Neuronal deactivation explains decreased cerebellar blood flow in response to focal cerebral ischemia or suppressed neocortical function

Neuroscience of coma

Coma and disorders of consciousness are frequently considered in terms of two linked anatomic-functional systems: the arousal system and the awareness system. The mesopontine tegmentum (namely the cuneiform/subcuneiform nuclei of the caudal midbrain and the pontis oralis nucleus of the rostral pons) and the monoamine nuclei generate signals of arousal. These signals are augmented in lateral hypothalamus and basal forebrain, which then project to the thalamus and diffusely across the cortex. The medial dorsal tegmental tract is the main conduit for the ascending arousal system to directly activate the thalamic intralaminar nuclei and modulate thalamocortical networks, while the lateral dorsal tegmental tract connects to the thalamic reticular nucleus for regulation of intrathalamic inhibitory networks. The central thalamus (particularly the intralaminar nuclei) and the mesocircuit regulate the arousal system. Lesions to any part of this system, particularly paramedian and bilateral lesions, result in a depressed level of arousal. Distinct from the arousal pathways, the awareness system runs continuously as a stream of consciousness. It consists of large-scale distributed cortical networks that are necessary for representations of the external (executive control network with the dorsal/ventral attention networks) and the internal world (executive control network in conjunction with the default network). A feature of the awareness system is that it does not capture external and internal worlds at once and instead, holds singular representations, serially moment-by-moment. The medial dorsal nucleus of the thalamus serves as the associative nuclei of the default network, and the thalamic reticular nucleus regulates the awareness system. Lesions that disrupt large-scale networks, particularly nodes of cortical hubs, result in lack of awareness. Integrative paradigms such as the integrated information theory and the global neuronal workspace models are attempts to bind awareness and arousal into a unified experience of consciousness.

Cardiac arrest and disorders of consciousness

As the second most common cause of coma and disorders of consciousness, cardiac arrest is defined as a cessation of cardiac mechanical activity and absence of circulation. Cardiac arrest can happen due to an intrinsic cardiac condition or secondary to noncardiac causes such as respiratory, neurologic, metabolic causes or external causes such as toxic ingestion, asphyxia, drowning, trauma, and other environmental exposures. While cardiac arrest resuscitation research and practice has evolved over decades, the overall survival to hospital discharge remains low across different types of cardiac arrest (about 9%-29%). This chapter focuses on disorders of consciousness after cardiac arrest and how it is different from other etiologies. It also discusses advances and controversies in diagnosis, management, prognostication and research.

Detecting awareness after acute brain injury

Advances over the past two decades in functional neuroimaging have provided new diagnostic and prognostic tools for patients with severe brain injury. Some of the most pertinent developments in this area involve the assessment of residual brain function in patients in the intensive care unit during the acute phase of severe injury, when they are at their most vulnerable and prognosis is uncertain. Advanced neuroimaging techniques, such as functional MRI and EEG, have now been used to identify preserved cognitive processing, including covert conscious awareness, and to relate them to outcome in patients who are behaviourally unresponsive. Yet, technical and logistical challenges to clinical integration of these advanced neuroimaging techniques remain, such as the need for specialised expertise to acquire, analyse, and interpret data and to determine the appropriate timing for such assessments. Once these barriers are overcome, advanced functional neuroimaging technologies could improve diagnosis and prognosis for millions of patients worldwide.

Modulation of brain activity in brain-injured patients with a disorder of consciousness in intensive care with repeated 10-Hz transcranial alternating current stimulation (tACS): a randomised controlled trial protocol

INTRODUCTION

Therapeutic interventions for disorders of consciousness lack consistency; evidence supports non-invasive brain stimulation, but few studies assess neuromodulation in acute-to-subacute brain-injured patients. This study aims to validate the feasibility and assess the effect of a multi-session transcranial alternating current stimulation (tACS) intervention in subacute brain-injured patients on recovery of consciousness, related brain oscillations and brain network dynamics.

METHODS AND ANALYSES

The study is comprised of two phases: a validation phase (n=12) and a randomised controlled trial (n=138). Both phases will be conducted in medically stable brain-injured adult patients (traumatic brain injury and hypoxic-ischaemic encephalopathy), with a Glasgow Coma Scale score ≤12 after continuous sedation withdrawal. Recruitment will occur at the intensive care unit of a Level 1 Trauma Centre in Montreal, Quebec, Canada. The intervention includes a 20 min 10 Hz tACS at 1 mA intensity or a sham session over parieto-occipital cortical sites, repeated over five consecutive days. The current's frequency targets alpha brain oscillations (8-13 Hz), known to be associated with consciousness. Resting-state electroencephalogram (EEG) will be recorded four times daily for five consecutive days: pre and post-intervention, at 60 and 120 min post-tACS. Two additional recordings will be included: 24 hours and 1-week post-protocol. Multimodal measures (blood samples, pupillometry, behavioural consciousness assessments (Coma Recovery Scale-revised), actigraphy measures) will be acquired from baseline up to 1 week after the stimulation. EEG signal analysis will focus on the alpha bandwidth (8-13 Hz) using spectral and functional network analyses. Phone assessments at 3, 6 and 12 months post-tACS, will measure long-term functional recovery, quality of life and caregivers' burden.

ETHICS AND DISSEMINATION

Ethical approval for this study has been granted by the Research Ethics Board of the CIUSSS du Nord-de-l'Île-de-Montréal (Project ID 2021-2279). The findings of this two-phase study will be submitted for publication in a peer-reviewed academic journal and submitted for presentation at conferences. The trial's results will be published on a public trial registry database (ClinicalTrials.gov).

TRIAL REGISTRATION NUMBER

NCT05833568.

Out of the core: the impact of focal ischemia in regions beyond the penumbra

The changes in the necrotic core and the penumbra following induction of focal ischemia have been the focus of attention for some time. However, evidence shows, that ischemic injury is not confined to the primarily affected structures and may influence the remote areas as well. Yet many studies fail to probe into the structures beyond the penumbra, and possibly do not even find any significant results due to their short-term design, as secondary damage occurs later. This slower reaction can be perceived as a therapeutic opportunity, in contrast to the ischemic core defined as irreversibly damaged tissue, where the window for salvation is comparatively short. The pathologies in remote structures occur relatively frequently and are clearly linked to the post-stroke neurological outcome. In order to develop efficient therapies, a deeper understanding of what exactly happens in the exo-focal regions is necessary. The mechanisms of glia contribution to the ischemic damage in core/penumbra are relatively well described and include impaired ion homeostasis, excessive cell swelling, glutamate excitotoxic mechanism, release of pro-inflammatory cytokines and phagocytosis or damage propagation via astrocytic syncytia. However, little is known about glia involvement in post-ischemic processes in remote areas. In this literature review, we discuss the definitions of the terms "ischemic core", "penumbra" and "remote areas." Furthermore, we present evidence showing the array of structural and functional changes in the more remote regions from the primary site of focal ischemia, with a special focus on glia and the extracellular matrix. The collected information is compared with the processes commonly occurring in the ischemic core or in the penumbra. Moreover, the possible causes of this phenomenon and the approaches for investigation are described, and finally, we evaluate the efficacy of therapies, which have been studied for their anti-ischemic effect in remote areas in recent years.

Resting-state functional connectivity in a non-human primate model of cortical ischemic stroke in area F1

BACKGROUND

The application of functional MRI to non-human primates after stroke has not yet been undertaken. This is the first study to explore the functional connectivity changes in non-human primate models during acute stages after stroke onset.

METHODS

Nineteen healthy male cynomolgus monkeys (4-5 years) were used in this study. The photothrombosis model was employed to induce focal ischemic stroke in F1 area in the monkey's left hemisphere. T1-weighted structural images and resting-state functional magnetic resonance imaging (rs-fMRI) of all subjects were obtained using a 3.0 Tesla MRI system on the third day following stroke. Based on the D99 atlas, the structural and functional changes of bilateral F1 areas in monkeys were analyzed using region of interest (ROI)-based functional connectivity (FC). The bilateral F1 areas were selected as the seed regions due to their crucial role in motor control and their potential to unveil the comprehensive functional reorganization of the motor system at a whole-brain level following stroke.

RESULTS

Ischemic lesions were observed after the stroke, with larger lesion volumes associated with poorer neurological dysfunction. Compared with baseline condition, left area F1 demonstrated decreased FC with the left cerebellum, left ventral pons and left 5_(PEa). When the ROI was located in the right area F1, ischemic monkeys showed decreased FC in left ventral pons, left cerebellum, left primary visual cortex and left 5_(PEa), accompanied by increased FC in the right orbitofrontal cortex. Importantly, the degree of altered FC between left area F1 and left cerebellum was associated with upper limb tone.

CONCLUSIONS

These results provide valuable insights into the early-stage functional connectivity changes in the F1 areas of monkeys under ischemic conditions, highlighting the potential involvement of specific brain regions in the pathophysiology of ischemic injury.

