identified between POCG-SMG FA and POCG-HG FA and proprioceptive impairment (r = -0.47, p = 0.001 and r = -0.51, p = 0.008, respectively). No relationships were significant at 6 months poststroke. Similar to previous studies, lower CST-FA correlated with motor impairment at 1 month poststroke (r = -0.58, p = 0.002). While CST-FA is considered a predictor of motor impairment, our findings suggest that the relationship between FA and tracts containing proprioceptive information is not as straightforward and highlights the importance of sensory association areas in proprioception.

Crossed Cerebellar Diaschisis Has an Adverse Effect on Functional Outcome in the Subacute Rehabilitation Phase of Stroke: A Case-Control Study

OBJECTIVE

To investigate whether crossed cerebellar diaschisis (CCD) is associated with functional outcome in the subacute rehabilitation phase of stroke.

DESIGN

Retrospective case-control study.

SETTING

Hospital-based cohort.

PARTICIPANTS

The study enrolled participants who underwent brain single-photon emission computed tomography (N=48). Patients with CCD were identified (n=24). Twenty-four controls were selected for each case-patient by matching age, stroke type (ischemic or hemorrhagic), lesion laterality, and lesion location.

INTERVENTION

Not applicable.

MAIN OUTCOME MEASURES

The functional ambulation category (FAC), modified Barthel Index (MBI), and Mini-Mental State Examination (MMSE) were administered at the initial (initiation of rehabilitation therapy) and the follow-up (4wk after rehabilitation therapy) assessments.

RESULTS

The CCD group had lower MMSE, FAC, MBI, and MMSE scores at the initial assessment (P=.032, .016, and .001, respectively) and lower FAC and MBI scores at the follow-up assessment, than the non-CCD group (P=.001 and .036, respectively). Although CCD was not associated with cognitive impairment, nonambulatory status, and dependent activities of daily living (ADL) at the initial assessment (P=.538, .083, and >.99, respectively), the CCD group had a higher risk of cognitive impairment (adjusted odds ratio [aOR]=4.044; 95% confidence interval [CI], 1.071-15.270; P=.039), nonambulatory status (aOR=7.000; 95% CI, 1.641-29.854; P=.009) and dependent ADL (aOR=13.500; 95% CI, 1.535-118.692; P=.019) at the follow-up assessment.

CONCLUSIONS

CCD is associated with severe functional impairment and may have an adverse effect on functional outcomes related to cognition, ambulatory function, and ADL during the subacute rehabilitation phase of stroke. This suggests that CCD may be a valuable predictor of functional outcome in the subacute rehabilitation phase of stroke.

Compensatory Relearning Following Stroke: Cellular and Plasticity Mechanisms in Rodents

von Monakow’s theory of diaschisis states the functional ‘standstill’ of intact brain regions that are remote from a damaged area, often implied in recovery of function. Accordingly, neural plasticity and activity patterns related to recovery are also occurring at the same regions. Recovery relies on plasticity in the periinfarct and homotopic contralesional regions and involves relearning to perform movements. Seeking evidence for a relearning mechanism following stroke, we found that rodents display many features that resemble classical learning and memory mechanisms. Compensatory relearning is likely to be accompanied by gradual shaping of these regions and pathways, with participating neurons progressively adapting cortico-striato-thalamic activity and synaptic strengths at different cortico-thalamic loops – adapting function relayed by the striatum. Motor cortex functional maps are progressively reinforced and shaped by these loops as the striatum searches for different functional actions. Several cortical and striatal cellular mechanisms that influence motor learning may also influence post-stroke compensatory relearning. Future research should focus on how different neuromodulatory systems could act before, during or after rehabilitation to improve stroke recovery.

