The corticospinal tract: Evolution, development, and human disorders

CRMP2 and its phosphorylation prevent axonal misrouting of the corticospinal tract

During the development of the central nervous system (CNS), the formation of neural circuits such as the corticospinal tract (CST) is crucial to control voluntary movement and is regulated by axonal guidance mechanisms. In this study, we examined the role of CRMP2 (Collapsin response mediator protein 2) in the formation of CST. CRMP2, which binds to actin and microtubules to control the cytoskeleton, is a phosphoprotein whose activity depends on its phosphorylated state. To inhibit Cyclin-dependent kinase 5 (Cdk5) phosphorylation, CRMP2 knock-in (crmp2ki/ki) mice were generated in which the serine residue at position 522 was replaced with alanine. Our results showed that both CRMP2 knock-out (crmp2-/-) and crmp2ki/ki mice exhibited higher percentages of CST axons that crossed the midline erroneously than wild-type (WT) mice. However, in mice lacking CRMP1, which is highly homologous to CRMP2, few axons crossed the midline, similar to WT mice. Additionally, crmp2-/- and crmp2ki/ki mice showed decreased proportions of independent forelimb movements. These findings emphasize that CRMP2 and its phosphorylation are necessary for proper CST formation in the mouse CNS.

Fiber Microstructure Quantile (FMQ) Regression: A Novel Statistical Approach for Analyzing White Matter Bundles from Periphery to Core

The structural connections of the brain's white matter are critical for brain function. Diffusion MRI tractography enables the in-vivo reconstruction of white matter fiber bundles and the study of their relationship to covariates of interest, such as neurobehavioral or clinical factors. In this work, we introduce Fiber Microstructure Quantile (FMQ) Regression, a new statistical approach for studying the association between white matter fiber bundles and scalar factors (e.g., cognitive scores). Our approach analyzes tissue microstructure measures based on quantile-specific bundle regions . These regions are defined in a data-driven fashion according to the quantiles of fractional anisotropy (FA) of a population fiber bundle, which pools all individuals' bundles. The FA quantiles induce a natural subdivision of a fiber bundle, defining regions from the periphery (low FA) to the core (high FA) of the population fiber bundle. To investigate how fiber bundle tissue microstructure relates to covariates of interest, we employ the statistical technique of quantile regression. Unlike ordinary regression, which only models a conditional mean, quantile regression models the conditional quantiles of a response variable. This enables the proposed analysis, where a quantile regression is fitted for each quantile-specific bundle region. To demonstrate FMQ Regression, we perform an illustrative study in a large healthy young adult tractography dataset derived from the Human Connectome Project-Young Adult (HCP-YA), focusing on particular bundles expected to relate to particular aspects of cognition and motor function. In comparison with traditional regression analyses based on FA Mean and Automated Fiber Quantification (AFQ), we find that FMQ Regression provides a superior model fit with the lowest mean squared error. This demonstrates that FMQ Regression captures the relationship between scalar factors and white matter microstructure more effectively than the compared approaches. Our results suggest that FMQ Regression, which enables FA analysis in data-driven regions defined by FA quantiles, is more powerful for detecting brain-behavior associations than AFQ, which enables FA analysis in regions defined along the trajectory of a bundle. FMQ Regression finds significant brain-behavior associations in multiple bundles, including findings unique to males or to females. In both males and females, language performance is significantly associated with FA in the left arcuate fasciculus, with stronger associations in the bundle's periphery. In males only, memory performance is significantly associated with FA in the left uncinate fasciculus, particularly in intermediate regions of the bundle. In females only, motor performance is significantly associated with FA in the left and right corticospinal tracts, with a slightly lower relationship at the bundle periphery and a slightly higher relationship toward the bundle core. No significant relationships are found between executive function and cingulum bundle FA. Our study demonstrates that FMQ Regression is a powerful statistical approach that can provide insight into associations from bundle periphery to bundle core. Our results also identify several brain-behavior relationships unique to males or to females, highlighting the importance of considering sex differences in future research.

Novel brain biomarkers of obesity in young adult women based on statistical measurements of white matter tracts

OBJECTIVE

Novel brain biomarkers of obesity were sought by studying statistical measurements on fractional anisotropy (FA) images of different white matter (WM) tracts from young adult women.

METHODS

Tract measurements were chosen that showed differences between two groups (normal weight and overweight/obese) and that were correlated with BMI. From these measurements, a simple and novel process was applied to select those that would allow the creation of models to quantify and classify the state of obesity of individuals. The biomarkers were created from the tract measurements used in the models.

RESULTS

Positive correlations were found between WM integrity and BMI, mainly in tracts involved in motor functions. From these results, two models were built to quantify and classify obesity status, whose regression coefficients formed the novel proposed obesity associated brain biomarkers.

CONCLUSION

A process for the selection of tract measurements was proposed, such models were built to determine the obesity status of subjects individually. From these models, novel brain biomarkers associated with obesity were created. These results generate new knowledge in the field, intended to be used in the future in the clinical environment as a prevention and treatment tool for brain changes associated with obesity.

SIGNIFICANCE

After studying young adult women, results opposed some of the previous results reported in literature. These consisted of positive correlations between WM integrity and obesity mainly in tracts involved in motor functions. Novel brain biomarkers of obesity were also proposed, formed by the regression coefficients involved in precise models of quantification and classification of obesity status. All this allows the generation of new knowledge and its probable subsequent clinical application.

Brain functional and structural alteration following acute carbon monoxide poisoning contribute to delayed neurological sequelae

PURPOSE

To investigate whether altered functional activity, functional connectivity (FC), and structural connectivity (SC) following acute carbon monoxide (CO) poisoning contribute to delayed neurological sequelae (DNS) occurrence.

METHODS

Binary degree centrality (DC) and seed-based FC were investigated in 18 patients with DNS, 26 patients without DNS, and 30 healthy controls. Duration of CO exposure and coma severity indices-related fibers was detected by connectometry analysis and the identified fiber tracts were tracked and their SC alteration was quantify by fractional anisotropy (FA).

RESULTS

Acute CO exposure induced DC change in the prefrontal cortex (PFC), visual cortex, primary sensory cortex, and anterior cerebellum, and FC alteration between the right fusiform gyrus (seed) and bilateral PFC and left inferior occipital gyrus (Gaussian random field corrected, P < 0.05). Poisoning severity indices-related WM fibers consisted of corpus callosum and some association and projection fibers (false discovery rate corrected, P < 0.05). Only altered DC in the right fusiform gyrus and right postcentral gyrus and reduced FC of the PFC could identify DNS occurrence (P < 0.05).

CONCLUSIONS

The functional abnormalities in the visual- and sensory- cortex and PFC subsequent to acute CO poisoning represent one of the potential neural mechanisms underlying the occurrence of DNS.