Injury patterns associated with cognitive motor dissociation

In unconscious appearing patients with acute brain injury, wilful brain activation to motor commands without behavioural signs of command following, known as cognitive motor dissociation (CMD), is associated with functional recovery. CMD can be detected by applying machine learning to EEG recorded during motor command presentation in behaviourally unresponsive patients. Identifying patients with CMD carries clinical implications for patient interactions, communication with families, and guidance of therapeutic decisions but underlying mechanisms of CMD remain unknown. By analysing structural lesion patterns and network level dysfunction we tested the hypothesis that, in cases with preserved arousal and command comprehension, a failure to integrate comprehended motor commands with motor outputs underlies CMD. Manual segmentation of T2-fluid attenuated inversion recovery and diffusion weighted imaging sequences quantifying structural injury was performed in consecutive unresponsive patients with acute brain injury (n = 107) who underwent EEG-based CMD assessments and MRI. Lesion pattern analysis was applied to identify lesion patterns common among patients with (n = 21) and without CMD (n = 86). Thalamocortical and cortico-cortical network connectivity were assessed applying ABCD classification of power spectral density plots and weighted pairwise phase consistency (WPPC) to resting EEG, respectively. Two distinct structural lesion patterns were identified on MRI for CMD and three for non-CMD patients. In non-CMD patients, injury to brainstem arousal pathways including the midbrain were seen, while no CMD patients had midbrain lesions. A group of non-CMD patients was identified with injury to the left thalamus, implicating possible language comprehension difficulties. Shared lesion patterns of globus pallidus and putamen were seen for a group of CMD patients, which have been implicated as part of the anterior forebrain mesocircuit in patients with reversible disorders of consciousness. Thalamocortical network dysfunction was less common in CMD patients [ABCD-index 2.3 (interquartile range, IQR 2.1-3.0) versus 1.4 (IQR 1.0-2.0), P < 0.0001; presence of D 36% versus 3%, P = 0.0006], but WPPC was not different. Bilateral cortical lesions were seen in patients with and without CMD. Thalamocortical disruption did not differ for those with CMD, but long-range WPPC was decreased in 1-4 Hz [odds ratio (OR) 0.8; 95% confidence interval (CI) 0.7-0.9] and increased in 14-30 Hz frequency ranges (OR 1.2; 95% CI 1.0-1.5). These structural and functional data implicate a failure of motor command integration at the anterior forebrain mesocircuit level with preserved thalamocortical network function for CMD patients with subcortical lesions. Amongst patients with bilateral cortical lesions preserved cortico-cortical network function is associated with CMD detection. These data may allow screening for CMD based on widely available structural MRI and resting EEG.

Disability and persistent motor deficits are linked to structural crossed cerebellar diaschisis in chronic stroke

Brain imaging has significantly contributed to our understanding of the cerebellum being involved in recovery after non-cerebellar stroke. Due to its connections with supratentorial brain networks, acute stroke can alter the function and structure of the contralesional cerebellum, known as crossed cerebellar diaschisis (CCD). Data on the spatially precise distribution of structural CCD and their implications for persistent deficits after stroke are notably limited. In this cross-sectional study, structural MRI and clinical data were analyzed from 32 chronic stroke patients, at least 6 months after the event. We quantified lobule-specific contralesional atrophy, as a surrogate of structural CCD, in patients and healthy controls. Volumetric data were integrated with clinical scores of disability and motor deficits. Diaschisis-outcome models were adjusted for the covariables age, lesion volume, and damage to the corticospinal tract. We found that structural CCD was evident for the whole cerebellum, and particularly for lobules V and VI. Lobule VI diaschisis was significantly correlated with clinical scores, that is, volume reductions in contralesional lobule VI were associated with higher levels of disability and motor deficits. Lobule V and the whole cerebellum did not show similar diaschisis-outcome relationships across the spectrum of the clinical scores. These results provide novel insights into stroke-related cerebellar plasticity and might thereby promote lobule VI as a key area prone to structural CCD and potentially involved in recovery and residual motor functioning.

A protocol for a multicenter randomized and personalized controlled trial using rTMS in patients with disorders of consciousness

Background

Improving the functional recovery of patients with DoC remains one of the greatest challenges of the field. Different theories exist about the role of the anterior (prefrontal areas) versus posterior (parietal areas) parts of the brain as hotspots for the recovery of consciousness. Repetitive transcranial magnetic stimulation (rTMS) is a powerful non-invasive brain stimulation technique for the treatment of DoC. However, a direct comparison of the effect of TMS treatment on the front versus the back of the brain has yet to be performed. In this study, we aim to assess the short- and long-term effects of frontal and parietal rTMS on DoC recovery and characterize responders phenotypically.

Methods/design

Ninety patients with subacute and prolonged DoC will be included in a two-part multicenter prospective study. In the first phase (randomized controlled trial, RCT), patients will undergo four rTMS sessions in a crossover design over 10 days, targeting (i) the left dorsolateral prefrontal cortex (DLPFC) and (ii) the left angular gyrus (AG), as well as (iii & iv) their sham alternatives. In the second phase (longitudinal personalized trial), patients will receive personalized stimulations for 20 working days targeting the brain area that showed the best results in the RCT and will be randomly assigned to either active or sham intervention. The effects of rTMS on neurobehavioral and neurophysiological functioning in patients with DoC will be evaluated using clinical biomarkers of responsiveness (i.e., the Coma Recovery Scale-Revised; CRS-R), and electrophysiological biomarkers (e.g., power spectra, functional and effective connectivity, perturbational complexity index before and after intervention). Functional long-term outcomes will be assessed at 3 and 6 months post-intervention. Adverse events will be recorded during the treatment phase.

Discussion

This study seeks to identify which brain region (front or back) is best to stimulate for the treatment of patients with DoC using rTMS, and to characterize the neural correlates of its action regarding recovery of consciousness and functional outcome. In addition, we will define the responders' profile based on patients' characteristics and functional impairments; and develop biomarkers of responsiveness using EEG analysis according to the clinical responsiveness to the treatment.

Clinical Trial Registration

https://clinicaltrials.gov/ct2/show/NCT04401319, Clinicaltrials.gov, n° NCT04401319.

Corticocerebellar White Matter Integrity Is Related to Naming Outcome in Post-Stroke Aphasia

Studies have shown that the integrity of white matter tracts connecting different regions in the left cerebral hemisphere is important for aphasia recovery after stroke. However, the impact of the underlying structural connection between the cortex and the cerebellum in post-stroke aphasia is poorly understood. We studied the microstructural integrity of the cerebellum and the corticocerebellar connections and their role in picture naming. Fifty-six patients with left cerebral infarcts (sparing the cerebellum) underwent diffusion tensor imaging (DTI) and Boston Naming Test. We compared the fractional anisotropy (FA) and mean diffusivity (MD) values of the right and the left cerebellum (lobular gray and white matter structures) and cerebellocortical connections. Recursive feature elimination and Spearman correlation analyses were performed to evaluate the relationship between naming performance and the corticocerebellar connections. We found that the right, relative to left, cerebellar structures and their connections with the left cerebrum showed lower FA and higher MD values, both reflecting lower microstructural integrity. This trend was not observed in the healthy controls. Higher MD values of the right major cerebellar outflow tract were associated with poorer picture naming performance. Our study provides the first DTI data demonstrating the critical importance of ascending and descending corticocerebellar connections for naming outcomes after stroke.

Resolvin D1 reprograms energy metabolism to promote microglia to phagocytize neutrophils after ischemic stroke

Neutrophil aggregation and clearance are important factors affecting neuroinflammatory injury during acute ischemic stroke. Emerging evidence suggests that energy metabolism is essential for microglial functions, especially microglial phagocytosis, which determines the degree of brain injury. Here, we demonstrate that Resolvin D1 (RvD1), a lipid mediator derived from docosahexaenic acid (DHA), promotes the phagocytosis of neutrophils by microglia, thereby reducing neutrophil accumulation in the brain and alleviating neuroinflammation in the ischemic brain. Further studies reveal that RvD1 reprograms energy metabolism from glycolysis to oxidative phosphorylation (OXPHOS), providing sufficient energy for microglial phagocytosis. Moreover, RvD1 enhances microglial glutamine uptake and stimulates glutaminolysis to support OXPHOS to boost ATP production depending on adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activation. Overall, our results reveal that RvD1 reprograms energy metabolism to promote the microglial phagocytosis of neutrophils after ischemic stroke. These findings may guide perspectives for stroke therapy from modulating microglial immunometabolism.