Contralesional Brain Activity in Acute Ischemic Stroke

Background: The noninjured, contralateral hemisphere is increasingly acknowledged in the process of recovery from acute ischemic stroke. We estimated the value of conventional electroencephalography (EEG) recordings for identifying contralateral hemisphere involvement in relation to functional recovery. Methods: We analyzed 2-min epochs from 21 electrode EEG registrations of 18 patients with acute hemispheric ischemic stroke and compared with 18 age-matched controls. Outcome was dichotomized as good (modified Rankin Scale [mRS] 0–2) or poor (mRS 3–5 or death) at 3 months. Effects of the infarct on the ipsi-and contralateral hemispheres were analyzed by the delta/alpha ratio (DAR) and 2 measures of functional connectivity (magnitude squared coherence [MSC] and weighted phase lag index [WPLI]). Results: DAR was higher in patients than in controls, both in the ipsilateral and in the contralateral hemisphere (median 4.5 ± 6.7 ipsilateral and 2.4 ± 2.0 contralateral vs. 0.5 ± 0.5 in the control group, p < 0.001), indicating robust EEG changes in both lesioned and non-lesioned hemisphere. MSC and WPLI in the alpha and beta frequency bands were lower in patients than in controls in both hemispheres, indicating clear disturbances of functional connectivity (p < 0.05). In the poor outcome group, contralateral MSC and WPLI were lower than in the good outcome group, although these differences did not reach statistical significance. Conclusions: Short conventional EEG measurements show robust changes of brain activity and functional connectivity in both ipsilateral and contralateral hemispheres of patients with acute ischemic stroke. Changes of remote functional connectivity tend to interact with functional recovery. Future studies should estimate predictive values for individual patients and interactions with plasticity enhancing treatments.

3D pseudocontinuous arterial spin-labeling perfusion imaging detected crossed cerebellar diaschisis in acute, subacute and chronic intracerebral hemorrhage

OBJECTIVE

We aimed to evaluate the value of 3D pseudocontinuous arterial spin-labeling (pCASL) perfusion imaging detected crossed cerebellar diaschisis (CCD) at different stages of intracerebral hemorrhage (ICH).

MATERIALS AND METHODS

We assessed bilateral cerebral blood flow (CBF) values of different brain regions and the relationships between the CCD and clinical status of 16 ICH patients.

RESULTS

The ICH patients had significantly lower CBF values in the contralateral cerebellum in acute, subacute and chronic stages. The subacute CCD had a significant correlation with clinical status.

CONCLUSIONS

3D pCASL may be an ideal tool to study the phenomenon and clinical consequences of ICH with CCD.

Hypoconnectivity of Resting-State Networks in Persons with Aphasia Compared with Healthy Age-Matched Adults

Aphasia is a language disorder affecting more than one million people in the US. While language function has traditionally been the focus of neuroimaging research, other cognitive functions are affected in this population, which has implications not only for those specific processes but also for the interaction of language and other cognitive functions. Resting state fMRI (rs-fMRI) is a practical and informative way to explore and characterize general cognitive engagement and/or health in this population, but it is currently underutilized. The aim of this study was to explore the functional connectivity in resting state networks (RSNs) and in the semantic network in seven persons with aphasia (PWA) who were at least 6 months post onset compared with 11 neurologically healthy adults (NHA) in order to gain a more comprehensive understanding of general cognitive engagement in aphasia. These preliminary results show that PWA exhibit hypoconnectivity in the semantic network and all RSNs except the visual network. Compared with NHA, PWA appear to have fewer cross- and left-hemispheric connections. However, PWA exhibit some stronger connections than NHA within the semantic network, which could indicate compensatory mechanisms. Importantly, connectivity for RSNs appear to increase with decreasing aphasia severity and decrease with increasing lesion size. This knowledge has the potential to improve aphasia therapy by furthering the understanding of lesion effects on the cognitive system as a whole, which can guide treatment target selection and promotion of favorable neural reorganization for optimal recovery of function.

Postural asymmetry correlated with lateralization of cerebellar perfusion in persons with chronic stroke: A role of crossed cerebellar diaschisis in left side

OBJECTIVE

Hemiplegia after stroke leads to impairment of the affected limbs and induces more weight on the non-paretic lower limb to form postural asymmetry. Studies of asymmetric cerebral functions have found similarly asymmetric functions in the cerebellum. Crossed cerebellar diaschisis (CCD) is defined as reduced blood flow and hypometabolism in the cerebellar hemisphere contralateral to supratentorial cerebral pathology. No study explored the relationship between posture (standing balance) and CCD in those persons yet. It was hypothesized that CCD would impair postural control and tend toward lateralization of cerebellar perfusion.

