Human Stroke Patients Research Articles

The Emerging Role of microRNA in Stroke

MicroRNAs (miRNAs) are small non-coding RNAs approximately 22 nucleotides in length that play a pivotal role in post-transcriptional gene regulation by binding to complementary sites in the 3'-untranslated region of messenger RNAs. In the past decade, their role in several human diseases, from cancer to cardiovascular disease, has been established by a wealth of evidence. Stroke is responsible for 10% of deaths worldwide and is one of the leading causes of disability. MiRNAs are involved in stroke risk factors including hypertension, atherosclerosis, atrial fibrillation, diabetes and dyslipidemia. The role of miRNAs in the pathophysiology of stroke has been the subject of more recent investigations. Animal studies, which dominate the field, have demonstrated the differential expression of miRNAs in brain and blood following ischemic or hemorrhagic insult and the potential use of miRNA antagonists to reduce focal cerebral damage. In particular, antagomirs to miR-145, -497, -181a, -1 and let-7f have been found to be neuroprotective in vivo. The discovery of circulating miRNAs in peripheral blood, which are unexpectedly stable, has allowed the recent completion of several studies in human stroke patients that have confirmed the differential expression of specific miRNAs following stroke and have addressed their potential use as diagnostic and prognostic markers. With miRNA research in stroke still in its infancy, it is anticipated that in the next few years significant discoveries that may have important therapeutic implications will emerge.

Opposing roles of PD-1 and PD-L in modulating CNS inflammation and infarct volume following experimental stroke in mice (P1012)

Abstract Stroke severity is worsened by recruitment of inflammatory immune cells into the brain. This process depends in part on T cell activation, in which the B7 family of co-stimulatory molecules plays a pivotal role. Previous studies demonstrated more severe infarcts in mice lacking Programmed Death-1 (PD-1), a member of the B7 family, thus implicating PD-1 as a key factor in limiting stroke severity. The purpose of this study was to determine if this protective effect of PD-1 involves either of its ligands, PD-L1 and PD-L2. Thus, CNS inflammation and stroke severity were evaluated in male PD-L1 and PD-L2 knockout (KO) mice undergoing 60 min middle cerebral artery occlusion (MCAO) followed by 96 h reperfusion. Unexpectedly, PD-L1 KO and to a lesser extent PD-L2 KO mice had reduced levels of activated microglia and infiltrating monocytes and total infarct volume compared to wild-type mice, as well as reduced splenic atrophy and MHC class II expression, suggesting a pathogenic rather than a regulatory role for both PD-ligands. Both positive and negative regulatory roles have been suggested for the PD-ligands in context of various diseases and our novel observations indicate that PD-L1 and PD-L2 might have proinflammatory functions independent of PD-1 binding that worsen stroke outcome. These results suggest the possibility of using antibodies to PD-L1/2 as a potential treatment for human stroke patients.

Early stimulation treatment provides complete sensory‐induced protection from ischemic stroke under isoflurane anesthesia

Using a rodent model of ischemia [permanent middle cerebral artery occlusion (pMCAO)], previous studies demonstrated that whisker stimulation treatment completely protects the cortex from impending stroke when initiated within 2h following pMCAO. When initiated 3h post-pMCAO, the identical treatment exacerbates stroke damage. Rats in these studies, however, were anesthetised with sodium pentobarbital, whereas human stroke patients are typically awake. To overcome this drawback, our laboratory has begun to use the anesthetic isoflurane, which allows rats to rapidly recover from pMCAO within minutes, to test stimulation treatment in awake rats and to determine whether isoflurane has an effect upon the pMCAO stroke model. We found no difference in infarct volume between pMCAO in untreated controls under either sodium pentobarbital or isoflurane, and the primary finding was that rats that received treatment immediately post-pMCAO maintain cortical function and no stroke damage, whereas rats that received treatment 3h post-pMCAO exhibited eliminated cortical activity and extensive stroke damage. The only difference between anesthetics was the broad extent of evoked cortical activity observed during both functional imaging and electrophysiological recording, suggesting that the extent of evoked activity evident under isoflurane anesthesia is supported by underlying neuronal activity. Given the high degree of similarity with previous data, we conclude that the pMCAO stroke model is upheld with the use of isoflurane. This study demonstrated that the isoflurane-anesthetised rat pMCAO model can be used for cerebrovascular studies, and allows for highly detailed investigation of potential novel treatments for ischemic stroke using awake, behaving animals.

