Intact Brain Research Articles

The role of neuroendothelial cells in aging-related vascular cognitive impairment

Vascular cognitive impairment (VCI) is a growing health problem in many developed countries due to aging of its population. Aging-induced impairment of neurovascular coupling (NVC) responses and brain microvascular rarefaction have been implicated as major driving mechanisms in age-related cognitive decline. One of the cellular hallmarks of NVC involve the release of vasodilator nitric oxide (NO) by endothelial cells in response to mediators released from activated neurons. Recent studies from our group identified and characterized a novel, minority subtype of scattered ECs with endothelial and neuronal characteristics, hence the name neuroendothelial cell (NECs). NECs present a well-defined arteriovenous zonal localization exclusively in small resistance arterioles with the highest density in the brain followed by the kidney. Intravital multiphoton microscopy (MPM) of intact brain arterioles in vivo suggest that NECs play an important role in regulating blood flow to the brain and able to detect changes in systemic blood pressure, hypoxia and perhaps other metabolic changes in the local microenvironment. Our central hypothesis is that NECs are novel key players in blood flow autoregulation, vascular control of organ functions in both short-term (hemodynamics) and long-term (angiogenesis, tissue regeneration). We further hypothesize that the decrease in NEC density and function in aged subjects is a major player in the development of age-related cerebral microvascular pathologies and that augmenting NEC number and function in aged animals will provide therapeutic benefit. This study used a NEC specific comprehensive research toolbox including NEC-GFP transgenic mouse models and high-resolution single-cell based transcriptome analysis to establish the NEC specific molecular atlas in young adult (3 month of age) and aged (2 years of age) animals. Furthermore, transgenic animal models combined with serial intravital imaging of the same tissue volume over consecutive days was used to study changes in vascular endothelial cell composition in response to NEC stimuli in young adult and aged mice. Cell fate tracking studies of the Nos1-lineage combined with Nos1 immunostaining revealed that NECs represent a permanent cell type with terminal neuronal differentiation. Importantly, NEC density is reduced with aging in all organs including the brain. High resolution single-cell based transcriptome analysis of 100K endothelial cells isolated from mouse brain demonstrated that, in contrast to other ECs, NECs highly express several traditional (e.g., Nos1, Angpt1, Egfl8) and novel (e.g., Cytl1, MGP, Gkn3) tissue trophic factors that are known to play important roles in acute hemodynamic responses including NO mediated functional hyperemia, and in chronic settings in angiogenesis, aging, vascular (dys)function, and chronic vascular diseases. Furthermore, the expression of many of these factors were significantly reduced in NECs isolated from aged animals. In conclusion, the newly discovered NEC-specific molecular and signaling mechanisms may play a role in the age-related decrease in NVC capacity and microvascular rarefaction and may be targeted for therapeutic benefits in age related VCI. American Society of Nephrology Carl W. Gottschalk Research Scholar Grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Pure-Shift-Based Proton Magnetic Resonance Spectroscopy for High-Resolution Studies of Biological Samples.

Proton magnetic resonance spectroscopy (1H MRS) presents a powerful tool for revealing molecular-level metabolite information, complementary to the anatomical insight delivered by magnetic resonance imaging (MRI), thus playing a significant role in in vivo/in vitro biological studies. However, its further applications are generally confined by spectral congestion caused by numerous biological metabolites contained within the limited proton frequency range. Herein, we propose a pure-shift-based 1H localized MRS method as a proof of concept for high-resolution studies of biological samples. Benefitting from the spectral simplification from multiplets to singlet peaks, this method addresses the challenge of spectral congestion encountered in conventional MRS experiments and facilitates metabolite analysis from crowded NMR resonances. The performance of the proposed pure-shift 1H MRS method is demonstrated on different kinds of samples, including brain metabolite phantom and in vitro biological samples of intact pig brain tissue and grape tissue, using a 7.0 T animal MRI scanner. This proposed MRS method is readily implemented in common commercial NMR/MRI instruments because of its generally adopted pulse-sequence modules. Therefore, this study takes a meaningful step for MRS studies toward potential applications in metabolite analysis and disease diagnosis.