METHODS

To determine the relationship between postural asymmetry and CCD among patients with chronic stroke while testing in the upright position. Based on images from Tc-99m-ECD brain perfusion, 42 patients were retrospectively allocated into three groups: left CCD, right CCD and no CCD. The ability to maintain an upright stance as assessed by postural parameters was evaluated using a force platform.

RESULTS

The sway intensity differed significantly between the groups with left CCD and no CCD (p = 0.0052), as did the sway velocities (p = 0.0010). The association between the duration of stroke and sway intensity was highly significant (p < 0.0001). The interval from the stroke onset to the postural analysis was significantly associated with sway intensity and velocity.

CONCLUSIONS

This study indicates that the impairment of posture sway control was more severe in left CCD than the other CCD types. The results support a relationship between the postural asymmetry and lateralization of CCD in patients with chronic stroke.

Arterial spin labelling shows functional depression of non-lesion tissue in chronic Wernicke's aphasia

Behavioural impairment post-stroke is a consequence of structural damage and altered functional network dynamics. Hypoperfusion of intact neural tissue is frequently observed in acute stroke, indicating reduced functional capacity of regions outside the lesion. However, cerebral blood flow (CBF) is rarely investigated in chronic stroke. This study investigated CBF in individuals with chronic Wernicke's aphasia (WA) and examined the relationship between lesion, CBF and neuropsychological impairment.

Arterial spin labelling CBF imaging and structural MRIs were collected in 12 individuals with chronic WA and 13 age-matched control participants. Joint independent component analysis (jICA) investigated the relationship between structural lesion and hypoperfusion. Partial correlations explored the relationship between lesion, hypoperfusion and language measures.

Joint ICA revealed significant differences between the control and WA groups reflecting a large area of structural lesion in the left posterior hemisphere and an associated area of hypoperfusion extending into grey matter surrounding the lesion. Small regions of remote cortical hypoperfusion were observed, ipsilateral and contralateral to the lesion. Significant correlations were observed between the neuropsychological measures (naming, repetition, reading and semantic association) and the jICA component of interest in the WA group. Additional ROI analyses found a relationship between perfusion surrounding the core lesion and the same neuropsychological measures.

This study found that core language impairments in chronic WA are associated with a combination of structural lesion and abnormal perfusion in non-lesioned tissue. This indicates that post-stroke impairments are due to a wider disruption of neural function than observable on structural T1w MRI.

Functional Neuroimaging in Stroke Recovery and Neurorehabilitation: Conceptual Issues and Perspectives

Background

In stroke, functional neuroimaging has become a potent diagnostic tool; opened new insights into the pathophysiology of ischaemic damage in the human brain; and made possible the assessment of functional–structural relationships in postlesion recovery.

Summary of review

Here, we give a critical account on the potential and limitation of functional neuroimaging and discuss concepts related to the use of neuroimaging for exploring the neurobiological and neuroanatomical mechanisms of poststroke recovery and neurorehabilitation. We identify and provide evidence for five hypotheses that functional neuroimaging can provide new insights into: adaptation occurs at the level of functional brain systems; the brain–behaviour relationship varies with recovery and over time; functional neuroimaging can improve our ability to predict recovery and select individuals for rehabilitation; mechanisms of recovery reflect different pathophysiological phases; and brain adaptation may be modulated by experience and specific rehabilitation. The significance and application of this new evidence is discussed, and recommendations made for investigations in the field.

Conclusion

Functional neuroimaging is an important tool to explore the mechanisms underlying brain plasticity and, thereby, to guide clinical research in neurorehabilitation.

