OUP accepted manuscript

Reduction of sleep-like perilesional slow waves and clinical evolution after stroke: A TMS-EEG study

OBJECTIVE

Recent studies indicate that brain injuries often lead to the occurrence of sleep-like slow waves in perilesional cortical areas. These slow waves may disrupt local cortico-cortical interactions and contribute to behavioral impairments but are, in principle, reversible. This study employs Transcranial Magnetic Stimulation (TMS) combined with Electroencephalography (EEG) to monitor changes in perilesional slow waves and local cortical interactions examining their relation to changes in stroke severity.

METHODS

Twelve patients with post-acute/chronic unilateral ischemic cortical stroke participated in a longitudinal study with two assessment points. Each assessment included a neurological evaluation using the National Institutes of Health Stroke Scale (NIHSS) and TMS-EEG recordings targeting perilesional cortical areas. Neurophysiological parameters, such as slow wave amplitude (SWa), high-frequency power (HFp) suppression, and the Perturbational Complexity Index-state transition (PCIst), were extracted from the perilesional EEG responses to TMS to quantify local sleep-like slow waves andcortical interactions.

RESULTS

We observed a perilesional reduction in sleep-like slow waves and a restoration of local cortical interactions. Notably, these changes significantly correlated with patients' clinical evolution as assessed by the NIHSS score.

CONCLUSIONS

These findings highlight the potential of TMS-EEG as an objective tool for tracking neurological evolution post-stroke.

SIGNIFICANCE

Targeting sleep-like cortical dynamics may be relevant for devising post-stroke rehabilitation strategies.

Beyond organ isolation: The bidirectional crosstalk between cerebral and intestinal ischemia-reperfusion injury via microbiota-gut-brain axis

Ischemia-reperfusion injury (IRI) represents a pathophysiological phenomenon of profound clinical relevance that poses considerable threats to patient safety. IRI may manifest in a variety of clinical contexts including, but not limited to, sepsis, organ transplantation, shock, myocardial infarction, cerebral ischemia, and stroke. Critically, IRI exhibits complex interactions across different organs, with effects that surpass mere localized tissue damage. These impacts can amplify damage to both adjacent and remote organs through pathways such as the gut-brain axis and the gut-lung axis, facilitated by intricate signaling mechanisms. Noteworthy is the interaction between gut IRI and brain IRI, which involves sophisticated neuroendocrine, systemic, and immune mechanisms coordinated through the microbiome-gut-brain axis. This review seeks to delve into the intricate interactions between gut and brain IRI, viewed through the lens of the microbiota-gut-brain axis. It aims to assess its translational potential in clinical settings, provide a theoretical foundation for developing relevant therapeutic strategies, and pinpoint novel directions for research.

Neurotransmitters' white matter mapping unveils the neurochemical fingerprints of stroke

Distinctive patterns of brain neurotransmission frame determinant circuits for behavior. Understanding the relationship between their damage and the cognitive impairment provoked by brain lesions could provide insights into the pathophysiology and therapeutics of disabling disorders, like stroke. Yet, the challenges of neurotransmitter circuits mapping in vivo have hampered this investigation. Here, we developed an MRI white matter atlas of neurotransmitter circuits and created a method to chart how stroke damages neurotransmitter systems, which distinguishes pre and postsynaptic disruption. Our model, trained and tested in two large stroke patient samples, identified eight clusters with different neurochemical patterns. The associations with patients' cognitive profiles were scarce, denoting that a particular cognitive deficit might have finer underlying neurochemical disturbances that are unfit to the granularity of our analyses. These findings depict stroke neurochemical diaschisis patterns, provide insights into stroke cognitive deficits and potential treatments, and open a new window for tailored neurotransmitter modulation.

Localisation of function in the brain: a rethink

A modular view of brain function dominates the teaching of medical students and clinical psychologists and is implicit in day-to-day clinical practice. This view glosses over a long-standing debate. The extent of one-to-one mappings between region and function remains a controversial topic. For the cortex, localisation of function versus 'cerebral equipotentiality' was debated less than 150 years ago, and traces of this debate remain active in systems neuroscience today. The advent of functional brain imaging led to an explosion of evidence on localisation of function studied in vivo, and a gold rush to map an ever-increasing range of 'functions'. Rapid growth in knowledge was accompanied, to some extent, by a flourishing neuromythology. There are currently few clinical applications of brain mapping techniques, but new areas are emerging. An understanding of the central debate on functional localisation will bring a more nuanced view of problems encountered in clinical practice.