Fibrin promotes oxidative stress and neuronal loss in traumatic brain injury via innate immune activation

BackgroundTraumatic brain injury (TBI) causes significant blood-brain barrier (BBB) breakdown, resulting in the extravasation of blood proteins into the brain. The impact of blood proteins, especially fibrinogen, on inflammation and neurodegeneration post-TBI is not fully understood, highlighting a critical gap in our comprehension of TBI pathology and its connection to innate immune activation.MethodsWe combined vascular casting with 3D imaging of solvent-cleared organs (uDISCO) to study the spatial distribution of the blood coagulation protein fibrinogen in large, intact brain volumes and assessed the temporal regulation of the fibrin(ogen) deposition by immunohistochemistry in a murine model of TBI. Fibrin(ogen) deposition and innate immune cell markers were co-localized by immunohistochemistry in mouse and human brains after TBI. We assessed the role of fibrinogen in TBI using unbiased transcriptomics, flow cytometry and immunohistochemistry for innate immune and neuronal markers in Fggγ390–396A knock-in mice, which express a mutant fibrinogen that retains normal clotting function, but lacks the γ390–396 binding motif to CD11b/CD18 integrin receptor.ResultsWe show that cerebral fibrinogen deposits were associated with activated innate immune cells in both human and murine TBI. Genetic elimination of fibrin-CD11b interaction reduced peripheral monocyte recruitment and the activation of inflammatory and reactive oxygen species (ROS) gene pathways in microglia and macrophages after TBI. Blockade of the fibrin-CD11b interaction was also protective from oxidative stress damage and cortical loss after TBI.ConclusionsThese data suggest that fibrinogen is a regulator of innate immune activation and neurodegeneration in TBI. Abrogating post-injury neuroinflammation by selective blockade of fibrin’s inflammatory functions may have implications for long-term neurologic recovery following brain trauma.

Functional sensory circuits built from neurons of two species

A central question for regenerative neuroscience is whether synthetic neural circuits, such as those built from two species, can function in an intact brain. Here, we apply blastocyst complementation to selectively build and test interspecies neural circuits. Despite approximately 10-20 million years of evolution, and prominent species differences in brain size, rat pluripotent stem cells injected into mouse blastocysts develop and persist throughout the mouse brain. Unexpectedly, the mouse niche reprograms the birth dates of rat neurons in the cortex and hippocampus, supporting rat-mouse synaptic activity. When mouse olfactory neurons are genetically silenced or killed, rat neurons restore information flow to odor processing circuits. Moreover, they rescue the primal behavior of food seeking, although less well than mouse neurons. By revealing that a mouse can sense the world using neurons from another species, we establish neural blastocyst complementation as a powerful tool to identify conserved mechanisms of brain development, plasticity, and repair.

Understanding the nervous system: lessons from Frontiers in Neurophotonics.

The Frontiers in Neurophotonics Symposium is a biennial event that brings together neurobiologists and physicists/engineers who share interest in the development of leading-edge photonics-based approaches to understand and manipulate the nervous system, from its individual molecular components to complex networks in the intact brain. In this Community paper, we highlight several topics that have been featured at the symposium that took place in October 2022 in Québec City, Canada.

Monitoring gene expression in the brain with synthetic serum markers

Blood tests are among the most common clinical tools due to their low cost, simplicity, and ability to observe many markers at once. However, currently, blood tests can only monitor a fraction of physiological processes that happen to have a serum marker. Here, we will present our work on the development of synthetic serum markers that can track gene expression in intact brain cells with a simple blood test. The synthetic marker approach has several advantages. First, detection of existing markers may be challenging due to their low levels in blood. With a synthetic marker, one can design a reporter that is easy to detect allowing for superior sensitivity. Second, there are large numbers of genes in each cell, but available brain imaging techniques can at most represent only a few signals (e.g., a few colors of fluorescent proteins, or types of MRI contrast). Synthetic serum markers use biochemical detection and can be designed to be massively multiplexed similarly to how thousands of proteins can be detected in blood simultaneously with mass spectrometry. Third, synthetic serum markers can surveil large brain regions, unlike invasive locally implanted devices. Finally, these markers have the potential for inexpensive and simple readout. We show applications of this concept with markers that can cross through an intact blood–brain barrier to report on gene expression and markers whose release from the brain relies on sonobiopsy to provide spatial selectivity.