Blood-Spinal Cord Barrier Alterations in Subacute and Chronic Stages of a Rat Model of Focal Cerebral Ischemia

We previously demonstrated blood-brain barrier impairment in remote contralateral brain areas in rats at 7 and 30 days after transient middle cerebral artery occlusion (tMCAO), indicating ischemic diaschisis. Here, we focused on effects of subacute and chronic focal cerebral ischemia on the blood-spinal cord barrier (BSCB). We observed BSCB damage on both sides of the cervical spinal cord in rats at 7 and 30 days post-tMCAO. Major BSCB ultrastructural changes in spinal cord gray and white matter included vacuolated endothelial cells containing autophagosomes, pericyte degeneration with enlarged mitochondria, astrocyte end-feet degeneration and perivascular edema; damaged motor neurons, swollen axons with unraveled myelin in ascending and descending tracts and astrogliosis were also observed. Evans Blue dye extravasation was maximal at 7 days. There was immunofluorescence evidence of reduction of microvascular expression of tight junction occludin, upregulation of Beclin-1 and LC3B immunoreactivities at 7 days and a reduction of the latter at 30 days post-ischemia. These novel pathological alterations on the cervical spinal cord microvasculature in rats after tMCAO suggest pervasive and long-lasting BSCB damage after focal cerebral ischemia, and that spinal cord ischemic diaschisis should be considered in the pathophysiology and therapeutic approaches in patients with ischemic cerebral infarction.

Brain plasticity and rehabilitation in stroke patients

In recent years, our understanding of motor learning, neuroplasticity and functional recovery after the occurrence of brain lesion has grown significantly. Novel findings in basic neuroscience have provided an impetus for research in motor rehabilitation. The brain reveals a spectrum of intrinsic capacities to react as a highly dynamic system which can change the properties of its neural circuits. This brain plasticity can lead to an extreme degree of spontaneous recovery and rehabilitative training may modify and boost the neuronal plasticity processes. Animal studies have extended these findings, providing insight into a broad range of underlying molecular and physiological events. Neuroimaging studies in human patients have provided observations at the systems level that often parallel findings in animals. In general, the best recoveries are associated with the greatest return toward the normal state of brain functional organization. Reorganization of surviving central nervous system elements supports behavioral recovery, for example, through changes in interhemispheric lateralization, activity of association cortices linked to injured zones, and organization of cortical representational maps. Evidence from animal models suggests that both motor learning and cortical stimulation alter intracortical inhibitory circuits and can facilitate long-term potentiation and cortical remodeling. Current researches on the physiology and use of cortical stimulation animal models and in humans with stroke related hemiplegia are reviewed in this article. In particular, electromyography (EMG) -controlled electrical muscle stimulation improves the motor function of the hemiparetic arm and hand. A multi-channel near-infrared spectroscopy (NIRS) studies in which the hemoglobin levels in the brain were non-invasively and dynamically measured during functional activity found that the cerebral blood flow in the injured sensory-motor cortex area is greatest during an EMG-controlled FES session. Only a few idea is, however, known for the optimal timing of the different processes and therapeutic interventions and for their interactions in detail. Finding optimal rehabilitation paradigms requires an optimal organization of the internal processes of neural plasticity and the therapeutic interventions in accordance with defined plastic time windows. In this review the mechanisms of spontaneous plasticity after stroke and experimental interventions to enhance plasticity are summarized, with an emphasis on functional electrical stimulation therapy.

Recovery of slow-5 oscillations in a longitudinal study of ischemic stroke patients

Functional networks in resting-state fMRI are identified by characteristics of their intrinsic low-frequency oscillations, more specifically in terms of their synchronicity. With advanced aging and in clinical populations, this synchronicity among functionally linked regions is known to decrease and become disrupted, which may be associated with observed cognitive and behavioral changes. Previous work from our group has revealed that oscillations within the slow-5 frequency range (0.01–0.027 Hz) are particularly susceptible to disruptions in aging and following a stroke. In this study, we characterized longitudinally the changes in the slow-5 oscillations in stroke patients across two different time-points. We followed a group of ischemic stroke patients (n = 20) and another group of healthy older adults (n = 14) over two visits separated by a minimum of three months (average of 9 months). For the stroke patients, one visit occurred in their subacute window (10 days to 6 months after stroke onset), the other took place in their chronic window (> 6 months after stroke). Using a mid-order group ICA method on 10-minutes eyes-closed resting-state fMRI data, we assessed the frequency distributions of a component's representative time-courses for differences in regards to slow-5 spectral power. First, our stroke patients, in their subacute stage, exhibited lower amplitude slow-5 oscillations in comparison to their healthy counterparts. Second, over time in their chronic stage, those same patients showed a recovery of those oscillations, reaching near equivalence to the healthy older adult group. Our results indicate the possibility of an eventual recovery of those initially disrupted network oscillations to a near-normal level, providing potentially a biomarker for stroke recovery of the cortical system. This finding opens new avenues in infra-slow oscillation research and could serve as a useful biomarker in future treatments aimed at recovery.