Structural cerebellar reserve positively influences outcome after severe stroke

The concept of brain reserve capacity positively influencing the process of recovery after stroke has been continuously developed in recent years. Global measures of brain health have been linked with a favourable outcome. Numerous studies have evidenced that the cerebellum is involved in recovery after stroke. However, it remains an open question whether characteristics of cerebellar anatomy, quantified directly after stroke, might have an impact on subsequent outcome after stroke. Thirty-nine first-ever ischaemic non-cerebellar stroke patients underwent MRI brain imaging early after stroke and longitudinal clinical follow-up. Structural images were used for volumetric analyses of distinct cerebellar regions. Ordinal logistic regression analyses were conducted to associate cerebellar volumes with functional outcome 3-6 months after stroke, operationalized by the modified Rankin Scale. Larger volumes of cerebellar lobules IV, VI, and VIIIB were positively correlated with favourable outcome, independent of the severity of initial impairment, age, and lesion volume (P < 0.01). The total cerebellar volume did not exhibit a significant structure-outcome association. The present study reveals that pre-stroke anatomy of distinct cerebellar lobules involved in motor and cognitive functioning might be linked to outcome after acute non-cerebellar stroke, thereby promoting the emerging concepts of structural brain reserve for recovery processes after stroke.

Quantitative Electroencephalographic Markers of Delirium in the Pediatric Intensive Care Unit: Insights From a Heterogenous Convenience Sample

OBJECTIVE

Little is known about the underlying neurophysiology of pediatric delirium. In adult patients, the sensitivity of EEG to clinical symptoms of delirium has been noted, with a slowing of background activity (alpha) and an increase in slow-wave activity (delta-theta). In this pilot study, the authors extended this investigation to a pediatric cohort.

METHODS

In a convenience sample, 23 critically ill children were screened for delirium, using the Cornell Assessment for Pediatric Delirium (CAPD), every 12 hours throughout their pediatric intensive care unit stay as part of standard intensive care unit procedure, and EEGs were performed as part of their clinical care. After hospital discharge, EEGs were reviewed using quantitative analysis, and the maximum delta-alpha ratio (DAR; eyes closed) was derived for each 12-hour period. DAR values were compared between delirious and nondelirious episodes, and the linear relationship between DAR and CAPD was assessed.

RESULTS

Higher DARs were associated with episodes of delirium. The DAR also positively correlated with CAPD assessments, with higher DARs relating to higher delirium scores.

CONCLUSIONS

Future prospective studies may further investigate this relationship in a more homogeneous and larger sample, and the DAR should be considered to track delirium and assess the effectiveness of therapeutic interventions.

Repetitive Transcranial Magnetic Stimulation Induces Quantified Functional and Structural Changes in Subcortical Stroke: A Combined Arterial Spin Labeling Perfusion and Diffusion Tensor Imaging Study

Purpose

To explore the changes of cerebral blood flow (CBF) and fractional anisotropy (FA) in stroke patients with motor dysfunction after repetitive transcranial magnetic stimulation (rTMS) treatment, and to better understand the role of rTMS on motor rehabilitation of subcortical stroke patients from the perfusion and structural level.

Materials and Methods

In total, 23 first-episode acute ischemic stroke patients and sixteen healthy controls (HCs) were included. The patients were divided into the rTMS and sham group. The rehabilitation assessments and examination of perfusion and structural MRI were performed before and after rTMS therapy for each patient. Voxel-based analysis was used to detect the difference in CBF and FA among all three groups. The Pearson correlation analysis was conducted to evaluate the relationship between the CBF/FA value and the motor scales.

Results

After rTMS, significantly increased CBF was found in the ipsilesional supplementary motor area, postcentral gyrus, precentral gyrus, pons, medulla oblongata, contralesional midbrain, superior cerebellar peduncle, and middle cerebellar peduncle compared to that during the prestimulation and in the sham group, these fasciculi comprise the cortex-pontine-cerebellum-cortex (CPC) loop. Besides, altered CBF in the ipsilesional precentral gyrus, postcentral gyrus, and pons was positively associated with the improved Fugl-Meyer assessment (FMA) scores. Significantly decreased FA was found in the contralesional precentral gyrus, increased FA was found in the ipsilesional postcentral gyrus, precentral gyrus, contralesional supplementary motor area, and bilateral cerebellum, these fasciculi comprise the corticospinal tract (CST). The change of FMA score was positively correlated with altered FA value in the ipsilesional postcentral gyrus and negatively correlated with altered FA value in the contralesional precentral gyrus.

Conclusion

Our results suggested that rTMS could facilitate the motor recovery of stroke patients. High frequency could promote the improvement of functional activity of ipsilesional CPC loop and the recovery of the microstructure of CST.

Crossed cerebellar diaschisis in Alzheimer's disease

BACKGROUND

Crossed cerebellar diaschisis (CCD) is characterized by hypometabolism and hypoperfusion on molecular imaging in the cerebellum due to a supratentorial lesion on the contralateral side. CCD is a well-established phenomenon in acute or subacute conditions such as infarction but it has been less well described in chronic conditions such as neurodegenerative dementias. Here, we investigate CCD in a large sample of 830 people meeting research criteria for Alzheimer's disease (AD) using [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET).

MATERIALS AND METHODS

This study is based on FDG-PET data collected at baseline as part of two large-scale Phase III clinical trials of a novel tau aggregation inhibitor medication, methylthioninium in mild to moderate AD participants. Quantification of FDG-PET hypometabolism was carried out using standardized uptake value ratio (SUVR), with the pons as the comparison region. SUVR was compared in different regions of interest between the right and left hemispheres of the brain and cerebellum in people with mild AD (Mini-Mental State Examination score ≥ 20).

RESULTS

Comparison of SUVR in different brain regions demonstrated significant differences in the temporal, occipital and cerebellar cortices. Right and left asymmetry was noted with lower SUVR in the left temporal and occipital regions, whereas SUVR was lower in the right side of the cerebellum.

CONCLUSION

Here, we found robust evidence of CCD in a large sample of people with AD, a chronic neurodegenerative condition. The presence of this phenomenon in AD opens up a new avenue of research in AD pathogenesis and has the potential to change future diagnostic and therapeutic strategies.

Organizing a Rational Approach to Treatments of Disorders of Consciousness Using the Anterior Forebrain Mesocircuit Model

SUMMARY

Organizing a rational treatment strategy for patients with multifocal structural brain injuries and disorders of consciousness (DOC) is an important and challenging clinical goal. Among potential clinical end points, restoring elements of communication to DOC patients can support improved patient care, caregiver satisfaction, and patients' quality of life. Over the past decade, several studies have considered the use of the anterior forebrain mesocircuit model to approach this problem because this model proposes a supervening circuit-level impairment arising across DOC of varying etiologies. We review both the conceptual foundation of the mesocircuit model and studies of mechanisms underlying DOC that test predictions of this model. We consider how this model can guide therapeutic interventions and discuss a proposed treatment algorithm based on these ideas. Although the approach reviewed originates in the evaluation of patients with chronic DOC, we consider some emerging implications for patients in acute and subacute settings.

Cerebellar spreading depolarization mediates paroxysmal movement disorder

Paroxysmal kinesigenic dyskinesia (PKD) is the most common paroxysmal dyskinesia, characterized by recurrent episodes of involuntary movements provoked by sudden changes in movement. Proline-rich transmembrane protein 2 (PRRT2) has been identified as the major causative gene for PKD. Here, we report that PRRT2 deficiency facilitates the induction of cerebellar spreading depolarization (SD) and inhibition of cerebellar SD prevents the occurrence of dyskinetic movements. Using Ca²⁺ imaging, we show that cerebellar SD depolarizes a large population of cerebellar granule cells and Purkinje cells in Prrt2-deficient mice. Electrophysiological recordings further reveal that cerebellar SD blocks Purkinje cell spiking and disturbs neuronal firing of the deep cerebellar nuclei (DCN). The resultant aberrant firing patterns in DCN are tightly, temporally coupled to dyskinetic episodes in Prrt2-deficient mice. Cumulatively, our findings uncover a pivotal role of cerebellar SD in paroxysmal dyskinesia, providing a potent target for treating PRRT2-related paroxysmal disorders.

Secondary Cerebellar Cortex Injury in Albino Male Rats after MCAO: A Histological and Biochemical Study

The present study focused on secondary injury following the middle cerebral artery (MCA) occlusion in rats not linked to the MCA’s feeding zone. This entity has been very rarely studied. Additionally, this study investigated the rates of expression of five fundamental angiogenic biomarkers called endoglin, vascular endothelial growth factors-A (VEGF-A), endothelin-1 (ET-1), 2granulocyte colony-stimulating factor (G-CSF), and angiopoietin-using the MCA occlusion (MCAO) model. The random allocation of twelve adult male albino rats was in two groups. As a sham control group, six rats were used. This group was subjected to a sham operation without MCAO. The MCAO group consisted of six rats that were subjected to MCAO operation. After three days, the rats were sacrificed. The cerebellar specimens were immediately processed for light microscopic examination. An angiogenic biomarkers multiplex assay from multiplex was used to assess endoglin levels, VEGF-A, ET-1, angiopoietin-2, and G-CSF in serum samples. Hematoxylin and eosin-stained sections showed that the cerebellar cortex of rats of the MCAO group was more affected than the sham control group. Furthermore, Nissl stain and immunohistochemical analysis revealed an apparent increase in the number of positive immunoreactive in the cerebellar cortex and an evident decrease in Nissl granules in Purkinje cells of the MCAO rats, in contrast to the control rats. In addition, there was a significant increase in angiogenic factors VEGF-A, ET-1, angiopoietin-2, and endoglin. Interestingly, there was an increase in the G-CSF but a non-significant in the MCAO rats compared to the control rats. Furthermore, there was a significant correlation between the angiopoietin-2 and ET-1, and between G-CSF and ET-1. VEGF-A also exhibited significant positive correlations with the G-CSF serum level parameter, Endoglin, and ET-1. Rats subjected to MCAO are a suitable model to study secondary injury away from MCA’s feeding zone. Additionally, valuable insights into the association and interaction between altered angiogenic factors and acute ischemic stroke induced by MCAO in rats.