Inhibition of a SNARE-Sensitive Pathway in Astrocytes Attenuates Damage following Stroke

A strong body of research has defined the role of excitotoxic glutamate in animal models of brain ischemia and stroke; however, clinical trials of glutamate receptor antagonists have demonstrated their limited capacity to prevent brain damage following ischemia. We propose that astrocyte-neuron signaling represents an important modulatory target that may be useful in mediating damage following stroke. To assess the impact of astrocyte signaling on damage following stroke, we have used the astrocyte-specific dominant-negative SNARE mouse model (dnSNARE). Recent findings have shown that the astrocytic SNARE signaling pathway can affect neuronal excitability by regulating the surface expression of NMDA receptors. Using focal photothrombosis via the Rose Bengal method, as well as excitotoxic NMDA lesions, we show that dnSNARE animals exhibited a sparing of damaged tissue quantified using Nissl and NeuN staining. At the same time point, animals were also tested in behavioral tasks that probe the functional integrity of stroke- or lesion-damaged motor and somatosensory areas. We found that dnSNARE mice performed significantly better than littermate controls on rung walk and adhesive dot removal tasks following lesion. Together, our results demonstrate the important role of astrocytic signaling under ischemic conditions. Drugs targeting astrocyte signaling have a potential benefit for the outcome of stroke in human patients by limiting the spread of damage.

Abstract TMP22: Intravenous Glyburide Treatment is Associated with Reduced Matrix Metalloproteinase-9 in Human Acute Stroke

Background: Elevated matrix metalloproteinase-9 (MMP-9) following acute ischemic stroke is associated with blood-brain barrier breakdown and hemorrhagic conversion. Prior retrospective evidence suggests that sulfonylurea use may be associated with reduced risk of hemorrhagic conversion. We hypothesized that sulfonylureas may reduce MMP-9 level in stroke patients. Methods: Using serial plasma samples from six subjects in the Glyburide Advantage in Malignant Edema and Stroke Pilot trial (GAMES-Pilot), we evaluated the level of MMP-9 in human subjects presenting with large hemispheric stroke who were treated with intravenous glyburide (RP-1127). MMP-9 was measured in a control cohort with large ischemic stroke who were not treated with glyburide. Commercially available ELISA kits and gel zymography were used to measure MMP-9 at baseline and at approximately 48 hours after stroke. GAMES subjects had additional time points analyzed until approximately 84 hours after stroke. Results: Average MMP-9 level in glyburide-treated stroke patients was 47.2 ± 8.0 ng/mL compared to 143.4 ± 60.35 ng/mL in untreated control subjects (p=0.004). Zymography analysis demonstrated a significant decrease in the pro-enzyme but no change in the active form of MMP-9. There was no difference in the level of the MMP-9 specific inhibitor, TIMP-1. No subjects exhibited parenchymal hemorrhagic conversion on 24 hour head CT scan. Conclusions: Glyburide treatment in human stroke patients with large hemispheric stroke is associated reduced level of MMP-9. Elucidating the underlying mechanism of glyburide’s effect on MMP-9 and the risk of hemorrhagic conversion may highlight future directions of therapy, including in combination with intravenous tissue plasminogen activator (IV t-PA).