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Slow-5 oscillation amplitudes are reduced in stroke patients at the subacute stage.

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Slow-5 oscillation amplitudes correlate with cognitive performance.

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Slow-5 oscillations recover in the same patients at the chronic stage.

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Findings support the high implication of slow-5 oscillations in network disruption.

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Slow-5 oscillations may serve as a bio-marker of functional network health.

Compromised blood-brain barrier competence in remote brain areas in ischemic stroke rats at the chronic stage

Stroke is a life-threatening disease leading to long-term disability in stroke survivors. Cerebral functional insufficiency in chronic stroke might be due to pathological changes in brain areas remote from the initial ischemic lesion, i.e., diaschisis. Previously, we showed that the damaged blood-brain barrier (BBB) was involved in subacute diaschisis. The present study investigated BBB competence in chronic diaschisis by using a transient middle cerebral artery occlusion (tMCAO) rat model. Our results demonstrated significant BBB damage mostly in the ipsilateral striatum and motor cortex in rats at 30 days after tMCAO. The BBB alterations were also determined in the contralateral hemisphere via ultrastructural and immunohistochemical analyses. Major BBB pathological changes in contralateral remote striatum and motor cortex areas included 1) vacuolated endothelial cells containing large autophagosomes, 2) degenerated pericytes displaying mitochondria with cristae disruption, 3) degenerated astrocytes and perivascular edema, 4) Evans blue extravasation, and 5) appearance of parenchymal astrogliosis. Discrete analyses of striatal and motor cortex areas revealed significantly higher autophagosome accumulation in capillaries of ventral striatum and astrogliosis in dorsal striatum in both cerebral hemispheres. These widespread microvascular alterations in ipsilateral and contralateral brain hemispheres suggest persistent and/or continued BBB damage in chronic ischemia. The pathological changes in remote brain areas likely indicate chronic ischemic diaschisis, which should be considered in the development of treatment strategies for stroke.

Chronic stress exacerbates neuronal loss associated with secondary neurodegeneration and suppresses microglial-like cells following focal motor cortex ischemia in the mouse

Post-stroke patients describe suffering from persistent and unremitting levels of distress. Using an experimental model of focal cortical ischemia in adult male C57BL/6 mice, we examined whether exposure to chronic stress could modify the development of secondary thalamic neurodegeneration (STND), which is commonly reported to be associated with impaired functional recovery. We were particularly focused on the modulatory role of microglia-like cells, as several clinical studies have linked microglial activation to the development of STND. One month following the induction of cortical ischemia we identified that numbers of microglial-like cells, as well as putative markers of microglial structural reorganization (Iba-1), complement processing (CD11b), phagocytosis (CD68), and antigen presentation (MHC-II) were all significantly elevated in response to occlusion. We further identified that these changes co-occurred with a decrease in the numbers of mature neurons within the thalamus. Occluded animals that were also exposed to chronic stress exhibited significantly lower levels of Iba-1 positive cells and a reduced expression of Iba-1 and CD11b compared to the 'occlusion-alone' group. Interestingly, the dampened expression of microglial/monocyte markers observed in stressed animals was associated with significant additional loss of neurons. These findings indicate that the process of STND can be negatively modified, potentially in a microglial dependent manner, by exposure to chronic stress.

Correlation of Asymmetry Indices Measured by Arterial Spin-Labeling MR Imaging and SPECT in Patients with Crossed Cerebellar Diaschisis

BACKGROUND AND PURPOSE

Crossed cerebellar diaschisis, not only a secondary result of supratentorial infarction but also an indicator of clinical outcomes, has frequently been reported on PET and SPECT but has been rarely described with arterial spin-labeling MR imaging. The purpose of this study was to determine the ability of arterial spin-labeling MR imaging to evaluate crossed cerebellar diaschisis compared with that of SPECT. To our knowledge, this is the first study to validate arterial spin-labeling in crossed cerebellar diaschisis by using SPECT as a reference standard.