Specific Mode Electroacupuncture Stimulation Mediates the Delivery of NGF Across the Hippocampus Blood-Brain Barrier Through p65-VEGFA-TJs to Improve the Cognitive Function of MCAO/R Convalescent Rats

Cognitive impairment frequently presents as a prevalent consequence following stroke, imposing significant burdens on patients, families, and society. The objective of this study was to assess the effectiveness and underlying mechanism of nerve growth factor (NGF) in treating post-stroke cognitive dysfunction in rats with cerebral ischemia-reperfusion injury (MCAO/R) through delivery into the brain using specific mode electroacupuncture stimulation (SMES). From the 28th day after modeling, the rats were treated with NGF mediated by SMES, and the cognitive function of the rats was observed after treatment. Learning and memory ability were evaluated using behavioral tests. The impact of SMES on blood-brain barrier (BBB) permeability, the underlying mechanism of cognitive enhancement in rats with MCAO/R, including transmission electron microscopy, enzyme-linked immunosorbent assay, immunohistochemistry, immunofluorescence, and TUNEL staining. We reported that SMES demonstrates a safe and efficient ability to open the BBB during the cerebral ischemia repair phase, facilitating the delivery of NGF to the brain by the p65-VEGFA-TJs pathway.

Mechanisms underlying the spontaneous reorganization of depression network after stroke

Exploring the causal relationship between focal brain lesions and post-stroke depression (PSD) can provide therapeutic insights. However, a gap exists between causal and therapeutic information. Exploring post-stroke brain repair processes post-stroke could bridge this gap. We defined a depression network using the normative connectome and investigated the predictive capacity of lesion-induced network damage on depressive symptoms in discovery cohort of 96 patients, at baseline and six months post-stroke. Stepwise functional connectivity (SFC) was used to examine topological changes in the depression network over time to identify patterns of network reorganization. The predictive value of reorganization information was evaluated for follow-up symptoms in discovery and validation cohort 1 (22 worsening PSD patients) as well as for treatment responsiveness in validation cohort 2 (23 antidepressant-treated patients). We evaluated the consistency of significant reorganization areas with neuromodulation targets. Spatial correlations of network reorganization patterns with gene expression and neurotransmitter maps were analyzed. The predictive power of network damage for symptoms diminished at follow-up compared to baseline (Δadjusted R2 = -0.070, p < 0.001). Reorganization information effectively predicted symptoms at follow-up in the discovery cohort (adjust R2 = 0.217, 95 %CI: 0.010 to 0.431), as well as symptom exacerbation (r = 0.421, p = 0.033) and treatment responsiveness (r = 0.587, p = 0.012) in the validation cohorts. Regions undergoing significant reorganization overlapped with neuromodulatory targets known to be effective in treating depression. The reorganization of the depression network was associated with immune-inflammatory responses gene expressions and gamma-aminobutyric acid. Our findings may yield important insights into the repair mechanisms of PSD and provide a critical context for developing post-stroke treatment strategies.

Cognition and maps of injury in small vessel disease: time to move on from the black and white era

This scientific commentary refers to ‘Enhancing cognitive performance prediction by white matter hyperintensity connectivity assessment’ by Petersen et al. (https://doi.org/10.1093/brain/awae315).

Establishing connectivity through microdissections of midbrain stimulation-related neural circuits

Comprehensive understanding of the neural circuits involving the ventral tegmental area is essential for elucidating the anatomofunctional mechanisms governing human behaviour, in addition to the therapeutic and adverse effects of deep brain stimulation for neuropsychiatric diseases. Although the ventral tegmental area has been targeted successfully with deep brain stimulation for different neuropsychiatric diseases, the axonal connectivity of the region is not fully understood. Here, using fibre microdissections in human cadaveric hemispheres, population-based high-definition fibre tractography and previously reported deep brain stimulation hotspots, we find that the ventral tegmental area participates in an intricate network involving the serotonergic pontine nuclei, basal ganglia, limbic system, basal forebrain and prefrontal cortex, which is implicated in the treatment of obsessive-compulsive disorder, major depressive disorder, Alzheimer's disease, cluster headaches and aggressive behaviours.