Assessing Post-Stroke Behavior in Mouse Models of Focal Ischemia

Experimental treatment strategies and neuroprotective drugs that showed therapeutic promise in animal models of stroke have failed to produce beneficial effects in human stroke patients. The difficulty in translating preclinical findings to humans represents a major challenge in cerebrovascular research. The reasons behind this translational road block might be explained by a number of factors, including poor quality control in various stages of the research process, the validity of experimental stroke models, and differences in drug administration and pharmacokinetics. Another major difference between animal studies and clinical trials is the choice of end point or outcome measures. Here, we discuss the necessity of poststroke behavioral testing to bridge the gap between clinical and experimental end points. We review established sensory-motor tests for outcome determination after focal ischemia based on the published literature as well as our own personal experience. Selected tests are described in more detail and good laboratory practice standards for behavioral testing are discussed. This review is intended for stroke researchers planning to use behavioral testing in mice.

Inhibition of 12/15‐lipoxygenase as therapeutic strategy to treat stroke

Targeting newly identified damage pathways in the ischemic brain can help to circumvent the currently severe limitations of acute stroke therapy. Here we show that the activity of 12/15-lipoxygenase was increased in the ischemic mouse brain, and 12/15-lipoxygenase colocalized with a marker for oxidized lipids, MDA2. This colocalization was also detected in the brain of 2 human stroke patients, where it also coincided with increased apoptosis-inducing factor. A novel inhibitor of 12/15-lipoxygenase, LOXBlock-1, protected neuronal HT22 cells against oxidative stress. In a mouse model of transient focal ischemia, the inhibitor reduced infarct sizes both 24 hours and 14 days poststroke, with improved behavioral parameters. Even when treatment was delayed until at least 4 hours after onset of ischemia, LOXBlock-1 was protective. Furthermore, it reduced tissue plasminogen activator-associated hemorrhage in a clot model of ischemia/reperfusion. This study establishes inhibition of 12/15-lipoxygenase as a viable strategy for first-line stroke treatment.

Multi-Session Transcranial Direct Current Stimulation (tDCS) Elicits Inflammatory and Regenerative Processes in the Rat Brain

Transcranial direct current stimulation (tDCS) is increasingly being used in human studies as an adjuvant tool to promote recovery of function after stroke. However, its neurobiological effects are still largely unknown. Electric fields are known to influence the migration of various cell types in vitro, but effects in vivo remain to be shown. Hypothesizing that tDCS might elicit the recruitment of cells to the cortex, we here studied the effects of tDCS in the rat brain in vivo. Adult Wistar rats (n = 16) were randomized to either anodal or cathodal stimulation for either 5 or 10 consecutive days (500 µA, 15 min). Bromodeoxyuridine (BrdU) was given systemically to label dividing cells throughout the experiment. Immunohistochemical analyses ex vivo included stainings for activated microglia and endogenous neural stem cells (NSC). Multi-session tDCS with the chosen parameters did not cause a cortical lesion. An innate immune response with early upregulation of Iba1-positive activated microglia occurred after both cathodal and anodal tDCS. The involvement of adaptive immunity as assessed by ICAM1-immunoreactivity was less pronounced. Most interestingly, only cathodal tDCS increased the number of endogenous NSC in the stimulated cortex. After 10 days of cathodal stimulation, proliferating NSC increased by ∼60%, with a significant effect of both polarity and number of tDCS sessions on the recruitment of NSC. We demonstrate a pro-inflammatory effect of both cathodal and anodal tDCS, and a polarity-specific migratory effect on endogenous NSC in vivo. Our data suggest that tDCS in human stroke patients might also elicit NSC activation and modulate neuroinflammation.

Changes in Spontaneous Activity Assessed by Accelerometry Correlate with Extent of Cerebral Ischemia-Reperfusion Injury in the Nonhuman Primate

The use of accelerometry to monitor activity in human stroke patients has revealed strong correlations between objective activity measurements and subjective neurological findings. The goal of our study was to assess the applicability of accelerometry-based measurements in experimental animals undergoing surgically-induced cerebral ischemia. Using a nonhuman primate cortical stroke model, we demonstrate for the first time that monitoring locomotor activity prior to and following cerebrovascular ischemic injury using an accelerometer is feasible in adult male rhesus macaques and that the measured activity outcomes significantly correlate with severity of brain injury. The use of accelerometry as an unobtrusive, objective preclinical efficacy determinant could complement standard practices involving subjective neurological scoring and magnetic resonance imaging in nonhuman primates. Similar activity monitoring devices to those employed in this study are currently in use in human clinical studies, underscoring the feasibility of this approach for assessing the clinical potential of novel treatments for cerebral ischemia.