Crossed cerebellar diaschisis on 18F-FDG PET: Frequency across neurodegenerative syndromes and association with 11C-PIB and 18F-Flortaucipir

We used 18F-FDG-PET to investigate the frequency of crossed cerebellar diaschisis (CCD) in 197 patients with various syndromes associated with neurodegenerative diseases. In a subset of 117 patients, we studied relationships between CCD and cortical asymmetry of Alzheimer's pathology (β-amyloid (11C-PIB) and tau (18F-Flortaucipir)). PET images were processed using MRIs to derive parametric SUVR images and define regions of interest. Indices of asymmetry were calculated in the cerebral cortex, basal ganglia and cerebellar cortex. Across all patients, cerebellar 18F-FDG asymmetry was associated with reverse asymmetry of 18F-FDG in the cerebral cortex (especially frontal and parietal areas) and basal ganglia. Based on our operational definition (cerebellar asymmetry >3% with contralateral supratentorial hypometabolism), significant CCD was present in 47/197 (24%) patients and was most frequent in corticobasal syndrome and semantic and logopenic variants of primary progressive aphasia. In β-amyloid-positive patients, mediation analyses showed that 18F-Flortaucipir cortical asymmetry was associated with cerebellar 18F-FDG asymmetry, but that cortical 18F-FDG asymmetry mediated this relationship. Analysis of 18F-FDG-SUVR values suggested that CCD might also occur in the absence of frank cerebellar 18F-FDG asymmetry due to symmetrical supratentorial degeneration resulting in a bilateral diaschisis process.

Cortical hypometabolism reflects local atrophy and tau pathology in symptomatic Alzheimer's disease

Posterior cortical hypometabolism measured with [18F]-Fluorodeoxyglucose (FDG)-PET is a well-known marker of Alzheimer's disease-related neurodegeneration, but its associations with underlying neuropathological processes are unclear. We assessed cross-sectionally the relative contributions of three potential mechanisms causing hypometabolism in the retrosplenial and inferior parietal cortices: local molecular (amyloid and tau) pathology and atrophy, distant factors including contributions from the degenerating medial temporal lobe or molecular pathology in functionally connected regions, and the presence of the apolipoprotein E (APOE) ε4 allele. Two hundred and thirty-two amyloid-positive cognitively impaired patients from two cohorts (University of California, San Francisco, UCSF, and Alzheimer's Disease Neuroimaging Initiative, ADNI) underwent MRI and PET with FDG, amyloid-PET using [11C]-Pittsburgh Compound B, [18F]-Florbetapir, or [18F]-Florbetaben, and [18F]-Flortaucipir tau-PET within one year. Standard uptake value ratios (SUVR) were calculated using tracer-specific reference regions. Regression analyses were run within cohorts to identify variables associated with retrosplenial or inferior parietal FDG SUVR. On average, ADNI patients were older and were less impaired than UCSF patients. Regional patterns of hypometabolism were similar between cohorts, though there were cohort differences in regional gray matter atrophy. Local cortical thickness and tau-PET (but not amyloid-PET) were independently associated with both retrosplenial and inferior parietal FDG SUVR (ΔR2 = .09 to .21) across cohorts in models that also included age and disease severity (local model). Including medial temporal lobe volume improved the retrosplenial FDG model in ADNI (ΔR2 = .04, p = .008) but not UCSF (ΔR2 < .01, p = .52), and did not improve the inferior parietal models (ΔR2s < .01, ps > .37). Interaction analyses revealed that medial temporal volume was more strongly associated with retrosplenial FDG SUVR at earlier disease stages (p = .06 in UCSF, p = .046 in ADNI). Exploratory analyses across the cortex confirmed overall associations between hypometabolism and local tau pathology and thickness and revealed associations between medial temporal degeneration and hypometabolism in retrosplenial, orbitofrontal, and anterior cingulate cortices. Finally, our data did not support hypotheses of a detrimental effect of pathology in connected regions or of an effect of the APOE ε4 allele in impaired participants. Overall, in two independent groups of patients at symptomatic stages of Alzheimer's disease, cortical hypometabolism mainly reflected structural neurodegeneration and tau, but not amyloid, pathology.

Crossed Cerebellar Diaschisis in Alzheimer's Disease Detected by Arterial Spin-labelling Perfusion MRI

BACKGROUND

Crossed cerebellar diaschisis (CCD) is a phenomenon with depressed metabolism and hypoperfusion in the cerebellum. Using arterial spin-labelling perfusion weighted magnetic resonance imaging (ASL PWI), we investigated the frequency of CCD in patients with Alzheimer's disease (AD) and differences between patients with and without CCD.

PATIENTS AND METHODS

In patients with AD who underwent a standardized magnetic resonance imaging including ASL PWI cerebral blood flow was evaluated in the cerebellum, and brain segmentation/volumetry was performed using mdbrain (mediaire GmbH, Berlin, Germany) and FSL FIRST (Functional Magnetic Resonance Imaging of the Brain Software Library).

RESULTS

In total, 65 patients were included, and 22 (33.8%) patients were assessed as being CCD-positive. Patients with CCD had a significantly smaller whole brain volume (862.8±49.9 vs. 893.7±62.7 ml, p=0.049) as well as white matter volume (352.9±28.0 vs. 374.3±30.7, p=0.008) in comparison to patients without CCD.

CONCLUSION

It was possible to detect CCD by ASL PWI in approximately one-third of patients with AD and was associated with smaller whole brain and white matter volume.

Crossed cerebellar diaschisis: risk factors and prognostic value in focal cortical dysplasia by 18F-FDG PET/CT

PURPOSE

Crossed cerebellar diaschisis (CCD) has been widely studied in hemispheric stroke but is less characterized in epilepsy. In this study, we used 18F-FDG PET/CT to investigate the risk factors for CCD and its prognostic value for intractable epilepsy caused by focal cortical dysplasia (FCD).

METHODS

One hundred medically intractable epilepsy patients pathologically diagnosed with FCD postoperatively were included and classified into two groups: CCD+ and CCD-. PET/CT images were analyzed qualitatively by visual assessment and semi-quantitatively using the absolute asymmetry index (|AI|). Clinical factors, including age, sex, body mass index (BMI), age at seizure onset, epilepsy duration, seizure type, seizure frequency, electroencephalography (EEG) and brain magnetic resonance imaging (MRI), were retrospectively assessed from medical records. Follow-up outcomes were evaluated according to the Engel classification at 3, 6, 12, 24 and 36 months postoperatively.

RESULTS

Of the 100 patients, 77 (77.0%) were classified as CCD-, and 23 (23.0%) were classified as CCD + . CCD+ patients had a higher number of lobes involved on PET (3.61 ± 2.16 vs 2.26 ± 1.01, P < 0.001) than CCD- patients. CCD- patients showed more negative MRI results than CCD + patients (P = 0.02). At 12 months postoperatively, 70.7% (29/41) of CCD- patients and 30.8% (4/13) of CCD + patients presented a favourable prognosis (P = 0.02). Significant differences in the average |AI| values in the posterior frontal and anterior temporal lobes were found between CCD+ and CCD- patients (P < 0.05).

CONCLUSION

The number of lobes involved on PET, structural anomalies on MRI, the |AI| values in the posterior frontal and anterior temporal lobes may be predisposing factors for CCD. CCD occurrence may help predict the prognosis of FCD patients at 12 months postoperatively.

Characterizing Diaschisis-Related Thalamic Perfusion and Diffusion After Middle Cerebral Artery Infarction

[Figure: see text].