Recording Quality Is Systematically Related to Electrode Impedance.

Extracellular recordings with planar microelectrodes are the gold standard technique for recording the fast action potentials of neurons in the intact brain. The introduction of microfabrication techniques has revolutionized the in vivo recording of neuronal activity and introduced high-density, multi-electrode arrays that increase the spatial resolution of recordings and the number of neurons that can be simultaneously recorded. Despite these innovations, there is still debate about the ideal electrical transfer characteristics of extracellular electrodes. This uncertainty is partly due to the lack of systematic studies comparing electrodes with different characteristics, particularly for chronically implanted arrays over extended time periods. Here a high-density, flexible, and thin-film array is fabricated and tested, containing four distinct electrode types differing in surface material and surface topology and, thus, impedance. It is found that recording quality is strongly related to electrode impedance with signal amplitude and unit yield negatively correlated to impedance. Electrode impedances are stable for the duration of the experiment (up to 12 weeks) and recording quality does not deteriorate. The findings support the expectation from the theory that recording quality will increase as impedance decreases.

Adaptation of Magnified Analysis of the Proteome for Excitatory Synaptic Proteins in Varied Samples and Evaluation of Cell Type-Specific Distributions.

Growing evidence suggests a remarkable diversity and complexity in the molecular composition of synapses, forming the basis for the brain to execute complex behaviors. Hence, there is considerable interest in visualizing the spatial distribution of such molecular diversity at individual synapses within intact brain circuits. Yet this task presents significant technical challenges. Expansion microscopy approaches have revolutionized our view of molecular anatomy. However, their use to study synapse-related questions outside of the labs developing them has been limited. Here we independently adapted a version of Magnified Analysis of the Proteome (MAP) and present a step-by-step protocol for visualizing over 40 synaptic proteins in brain circuits. Surprisingly, our findings show that the advantage of MAP over conventional immunolabeling was primarily due to improved antigen recognition and secondarily physical expansion. Furthermore, we demonstrated the versatile use of MAP in brains perfused with paraformaldehyde or fresh-fixed with formalin and in formalin-fixed paraffin-embedded tissue. These tests expand the potential applications of MAP to combinations with slice electrophysiology or clinical pathology specimens. Using male and female mice expressing YFP-ChR2 exclusively in interneurons, we revealed a distinct composition of AMPA and NMDA receptors and Shank family members at synapses on hippocampal interneurons versus on pyramidal neurons. Quantitative single synapse analyses yielded comprehensive cell type distributions of synaptic proteins and their relationships. These findings exemplify the value of the versatile adapted MAP procedure presented here as an accessible tool for the broad neuroscience community to unravel the complexity of the "synaptome" across brain circuits and disease states.

Bioorthogonal chemical labeling of endogenous neurotransmitter receptors in living mouse brains

Neurotransmitter receptors are essential components of synapses for communication between neurons in the brain. Because the spatiotemporal expression profiles and dynamics of neurotransmitter receptors involved in many functions are delicately governed in the brain, in vivo research tools with high spatiotemporal resolution for receptors in intact brains are highly desirable. Covalent labeling by chemical reaction (chemical labeling) of proteins without genetic manipulation is now a powerful method for analyzing receptors in vitro. However, selective target receptor labeling in the brain has not yet been achieved. This study shows that ligand-directed alkoxyacylimidazole (LDAI) chemistry can be used to selectively tether synthetic probes to target endogenous receptors in living mouse brains. The reactive LDAI reagents with negative charges were found to diffuse well over the whole brain and could selectively label target endogenous receptors, including AMPAR, NMDAR, mGlu1, and GABAAR. This simple and robust labeling protocol was then used for various applications: three-dimensional spatial mapping of endogenous receptors in the brains of healthy and disease-model mice; multi-color receptor imaging; and pulse-chase analysis of the receptor dynamics in postnatal mouse brains. Here, results demonstrated that bioorthogonal receptor modification in living animal brains may provide innovative molecular tools that contribute to the in-depth understanding of complicated brain functions.