Application of Mild Therapeutic Hypothermia on Stroke: A Meta-Analysis (P04.055)

Objective: This meta-analysis aims to summarize the available clinical studies on the relation between low body temperature (hypothermia) and post-stroke symptomatology. We aim to collect solid evidence to define whether induced hypothermia is a useful and safe procedure providing long-term benefits to acute stroke patients. Background Stroke occurs due to interruption in cerebral blood supply affecting neuronal function, and a high mortality risk is observed in the stroke aftermath. Body temperature on hospital admission is an important predictor of clinical outcome. Fever in the early aftermath of symptom onset predicts worse clinical outcome. Therapeutic hypothermia is promising in clinical settings and may be applied with external or endovascular methods. Side-effects include shivering, coagulopathy, and pneumonia. Design/Methods: MEDLINE/PubMed, CENTRAL, Stroke Center, and ClinicalTrials.gov were systematically searched. Articles written in English on human stroke patients with hypothermia used as intervention were identified. Papers with no data reported, multiple treatments, incompatible outcome measurement, poorly defined stroke criteria, case reports, review papers and meta-analyses were excluded. Observational studies, self-controlled and randomized trials were included. Hypothermia was induced by external or endovascular cooling. NIH Stroke Scale (NIHSS) and modified Rankin Scale (mRS) were the main stroke scales used, and mortality was also reported. Results: Seven parallel-controlled clinical trials were included in the meta-analysis. Sample sizes ranged from 18 to 62 patients, yielding a total of 288. Target temperature (∼33oC) was reached within 3-4 hours. Stroke severity (Cohen9s d = -0.17, 95% CI: -0.42 to 0.08, p=0.32; I2 =73%; Chi2=21.89, p=0.0001) and mortality (RR = 1.60, 95% CI: 0.93 to 2.78, p=0.11; I2 = 0%; Chi2=2.88, p=0.72) were not significantly affected by hypothermia. Conclusions: Hypothermia does not significantly improve stroke severity; however, this finding should be taken with caution due to the high heterogeneity of included studies. No impact on mortality was observed. Supported by: Global Neuroscience Initiative Foundation (GNIF), Los Angeles, CA. Disclosure: Dr. Lakhan has nothing to disclose.

Repetitive Transcranial Magnetic Stimulation (rTMS) in the rehabilitation of visuo-spatial neglect in human stroke patients: Details from an ongoing multicentric double blind clinical trial

Repetitive Transcranial Magnetic Stimulation (rTMS) in the rehabilitation of visuo-spatial neglect in human stroke patients: Details from an ongoing multicentric double blind clinical trial

Functional recovery following motor cortex lesions in non-human primates: experimental implications for human stroke patients.

This review discusses selected classical works and contemporary research on recovery of contralesional fine hand motor function following lesions to motor areas of the cerebral cortex in non-human primates. Findings from both the classical literature and contemporary studies show that lesions of cortical motor areas induce paresis initially, but are followed by remarkable recovery of fine hand/digit motor function that depends on lesion size and post-lesion training. Indeed, in recent work where considerable quantification of fine digit function associated with grasping and manipulating small objects has been observed, very favorable recovery is possible with minimal forced use of the contralesional limb. Studies of the mechanisms underlying recovery have shown that following small lesions of the digit areas of primary motor cortex (M1), there is expansion of the digit motor representations into areas of M1 that did not produce digit movements prior to the lesion. However, after larger lesions involving the elbow, wrist and digit areas of M1, no such expansion of the motor representation was observed, suggesting that recovery was due to other cortical or subcortical areas taking over control of hand/digit movements. Recently, we showed that one possible mechanism of recovery after lesion to the arm areas of M1 and lateral premotor cortex is enhancement of corticospinal projections from the medially located supplementary motor area (M2) to spinal cord laminae containing neurons which have lost substantial input from the lateral motor areas and play a critical role in reaching and digit movements. Because human stroke and brain injury patients show variable, and usually poorer, recovery of hand motor function than that of nonhuman primates after motor cortex damage, we conclude with a discussion of implications of this work for further experimentation to improve recovery of hand function in human stroke patients.