Recovery from disorders of consciousness: mechanisms, prognosis and emerging therapies

Substantial progress has been made over the past two decades in detecting, predicting and promoting recovery of consciousness in patients with disorders of consciousness (DoC) caused by severe brain injuries. Advanced neuroimaging and electrophysiological techniques have revealed new insights into the biological mechanisms underlying recovery of consciousness and have enabled the identification of preserved brain networks in patients who seem unresponsive, thus raising hope for more accurate diagnosis and prognosis. Emerging evidence suggests that covert consciousness, or cognitive motor dissociation (CMD), is present in up to 15-20% of patients with DoC and that detection of CMD in the intensive care unit can predict functional recovery at 1 year post injury. Although fundamental questions remain about which patients with DoC have the potential for recovery, novel pharmacological and electrophysiological therapies have shown the potential to reactivate injured neural networks and promote re-emergence of consciousness. In this Review, we focus on mechanisms of recovery from DoC in the acute and subacute-to-chronic stages, and we discuss recent progress in detecting and predicting recovery of consciousness. We also describe the developments in pharmacological and electrophysiological therapies that are creating new opportunities to improve the lives of patients with DoC.

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.

Complete hemispherotomy leads to lateralized functional organization and lower level of consciousness in the isolated hemisphere

OBJECTIVE

To quantify whole-brain functional organization after complete hemispherotomy, characterizing unexplored plasticity pathways and the conscious level of the dissected hemispheres.

METHODS

Evaluation with multimodal magnetic resonance imaging in two pediatric patients undergoing right hemispherotomy including complete callosotomy with a perithalamic section. Regional cerebral blood flow and fMRI network connectivity assessed the functional integrity of both hemispheres after surgery. The level of consciousness was tested by means of a support vector machine classifier which compared the intrinsic organization of the dissected hemispheres with those of patients suffering from disorders of consciousness.

RESULTS

After hemispherotomy, both patients showed typical daily functionality. We found no interhemispheric transfer of functional connectivity in either patient as predicted by the operation. The healthy left hemispheres displayed focal blood hyperperfusion in motor and limbic areas, with preserved network-level organization. Unexpectedly, the disconnected right hemispheres showed sustained network organization despite low regional cerebral blood flow. Subcortically, functional connectivity was increased in the left thalamo-cortical loop and between the cerebelli. One patient further showed unusual ipsilateral right cerebello-cortical connectivity, which was explained by the mediation of the vascular system. The healthy left hemisphere had higher probability to be classified as in a minimally conscious state compared to the isolated right hemisphere.

SIGNIFICANCE

Complete hemispherotomy leads to a lateralized whole-brain organization, with the remaining hemisphere claiming most of the brain's energetic reserves supported by subcortical structures. Our results further underline the contribution of nonneuronal vascular signals on contralateral connectivity, shedding light on the nature of network organization in the isolated tissue. The disconnected hemisphere is characterized by a level of consciousness which is necessary but insufficient for conscious processing, paving the way for more specific inquiries about its role in awareness in the absence of behavioral output.

Crossed cerebellar diaschisis after stroke detected noninvasively by arterial spin-labeling MR imaging

Background

As a noninvasive perfusion-weighted MRI technique, arterial spin-labeling (ASL) was becoming increasingly used to evaluate cerebral hemodynamics in many studies. The relation between ASL-MRI and crossed cerebellar diaschisis (CCD) was rarely discussed. In this study, the aim of our study was to assess the performance of ASL-MRI in the detection of crossed cerebellar diaschisis after stroke in compared with single-photon emission CT (SPECT).

Results

17 of 51(33.3%) patients revealed CCD phenomenon by the SPECT method. In CCD-positive group, CBF_ASL of ipsilateral cerebellar were significantly increased compared with contralateral cerebellar (p < 0.0001) while no significant differences (p = 0.063, > 0.001) in the CCD-negative group. Positive correlation was detected between admission National institute of health stroke scale (NIHSS) and asymmetry index of SPECT (AI_SPECT) (r = 0.351, p = 0.011), AI_ASL (r = 0.372, p = 0.007); infract volume and AI_SPECT (r = 0.443, p = 0.001), AI_ASL (r = 0.426, p = 0.002). Significant correlation was also found between cerebral blood flow of SPECT (CBF_SPECT) and CBF_ASL, AI_SPECT and AI_ASL (r = 0.204, p = 0.04; r = 0.467, p = 0.001, respectively). Furthermore, the area under the receiver operating characteristic (ROC) curve value of AI_ASL was 0.829.

Conclusions

CBF derived from ASL-MRI could be valuable for assessment of CCD in supratentorial stroke patients. Additionally, CCD was significantly associated with larger ischemic volume and higher initial NIHSS score.

Arterial spin labeling perfusion in neonates

Abnormal brain perfusion is a key mechanism underlying neonatal brain injury. Understanding the mechanisms leading to brain perfusion changes in high-risk neonates and how these alterations may influence brain development is key to improve therapeutic strategies preventing brain injury and the neurodevelopmental outcome of these infants. To date, several studies demonstrated that Arterial Spin Labeling is a reliable tool to accurately and non-invasively analyze brain perfusion, facilitating the understanding of normal and pathological mechanisms underlying neonatal brain maturation and injury. This paper provides an overview of the normal pattern of brain perfusion on Arterial Spin Labeling in term and preterm neonates, and reviews perfusion abnormalities associated with common neonatal neurological disorders.

Indirect Structural Connectivity Identifies Changes in Brain Networks After Stroke

Background/Purpose: The purpose of this study was (1) to identify changes in structural connectivity after stroke and (2) to relate changes in indirect connectivity to post-stroke impairment. Methods: A novel measure of indirect connectivity was implemented to assess the impact of stroke on brain connectivity. Probabilistic tractography was performed on 13 chronic stroke and 16 control participants to estimate connectivity between gray matter (GM) regions. The Fugl-Meyer assessment of motor impairment was measured for stroke participants. Network measures of direct and indirect connectivity were calculated, and these measures were linearly combined with measures of white matter integrity to predict motor impairment. Results: We found significantly reduced indirect connectivity in the frontal and parietal lobes, ipsilesional subcortical regions, and bilateral cerebellum after stroke. When added to the regression analysis, the volume of GM with reduced indirect connectivity significantly improved the correlation between image parameters and upper extremity motor impairment (R² = 0.71, p < 0.05). Conclusion: This study provides evidence of changes in indirect connectivity in regions remote from the lesion, particularly in the cerebellum and regions in the fronto-parietal cortices, and these changes correlate with upper extremity motor impairment. These results highlight the value of using measures of indirect connectivity to identify the effect of stroke on brain networks. Impact statement Changes in indirect structural connectivity occur in regions distant from a lesion after stroke, highlighting the impact that stroke has on brain functional networks. Specifically, losses in indirect structural connectivity occur in hubs with high centrality, including the fronto-parietal cortices and cerebellum. These losses in indirect connectivity more accurately reflect motor impairments than measures of direct structural connectivity. As a consequence, indirect structural connectivity appears to be important to recovery after stroke and imaging biomarkers that incorporate indirect structural connectivity might improve prognostication of stroke outcomes.

Novel quantitative approach for crossed cerebellar diaschisis detection in acute ischemic stroke using CT perfusion

PURPOSE

Crossed cerebellar diaschisis (CCD) is a common finding in hyper-acute ischemic stroke, related to supratentorial dysfunction of the contralateral hemisphere. Several studies investigated a possible relationship between CCD and clinical outcomes but still no evidence emerged. We proposed a novel quantitative whole cerebellum analysis using CT perfusion (CTP) imaging to investigate the relationship between CCD and stroke severity, hypoperfused volume and outcome measures.

METHODS

55 patients with supratentorial ischemic stroke who underwent CTP evaluation within 4.5 h since symptom onset were enrolled. CCD was evaluated by CTP image-processing and by calculating the mean transit time (MTT)-map asymmetry index in the whole cerebellum. MTT asymmetry correlation with ischemic volume and clinical outcomes was investigated.

RESULTS

MTT asymmetry was found in most of the included patients and significantly correlated with NIH Stroke Scale (NIHSS) score at baseline and CTP ischemic volume. MTT asymmetry was significantly correlated with hemorrhagic transformation, NIHSS and modified Rankin Scale (mRS) score on discharge in treated patients.

CONCLUSIONS

CCD was detectable by CTP in acute supratentorial ischemic stroke by processing the whole cerebellum volume. CCD perfusion asymmetry was significantly correlated with neurological and perfusion deficit on admission as well as with clinical outcomes in treated patients.

Cerebellar Blood Flow and Gene Expression in Crossed Cerebellar Diaschisis after Transient Middle Cerebral Artery Occlusion in Rats

Crossed cerebellar diaschisis (CCD) is a state of hypoperfusion and hypometabolism in the contralesional cerebellar hemisphere caused by a supratentorial lesion, but its pathophysiology is not fully understood. We evaluated chronological changes in cerebellar blood flow (CbBF) and gene expressions in the cerebellum using a rat model of transient middle cerebral artery occlusion (MCAO). CbBF was analyzed at two and seven days after MCAO using single photon emission computed tomography (SPECT). DNA microarray analysis and western blotting of the cerebellar cortex were performed and apoptotic cells in the cerebellar cortex were stained. CbBF in the contralesional hemisphere was significantly decreased and this lateral imbalance recovered over one week. Gene set enrichment analysis revealed that a gene set for “oxidative phosphorylation” was significantly upregulated while fourteen other gene sets including “apoptosis”, “hypoxia” and “reactive oxygen species” showed a tendency toward upregulation in the contralesional cerebellum. MCAO upregulated the expressions of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in the contralesional cerebellar cortex. The number of apoptotic cells increased in the molecular layer of the contralesional cerebellum. Focal cerebral ischemia in our rat MCAO model caused CCD along with enhanced expression of genes related to oxidative stress and apoptosis.