Wired together, change together: Spike timing modifies transmission in converging assemblies.

The precise timing of neuronal spikes may lead to changes in synaptic connectivity and is thought to be crucial for learning and memory. However, the effect of spike timing on neuronal connectivity in the intact brain remains unknown. Using closed-loop optogenetic stimulation in CA1 of freely moving mice, we generated unique spike patterns between presynaptic pyramidal cells (PYRs) and postsynaptic parvalbumin (PV)-immunoreactive cells. The stimulation led to spike transmission changes that occurred together across all presynaptic PYRs connected to the same postsynaptic PV cell. The precise timing of all presynaptic and postsynaptic cell spikes affected transmission changes. These findings reveal an unexpected plasticity mechanism, in which the spike timing of an entire cell assembly has a more substantial impact on effective connectivity than that of individual cell pairs.

Engineered serum markers for non-invasive monitoring of gene expression in the brain.

Measurement of gene expression in the brain requires invasive analysis of brain tissue or non-invasive methods that are limited by low sensitivity. Here we introduce a method for non-invasive, multiplexed, site-specific monitoring of endogenous gene or transgene expression in the brain through engineered reporters called released markers of activity (RMAs). RMAs consist of an easily detectable reporter and a receptor-binding domain that enables transcytosis across the brain endothelium. RMAs are expressed in the brain but exit into the blood, where they can be easily measured. We show that expressing RMAs at a single mouse brain site representing approximately 1% of the brain volume provides up to a 100,000-fold signal increase over the baseline. Expression of RMAs in tens to hundreds of neurons is sufficient for their reliable detection. We demonstrate that chemogenetic activation of cells expressing Fos-responsive RMA increases serum RMA levels >6-fold compared to non-activated controls. RMAs provide a non-invasive method for repeatable, multiplexed monitoring of gene expression in the intact animal brain.

Optical Methods for the Study of Brain Metabolism In Situ.

From its inception, the International Society of Oxygen Transport to Tissue (ISOTT) included several core members who were intrigued by the possibility of using light to probe the metabolic state of the cerebral cortex. This 50th anniversary review will focus on optical methods (UV, Visible, NIR) used to study brain oxygen metabolism in the intact brain. Chance, Lübbers, and Jöbsis did fundamental work in the 1970s and 1980s. These investigators spearheaded the use of fluorescence of pyridine nucleotides (e.g., NADH) and flavoprotein, and visible and near-infrared spectroscopy of haemoglobin amount and saturation, as well as the mitochondrial cytochrome chain. Two of our society awards are named for these pioneers and founders. By the new millennium, their many scientific descendants (although still too few for the task at hand) have been productive and moved the field forward. Technical advances in materials, detectors, devices, and computer power have made great advances possible. Physiological theory and understanding of cell and molecular mechanisms still lag, providing fertile territory for future goals. There are at least two major directions currently that will certainly continue to illuminate brain metabolism (obvious-and well worn-pun intended). These are the burgeoning NIR instrumentation variations, and second, the tremendous potential of two-photon phosphorescence lifetime microscopy. These advances have been introduced through the years and continue to be advanced at our annual ISOTT symposia.

Гистологические и иммуногистохимические изменения префронтальной коры головного мозга мышей под действием дексаметазона