Systemic augmentation of αB-crystallin provides therapeutic benefit twelve hours post-stroke onset via immune modulation

Tissue plasminogen activator is the only treatment option for stroke victims; however, it has to be administered within 4.5 h after symptom onset, making its use very limited. This report describes a unique target for effective treatment of stroke, even 12 h after onset, by the administration of αB-crystallin (Cryab), an endogenous immunomodulatory neuroprotectant. In Cryab(-/-) mice, there was increased lesion size and diminished neurologic function after stroke compared with wild-type mice. Increased plasma Cryab was detected after experimental stroke in mice and after stroke in human patients. Administration of Cryab even 12 h after experimental stroke reduced both stroke volume and inflammatory cytokines associated with stroke pathology. Cryab is an endogenous anti-inflammatory and neuroprotectant molecule produced after stroke, whose beneficial properties can be augmented when administered therapeutically after stroke.

Potential for Transcranial Laser or LED Therapy to Treat Stroke, Traumatic Brain Injury, and Neurodegenerative Disease

Near-infrared (NIR) light passes readily through the scalp and skull and a small percentage of incident power density can arrive at the cortical surface in humans.1 The primary photoreceptors for red and NIR light are mitochondria, and cortical neurons are exceptionally rich in mitochondria. It is likely that brain cells are ideally set up to respond to light therapy. The basic biochemical pathways activated by NIR light, e.g., increased adenosine-5′-triphosphate (ATP) production, and signaling pathways activated by reactive oxygen species, nitric oxide release, and increased cyclic adenosine monophosphate (AMP) all work together to produce beneficial effects in brains whose function has been compromised by ischemia, traumatic injury, or neurodegeneration. One of the main mechanisms of action of transcranial light therapy (TLT) is to prevent neurons from dying, when they have been subjected to some sort of hypoxic, traumatic, or toxic insult. This is probably because of light-mediated upregulation of cytoprotective gene products such as anti-oxidant enzymes, heat shock proteins, and anti-apoptotic proteins. Light therapy in vitro has been shown to protect neurons from death caused by methanol,2 cyanide or tetrodotoxin,3 and amyloid beta peptide.4 There is also probably a second mechanism operating in TLT; increased neurogenesis. Neurogenesis is the generation of neuronal precursors and birth of new neural cells.5 Two key sites for adult neurogenesis include the subventricular zone (SVZ) of the lateral ventricles, and the subgranular layer (SGL) of the dentate gyrus in the hippocampus.6 Neurogenesis can be stimulated by physiological factors, such as growth factors and environmental enrichment, and by pathological processes, including ischemia and neurodegeneration.7 Adult neurogenesis (in the hippocampus particularly) is now recognized as a major determinant of brain function both in experimental animals and in humans. Neural progenitor cells in their niche in the SGL of the dentate gyrus give birth to newly formed neurons that are thought to play a role in brain function, particularly in olfaction and in hippocampal-dependent learning and memory.8 In small animal models neurogenesis can be readily detected by incorporation of bromodeoxyuridine (BrdU), injected before euthanasia, into proliferating brain cells. Increased neurogenesis after TLT, has been demonstrated in a rat model of stroke,9 and in the Hamblin laboratory after TLT for acute traumatic brain injury (TBI) in mice (W. Xuan, T. Ando, et al., unpublished data). These two mechanisms of action of TLT in ameliorating brain damage (prevention of neuronal death and increased neurogenesis) have motivated studies in both animals and humans for diverse brain disorders and diseases. TLT for acute stroke is the most developed,10 but acute TBI has also been shown to benefit from TLT.11 These areas are reviewed further.