Vagus Nerve Stimulation in Ischemic Stroke

PURPOSE OF REVIEW

Vagus nerve stimulation (VNS) has emerged as a potential therapeutic approach for neurological and psychiatric disorders. In recent years, there has been increasing interest in VNS for treating ischemic stroke. This review discusses the evidence supporting VNS as a treatment option for ischemic stroke and elucidates its underlying mechanisms.

RECENT FINDINGS

Preclinical studies investigating VNS in stroke models have shown reduced infarct volumes and improved neurological deficits. Additionally, VNS has been found to reduce reperfusion injury. VNS may promote neuroprotection by reducing inflammation, enhancing cerebral blood flow, and modulating the release of neurotransmitters. Additionally, VNS may stimulate neuroplasticity, thereby facilitating post-stroke recovery. The Food and Drug Administration has approved invasive VNS (iVNS) combined with rehabilitation for ischemic stroke patients with moderate to severe upper limb deficits. However, iVNS is not feasible in acute stroke due to its time-sensitive nature. Non-invasive VNS (nVNS) may be an alternative approach for treating ischemic stroke. While the evidence from preclinical studies and clinical trials of nVNS is promising, the mechanisms through which VNS exerts its beneficial effects on ischemic stroke are still being elucidated. Therefore, further research is needed to better understand the efficacy and underlying mechanisms of nVNS in ischemic stroke. Moreover, large-scale randomized clinical trials are necessary to determine the optimal nVNS protocols, assess its long-term effects on stroke recovery and outcomes, and identify the potential benefits of combining nVNS with other rehabilitation strategies.

Post-Stroke Neuropsychiatric Complications: Types, Pathogenesis, and Therapeutic Intervention

Almost all stroke survivors suffer physical disabilities and neuropsychiatric disturbances, which can be briefly divided into post-stroke neurological diseases and post-stroke psychiatric disorders. The former type mainly includes post-stroke pain, post-stroke epilepsy, and post-stroke dementia while the latter one includes post-stroke depression, post-stroke anxiety, post-stroke apathy and post-stroke fatigue. Multiple risk factors are related to these post-stroke neuropsychiatric complications, such as age, gender, lifestyle, stroke type, medication, lesion location, and comorbidities. Recent studies have revealed several critical mechanisms underlying these complications, namely inflammatory response, dysregulation of the hypothalamic pituitary adrenal axis, cholinergic dysfunction, reduced level of 5-hydroxytryptamine, glutamate-mediated excitotoxicity and mitochondrial dysfunction. Moreover, clinical efforts have successfully given birth to many practical pharmaceutic strategies, such as anti-inflammatory medications, acetylcholinesterase inhibitors, and selective serotonin reuptake inhibitors, as well as diverse rehabilitative modalities to help patients physically and mentally. However, the efficacy of these interventions is still under debate. Further investigations into these post-stroke neuropsychiatric complications, from both basic and clinical perspectives, are urgent for the development of effective treatment strategies.

Turning the Spotlight to Cholinergic Pharmacotherapy of the Human Language System

Even though language is essential in human communication, research on pharmacological therapies for language deficits in highly prevalent neurodegenerative and vascular brain diseases has received little attention. Emerging scientific evidence suggests that disruption of the cholinergic system may play an essential role in language deficits associated with Alzheimer's disease and vascular cognitive impairment, including post-stroke aphasia. Therefore, current models of cognitive processing are beginning to appraise the implications of the brain modulator acetylcholine in human language functions. Future work should be directed further to analyze the interplay between the cholinergic system and language, focusing on identifying brain regions receiving cholinergic innervation susceptible to modulation with pharmacotherapy to improve affected language domains. The evaluation of language deficits in pharmacological cholinergic trials for Alzheimer's disease and vascular cognitive impairment has thus far been limited to coarse-grained methods. More precise, fine-grained language testing is needed to refine patient selection for pharmacotherapy to detect subtle deficits in the initial phases of cognitive decline. Additionally, noninvasive biomarkers can help identify cholinergic depletion. However, despite the investigation of cholinergic treatment for language deficits in Alzheimer's disease and vascular cognitive impairment, data on its effectiveness are insufficient and controversial. In the case of post-stroke aphasia, cholinergic agents are showing promise, particularly when combined with speech-language therapy to promote trained-dependent neural plasticity. Future research should explore the potential benefits of cholinergic pharmacotherapy in language deficits and investigate optimal strategies for combining these agents with other therapeutic approaches.