Introduction. The effects of the synthetic glucocorticoid dexamethasone on target organs are mediated by the interaction with the glucocorticoid receptor, but the effects of the drug on the intact brain have been poorly studied. We aimed to look at a one-time and repeated exposure to a two-dose dexamethasone on the expression of the glucocorticoid receptor and cellular changes in the prefrontal cortex over time. Materials and methods. Male C57Bl/6 mice aged 7–8 weeks received a one-time or multiple intraperitoneal injections of dexamethasone in doses of 1.0 or 2.5 mg/kg. Structural changes in the prefrontal cortex were analyzed on paraffin sections stained by hematoxylin and eosin 90 days after the injection. The expression of the glucocorticoid receptor was studied with immunohistochemistry using monoclonal antibodies and quantitative analysis. Results. A histological study of the prefrontal cortex exposed to a two-dose dexamethasone revealed the absence of an obvious dose dependence and the reversibility of dystrophic and hydropic changes. The most pronounced changes were revealed with a one-time administration of the drug (on day 7) and repeated administration (on day 15) while normal tissue architecture returned to that of the control groups. The expression level of the glucocorticoid receptor after a one-time dexamethasone injection at a dose of 2.5 mg/kg showed a significant growth (р<0.05) on days 3 and 10 compared to that of the control group, while after multiple dexamethasone injections, the GR expression decreased on day 15, but by day 30 it returned to its initial level. Conclusion. Stereotypical dystrophic and hydropic changes in the prefrontal cortex during exposure to two different regimens and dexamethasone doses developed on days 7 and 15. We revealed an opposite effect of 2.5 mg/kg dexamethasone administration regimens on the expression of the glucocorticoid receptor in the prefrontal cortex of mice relative to the control group: at a one-time administration the expression increased by 8.1% on day 10 and at multiple administration the expression grew by 9.9% on day 15. Keywords: dexamethasone, glucocorticoids, brain, prefrontal cortex, glucocorticoid receptor, immunohistochemistry

The corpus callosum and creativity revisited.

In 1969 Joseph Bogen, a colleague of Roger Sperry and the neurosurgeon who performed commissurotomy on Sperry's "split-brain" study participants, wrote an article subtitled "The Corpus Callosum and Creativity." The article argued for the critical role of the corpus callosum and hemispheric specialization in creativity. Building on a four-stage model of creativity (learning, incubation, illumination, refinement) and Sperry's innovative studies, the Bogens posited that in the intact brain, creativity relies on two opposing functions of the corpus callosum: (a) interhemispheric inhibition to facilitate simultaneous and independent activity of uniquely-specialized processing centers during learning and incubation and (b) interhemispheric facilitation to support the increased bi-hemispheric integration and coordination which produces illumination. This article revisits the Bogens' theory considering scientific discoveries over the past 50 years. We begin by reviewing relevant findings from split-brain studies, and then briefly consider findings from studies that examine the association of creativity with callosal structure and function in neurotypical participants. Finally, we provide an in-depth discussion of creativity in persons with agenesis of the corpus callosum (ACC)-the congenital absence of the corpus callosum. These three lines of inquiry strongly support the theory suggested by Bogen and Bogen in 1969 and provide further clarification regarding the critical and unique role of the corpus callosum in creative cognition.

Inflammatory response of both retinas and superior colliculi to unilateral optic nerve axotomy

Objective: Unilateral optic nerve crush (ONC) induces a bilateral inflammatory reaction affecting both injured and contralateral un‐injured retinas. However, few works have investigated the spread of inflammation along visual pathway. Our aim was to study the glial response and the underlying molecular changes in both retinas and the superior colliculi (SCi), the main projection areas of retinal ganglion cells in mice. In this species, >90% of RGCs project to the contralateral SC (cSCi).Methods: The left optic nerve of adult pigmented C57Bl/6 male mice were crushed (ONC) at 0.5 mm from the optic disk or underwent surgery without crushing (Sham). One group of intact mice was used as controls. Two studies were carried out:1) At 1, 3, 9 and 30 days post lesion (dpl) both retinas and SCi were freshly dissected and their RNA extracted. Using qPCR we measured the expression levels of TGF‐β1, IL‐1β, TNF‐α, Iba1, GFAP, MHC II and TSPO in retinas and SCi. In SCi extracts we also studied Casp3, CXCR1, Lcn2, IL‐6, CD206, IL‐4, and AQ4. Hptr and Gapdh were used as houskeepings. Intact retinas and SCi were used as controls.2) Three, 9 and 30 days after ONC or sham‐surgery immunodetection of microglia and macroglial cells was carried out in sagittal brain sections. The area occupied by GFAP and MHC II signal as well as the density of Iba1+ and CD68+ cells was quantified in both SCi. Intact brains were used as controls.Results: Sham surgery alone modified gene expression in both retinas and SCi compared to intact animals. Therefore, to isolate the effect of ONC, we compared ONC vs. Sham. After ONC, TNF‐α upregulated early in both retinas and IL‐β remained overexpressed in injured retina at day 30. GFAP overexpression was exclusively observed in injured retina while Iba1 overexpression was presented in both. TSPO and MHCII and Casp3 overexpression was observed only in the cSC.Anatomical microglial activation (rounded somas and CD68 expression) was observed in the cSC from day 3 onwards after ONC. In the ipsilateral SC (iSC) microglial cells did not show signs of activation. Astrocytes hypertrophied in both SCi from day 9 after ONC, but this response was also observed in Sham‐animals.Conclusions: Sham surgery promotes an inflammatory and glial response that must be considered in experimental designs. Unilateral ONC triggers a bilateral response which extends anterogradely and retrogradely along the visual pathway.