Identification of oxidized serum albumin in the cerebrospinal fluid of ischaemic stroke patients

Extensive evidence has shown that oxidative stress mediates neuronal death in animal models of hypoxic-ischaemia. Brain biomarkers of oxidative stress need to be identified in order to better understand and treat brain damage in human stroke patients. The present study was conducted to identify potential target proteins of oxidative stress in the cerebrospinal fluid (CSF) of stroke patients with acute ischaemic brain injury. We performed two-dimensional polyacrylamide gel electrophoresis to separate protein samples obtained from the CSF of control and stroke patients. To determine protein oxidation levels, oxyblot was then used to detect protein carbonyls that were determined by formation of a stable 2,4-dinitrophenylhydrazine (DNP) product using an anti-DNP antibody. We found that oxidation of serum albumin was increased in the CSF from stroke patients as well as rats who underwent permanent middle cerebral artery occlusion (6.5%, 23%, respectively). In stroke patients, oxidized albumin levels correlated to neurologic indications. The present study suggests that oxidized albumin in CSF can be utilized as an oxidative stress marker in human stroke patients.

Hypoxia induces T Helper 17 cell upregulation in cultured peripheral blood mononuclear cells from chronic stage patients of severe cerebral infarction

Studies have shown the IL-17A involvement in human ischemic stroke patients in vivo. Whether the IL-17A expression was originated from Th17 and could be stimulated by hypoxia remained unknown. Here we report the Th17 upregulation in anaerobic cultured PBMC from chronic stage patients of severe cerebral infarction. By using ELISA and FACS we examined IL-1β, IFN-γ, IL-23 and IL-17A protein levels in the supernatants and Th1/Th17 ratios in PBMC. Statistical significance of Th17 but not Th1 upregulation was proved in 6-hr anaerobic cultured patient groups (P < 0.001). Hence, Th17 might be essential in the autoimmune pathogenesis when hypoxia recurs in severe ischemic stroke patients.

Proteomic Temporal Profile of Human Brain Endothelium After Oxidative Stress

because brain endothelial cells exist at the neurovascular interface, they may serve as cellular reporters of brain dysfunction by releasing biomarkers into the circulation. we used proteomic techniques to screen conditioned media from human brain endothelial cultures subjected to oxidative stress induced by nitric oxide over 24 hours. Plasma samples from human stroke patients were analyzed by enzyme-linked immunosorbent assay. in healthy endothelial cells, interaction mapping demonstrated cross-talk involving secreted factors, membrane receptors, and matrix components. In oxidatively challenged endothelial cells, networks of interacting proteins failed to emerge. Instead, inflammatory markers increased, secreted factors oscillated over time, and endothelial injury repair was manifested as changes in factors related to matrix integrity. Elevated inflammatory markers included heat shock protein, chemokine ligand-1, serum amyloid-A1, annexin-A5, and thrombospondin-1. Neurotrophic factors (prosaposin, nucleobindin-1, and tachykinin precursors) peaked at 12 hours, then rapidly decreased by 24 hours. Basement membrane components (fibronectin, desomoglein, profiling-1) were decreased. Cytoskeletal markers (actin, vimentin, nidogen, and filamin B) increased over time. From this initial analysis, the high-ranking candidate thrombospondin-1 was further explored in human plasma. Acute ischemic stroke patients had significantly higher thrombospondin-1 levels within 8 hours of symptom onset compared to controls with similar clinical risk factors (659 ± 81 vs 1132 ± 98 ng/mL; P<0.05; n=20). screening of simplified cell culture systems may aid the discovery of novel biomarkers in clinical neurovascular injury. Further collaborative efforts are warranted to discover and validate more candidates of interest.