Cognitive Recovery After Stroke: Memory

Memory impairment occurs in over a third of patients after symptomatic stroke. Memory deficits rarely occur in isolation but are an important component of the poststroke cognitive syndrome because of the strong relationship with the risk of poststroke dementia. In this review, we summarize available data on impairment of episodic memory, with a particular emphasis on the natural history of memory impairment after stroke and the factors influencing trajectory informed by an updated systematic review. We next discuss the pathophysiology of memory impairment and mechanisms of both decline and recovery of function. We then turn to the practical issue of measurement of memory deficits after stroke, emerging biomarkers, and therapeutic approaches. Our review identifies critical gaps, particularly in studies of the natural history that properly map the long-term trajectory of memory and the associations with factors that modulate prognosis. Few studies have used advanced neuroimaging and this, in conjunction with other biomarker approaches, has the potential to provide a much richer understanding of the mechanisms at play and promising therapeutic avenues.

Therapies Targeting Stroke Recovery

Stroke recovery therapeutics include many classes of intervention and numerous treatment targets. Stroke is a very heterogeneous disease. As such, stroke recovery therapeutics benefit from a personalized medicine approach that considers intersubject differences, such as in infarct location or stroke severity, when assigning treatment. Prediction of treatment responders can be improved by incorporating biological measures, such as neural injury and neural function, as the bedside behavioral phenotype has an incomplete relationship with the biological events underlying stroke recovery. Another ramification of high variability between patients is the need to examine effects of restorative therapies in relation to dose, time poststroke, and stroke severity in clinical trials. For example, enrollment across a wide time interval poststroke or in a population with a very broad range of deficits means high variance across patients in the biological state of the brain. The doses of rehabilitation therapy being studied are often low; it takes substantial practice to acquire a skill in the healthy brain; this is more, not less, pronounced after a stroke. Recognition and treatment of poststroke depression represents a major unmet need. These points are considered in the context of a review of recent advances in stroke recovery therapeutics.

Use of an Automated Mouse Touchscreen Platform for Quantification of Cognitive Deficits After Central Nervous System Injury

Analyzing cognitive performance is an important aspect of assessing physiological deficits after stroke or other central nervous system (CNS) injuries in both humans and in basic science animal models. Cognitive testing on an automated touchscreen operant platform began in humans but is now increasingly popular in preclinical studies as it enables testing in many cognitive domains in a highly reproducible way while minimizing stress to the laboratory animal. Here, we describe the step-by-step setup and application of four operant touchscreen tests used on adult mice. In brief, mice are trained to touch a graphical image on a lit screen and initiate subsequent trials for a reward. Following initial training, mice can be tested on tasks that probe performance in many cognitive domains and thus infer the integrity of brain circuits and regions. There are already many outstanding published protocols on touchscreen cognitive testing. This chapter is designed to add to the literature in two specific ways. First, this chapter provides in a single location practical, behind-the-scenes tips for setup and testing of mice in four touchscreen tasks that are useful to assess in CNS injury models: Paired Associates Learning (PAL), a task of episodic, associative (object-location) memory; Location Discrimination Reversal (LDR), a test for mnemonic discrimination (also called behavioral pattern separation) and cognitive flexibility; Autoshaping (AUTO), a test of Pavlovian or classical conditioning; and Extinction (EXT), tasks of stimulus-response and response inhibition, respectively. Second, this chapter summarizes issues to consider when performing touchscreen tests in mouse models of CNS injury. Quantifying gross and fine aspects of cognitive function is essential to improved treatment for brain dysfunction after stroke or CNS injury as well as other brain diseases, and touchscreen testing provides a sensitive, reliable, and robust way to achieve this.

Cholinergic neurotransmitter system: a potential marker for post-stroke cognitive recovery

This scientific commentary refers to ‘Cholinergic and hippocampal systems facilitate cross-domain cognitive recovery after stroke’ by O’Sullivan et al. (https://doi.org/10.1093/brain/awac070).