Progress in Structural and Functional In Vivo Imaging of Microglia and Their Application in Health and Disease.

The first line of defense for the central nervous system (CNS) against injury or disease is provided by microglia. Microglia were long believed to stay in a dormant/resting state, reacting only to injury or disease. This view changed dramatically with the development of modern imaging techniques that allowed the study of microglial behavior in the intact brain over time, to reveal the dynamic nature of their responses. Over the past two decades, in vivo imaging using multiphoton microscopy has revealed numerous new functions of microglia in the developing, adult, aged, injured, and diseased CNS. As the most dynamic cells in the brain, microglia continuously contact all structures and cell types, such as glial and vascular cells, neuronal cell bodies, axons, dendrites, and dendritic spines, and are believed to play a central role in sculpting neuronal networks throughout life. Following trauma, or in neurodegenerative or neuroinflammatory diseases, microglial responses range from protective to harmful, underscoring the need to better understand their diverse roles and states in different pathological conditions. In this chapter, we introduce multiphoton microscopy and discuss recent advances in structural and functional imaging technologies that have expanded our toolbox to study microglial states and behaviors in new ways and depths. We also discuss relevant mouse models available for in vivo imaging studies of microglia and review how such studies are constantly refining our understanding of the multifaceted role of microglia in the healthy and diseased CNS.

Quantifying Dendritic Arbors In Vitro and In Vivo in Rodent Models.

Dendritic arborization is a critical determinant of neuronal connectivity. The structure of a neuron's dendritic arbor determines the number of synaptic inputs a neuron can receive and how it processes synaptic input from other neurons. Here, we describe methods for visualizing and quantifying the dendritic arbor in primary cell cultures and in the intact rodent brain. These techniques can be used to answer significant scientific questions, such as the effects of disease processes, drugs, growth factors, and diverse environmental stressors on dendritogenesis in both in vitro and in vivo rodent models.

Memory Storage in Distributed Engram Cell Ensembles.

One of the most fascinating aspects of the brain is its ability to acquire new information from experience and retain it over time as memory. The search for physical correlates of memory, the memory engram, has been a longstanding priority in modern neurobiology. Advanced genetic approaches have led to the localization of engram cells in a few brain regions, including the hippocampus and cortex. Additionally, engram cells exhibit learning-induced, persistent modifications and have at least two states, active and silent. However, it has been hypothesized that engrams for a specific memory are distributed among multiple brain regions that are functionally connected, referred to as a unified engram complex. Recent tissue-clearing techniques have permitted high-throughput analyses of intact brain samples, which have been used to obtain a map of the engram complex for a contextual fear memory. Careful examination of these engram complex maps has revealed a potentially underappreciated contribution of subcortical regions, specifically thalamic nuclei, to memory function. These more holistic studies support the unified engram complex hypothesis for memory storage and have important implications for understanding dysfunctional engrams in the context of human disease.