In vivo imaging of autophagy in a mouse stroke model

Recent studies have suggested that autophagy is involved in a neural death pathway following cerebral ischemia. In vivo detection of autophagy could be important for evaluating ischemic neural cell damage for human stroke patients. Using novel green fluorescent protein (GFP)-fused microtubule-associated protein 1 light chain 3 (LC3) transgenic (Tg) mice, in vivo imaging of autophagy was performed at 1, 3 and 6 d after 60 min transient middle cerebral artery occlusion (tMCAO). Ex vivo imaging of autophagy, testing of the autophagy inhibitor 3-methyladenine (3-MA), estern blot analysis, immunohistochemistry, terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) and fluorescent analyses were performed on brain sections following tMCAO. In vivo fluorescent signals were detected above the ischemic hemisphere through the skull bone at 1, 3 and 6 d after tMCAO, with a peak at 1 d. Similar results were obtained with ex vivo fluorescence imaging. western blot analysis revealed maximum LC3-I and LC3-II expression at 1 d after tMCAO and fluorescence immunohistochemistry demonstrated that GFP-LC3-positive cells were primarily neuronal, not astroglial or microglial, cells. The number of GFP-LC3/TUNEL double-positive cells was greater in the periischemic area than in the core. These results provided evidence of in vivo autophagy detection, with a peak at 1 d, in a live animal model following cerebral ischemia. This novel technique could be valuable for monitoring autophagic processes in vivo in live stroke patients, as well as for clarifying the detailed role of autophagy in the ischemic brain, as well as in other neurological diseases.

The Dorsal Attention Network Mediates Orienting toward Behaviorally Relevant Stimuli in Spatial Neglect

Experimental neurophysiology and functional neuroimaging have identified a dorsal attention network that encodes neural signals related to the behavioral significance of a stimulus. The core anatomical areas of this network are the frontal eye fields and the posterior parietal cortex, which are interconnected by the superior longitudinal fasciculus. Here, we show that damage or disconnection of this network predicts the extent to which task-relevant stimuli capture attention of human stroke patients with spatial neglect. Healthy volunteers, right-hemisphere-damaged control participants, and patients with left neglect reacted to peripheral targets defined by their color, which were preceded by a brief distracter stimulus. The position of the distracter and its relevance for the current trial were independently varied. In neglect patients with damage including the frontal eye fields and the superior longitudinal fasciculus, ipsilesional distracters impaired orienting into contralesional space regardless of their relevance for the current task. In contrast, patients with sparing of these regions were only impaired when distracters were task-relevant. These findings indicate that the dorsal attention network controls spatial orienting by modulating the saliency of distracter stimuli according to current action goals.

The Role of Contralesional Dorsal Premotor Cortex after Stroke as Studied with Concurrent TMS-fMRI

Contralesional dorsal premotor cortex (cPMd) may support residual motor function following stroke. We performed two complementary experiments to explore how cPMd might perform this role in a group of chronic human stroke patients. First, we used paired-coil transcranial magnetic stimulation (TMS) to establish the physiological influence of cPMd on ipsilesional primary motor cortex (iM1) at rest. We found that this influence became less inhibitory/more facilitatory in patients with greater clinical impairment. Second, we applied TMS over cPMd during functional magnetic resonance imaging (fMRI) in these patients to examine the causal influence of cPMd TMS on the whole network of surviving cortical motor areas in either hemisphere and whether these influences changed during affected hand movement. We confirmed that hand grip-related activation in cPMd was greater in more impaired patients. Furthermore, the peak ipsilesional sensorimotor cortex activity shifted posteriorly in more impaired patients. Critical new findings were that concurrent TMS-fMRI results correlated with the level of both clinical impairment and neurophysiological impairment (i.e., less inhibitory/more facilitatory cPMd-iM1 measure at rest as assessed with paired-coil TMS). Specifically, greater clinical and neurophysiological impairment was associated with a stronger facilitatory influence of cPMd TMS on blood oxygenation level-dependent signal in posterior parts of ipsilesional sensorimotor cortex during hand grip, corresponding to the posteriorly shifted sensorimotor activity seen in more impaired patients. cPMd TMS was not found to influence activity in other brain regions in either hemisphere. This state-dependent influence on ipsilesional sensorimotor regions may provide a mechanism by which cPMd supports recovered function after stroke.