The diversity and plasticity of descending motor pathways rewired after stroke and trauma in rodents

Descending neural pathways to the spinal cord plays vital roles in motor control. They are often damaged by brain injuries such as stroke and trauma, which lead to severe motor impairments. Due to the limited capacity for regeneration of neural circuits in the adult central nervous system, currently no essential treatments are available for complete recovery. Notably, accumulating evidence shows that residual circuits of the descending pathways are dynamically reorganized after injury and contribute to motor recovery. Furthermore, recent technological advances in cell-type classification and manipulation have highlighted the structural and functional diversity of these pathways. Here, we focus on three major descending pathways, namely, the corticospinal tract from the cerebral cortex, the rubrospinal tract from the red nucleus, and the reticulospinal tract from the reticular formation, and summarize the current knowledge of their structures and functions, especially in rodent models (mice and rats). We then review and discuss the process and patterns of reorganization induced in these pathways following injury, which compensate for lost connections for recovery. Understanding the basic structural and functional properties of each descending pathway and the principles of the induction and outcome of the rewired circuits will provide therapeutic insights to enhance interactive rewiring of the multiple descending pathways for motor recovery.

Altered Functional Connectivity Between Cortical Premotor Areas and the Spinal Cord in Chronic Stroke

BACKGROUND

Neuroscience research has contributed significantly to understanding alterations in brain structure and function after ischemic stroke. Technical limitations have excluded the spinal cord from imaging-based research. Available data are restricted to a few microstructural analyses, and functional connectivity data are absent. The present study attempted to close this knowledge gap and assess alterations in corticospinal coupling in chronic stroke and their relation to motor deficits.

METHODS

In this cross-sectional study, patients with chronic stroke and healthy controls underwent corticospinal functional magnetic resonance imaging while performing a simple force generation task at the University Medical Center Hamburg-Eppendorf between September 2021 and June 2023. Task-related activation was localized in the ipsilesional ventral premotor cortex, the supplementary motor area, and the cervical spinal cord. Psycho-physiological interactions and linear modeling were used to infer functional connectivity between cortical motor regions and the cervical spinal cord and their associations with clinical scores.

RESULTS

Thirteen well-recovered patients with stroke (1 woman, 12 men; mean age, 62.6 years; mean time after stroke: 47.6 months) and 13 healthy controls (5 women, 8 men; mean age, 64.5 years) were included. The main finding was that ventral premotor cortex and supplementary motor area showed topographically distinct alterations in their connectivity with the spinal cord. Specifically, we found a reduced coupling between the supplementary motor area and the ipsilateral ventral spinal cord and an enhanced coupling between the ventral premotor cortex and ventral and intermediate central spinal zones. Lower supplementary motor area and higher ventral premotor cortex-related spinal cord couplings were correlated with residual deficits.

CONCLUSIONS

This work provides first-in-human functional insights into stroke-related alterations in the functional connectivity between cortical premotor areas and the spinal cord, suggesting that different premotor areas and spinal neuronal assemblies might be involved in coupling changes. It adds a novel, promising approach to better understanding stroke recovery and developing innovative models to comprehend treatment strategies with spinal cord stimulation.

Goal-directed action preparation in humans entails a mixture of corticospinal neural computations

The seemingly effortless ability of humans to transition from thinking about actions to initiating them relies on sculpting corticospinal (CS) output from the primary motor cortex. The present study tested whether canonical additive and multiplicative neural computations, well-described in sensory systems, generalize to the CS pathway during human action preparation. We used non-invasive brain stimulation to measure CS input-output across varying action preparation contexts during instructed-delay finger response tasks. Goal-directed action preparation was marked by increased multiplicative gain of CS projections to task-relevant muscles and additive suppression of CS projections to non-selected and task-irrelevant muscles. Individuals who modulated CS gain to a greater extent were faster to initiate prepared responses. Our findings provide physiological evidence of combined additive suppression and gain modulation in the human motor system. We propose that these computations support action preparation by enhancing the contrast between selected motor representations and surrounding background activity to facilitate response selection and execution. KEY POINTS: Neural computations determine what information is transmitted through brain circuits. We investigated whether the motor system uses computations similar to those observed in sensory systems by non-invasively stimulating the corticospinal pathway in humans during goal-directed action preparation. We discovered physiological evidence indicating that corticospinal projections to behaviourally relevant muscles exhibit non-linear gain computations, whereas projections to behaviourally irrelevant muscles exhibit linear suppression. Our findings suggest that certain computational principles generalize to the human motor system and serve to enhance the contrast between relevant and background neural activity. These results indicate that neural computations during goal-directed action preparation may support motor control by increasing signal-to-noise within the corticospinal pathway.

White matter microstructure in school-age children with down syndrome

Down syndrome (DS) is the most common genetic cause of intellectual disability, but our understanding of white matter microstructure in children with DS remains limited. Previous studies have reported reductions in white matter integrity, but nearly all studies to date have been conducted in adults or relied solely on diffusion tensor imaging (DTI), which lacks the ability to disentangle underlying properties of white matter organization. This study examined white matter microstructural differences in 7- to 12-year-old children with DS (n = 23), autism (n = 27), and typical development (n = 50) using DTI as well as High Angular Resolution Diffusion Imaging, and Neurite Orientation and Dispersion Imaging. There was a spatially specific pattern of results that showed a dissociation between intra- and inter-hemispheric pathways. Intra-hemispheric pathways (e.g., inferior fronto-occipital fasciculus, superior longitudinal fasciculus) exhibited reduced organization and structural integrity. Inter-hemispheric pathways (e.g., corpus callosum projections) and motor pathways (e.g., corticospinal tract) showed denser neurite packing and lower neurite dispersion. The current findings provide early insight into white matter development in school-aged children with DS and have the potential to further elucidate microstructural differences and inform more targeted clinical trials than what has previously been observed through DTI models alone.

Targeting Spinal Interneurons for Respiratory Recovery After Spinal Cord Injury

Spinal interneurons (SpINs) are pivotal to the function of neural circuits, orchestrating motor, sensory, and autonomic functions in the healthy, intact central nervous system. These interneurons (INs) are heterogeneous, with diverse types contributing to various neural systems, including those that control respiratory function. Research in the last few decades has highlighted the complex involvement of SpINs in modulating motor control. SpINs also partake in motor plasticity by aiding in adapting and rewiring neural circuits in response to injury or disease. This plasticity is crucial in the context of spinal cord injury (SCI), where damage often leads to severe and long-term breathing deficits. Such deficits are a leading cause of morbidity and mortality in individuals with SCI, emphasizing the need for effective interventions. This review will focus on SpIN circuits involved in the modulation of breathing and explore current and emerging approaches that leverage SpINs as therapeutic targets to promote respiratory recovery following SCI.