MATERIALS AND METHODS

This study included 16 patients in whom crossed cerebellar diaschisis was shown on SPECT and 10 control subjects in whom crossed cerebellar diaschisis was not shown on SPECT. During the qualitative analysis, asymmetric cerebellar perfusion on arterial spin-labeling was divided into 1 of the following 3 grades by 2 blinded observers: the affected cerebellum was isointense compared with the unaffected cerebellum (grade I), it was slightly hypointense (grade II), or it was markedly hypointense (grade III). In the quantitative analysis, asymmetry indices were calculated by using SPECT and arterial spin-labeling images. For statistical analysis, κ statistics, the interobserver correlation coefficient, the independent t test, Pearson correlation, and linear regression analysis were used.

RESULTS

Almost all the diagnoses of crossed cerebellar diaschisis on SPECT were noted on arterial spin-labeling in both qualitative and quantitative analyses with good interobserver agreement (κ = 0.961; interobserver correlation coefficient, 0.806). The mean asymmetry index of arterial spin-labeling (26.06 ± 9.00) was significantly larger than that for SPECT (15.28 ± 5.34; P < .001). There was a significant positive correlation between the asymmetry indices obtained for SPECT and those for arterial spin-labeling (r = 0.77 [95% CI, 0.443-0.916]; P < .001). The relationship of asymmetry indices between SPECT and arterial spin-labeling (x, y) was calculated as y = 6.2131 + 1.2986x (R(2) = 0.592; P < .001).

CONCLUSIONS

Arterial spin-labeling can be a noninvasive alternative to SPECT for evaluating crossed cerebellar diaschisis.

Combining diffusion tensor imaging and gray matter volumetry to investigate motor functioning in chronic stroke

Motor impairment after stroke is related to the integrity of the corticospinal tract (CST). However, considerable variability in motor impairment remains unexplained. To increase the accuracy in evaluating long-term motor function after ischemic stroke, we tested the hypothesis that combining diffusion tensor imaging (DTI) and gray matter (GM) volumetry can better characterize long-term motor deficit than either method alone in patients with chronic stroke. We recruited 31 patients whose Medical Research Council strength grade was ≤ 3/5 in the extensor muscles of the affected upper extremity in the acute phase. We used the Upper Extremity Fugl-Meyer (UE-FM) assessment to evaluate motor impairment, and as the primary outcome variable. We computed the fractional anisotropy ratio of the entire CST (CST_ratio) and the volume of interest ratio (VOI_ratio), between ipsilesional and contralesional hemispheres, to explain long-term motor impairment. The results showed that CST_ratio, VOI_ratio of motor-related brain regions, and VOI_ratio in the temporal lobe were correlated with UE-FM. A multiple regression model including CST_ratio and VOI_ratio of the caudate nucleus explained 40.7% of the variability in UE-FM. The adjusted R2 of the regression model with CST_ratio as an independent variable was 29.4%, and that of using VOI_ratio of the caudate nucleus as an independent variable was 23.1%. These results suggest that combining DTI and GM volumetry may achieve better explanation of long-term motor deficit in stroke patients, than using either measure individually. This finding may provide guidance in determining optimal neurorehabilitative interventions.

Motor cortex is required for learning but not for executing a motor skill

Motor cortex is widely believed to underlie the acquisition and execution of motor skills, but its contributions to these processes are not fully understood. One reason is that studies on motor skills often conflate motor cortex's established role in dexterous control with roles in learning and producing task-specific motor sequences. To dissociate these aspects, we developed a motor task for rats that trains spatiotemporally precise movement patterns without requirements for dexterity. Remarkably, motor cortex lesions had no discernible effect on the acquired skills, which were expressed in their distinct pre-lesion forms on the very first day of post-lesion training. Motor cortex lesions prior to training, however, rendered rats unable to acquire the stereotyped motor sequences required for the task. These results suggest a remarkable capacity of subcortical motor circuits to execute learned skills and a previously unappreciated role for motor cortex in "tutoring" these circuits during learning.