Crossed Cerebellar Diaschisis Indicates Hemodynamic Compromise in Ischemic Stroke Patients

Crossed cerebellar diaschisis (CCD) in internal carotid artery (ICA) stroke refers to attenuated blood flow and energy metabolism in the contralateral cerebellar hemisphere. CCD is associated with an interruption of cerebro-cerebellar tracts, but the precise mechanism is unknown. We hypothesized that in patients with ICA occlusions, CCD might indicate severe hemodynamic impairment in addition to tissue damage. Duplex sonography and clinical data from stroke patients with unilateral ICAO who underwent blood oxygen-level-dependent MRI cerebrovascular reserve (BOLD-CVR) assessment were analysed. The presence of CCD (either CCD+ or CCD−) was inferred from BOLD-CVR. We considered regions with negative BOLD-CVR signal as areas suffering from hemodynamic steal. Twenty-five patients were included (11 CCD+ and 14 CCD−). Stroke deficits on admission and at 3 months were more severe in the CCD+ group. While infarct volumes were similar, CCD+ patients had markedly larger BOLD steal volumes than CCD− patients (median [IQR] 122.2 [111] vs. 11.6 [50.6] ml; p < 0.001). Furthermore, duplex revealed higher peak-systolic flow velocities in the intracranial collateral pathways. Strikingly, posterior cerebral artery (PCA)-P2 velocities strongly correlated with the National Institute of Health Stroke Scale on admission and BOLD-CVR steal volume. In patients with strokes due to ICAO, the presence of CCD indicated hemodynamic impairment with larger BOLD-defined steal volume and higher flow in the ACA/PCA collateral system. Our data support the concept of a vascular component of CCD as an indicator of hemodynamic failure in patients with ICAO.

Spreading depolarizations in the rat endothelin-1 model of focal cerebellar ischemia

Focal brain ischemia is best studied in neocortex and striatum. Both show highly vulnerable neurons and high susceptibility to spreading depolarization (SD). Therefore, it has been hypothesized that these two variables generally correlate. However, this hypothesis is contradicted by findings in cerebellar cortex, which contains highly vulnerable neurons to ischemia, the Purkinje cells, but is said to be less susceptible to SD. Here, we found in the rat cerebellar cortex that elevated K⁺ induced a long-lasting depolarizing event superimposed with SDs. Cerebellar SDs resembled those in neocortex, but negative direct current (DC) shifts and regional blood flow responses were usually smaller. The K⁺ threshold for SD was higher in cerebellum than in previous studies in neocortex. We then topically applied endothelin-1 (ET-1) to the cerebellum, which is assumed to cause SD via vasoconstriction-induced focal ischemia. Although the blood flow decrease was similar to that in previous studies in neocortex, the ET-1 threshold for SD was higher. Quantitative cell counting found that the proportion of necrotic Purkinje cells was significantly higher in ET-1-treated rats than sham controls even if ET-1 had not caused SDs. Our results suggest that ischemic death of Purkinje cells does not require the occurrence of SD.

Independent Functional Outcomes after Prolonged Coma following Cardiac Arrest: A Mechanistic Hypothesis

OBJECTIVE

Survivors of prolonged (>2 weeks) post-cardiac arrest (CA) coma are expected to remain permanently disabled. We aimed to investigate 3 outlier patients who ultimately achieved independent functional outcomes after prolonged post-CA coma to identify electroencephalographic (EEG) markers of their recovery potential. For validation purposes, we also aimed to evaluate these markers in an independent cohort of post-CA patients.

METHODS

We identified 3 patients with late recovery from coma (17-37 days) following CA who recovered to functionally independent behavioral levels. We performed spectral power analyses of available EEGs during prominent burst suppression patterns (BSP) present in all 3 patients. Using identical methods, we also assessed the relationship of intraburst spectral power and outcomes in a prospectively enrolled cohort of post-CA patients. We performed chart reviews of common clinical, imaging, and EEG prognostic variables and clinical outcomes for all patients.

RESULTS

All 3 patients with late recovery from coma lacked evidence of overwhelming cortical injury but demonstrated prominent BSP on EEG. Spectral analyses revealed a prominent theta (~4-7Hz) feature dominating the bursts during BSP in these patients. In the prospective cohort, similar intraburst theta spectral features were evident in patients with favorable outcomes; patients with BSP and unfavorable outcomes showed either no features, transient burst features, or decreasing intraburst frequencies with time.

INTERPRETATION

BSP with theta (~4-7Hz) peak intraburst spectral power after CA may index a recovery potential. We discuss our results in the context of optimizing metabolic substrate availability and stimulating the corticothalamic system during recovery from prolonged post-CA coma. ANN NEUROL 2020;87:618-632.

Cerebellar Neuromodulation for Stroke

Purpose of Review

This paper reviews the current preclinical and clinical evidence for cerebellar deep brain stimulation for stroke rehabilitation.

Recent Findings

We have demonstrated the effectiveness of cerebellar stimulation for stroke rehabilitation in rodent models, which has been reproduced by other groups. Synaptogenesis, neurogenesis, and vicariation of function in the perilesional cortex likely contribute to the mechanistic underpinnings of the effectiveness of this therapy. A Phase I clinical trial investigating dentate nucleus stimulation for improvement of hemiparesis due to stroke is currently underway, and results thus far are encouraging.

Summary

Activation of the rodent cerebellar dentate nucleus promotes functional motor recovery following stroke. Although results of a Phase I clinical trial are pending, substantial preclinical evidence indicates that deep brain stimulation of the dentate nucleus is a promising therapeutic modality.

Direct electrophysiological evidence that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura and a review of the spreading depolarization continuum of acute neuronal mass injury

Spreading depolarization is observed as a large negative shift of the direct current potential, swelling of neuronal somas, and dendritic beading in the brain's gray matter and represents a state of a potentially reversible mass injury. Its hallmark is the abrupt, massive ion translocation between intraneuronal and extracellular compartment that causes water uptake (= cytotoxic edema) and massive glutamate release. Dependent on the tissue's energy status, spreading depolarization can co-occur with different depression or silencing patterns of spontaneous activity. In adequately supplied tissue, spreading depolarization induces spreading depression of activity. In severely ischemic tissue, nonspreading depression of activity precedes spreading depolarization. The depression pattern determines the neurological deficit which is either spreading such as in migraine aura or migraine stroke or nonspreading such as in transient ischemic attack or typical stroke. Although a clinical distinction between spreading and nonspreading focal neurological deficits is useful because they are associated with different probabilities of permanent damage, it is important to note that spreading depolarization, the neuronal injury potential, occurs in all of these conditions. Here, we first review the scientific basis of the continuum of spreading depolarizations. Second, we highlight the transition zone of the continuum from reversibility to irreversibility using clinical cases of aneurysmal subarachnoid hemorrhage and cerebral amyloid angiopathy. These illustrate how modern neuroimaging and neuromonitoring technologies increasingly bridge the gap between basic sciences and clinic. For example, we provide direct electrophysiological evidence for the first time that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura.

Two Different Manifestations of Neonatal Vascular Injury: Dyke-Davidoff-Masson Syndrome and Crossed Cerebellar Atrophy

Dyke-Davidoff-Masson syndrome (DDMS) was first described in 1933 as a clinical condition characterized by hemiatrophy, hyperpneumatization of paranasal sinuses, contralateral hemiparesis, facial asymmetry, seizures, and mental retardation.¹ DDMS can be of 2 types: congenital and acquired. The congenital type can be caused by various conditions experienced during fetal or early childhood development, including ischemia, infarction, trauma, infections, and hemorrhage. The acquired type is mostly associated with hemorrhage, trauma, and infections experienced after 1 month of age. DDMS can manifest alone or can be accompanied by crossed cerebellar atrophy (CCA) which is a newly discovered radiological marker characterized by prominent cortical sulci and loss of cerebellar parenchyma. The congenital type of DDMS is known to be accompanied by ipsilateral cerebellar atrophy and the acquired type is known to be accompanied by contralateral cerebellar atrophy.^2,3 Supratentorial events may lead to destruction in the cortico-ponto-cerebellar pathways, mostly in the contralateral side of the body (80%) due to decussation.⁴ In this report, we present 2 cases of DDMS accompanied by CCA to emphasize the possibility that the DDMS cases with severe intrauterine hemorrhage can be accompanied by contralateral CCA and migratory abnormalities rather than ipsilateral CCA and clinical survey.