Cervical spinal cord stimulation for treatment of upper limb paralysis: a narrative review

Recent advances in cervical spinal cord stimulation (SCS) have demonstrated improved efficacy as a therapeutic intervention for restoring hand functions in individuals with spinal cord injuries or stroke. Accumulating evidence consistently shows that cervical SCS yields significant improvements in grip force, proximal arm strength and muscle activation, with both immediate and sustained effects. This review synthesizes the evidence that electrical stimulations modulate the spinal and supraspinal organization of uninjured descending motor tracts, primarily the residual corticospinal tract, reticulospinal tract and propriospinal network of neurons, as well as increasing the sensitivity of spinal interneurons at the stimulated segments to these inputs. Additionally, we examine contemporary strategies aimed at achieving more precise patterned stimulations, including intraspinal microstimulation, ventral cord stimulation and closed-loop neuromodulation, and discuss the potential benefits of incorporating cervical SCS into a multimodal treatment paradigm.Level of evidence: V.

Goal-directed action preparation in humans entails a mixture of corticospinal neural computations

The seemingly effortless ability of humans to transition from thinking about actions to initiating them relies on sculpting corticospinal output from primary motor cortex. This study tested whether canonical additive and multiplicative neural computations, well-described in sensory systems, generalize to the corticospinal pathway during human action preparation. We used non-invasive brain stimulation to measure corticospinal input-output across varying action preparation contexts during instructed-delay finger response tasks. Goal-directed action preparation was marked by increased multiplicative gain of corticospinal projections to task-relevant muscles and additive suppression of corticospinal projections to non-selected and task-irrelevant muscles. Individuals who modulated corticospinal gain to a greater extent were faster to initiate prepared responses. Our findings provide physiological evidence of combined additive suppression and gain modulation in the human motor system. We propose these computations support action preparation by enhancing the contrast between selected motor representations and surrounding background activity to facilitate response selection and execution.

Age-related differences in agility are related to both muscle strength and corticospinal tract function

Agility is essential for "healthy" aging, but neuromuscular contributions to age-related differences in agility are not entirely understood. We recruited healthy (n = 32) non-athletes (30-84 years) to determine: (1) if aging is associated with agility and (2) whether muscle strength or corticospinal tract function predicts agility. We assessed muscle strength via a validated knee extension test, corticospinal tract function via transcranial magnetic stimulation, and agility via spatiotemporal values (i.e., leg length-adjusted hop length and hop length variability) collected during a novel propulsive bipedal hopping (agility) task on an electronic walkway. Pearson correlation revealed aging is associated with leg length-adjusted hop length (r = -0.671, p < 0.001) and hop length variability (r = 0.423, p = 0.016). Further, leg length-adjusted hop length and hop length variability correlated with quadriceps strength (r = 0.581, p < 0.001; r = -0.364, p = 0.048) and corticospinal tract function (r = -0.384, p = 0.039; r = 0.478, p = 0.007). However, hierarchical regressions indicated that, when controlling for sex, muscle strength only predicts leg length-adjusted hop length (R2 = 0.345, p = 0.002), whereas corticospinal tract function only predicts hop length variability (R2 = 0.239, p = 0.014). Therefore, weaker quadriceps decrease the distance hopped, and deteriorating corticospinal tract function increases variability in hop length.

Wider and faster degeneration of white matter in Parkinson's disease with possible REM sleep behaviour disorder

BACKGROUND

In Parkinson's disease (PD), rapid eye movement (REM) sleep behaviour disorder (RBD) signifies a poorer prognosis, yet its impact on white matter (WM) degeneration remains unclear. The study examined the effect of RBD on WM alterations in PD progression.

METHODS

The study included 45 PD patients with possible RBD (PD-pRBD), 38 PD patients without possible RBD (PD-npRBD), and 79 healthy controls (HC). All patients underwent clinical assessments and diffusion MRI scans at least once a year for up to 4 visits. 79 HC underwent the same protocol at baseline. WM metrics, including fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD), were calculated using tract-based spatial statistics. Linear mixed-effects models were conducted to examine the changes in clinical features and WM fibers.

RESULTS

At baseline, PD-npRBD showed increased RD in several regions, predominantly in bilateral uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF), compared to HC (PFDR<0.05). During follow-up, PD-npRBD had further FA decrease in left UF and ILF (PFDR<0.05). PD-pRBD showed reduced FA in several regions relative to HC at baseline (PFDR<0.05), and faster FA decline in left UF and ILF than PD-npRBD during follow-up, with more extensive FA decrease in other regions such as anterior thalamic radiation and inferior fronto-occipital fasciculus (PFDR<0.05). Moreover, increased RD in the left corticospinal tract correlated with motor symptoms (p = 0.045) in PD-pRBD.

CONCLUSIONS

PD patients with pRBD demonstrated more extensive WM degeneration and accelerated degeneration in the left ILF and UF during the disease course. However, due to the lack of PSG verification, these results should be interpreted cautiously while directly relating to RBD. These findings provide new insights into the neural structural basis associated with the potential impact of RBD on PD progression.

A bibliometric analysis of the top 100 most cited articles on corticospinal tract regeneration from 2004 to 2024

Objective

Here, bibliometric and visual analytical techniques were employed to assess the key features of the 100 most cited publications concerning corticospinal tract (CST) regeneration.

Methods

Research was conducted within the Web of Science Core Collection to pinpoint the 100 most cited publications on CST regeneration. From these, comprehensive data encompassing titles, authorship, key terms, publication venues, release timelines, geographic origins, and institutional affiliations were extracted, followed by an in-depth bibliometric examination.

Results

The 100 most cited publications were all published between 2004 and 2024. These seminal papers amassed an aggregate of 18,321 citations, with individual citation counts ranging from 83 to 871 and a median of 136 citations per paper. Schwab M. E., stood out as the most prominent contributor, with significant authorship in 9 of the 100 papers. The United States dominated the geographical distribution, accounting for 49 of the articles. With 17 publications, the University of California System led the institutional rankings. A thorough keyword analysis revealed pivotal themes in the field, encompassing the optic nerve, gene expression, CST integrity and regeneration, diffusion tensor imaging, myelin-associated glycoproteins, inhibitors of neurite outgrowth, and methods of electrical and intracortical microstimulation.

Conclusion

This investigation provides a bibliometric analysis of CST regeneration, underscoring the significant contribution of the United States to this field. Our findings unveiled the dynamics and trends within the field of CST regeneration, providing a scientific foundation for advancing clinical applications. Building on this analysis, the clinical application of CST regeneration should be optimized through interdisciplinary collaboration, enabling the exploration and validation of a variety of therapeutic approaches, including the use of neurotrophic factors, stem cell therapies, biomaterials, and electrical stimulation. Concurrently, additional clinical trials are necessary to test the safety and efficacy of these therapeutic methods and develop assessment tools for monitoring the recovery of patients. Furthermore, rehabilitation strategies should be refined, and professional education and training should be provided to enhance the understanding of CST regeneration treatments among both medical professionals and patients. The implementation of these strategies promises to enhance therapeutic outcomes and the quality of life of patients with spinal cord injury (SCI).

Reduced white matter integrity and disrupted brain network in children with type 2 and 3 spinal muscular atrophy

BACKGROUND

Spinal muscular atrophy (SMA) is caused by reduced expression of survival motor neuron (SMN) protein. Previous studies indicated SMA causes not only lower motor neuron degeneration but also extensive brain involvement. This study aimed to investigate the changes of brain white matter and structural network using diffusion tensor imaging (DTI) in children with type 2 and 3 SMA.