Contralesional Thalamic Surface Atrophy and Functional Disconnection 3 Months after Ischemic Stroke

Background: Remote structural and functional changes have been previously described after stroke and may have an impact on clinical outcome. We aimed to use multimodal MRI to investigate contralesional subcortical structural and functional changes 3 months after anterior circulation ischemic stroke. Methods: Fifteen patients with acute ischemic stroke had multimodal MRI imaging (including high resolution structural T1-MPRAGE and resting state fMRI) within 1 week of onset and at 1 and 3 months. Seven healthy controls of similar age group were also imaged at a single time point. Contralesional subcortical structural volume was assessed using an automated segmentation algorithm in FMRIB's Integrated Registration and Segmentation Tool (FIRST). Functional connectivity changes were assessed using the intrinsic connectivity contrast (ICC), which was calculated using the functional connectivity toolbox for correlated and anticorrelated networks (Conn). Results: Contralesional thalamic volume in the stroke patients was significantly reduced at 3 months compared to baseline (median change -2.1%, interquartile range [IQR] -3.4-0.4, p = 0.047), with the predominant areas demonstrating atrophy geometrically appearing to be the superior and inferior surface. The difference in volume between the contralesional thalamus at baseline (mean 6.41 ml, standard deviation [SD] 0.6 ml) and the mean volume of the 2 thalami in controls (mean 7.22 ml, SD 1.1 ml) was not statistically significant. The degree of longitudinal thalamic atrophy in patients was correlated with baseline stroke severity with more severe strokes being associated with a greater degree of atrophy (Spearman's rho -0.54, p = 0.037). There was no significant difference between baseline contralesional thalamic ICC in patients and control thalamic ICC. However, in patients, there was a significant linear reduction in the mean ICC of the contralesional thalamus over the imaging time points (p = 0.041), indicating reduced connectivity to the remainder of the brain. Conclusions: These findings highlight the importance of remote brain areas, such as the contralesional thalamus, in stroke recovery. Similar methods have the potential to be used in the prediction of stroke outcome or as imaging biomarkers of stroke recovery.

Optogenetic mapping after stroke reveals network-wide scaling of functional connections and heterogeneous recovery of the peri-infarct

We used arbitrary point channelrhodopsin-2 (ChR2) stimulation and wide-scale voltage sensitive dye (VSD) imaging in mice to map altered cortical connectivity at 1 and 8 weeks after a targeted cortical stroke. Network analysis based on optogenetic stimulation revealed a symmetrical sham network with distinct sensorimotor and association groupings. This symmetry was disrupted after stroke: at 1 week after stroke, we observed a widespread depression of optogenetically evoked activity that extended to the non-injured hemisphere; by 8 weeks, significant recovery was observed. When we considered the network as a whole, scaling the ChR2-evoked VSD responses from the stroke groups to match the sham group mean resulted in a relative distribution of responses that was indistinguishable from the sham group, suggesting network-wide down-scaling and connectional diaschisis after stroke. Closer inspection revealed that connections that had little connectivity with the peri-infarct, such as contralateral visual areas, tended to escape damage, whereas some connections near the peri-infarct were more severely affected. When connections within the peri-infarct were isolated, we did not observe equal down-scaling of responses after stroke. Peri-infarct sites that had weak connection strength in the sham condition tended to have the greatest relative post-stroke recovery. Our findings suggest that, during recovery, most cortical areas undergo homeostatic upscaling, resulting in a relative distribution of responses that is similar to the pre-stroke (sham) network, albeit still depressed. However, recovery within the peri-infarct zone is heterogeneous and these cortical points do not follow the recovery scaling factor expected for the entire network.