Stroke and potential benefits of brain-computer interface

To treat stroke and, in particular, to alleviate the personal and social burden of stroke survivors is a main challenge for neuroscience research. Advancements in the knowledge of neurobiologic mechanisms subserving stroke-related damage and recovery provide key data to guide clinicians to tailor interventions to specific patient's needs. How does the brain-computer interface (BCI) fit into this scenario? A technique created to allow completely paralyzed individuals to control the environment recently introduced a new line of development: to provide a means to possibly control formation and changes in the brain network organization. In a sort of revolution, similar to the change from geocentric to heliocentric planet organization envisioned by Copernicus, we are facing a critical change in BCI research, moving from a brain to computer direction to a computer to brain one. This direction change will profoundly open up new avenues for BCI research and clinical applications. In this chapter, we address this change and discuss present and future applications of this new line idea of BCI use in stroke.

A neuroprotective brain stimulation for vulnerable cerebellar Purkinje cell after ischemic stroke: a study with low-intensity focused ultrasound

The role of established contralateral cerebrocerebellar connections on cerebellar injury during stroke has been increasingly revealed in recent years. An extensive number of studies have investigated alteration in inter-hemispheric correlation in order to find brain regions whose responses are specific to restore functional loss and enhance adaptive neural plasticity after stroke. Although, several non-invasive brain stimulation studies have proven their efficacy in the treatment of stroke recovery, finding more effective brain regions that responsible for stroke rehabilitation as well as optimizing neural stimulation protocol are the main goals of further investigations. In this study, the lateral cerebellar nucleus (LCN) was exposed to Low-Intensity Focused Ultrasound (LIFU) to reduce the cerebellar damage resulting from crossed cerebellar diaschisis (CCD) phenomenon after cerebral ischemia. A mouse brain ischemia was induced by middle cerebral artery occlusion (MCAO). A level of decrease in Purkinje cell (PC) number and a quantity of myeloperoxidase (MPO) positive neutrophils in the cerebral cortex were compared between stroke and stroke+LIFU groups after MCAO. In stroke+LIFU group, the increased ipsilateral water content due to tissue swelling was observed, showing an attenuation of brain edema. Prominently, the reduction of the neuroimmune reactivity at the infarct core and the peri-infarct regions, and the increased rate of survival among PCs clearly demonstrated primary evidence of neuroprotective effect induced by LIFU-mediated cerebellar modulation.

The effect of cerebellar transcranial direct current stimulation to improve standing balance performance early post-stroke, study protocol of a randomized controlled trial

RATIONALE

Restoration of adequate standing balance after stroke is of major importance for functional recovery. POstural feedback ThErapy combined with Non-invasive TranscranIAL direct current stimulation (tDCS) in patients with stroke (POTENTIAL) aims to establish if cerebellar tDCS has added value in improving standing balance performance early post-stroke.

METHODS

Forty-six patients with a first-ever ischemic stroke will be enrolled in this double-blind controlled trial within five weeks post-stroke. All patients will receive 15 sessions of virtual reality-based postural feedback training (VR-PFT) in addition to usual care. VR-PFT will be given five days per week for 1 h, starting within five weeks post-stroke. During VR-PFT, 23 patients will receive 25 min of cerebellar anodal tDCS (cb_tDCS), and 23 patients will receive sham stimulation.

STUDY OUTCOME

Clinical, posturographic, and neurophysiological measurements will be performed at baseline, directly post-intervention, two weeks post-intervention and at 15 weeks post-stroke. The primary outcome measure will be the Berg Balance Scale (BBS) for which a clinical meaningful difference of six points needs to be established between the intervention and control group at 15 weeks post-stroke.

DISCUSSION

POTENTIAL will be the first proof-of-concept randomized controlled trial to assess the effects of VR-PFT combined with cerebellar tDCS in terms of standing balance performance in patients early post-stroke. Due to the combined clinical, posturographical and neurophysiological measurements, this trial may give more insights in underlying post-stroke recovery processes and whether these can be influenced by tDCS.

Searching for the optimal tDCS target for motor rehabilitation

BACKGROUND

Transcranial direct current stimulation (tDCS) has been investigated over the years due to its short and also long-term effects on cortical excitability and neuroplasticity. Although its mechanisms to improve motor function are not fully understood, this technique has been suggested as an alternative therapeutic method for motor rehabilitation, especially those with motor function deficits. When applied to the primary motor cortex, tDCS has shown to improve motor function in healthy individuals, as well as in patients with neurological disorders. Based on its potential effects on motor recovery, identifying optimal targets for tDCS stimulation is essential to improve knowledge regarding neuromodulation as well as to advance the use of tDCS in clinical motor rehabilitation.

METHODS AND RESULTS

Therefore, this review discusses the existing evidence on the application of four different tDCS montages to promote and enhance motor rehabilitation: (1) anodal ipsilesional and cathodal contralesional primary motor cortex tDCS, (2) combination of central tDCS and peripheral electrical stimulation, (3) prefrontal tDCS montage and (4) cerebellar tDCS stimulation. Although there is a significant amount of data testing primary motor cortex tDCS for motor recovery, other targets and strategies have not been sufficiently tested. This review then presents the potential mechanisms and available evidence of these other tDCS strategies to promote motor recovery.

CONCLUSIONS

In spite of the large amount of data showing that tDCS is a promising adjuvant tool for motor rehabilitation, the diversity of parameters, associated with different characteristics of the clinical populations, has generated studies with heterogeneous methodologies and controversial results. The ideal montage for motor rehabilitation should be based on a patient-tailored approach that takes into account aspects related to the safety of the technique and the quality of the available evidence.

Effects of two different protocols of cerebellar transcranial direct current stimulation combined with transcutaneous spinal direct current stimulation on robot-assisted gait training in patients with chronic supratentorial stroke: A single blind, randomized controlled trial

BACKGROUND

The neural organization of locomotion involves motor patterns generated by spinal interneuronal networks and supraspinal structures, which are approachable by noninvasive stimulation techniques. Recent evidences supported the hypothesis that transcranial direct current stimulation (combined with transcutaneous spinal direct current stimulation) may actually enhance the effects of robot-assisted gait training in chronic stroke patients. The cerebellum has many connections to interact with neocortical areas and may provide some peculiar plasticity mechanisms. So, it has been proposed as "non-lesioned entry" to the motor or cognitive system for the application of noninvasive stimulation techniques in patients with supratentorial stroke.

OBJECTIVE

To compare the effects of two different protocols of cerebellar transcranial direct current stimulation combined with transcutaneous spinal direct current stimulation on robotic gait training in patients with chronic supratentorial stroke.

METHODS

Forty patients with chronic supratentorial stroke were randomly assigned into two groups. All patients received ten, 20-minute robotic gait training sessions, five days a week, for two consecutive weeks. Group 1 underwent cathodal transcranial direct current stimulation over the contralesional cerebellar hemisphere + cathodal transcutaneous spinal direct current stimulation in combination with robotic training. Group 2 underwent cathodal transcranial direct current stimulation over the ipsilesional cerebellar hemisphere + cathodal transcutaneous spinal direct current stimulation in combination with robotic training. The primary outcome was the 6-minute walk test performed before, after, and at follow-up at 2 and 4 weeks post-treatment.

RESULTS

No significant difference in the 6-minute walk test between groups was found at the first post-treatment evaluation (P = 0.976), as well as at the 2-week (P = 0.178) and the 4-week (P = 0.069) follow-up evaluations. Both groups showed significant within-group improvements in the 6-minute walk test at all time points.∥Conclusions: Our findings support the hypothesis that cathodal transcranial direct current stimulation over the contralesional or ipsilesional cerebellar hemisphere in combination with cathodal transcutaneous spinal direct current stimulation may lead to similar effects on robotic gait training in chronic supratentorial stroke patients.

Ischemic Postconditioning Recovers Cortex Ascorbic Acid during Ischemia/Reperfusion Monitored with an Online Electrochemical System

As a promising therapeutic treatment, ischemic postconditioning has recently received considerable attention. Although the neuroprotection effect of postconditioning has been observed, a reliable approach that can evaluate the neuroprotective efficiency of postconditioning treatment during the acute period after ischemia remains to be developed. This study investigates the dynamics of cortex ascorbic acid during the acute period of cerebral ischemia before and after ischemic postconditioning with an online electrochemical system (OECS). The cerebral ischemia/reperfusion injury and the neuronal functional outcome are evaluated with triphenyltetrazolium chloride staining, immunohistochemistry, and electrophysiological recording techniques. Electrochemical recording results show that cortex ascorbic acid sharply increases 10 min after middle cerebral artery occlusion and then reaches a plateau. After direct reperfusion following ischemia (i.e., without ischemic postconditioning), the cortex ascorbic acid further increases and then starts to decrease slowly at a time point of about 40 min after reperfusion. In striking contrast, the cortex ascorbic acid drops and recovers to its basal level after ischemic postconditioning followed by reperfusion. With the recovery of cortex ascorbic acid, ischemic postconditioning concomitantly promotes the recovery of neural function and reduces the oxidative damage. These results demonstrate that our OECS for monitoring cortex ascorbic acid can be used as a platform for evaluating the neuroprotective efficiency of ischemic postconditioning in the acute phase of cerebral ischemia, which is of great importance for screening proper postconditioning parameters for preventing ischemic damages.