METHODS

Forty-two type 2 and 3 pediatric SMA patients and 42 age- and gender-matched healthy controls (HC) were prospectively enrolled in this study. The tract-based spatial statistics (TBSS) was used to assess white matter integrity and the structural network properties were calculated based on DTI white matter fiber tracking and the graph theory approach. A partial correlation was performed to explore the relationship between white matter parameters and clinical characteristics.

RESULTS

In total, 42 patients (mean age, 10.86 ± 4.07 years; 23 men) were included. TBSS analysis revealed widespread white matter changes in SMA patients. The SMA patients showed changes in multiple small-world and network efficiency parameters. Compared to the HC group, SMA showed increased characteristic path length (Lp), normalized clustering coefficient (γ), small-world characteristic (σ), and decreased global efficiency (Eglob) (all p < 0.05). In the node properties, right supramarginal gyrus, right orbital part of superior frontal gyrus, right supplementary motor area, and left median cingulate and paracingulate gyri changed in SMA patients. A decreased axial diffusivity (AD) value was associated with lower Hammersmith Functional Motor Scale-Expanded scores (r = 0.45, p = 0.02), which means that the symptoms of SMA patients are more severe.

CONCLUSIONS

This study found white matter and DTI-based brain network abnormalities in SMA patients, suggesting SMN protein deficiency may affect white matter development.

Wallerian degeneration: From mechanism to disease to imaging

Wallerian degeneration (WD) was first discovered by Augustus Waller in 1850 in a transection of the glossopharyngeal and hypoglossal nerves in frogs. Initial studies suggested that the formation mechanism of WD is related to the nutrition of neuronal cell bodies to axons. However, with the wide application of transgenic mice in experiments, the latest studies have found that the mechanism of WD is related to axonal degeneration, myelin clearance and extracellular matrix. This review summarizes the discovery and research progress of WD and discusses the mechanism of WD from the perspective of molecular biology. In addition, this review combines the etiology, symptoms and imaging results of WD patients, and analyzes the clinical and imaging characteristics of WD, to provide the best perspective for future clinical research.

Balance recovery and its link to vestibular agnosia in traumatic brain injury: a longitudinal behavioural and neuro-imaging study

BACKGROUND

Vestibular dysfunction causing imbalance affects c. 80% of acute hospitalized traumatic brain injury (TBI) cases. Poor balance recovery is linked to worse return-to-work rates and reduced longevity. We previously showed that white matter network disruption, particularly of right inferior longitudinal fasciculus, mediates the overlap between imbalance and impaired vestibular perception of self-motion (i.e., vestibular agnosia) in acute hospitalized TBI. However, there are no prior reports tracking the acute-longitudinal trajectory of objectively measured vestibular function for hospitalized TBI patients. We hypothesized that recovery of vestibular agnosia and imbalance is linked and mediated by overlapping brain networks.

METHODS

We screened 918 acute major trauma in-patients, assessed 146, recruited 39 acutely, and retested 34 at 6 months. Inclusion criteria were 18-65-year-old adults hospitalized for TBI with laboratory-confirmed preserved peripheral vestibular function. Benign paroxysmal positional vertigo and migraine were treated prior to testing. Vestibular agnosia was quantified by participants' ability to perceive whole-body yaw plane rotations via an automated rotating-chair algorithm. Subjective symptoms of imbalance (via questionnaires) and objective imbalance (via posturography) were also assessed.

RESULTS

Acute vestibular agnosia predicted poor balance recovery at 6 months. Recovery of vestibular agnosia and linked imbalance was mediated by bihemispheric fronto-posterior cortical circuits. Recovery of subjective symptoms of imbalance and objective imbalance were not correlated.

CONCLUSION

Vestibular agnosia mediates balance recovery post-TBI. The link between subjective dizziness and brain injury recovery, although important, is unclear. Therapeutic trials of vestibular recovery post-TBI should target enhancing bi-hemispheric connectivity and linked objective clinical measures (e.g., posturography).

Claire M, Whitehead SS, Kanakabandi K, Sheng ZM, Xiao Y, Kash JC, Taubenberger JK, Martens C, Cohen JI. Spatiotemporal profile of an optimal host response to virus infection in the primate central nervous system

Viral infections of the central nervous system (CNS) are a major cause of morbidity largely due to lack of prevention and inadequate treatments. While mortality from viral CNS infections is significant, nearly two thirds of the patients survive. Thus, it is important to understand how the human CNS can successfully control virus infection and recover. Since it is not possible to study the human CNS throughout the course of viral infection at the cellular level, here we analyzed a non-lethal viral infection in the CNS of nonhuman primates (NHPs). We inoculated NHPs intracerebrally with a high dose of La Crosse virus (LACV), a bunyavirus that can infect neurons and cause encephalitis primarily in children, but with a very low (≤ 1%) mortality rate. To profile the CNS response to LACV infection, we used an integrative approach that was based on comprehensive analyses of (i) spatiotemporal dynamics of virus replication, (ii) identification of types of infected neurons, (iii) spatiotemporal transcriptomics, and (iv) morphological and functional changes in CNS intrinsic and extrinsic cells. We identified the location, timing, and functional repertoire of optimal transcriptional and translational regulation of the primate CNS in response to virus infection of neurons. These CNS responses involved a well-coordinated spatiotemporal interplay between astrocytes, lymphocytes, microglia, and CNS-border macrophages. Our findings suggest a multifaceted program governing an optimal CNS response to virus infection with specific events coordinated in space and time. This allowed the CNS to successfully control the infection by rapidly clearing the virus from infected neurons, mitigate damage to neurophysiology, activate and terminate immune responses in a timely manner, resolve inflammation, restore homeostasis, and initiate tissue repair. An increased understanding of these processes may provide new therapeutic opportunities to improve outcomes of viral CNS diseases in humans.

The Implementation of the Biopsychosocial Model: Individuals With Alcohol Use Disorder and Post-Traumatic Stress Disorder

INTRODUCTION

This extensive literature review investigates the relationship between post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD), focusing on the neurobiological changes associated with their co-occurrence. Given that these disorders frequently coexist, we analyze mechanisms through which alcohol serves as a coping strategy for PTSD symptoms, particularly highlighting the drinking-to-cope self-medication model, which suggests that alcohol use exacerbates PTSD symptoms and complicates recovery.

METHODS

A systematic literature search was conducted across multiple databases, including PubMed and Google Scholar, to identify studies examining the intersection of the biopsychosocial model with PTSD, AUD, and associated neural alterations.

RESULTS

Findings demonstrate that chronic PTSD is associated with progressive dysfunction in the amygdala, hippocampus, prefrontal cortex, hypothalamic-pituitary-adrenal axis, and white matter pathways. Also, our findings underscore alterations within the reward system, prefrontal cortex, hippocampus, amygdala, basal ganglia, and hypothalamic-pituitary-adrenal axis that contribute to the pathophysiology of AUD. Our results support the notion that a biopsychosocial framework is essential for contemporary addiction treatment, particularly in the context of alcohol addiction and PTSD.