Effects of transcranial magnetic stimulation on cortical structures during motor imagination performance in the brain-computer interface

The aftermath of a stroke can frequently result in impaired motor functions causing problems performing habitual limb movements. These movement disorders stem from damage to the cerebral cortex and disruptions to neuronal connections in the central pyramidal pathways [1]. Restoring motor skills following a stroke is a time-consuming and challenging process, requiring resources from both external medical sources and the patient. Despite these challenges, it is still feasible for patients to regain control over their limb movements. The common approach for stroke neurorehabilitation consists of therapeutic physical activities and kinesiotherapy. These methods rely on afferent information during motor tasks to repair connections between intact brain areas [2]. Through exercising the impacted limbs, synaptic rearrangement happens in the cortex, awakening dormant neurons and increasing cortical areas adjacent to inactive regions. Although these techniques can partially restore movement, a significant number of stroke patients still face impairments. It is crucial to acknowledge the limitations of the current interventions and explore new approaches for better outcomes. Traditional rehabilitation methods often do not fully restore movement control, prompting researchers to explore alternative approaches. Motor-imagery-based brain-computer interfaces (BCIs) have gained attention recently [3, 4]. They allow for integrating various feedback mechanisms, which can be combined with upper and lower limb exoskeletons. The level of control a subject has over a BCI system directly affects the recovery process [5]. Introducing transcranial magnetic stimulation (TMS) into motor-imagery BCIs shows promise for developing a unified and highly efficient approach to post-stroke rehabilitation. Twenty-nine healthy adult participants (21 females) with a mean age of 20.93±2.14 years were recruited for this experiment. All participants were right-handed and had no prior experience with brain-computer interfaces. Ethical approval was obtained from the local ethics committee of Lobachevsky State University of Nizhny Novgorod (ethical approval No. 2, dated 03/19/2021), and written informed consent was obtained from all participants. Subjects were randomly assigned to receive either a sham intervention (n=15) or active TMS (n=14). The experiment displayed tasks on a 24-inch LCD screen placed 2 meters away. Participants sat in a reclining chair with hands on adjustable armrests for EEG signal recording. Motor-imagery-based BCI training took place over two days with four daily tasks: motor performance, quasi-motor, and two motor imaginations of the dominant hand. EEG activity was recorded prior to and after completing the tasks. Each task comprised of 20 trials, each lasting 10 seconds. TMS was administered in between two motor imagination tasks, and a rest period of 2 minutes followed the stimulation. The researcher objectively monitored electromyography (EMG) in real-time during motor tasks. Certified NVX 52 amplifiers with 32 Cl/Ag electrodes positioned according to the international 10-10 system recorded electroencephalography (EEG) signals. The EEG was digitized at a sampling rate of 1000 Hz and filtered with a 50 Hz Notch filter. Disposable electrodes were used to record EMG data from musculus flexor digitorum superficialis on the right hand. EMG signals were digitized at 1000 Hz and filtered using a 50 Hz Notch filter. TMS was applied to the dorsolateral prefrontal cortex (dlPFC) using a figure-8 coil connected to a Neuro MS/D magnetic stimulator. Sham stimulation was performed with the same parameters, except the coil was tilted 90 degrees to simulate the sound of real stimulation. A nonparametric permutation test was conducted to assess the statistically significant dissimilarities between rest periods and periods subsequent to conducting motor imagery after TMS. Significant clusters of the highest event-related desynchronization (ERD) were observed. The analysis demonstrated a significant negative cluster in the theta rhythm (0–6 Hz) that was distinct from the magnetic stimulation site. Similar significant ERD clusters were identified during the first and second series of imaginary movements. The study examined alterations in motor cortex function following targeted rTMS. The results demonstrated that TMS using particular parameters resulted in the pre-activation of brain regions comparable to those stimulated during motor imagery. The implementation of this stimulation protocol increased activity in cortical regions related to motor imagery. The outcomes propose the probable effectiveness of TMS in elevating motor cortex activation during the rehabilitation process.

Magnetic Resonance Imaging in Studies of Perifocal Zone of Brain Gliomas (a Literature Review)

This review provides insight into application of modern MRI modalities including diffusion kurtosis imaging in assessment of perifocal glioma zone. Differentiation of “pure” perifocal vasogenic edema from edema infiltrated by glioma cells, as well as identification of peritumoral intact (on conventional MRI) brain matter infiltration make it possible to determine glial tumor borders more accurately. Analysis of diffusion and perfusion quantitative MR data allow determining glioma borders in areas with unaltered blood-brain barrier. There is a growing possibility to develop a personalized navigation algorithm for surgical removal of the tumor, followed by the determination of an individual plan for radiation and chemotherapy, as well as prediction of disease outcomes.