Longitudinal changes in resting-state brain activity in a capsular infarct model

Strokes attributable to subcortical infarcts have been increasing recently in elderly patients. To gain insight how this lesion influences the motor outcome and responds to rehabilitative training, we used circumscribed photothrombotic capsular infarct models on 36 Sprague-Dawley rats (24 experimental and 12 sham-operated). We used 2-deoxy-2-[(18)F]-fluoro-D-glucose-micro positron emission tomography (FDG-microPET) to assess longitudinal changes in resting-state brain activity (rs-BA) and daily single-pellet reaching task (SPRT) trainings to evaluate motor recovery. Longitudinal FDG-microPET results showed that capsular infarct resulted in a persistent decrease in rs-BA in bilateral sensory and auditory cortices, and ipsilesional motor cortex, thalamus, and inferior colliculus (P<0.0025, false discovery rate (FDR) q<0.05). The decreased rs-BA is compatible with diaschisis and contributes to manifest the malfunctions of lesion-specific functional connectivity. In contrast, capsular infarct resulted in increase of rs-BA in the ipsilesional internal capsule, and contralesional red nucleus and ventral hippocampus in recovery group (P<0.0025, FDR q<0.05), implying that remaining subcortical structures have an important role in conducting the recovery process in capsular infarct. The SPRT training facilitated motor recovery only in rats with an incomplete destruction of the posterior limb of the internal capsule (PLIC) (Pearson's correlation, P<0.05). Alternative therapeutic interventions are required to enhance the potential for recovery in capsular infarct with complete destruction of PLIC.

Voluntary Activation is Reduced in Both the More- and Less-Affected Upper Limbs after Unilateral Stroke

Objective: Measurement of voluntary activation gives an indication of neural drive to the muscle. This study aimed to identify the site of impairment in neural drive during voluntary contractions post-stroke.

Methods: Elbow-flexor voluntary activation was assessed bilaterally for 10 stroke patients (mean 61.2 ± 12.3 years) and 6 age-matched controls (61.3 ± 14.0 years) by stimulating either the peripheral nerve or the motor cortex during maximal voluntary contractions. Any additional evoked force during maximal contractions implies neural drive is incomplete. Peripheral stimulation can detect deficits at or above the stimulation level, while cortical stimulation can identify suboptimal supraspinal output.

Results: Impairments were apparent on the less-affected side in addition to the more-affected side after stroke in voluntary activation, torque, and electromyographic activity (EMG) response. Maximal torque was reduced by 44% on the more-affected and 31% on the less-affected side compared to healthy controls (p < 0.001). Peripheral voluntary activation was reduced to 81% on the more-affected side and 86% on the less-affected side, with healthy subjects at 96% (p < 0.05). Although EMG was bilaterally impaired after stroke, the pattern of response was different between sides. Voluntary activation could not be calculated for cortical stimulation post-stroke due to variability in the evoked force, but EMG results from cortical stimulation showed significant differences in the neural drive to each side.

Conclusion: Voluntary activation is impaired bilaterally in the upper-limb after stroke, with reduced cortical connectivity on the more-affected side.

Significance: Although the muscle itself did not change post-stroke, altered descending drive and connectivity were the critical factors explaining post-stroke paresis.

Crossed cerebellar diaschisis detected by arterial spin-labeled perfusion magnetic resonance imaging in subacute ischemic stroke

BACKGROUND

Crossed cerebellar diaschisis (CCD) was a common radiological phenomenon manifested as reduced blood flow and metabolism in the cerebellar hemisphere contralateral to a supratentorial cerebral lesion. The hypoperfusion and hypometabolism in the contralateral cerebellum in CCD was traditionally detected by positron emission tomography (PET) and single-photon emission computed tomography (SPECT). The present prospective study aimed to assess the detection of CCD in subacute stage ischemic stroke by arterial spin-labeling (ASL) perfusion technique with a 3.0-T magnetic resonance imaging (MRI) scanner.

METHODS

ASL images were obtained from 46 patients with supratentorial ischemic stroke at subacute stage. Regional cerebral blood flow values in the cerebellar hemispheres were measured on a region of interest basis.

RESULTS

Twenty-four of 46 (52%) patients showed CCD phenomenon by ASL-MRI method, which was in line with the PET/SPECT series. Infarctions in basal ganglia areas are prone to cause CCD.

CONCLUSIONS

With advantages in easy acquisition and no radiation, ASL-MRI seems to be an ideal tool for the detection and follow-up of CCD.