CONCLUSION

PTSD frequently leads individuals to use alcohol as a maladaptive coping strategy, ultimately resulting in neuroadaptive alterations across critical brain regions. These neurobiological changes contribute to the development and maintenance of AUD. The findings reiterate the necessity of employing a biopsychosocial model in treating individuals grappling with both PTSD and AUD. This model allows for a comprehensive understanding of the unique challenges faced by this population, integrating biological, psychological, and social factors that influence recovery.

The relationship between corticospinal excitability and structural integrity in stroke patients

BACKGROUND

Evaluation of the structural integrity and functional excitability of the corticospinal tract (CST) is likely to be important in predicting motor recovery after stroke. Previous reports are inconsistent regarding a possible link between CST structure and CST function in this setting. This study aims to investigate the structure‒function relationship of the CST at the acute phase of stroke (<7 days).

METHODS

We enrolled 70 patients who had an acute ischaemic stroke with unilateral upper extremity (UE) weakness. They underwent a multimodal assessment including clinical severity (UE Fugl Meyer at day 7 and 3 months), MRI to evaluate the CST lesion load and transcranial magnetic stimulation to measure the maximum amplitude of motor evoked potential (MEP).

RESULTS

A cross-sectional lesion load above 87% predicted the absence of MEPs with an accuracy of 80.4%. In MEP-positive patients, the CST structure/function relationship was bimodal with a switch from a linear relationship (rho=-0.600, 95% CI -0.873; -0.039, p<0.03) for small MEP amplitudes (<0.703 mV) to a non-linear relationship for higher MEP amplitudes (p=0.72). In MEP-positive patients, recovery correlated with initial severity. In patients with a positive MEP <0.703 mV but not in patients with an MEP ≥0.703 mV, MEP amplitude was an additional independent predictor of recovery. In MEP-negative patients, we failed to identify any factor predicting recovery.

CONCLUSION

This large multimodal study on the structure/function of the CST and stroke recovery proposes a paradigm change for the MEP-positive patients phenotypes and refines the nature of the link between structural integrity and neurophysiological function, with implications for study design and prognostic information.

Selective Targeting of a Defined Subpopulation of Corticospinal Neurons using a Novel Klhl14-Cre Mouse Line Enables Molecular and Anatomical Investigations through Development into Maturity

The corticospinal tract (CST) facilitates skilled, precise movements, which necessitates that subcerebral projection neurons (SCPN) establish segmentally specific connectivity with brainstem and spinal circuits. Developmental molecular delineation enables prospective identification of corticospinal neurons (CSN) projecting to thoraco-lumbar spinal segments; however, it remains unclear whether other SCPN subpopulations in developing sensorimotor cortex can be prospectively identified in this manner. Such molecular tools could enable investigations of SCPN circuitry with precision and specificity. During development, Kelch-like 14 (Klhl14) is specifically expressed by a specific SCPN subpopulation, CSNBC-lat, that reside in lateral sensorimotor cortex with axonal projections exclusively to bulbar-cervical targets. In this study, we generated Klhl14-T2A-Cre knock-in mice to investigate SCPN that are Klhl14+ during development into maturity. Using conditional anterograde and retrograde labeling, we find that Klhl14-Cre is specifically expressed by CSNBC-lat only at specific developmental time points. We establish conditional viral labeling in Klhl14-T2A-Cre mice as a new approach to reliably investigate CSNBC-lat axon targeting and confirm that this identifies known molecular regulators of CSN axon targeting. Therefore, Klhl14-T2A-Cre mice can be used as a novel tool for identifying molecular regulators of CST axon guidance in a relatively high-throughput manner in vivo. Finally, we demonstrate that intersectional viral labeling enables precise targeting of only Klhl14-Cre+ CSNBC-lat in the adult central nervous system. Together, our results establish that developmental molecular delineation of SCPN subpopulations can be used to selectively and specifically investigate their development, as well as anatomical and functional organization into maturity.

Automated fiber quantification analysis identifies tract-specific microstructural alterations in brain in intermittent exotropia

BACKGROUND

Growing evidence of neuroimaging has indicated brain microstructural abnormalities in comitant strabismus. Nonetheless, few studies have investigated neuropathological alterations in patients with intermittent exotropia (IXT). This study aimed at examining the characteristics of brain microstructure along major fiber tracts in IXT patients using an automated fiber quantification analysis.

METHODS

A total of 25 patients with IXT as well as 25 healthy participants matched for age and gender finished the diffusion tensor imaging scanning and the ophthalmic examination. Automated fiber quantification analysis of 20 major fiber tracts was carried out for IXT patients and healthy subjects, respectively. Diffusion metrics of 100 equidistant nodes resampled along each tract were measured for every subject and compared between two groups. Effect size analysis was performed to identify the most affected fiber tracts in IXT.

RESULTS

Widely declined mean diffusivity was noted in IXT along major tracts containing bilateral thalamic radiations, bilateral corticospinal fasciculi, bilateral cingulum cingulate, left inferior fronto-occipital fasciculus, right arcuate fasciculus and superior longitudinal fasciculus. Local reduction in fractional anisotropy was observed in IXT along left cingulum hippocampus, right inferior longitudinal fasciculus and right uncinate fasciculus, in contrast to the regionally increased fractional anisotropy along bilateral thalamic radiation, left corticospinal tract and left arcuate fasciculus. Among the tracts with significantly changed diffusion metrics in IXT, right inferior longitudinal fasciculus was the most affected one in fractional anisotropy while left thalamic radiation was the most influenced one in mean diffusivity.

CONCLUSIONS

Abnormalities in microstructural properties along visual-related fiber tracts are likely to contribute to difficulties in visual information processing in IXT patients, which could serve as the neural basis of underlying pathological mechanism of IXT.

Comparative review of the brain development in Acomys cahirinus

Acomys cahirinus (referred to as "acomys" in this article) is a precocial rodent, born well-developed and mobile, capable of feeding independently and escaping predators shortly after birth. Notable for its advanced regenerative abilities and menstrual cycle, acomys serves as a unique model for studying diverse aspects of physiology and neuroscience, including developmental and regenerative neuroscience. Despite its significance, only sporadic and unsystematic data on the structure and development of the acomys brain are available. Therefore, the aim of this study was to systematically organize the existing information on the structure and development of the acomys brain and to compare it with that of commonly studied altricial rodent species (rats, mice, hamsters, and gerbils). This review is organized into several sections, focusing on general aspects of brain development, such as myelination and brain growth. It also discusses the development of brain structures involved in sensory processing (olfactory, visual, and auditory), motor control, learning and memory, and social behavior.