PET Imaging of Crossed Cerebellar Diaschisis after Long-Term Cerebral Ischemia in Rats

Crossed cerebellar diaschisis (CCD) is a decrease of regional blood flow and metabolism in the cerebellar hemisphere contralateral to the injured brain hemisphere as a common consequence of stroke. Despite CCD has been detected in patients with stroke using neuroimaging modalities, the evaluation of this phenomenon in rodent models of cerebral ischemia has been scarcely evaluated so far. Here, we report the in vivo evaluation of CCD after long-term cerebral ischemia in rats using positron emission tomography (PET) imaging with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG). Imaging studies were combined with neurological evaluation to assess functional recovery. In the ischemic territory, imaging studies showed a significant decrease in glucose metabolism followed by a progressive recovery later on. Conversely, the cerebellum showed a contralateral hypometabolism from days 7 to 14 after reperfusion. Neurological behavior showed major impaired outcome at day 1 after ischemia followed by a significant recovery of the sensorimotor function from days 7 to 28 after experimental stroke. Taken together, these results suggest that the degree of CCD after cerebral ischemia might be predictive of neurological recovery.

Detection of subthreshold atrophy in crossed cerebellar degeneration via two-compartment mathematical modeling of cell density in DWI: A proof of concept study

Crossed cerebellar diaschisis (CCD) refers to transneuronal degeneration of the corticopontocerebellar pathway, resulting in atrophy of cerebellum contralateral to supratentorial pathology. CCD is traditionally diagnosed on nuclear medicine studies. Our aim is to apply a biexponential diffusion model, composed of intracellular and extracellular compartments, to the detection of subthreshold CCD on DWI, with the calculated fraction of the intracellular compartment as a proposed measure of cell density. At a voxel-by-voxel basis, we solve for intracellular and extracellular coefficients in each side of the cerebellum and compare the distribution of coefficients between each hemisphere. We demonstrate, in all six CCD cases, a significantly lower contribution of the intracellular compartment to the cerebellar hemisphere contralateral to supratentorial pathology (p < 0.01). In a separate, proof-of-concept case of pontine stroke, we also demonstrate reduced intracellular coefficients in bilateral cerebellar hemispheres, excluding middle cerebellar peduncles (p < 0.01). Our findings are consistent with a decreased intracellular fraction, presumably a surrogate for reduced cellular density in corticopontocerebellar degeneration, despite normal-appearing scans. Our approach allows detection of subthreshold structural changes and offers the additional advantage of applicability to most clinical cases, where only three DWI beta values are available.

Modulation of Cerebellar Cortical Plasticity Using Low-Intensity Focused Ultrasound for Poststroke Sensorimotor Function Recovery

BACKGROUND

Stroke affects widespread brain regions through interhemispheric connections by influencing bilateral motor activity. Several noninvasive brain stimulation techniques have proved their capacity to compensate the functional loss by manipulating the neural activity of alternative pathways. Over the past few decades, brain stimulation therapies have been tailored within the theoretical framework of modulation of cortical excitability to enhance adaptive plasticity after stroke.

OBJECTIVE

However, considering the vast difference between animal and human cerebral cortical structures, it is important to approach specific neuronal target starting from the higher order brain structure for human translation. The present study focuses on stimulating the lateral cerebellar nucleus (LCN), which sends major cerebellar output to extensive cortical regions.

METHODS

In this study, in vivo stroke mouse LCN was exposed to low-intensity focused ultrasound (LIFU). After the LIFU exposure, animals underwent 4 weeks of rehabilitative training.

RESULTS

During the cerebellar LIFU session, motor-evoked potentials (MEPs) were generated in both forelimbs accompanying excitatory sonication parameter. LCN stimulation group on day 1 after stroke significantly enhanced sensorimotor recovery compared with the group without stimulation. The recovery has maintained for a 4-week period in 2 behavior tests. Furthermore, we observed a significantly decreased level of brain edema and tissue swelling in the affected hemisphere 3 days after the stroke.

CONCLUSIONS

This study provides the first evidence showing that LIFU-induced cerebellar modulation could be an important strategy for poststroke recovery. A longer follow-up study is, however, necessary in order to fully confirm the effects of LIFU on poststroke recovery.

Crossed cerebellar hyperperfusion in patients with seizure-related cerebral cortical lesions: an evaluation with arterial spin labelling perfusion MR imaging

PURPOSE

Crossed cerebellar (CC) diaschisis refers to a decrease in cerebellar perfusion in the presence of contralateral supratentorial lesions. Most of the previous studies have examined stroke patients. In contrast to strokes, seizure-related cerebral cortical lesions (SCCLs) usually show hyperperfusion, and therefore, cerebellar perfusion patterns are expected to be different from those of strokes. With arterial spin labelling (ASL), we evaluated the cerebellar perfusion status in patients with SCCLs.

MATERIALS AND METHODS

Using a search of the recent database over the last 31 months, 26 patients were enrolled in this study. The inclusion criteria were as follows: (1) a history of seizures, (2) MR examination taken within 24 h from the last seizure, (3) the presence of SCCLs on T2/FLAIR or DWI, (4) hyperperfusion in the corresponding areas of SCCLs on ASL, and (5) no structural abnormality in the cerebellum. The perfusion status in the contralateral cerebellum was evaluated and categorized as hyper-, iso- and hypoperfusion. The asymmetric index (AI) of cerebellar perfusion was calculated by ROI measurement of the signal intensity on ASL.

RESULTS

The mean time between the last seizure and MR examinations was 5 h 30 min. CC hyperperfusion was observed in 17 patients (65.4%), hypoperfusion in 7 (26.9%) and isoperfusion in 2 (7.7%). Regarding the location of SCCLs, CC hyperperfusion was more frequent (71.4 vs. 58.3%), and the mean AI was higher (42.0 vs. 11.5) when the lesion involved the frontal lobe.

CONCLUSIONS

In patients with SCCLs, CC hyperperfusion occurred more often than hypo- and isoperfusion, especially when the lesions involved the frontal lobe.

The modular architecture and neurochemical patterns in the cerebellar cortex

The review deals with topical issues of the neuronal arrangement underlying basic cerebellar functions. The cerebellum and its auxiliary structures contain several hundreds of modules (so called "microzones"). Each module receives the corticopetal input specific for the lobule it belongs to and forms the topographic projection. The precision of the major input-output signal flow in the cerebellar cortex is provided by a pronounced stratification of its synaptic zones of a various origin and regular topography of its afferent connections, interneurons, and efferent neurons. There is a nice match between the anatomical and functional coordinates of the modules, whose spatial boundaries are determined by the spread of afferent excitation and local interneuron connections. The dynamic characteristics of the modules are analyzed by the example of the formation of the nitrergic neuron ensembles and cerebellar projections of corticopetal fibers. The authors discuss the cerebellar blood flow and its relation to the activity of NO/GABAergic Lugaro cells and other interneurons in the cerebellar cortex. A generalized scheme of intra- and intermodular communication is proposed.

Pathological factors contributing to crossed cerebellar diaschisis in cerebral gliomas: a study combining perfusion, diffusion, and structural MR imaging

PURPOSE

To investigate imaging features of crossed cerebellar diaschisis (CCD) in cerebral gliomas, and its underlying pathophysiological mechanisms.

METHODS

Thirty-three pre-surgical patients with cerebral gliomas and 33 healthy controls underwent arterial spin-labeling, diffusion tensor imaging, and high-resolution T1-weighted imaging using MRI, in order to estimate cerebral blood flow (CBF), white matter integrity, and lesion volume, respectively. Asymmetry indices of CBF in the cerebellum were used for evaluating the level of CCD in the patients. These indices were correlated with clinical variables (lesion size and position, tumor histological grade, and CBF asymmetry) and diffusion tensor imaging parameters (fractional anisotropy and number of fibers in the cortico-ponto-cerebellar pathway and across the cerebral hemispheres), respectively.

RESULTS

The patients showed decreased CBF in the cerebellar hemisphere contralateral to the supratentorial tumor, and increased CBF asymmetry in the cerebellum (both P < 0.05). CCD levels in high-grade gliomas were higher than those of low-grade gliomas (P < 0.05). CCD levels were negatively correlated with the size of the supratentorial lesions, and positively correlated with FA asymmetry in the cerebral fibers (both P < 0.05).

CONCLUSIONS

CCD in cerebral gliomas was specifically associated with tumor histological grade, lesion size, and white matter impairments in the hemisphere ipsilateral to the tumor. The findings implicated that observing CCD might have potential for assisting grading diagnosis of cerebral gliomas.