Multiple roles for TFG ring complexes in neuronal cargo trafficking

Pathological variants in Trk-fused gene (TFG) have been implicated in a variety of neurodegenerative conditions. In particular, mutations within its amino-terminal PB1 domain have been suggested to cause hereditary spastic paraplegia (HSP), resulting in progressive lower limb spasticity and weakness. The structural basis for this effect is unknown. Here, we combine X-ray crystallography and cryo-electron microscopy to determine a structural model of TFG, demonstrating the mechanism by which it forms octameric ring complexes. A network of electrostatic and hydrophobic interactions defines the interface between protomers. Moreover, we show that mutations identified previously in HSP patients disrupt this interface, destabilizing octamers, which ultimately leads to axonopathy. Surprisingly, the impacts of these variants are not equivalent in vivo, highlighting the existence of multiple, distinct mechanisms by which TFG mutations contribute to neurodegenerative disease.

Concurrent optogenetic motor mapping of multiple limbs in awake mice reveals cortical organization of coordinated movements

BACKGROUND

Motor mapping allows for determining the macroscopic organization of motor circuits and corresponding motor movement representations on the cortex. Techniques such as intracortical microstimulation (ICMS) are robust, but can be time consuming and invasive, making them non-ideal for cortex-wide mapping or longitudinal studies. In contrast, optogenetic motor mapping offers a rapid and minimally invasive technique, enabling mapping with high spatiotemporal resolution. However, motor mapping has seen limited use in tracking 3-dimensonal, multi-limb movements in awake animals. This gap has left open questions regarding the underlying organizational principles of motor control of coordinated, ethologically-relevant movements involving multiple limbs.

OBJECTIVE

Our first objective was to develop Multi-limb Optogenetic Motor Mapping (MOMM) to concurrently map motor movement representations of multiple limbs with high fidelity in awake mice. Having established MOMM, our next objective was determine whether maps of coordinated and ethologically-relevant motor output were topographically organized on the cortex.

METHODS

We combine optogenetic stimulation with a deep learning driven pose-estimation toolbox, DeepLabCut (DLC), and 3-dimensional triangulation to concurrently map motor movements of multiple limbs in awake mice.

RESULTS

MOMM consistently revealed cortical topographies for all mapped features within and across mice. Many motor maps overlapped and were topographically similar. Several motor movement representations extended beyond cytoarchitecturally defined somatomotor cortex. Finer articulations of the forepaw resided within gross motor movement representations of the forelimb. Moreover, many cortical sites exhibited concurrent limb coactivation when photostimulated, prompting the identification of several cortical regions harboring coordinated and ethologically-relevant movements.

CONCLUSIONS

The cortex appears to be topographically organized by motor programs, which are responsible for coordinated, multi-limbed, and behavior-like movements.

SpinalTRAQ: A novel volumetric cervical spinal cord atlas identifies the corticospinal tract synaptic projectome in healthy and post-stroke mice

Descending corticospinal tract (CST) connections to the neurons of the cervical spinal cord are vital for performance of forelimb-specific fine motor skills. In rodents, CST axons are almost entirely crossed at the level of the medullary decussation. While specific contralateral axon projections have been well-characterized using anatomic and molecular approaches, the field currently lacks a cohesive imaging modality allowing rapid quantitative assessment of the entire, bilateral cervical cord projectome at the level of individual laminae and cervical levels. This is potentially important as the CST is known to undergo marked structural remodeling in development, injury, and disease. We developed SpinalTRAQ (Spinal cord Tomographic Registration and Automated Quantification), a novel volumetric cervical spinal cord atlas and machine learning-driven microscopy acquisition and analysis pipeline that uses serial two-photon tomography- images to generate unbiased, region-specific quantification of the fluorescent pixels of anterograde AAV-labeled CST pre-synaptic terminals. In adult mice, the CST synaptic projectome densely innervates the contralateral hemicord, particularly in laminae 5 and 7, with sparse, monosynaptic input to motoneurons in lamina 9. Motor pools supplying axial musculature in the upper cervical cord are bilaterally innervated. The remainder of the ipsilateral cord has sparse labeling in a distinct distribution compared to the contralateral side. Following a focal stroke of the motor cortex, there is a complete loss of descending corticospinal axons from the injured side. Consistent with prior reports of axon collateralization, the CST spinal projectome increases at four weeks post-stroke and continues to elevate by six weeks post stroke. At six weeks post-stroke, we observed striking synapse formation in the denervated hemicord from the uninjured CST in a homotopic distribution. Additionally, CST synaptic reinnervation increases in the denervated lamina 9 in nearly all motoneuron pools, exhibiting novel patterns of connectivity. Detailed level- and lamina-specific quantification of the bilateral cervical spinal cord synaptic projectome reveals previously undescribed patterns of CST connectivity in health and injury-related plasticity.

Acute stress differently modulates interneurons excitability and synaptic plasticity in the primary motor cortex of wild-type and SOD1G93A mouse model of ALS

Primary motor cortex (M1) network stability depends on activity of inhibitory interneurons, for which susceptibility to stress was previously demonstrated in limbic regions. Hyperexcitability in M1 following changes in the excitatory/inhibitory balance is a key pathological hallmark of amyotrophic lateral sclerosis (ALS). Using electrophysiological approaches, we assessed the impact of acute restraint stress on inhibitory interneurons excitability and global synaptic plasticity in M1 of the SOD1G93A ALS mouse model at a late pre-symptomatic stage (10-12.5 weeks). Based on their firing type (continuous, discontinuous, with accommodation or not) and electrophysiological characteristics (resting potential, rheobase, firing frequency), interneurons from M1 slices were separated into four clusters, labelled from 1 to 4. Among them, only interneurons from the first cluster, presenting continuous firing with few accommodations, tended to show increased excitability in wild-type (WT) and decreased excitability in SOD1G93A animals following stress. In vivo analyses of evoked field potentials showed that stress suppressed the theta burst-induced plasticity of an excitatory component (N1) recorded in the superficial layers of M1 in WT, with no impact on an inhibitory complex (N2-P1) from the deeper layers. In SOD1G93A mice, stress did not affect N1 but suppressed the N2-P1 plasticity. These data suggest that stress can alter M1 network functioning in a different manner in WT and SOD1G93A mice, possibly through changes of inhibitory interneurons excitability and synaptic plasticity. This suggests that stress-induced activity changes in M1 may therefore influence ALS outcomes. KEY POINTS: Disruption of the excitatory/inhibitory balance in the primary motor cortex (M1) has been linked to cortical hyperexcitability development, a key pathological hallmark of amyotrophic lateral sclerosis (ALS). Psychological stress was reported to influence excitatory/inhibitory balance in limbic regions, but very little is known about its influence on the M1 functioning under physiological or pathological conditions. Our study revealed that acute stress influences the excitatory/inhibitory balance within the M1, through changes in interneurons excitability along with network plasticity. Such changes were different in pathological (SOD1G93A ALS mouse model) vs. physiological (wild-type) conditions. The results of our study help us to better understand how stress modulates the M1 and highlight the need to further characterize stress-induced motor cortex changes because it may be of importance when evaluating ALS outcomes.

Glioma lateralization: Focus on the anatomical localization and the distribution of molecular alterations (Review)

It is well known how the precise localization of glioblastoma multiforme (GBM) predicts the direction of tumor spread in the surrounding neuronal structures. The aim of the present review is to reveal the lateralization of GBM by evaluating the anatomical regions where it is frequently located as well as the main molecular alterations observed in different brain regions. According to the literature, the precise or most frequent lateralization of GBM has yet to be determined. However, it can be said that GBM is more frequently observed in the frontal lobe. Tractus and fascicles involved in GBM appear to be focused on the corticospinal tract, superior longitudinal I, II and III fascicles, arcuate fascicle long segment, frontal strait tract, and inferior fronto‑occipital fasciculus. Considering the anatomical features of GBM and its brain involvement, it is logical that the main brain regions involved are the frontal‑temporal‑parietal‑occipital lobes, respectively. Although tumor volumes are higher in the right hemisphere, it has been determined that the prognosis of patients diagnosed with cancer in the left hemisphere is worse, probably reflecting the anatomical distribution of some detrimental alterations such as TP53 mutations, PTEN loss, EGFR amplification, and MGMT promoter methylation. There are theories stating that the right hemisphere is less exposed to external influences in its development as it is responsible for the functions necessary for survival while tumors in the left hemisphere may be more aggressive. To shed light on specific anatomical and molecular features of GBM in different brain regions, the present review article is aimed at describing the main lateralization pathways as well as gene mutations or epigenetic modifications associated with the development of brain tumors.

Subtle motor signs in children with ADHD and their white matter correlates

Subtle motor signs are a common feature in children with attention-deficit/hyperactivity disorder (ADHD). It has long been suggested that white matter abnormalities may be involved in their presentation, though no study has directly probed this question. The aim of this study was to investigate the relationship between white matter organization and the severity of subtle motor signs in children with and without ADHD. Participants were 92 children with ADHD aged between 8 and 12 years, and 185 typically developing controls. Subtle motor signs were examined using the Physical and Neurological Examination for Soft Signs (PANESS). Children completed diffusion MRI, and fixel-based analysis was performed after preprocessing. Tracts of interest were delineated using TractSeg including the corpus callosum (CC), the bilateral corticospinal tracts (CST), superior longitudinal fasciculus, and fronto-pontine tracts (FPT). Fiber cross-section (FC) was calculated for each tract. Across all participants, lower FC in the CST was associated with higher PANESS Total score (greater motor deficits). Within the PANESS, similar effects were observed for Timed Left and Right maneuvers of the hands and feet, with lower FC of the CST, CC, and FPT associated with poorer performance. No significant group differences were observed in FC in white matter regions associated with PANESS performance. Our data are consistent with theoretical accounts implicating white matter organization in the expression of motor signs in childhood. However, rather than contributing uniquely to the increased severity of soft motor signs in those with ADHD, white matter appears to contribute to these symptoms in childhood in general.

Alternative Balance between Transcriptional and Epigenetic Regulation during Developmental Proliferation of Human Cranial Neural Crest Cells

Cranial neural crest cells are implicated in multiple transcriptional events at the different stages of differentiation during development. The alteration of some transcription factors expressed during neural crest development, like PAX7, could be implicated in the etiology of face malformation in murine models. Epigenetic regulation has been shown to be an important mechanistic actor in the control of timing and the level of gene expression at different stages of neural crest development. During this work, we investigated the interconnection between epigenetics and transcription factors across a diversity of human development cranial neural crest cells. Across a diversity of neural cells from human developing cranial tissues, in accordance with their proliferation stage, an alternative balance of regulation between transcription factors and epigenetic factors was identified.

Differences in corticospinal drive and co-activations of antagonist muscles during forward leaning and backward returning tasks between children and young adults

BACKGROUND

Postural control imposes higher demands on the central neural system (CNS), and age-related declines or incomplete CNS development often result in challenges performing tasks like forward postural leaning. Studies on older adults suggest increased variability in center of pressure (COP), greater muscle co-activations, and reduced corticospinal control during forward leaning tasks. However, the understanding of these features in children remains unclear. Specifically, it is uncertain whether forward leaning poses greater challenges for young children compared to adults, given the ongoing maturation of CNS during development. Understanding the distinct neuromuscular patterns observed during postural leaning could help optimize therapeutic strategies aimed at improving postural control in pediatric populations.

METHODS

12 typically developing children (5.91 ± 1.37 years) and 12 healthy young adults (23.16 ± 1.52 years) participated in a dynamic leaning forward task aimed at matching a COP target in the anterior-posterior direction as steadily as possible. Participants traced a triangular trajectory involving forward leaning (FW phase) to 60 % of their maximum lean distance and backward returning (BW phase) to the neutral standing position. Surface electromyography (sEMG) from muscles including gastrocnemius medialis (GM), soleus (SOL), and tibialis anterior (TA) were collected during both phases. COP variability was assessed using the standard deviation (SD) of COP displacements. Muscle co-activation indexes (CI) for ankle plantar and dorsal flexors (SOL/TA, GM/TA) were derived from sEMG activities. Intermuscular coherence in the beta band (15-30 Hz) was also analyzed to evaluate corticospinal drive.

RESULTS

Children exhibited a significantly greater SD of COP compared to young adults (p < 0.01) during the BW phase. They also demonstrated higher CI (p < 0.05) and reduced coherence of SOL/TA (p < 0.05) compared to young adults during this phase. No significant group differences were observed during the FW phase. Within the children's group, COP variability was significantly higher in the BW phase compared to the FW phase (p < 0.01). Moreover, children displayed greater CI (p < 0.01) and reduced coherence of SOL/TA (p < 0.01) during the BW phase compared to the FW phase. Conversely, no significant phase effects were observed in the adult group. Furthermore, sEMG measures were significantly correlated with COP variability (p < 0.05).

CONCLUSIONS

The findings of this small study suggest that age-related differences in CNS development influence the modulation of corticospinal drive to ankle muscles (e.g., SOL/TA) during childhood, particularly supporting the existence of a separate pathway underlying the control of forward lean and backward returning.

White matter organisation of sensorimotor tracts is associated with motor imagery in childhood

Despite the important role of motor imagery (MI) in motor development, our understanding of the contribution of white matter fibre properties to MI performance in childhood remains limited. To provide novel insight into the white matter correlates of MI performance, this study examined the association between white matter fibre properties and motor imagery performance in a sample of typically developing children. High angular diffusion weighted imaging data were collected from 22 typically developing children aged 6-14 years (12 female, MAge= 10.56). Implicit motor imagery performance was assessed using a mental hand rotation paradigm. The cerebellar peduncles and the superior longitudinal fasciculus were reconstructed using TractSeg, a semi-automated method. For each tract, white matter microstructure (fibre density, FD) and morphology (fibre bundle cross-section, FC) were estimated using Fixel-Based Analysis. Permutation-based inference testing and partial correlation analyses demonstrated that higher FC in the middle cerebellar peduncles was associated with better MI performance. Tract-based region of interest analyses showed that higher FC in the middle and superior cerebellar peduncles were associated with better MI performance. Results suggest that white matter connectivity along the cerebellar peduncles may facilitate MI performance in childhood. These findings advance our understanding of the neurobiological systems that underlie MI performance in childhood and provide early evidence for the relevance of white matter sensorimotor pathways to internal action representations.

Long-term table tennis training alters dynamic functional connectivity and white matter microstructure in large scale brain regions

Table tennis training has been employed as an exercise treatment to enhance cognitive brain functioning in patients with mental illnesses. However, research on its underlying mechanisms remains limited. In this study, we investigated functional and structural changes in large-scale brain regions between 20 table tennis players (TTPs) and 21 healthy controls (HCs) using 7-Tesla magnetic resonance imaging (MRI) techniques. Compared with those of HCs, TTPs exhibited significantly greater fractional anisotropy (FA) and axial diffusivity (AD) values in multiple fiber tracts. We used the locations with the most significant structural changes in white matter as the seed areas and then compared static and dynamic functional connectivity (sFC and dFC). Brodmann 11, located in the orbitofrontal cortex, showed altered dFC values to large-scale brain regions, such as the occipital lobe, thalamus, and cerebellar hemispheres, in TTPs. Brodmann 48, located in the temporal lobe, showed altered dFC to the parietal lobe, frontal lobe, cerebellum, and occipital lobe. Furthermore, the AD values of the forceps minor (Fmi) and right anterior thalamic radiations (ATRs) were negatively correlated with useful field of view (UFOV) test scores in TTPs. Our results suggest that table tennis players exhibit a unique pattern of dynamic neural activity, this provides evidence for potential mechanisms through which table tennis interventions can enhance attention and other cognitive functions.

Bundle-specific tractogram distribution estimation using higher-order streamline differential equation

Streamline tractography locally traces peak directions extracted from fiber orientation distribution (FOD) functions, lacking global information about the trend of the whole fiber bundle. Therefore, it is prone to producing erroneous tracks while missing true positive connections. In this work, we propose a new bundle-specific tractography (BST) method based on a bundle-specific tractogram distribution (BTD) function, which directly reconstructs the fiber trajectory from the start region to the termination region by incorporating the global information in the fiber bundle mask. A unified framework for any higher-order streamline differential equation is presented to describe the fiber bundles with disjoint streamlines defined based on the diffusion vectorial field. At the global level, the tractography process is simplified as the estimation of BTD coefficients by minimizing the energy optimization model, and is used to characterize the relations between BTD and diffusion tensor vector under the prior guidance by introducing the tractogram bundle information to provide anatomic priors. Experiments are performed on simulated Hough, Sine, Circle data, ISMRM 2015 Tractography Challenge data, FiberCup data, and in vivo data from the Human Connectome Project (HCP) for qualitative and quantitative evaluation. Results demonstrate that our approach reconstructs complex fiber geometry more accurately. BTD reduces the error deviation and accumulation at the local level and shows better results in reconstructing long-range, twisting, and large fanning tracts.

A facilitatory role of astrocytes in axonal regeneration after acute and chronic spinal cord injury

Neuroscience dogma avers that astrocytic "scars" inhibit axonal regeneration after spinal cord injury (SCI). A recent report suggested however that astrocytes form "borders" around lesions that are permissive rather than inhibitory to axonal growth. We now provide further evidence supporting a facilitatory role of astrocytes in axonal regeneration after SCI. First, even 6months after SCI, injured axons are retained within regions of densely reactive astrocytes, in direct contact with astrocyte processes without being repelled. Second, 6 month-delayed implants of neural stem cells extend axons into reactive astrocyte borders surrounding lesions, densely contacting astrocyte surfaces. Third, bioengineered hydrogels implanted into sites of SCI re-orient reactive astrocytic processes to align along the rostral-to-caudal spinal cord axis resulting in successful regeneration into the lesion/scaffold in close association with astrocytic processes. Fourth, corticospinal axons regenerate into neural progenitor cells implanted six months after injury in close association with host astrocytic processes. Thus, astrocytes do not appear to inhibit axonal regeneration, and the close association of newly growing axons with astrocytic processes suggests a facilitatory role in axonal regeneration.

Concurrent optogenetic motor mapping of multiple limbs in awake mice reveals cortical organization of coordinated movements

Background

Motor mapping allows for determining the macroscopic organization of motor circuits and corresponding motor movement representations on the cortex. Techniques such as intracortical microstimulation (ICMS) are robust, but can be time consuming and invasive, making them non-ideal for cortex-wide mapping or longitudinal studies. In contrast, optogenetic motor mapping offers a rapid and minimally invasive technique, enabling mapping with high spatiotemporal resolution. However, motor mapping has seen limited use in tracking 3-dimensonal, multi-limb movements in awake animals. This gap has left open questions regarding the underlying organizational principles of motor control of coordinated, ethologically relevant movements involving multiple limbs.

Objective

Our first objective was to develop Multi-limb Optogenetic Motor Mapping (MOMM) to concurrently map motor movement representations of multiple limbs with high fidelity in awake mice. Having established MOMM, our next objective was determine whether maps of coordinated and ethologically relevant motor output were topographically organized on the cortex.

Methods

We combine optogenetic stimulation with a deep learning driven pose-estimation toolbox, DeepLabCut (DLC), and 3-dimentional triangulation to concurrently map motor movements of multiple limbs in awake mice.

Results

MOMM consistently revealed cortical topographies for all mapped features within and across mice. Many motor maps overlapped and were topographically similar. Several motor movement representations extended beyond cytoarchitecturally defined somatomotor cortex. Finer articulations of the forepaw resided within gross motor movement representations of the forelimb. Moreover, many cortical sites exhibited concurrent limb coactivation when photostimulated, prompting the identification of several cortical regions harboring coordinated and ethologically relevant movements.

Conclusions

The cortex appears to be topographically organized by motor programs, which are responsible for coordinated, multi-limbed, and behavioral-like movements.

Evolutionary changes in the capacity for organismic autonomy

Studies of macroevolution have revealed various trends in evolution - which have been documented and discussed. There is, however, no consensus on this topic. Since Darwin's time one presumption has persisted: that throughout evolution organisms increase their independence from and stability towards environmental influences. Although this principle has often been stated in the literature, it played no role in mainstream theory. In a closer examination, we studied this particular feature and described that many of the major transitions in animal evolution have been characterized by changes in the capacity for physiological regulation. Organisms gained in robustness, self-regulation, homeostasis and stabilized self-referential, intrinsic functions within their respective systems. This is associated with expanded environmental flexibility, such as new opportunities for movement and behaviour. Together, these aspects can be described as changes in the capacity for autonomy. There seems to be a large-scale trajectory in evolution during which some organisms gained in autonomy and flexibility. At the same time, adaptations to the environment emerged that were a prerequisite for survival. Apparently, evolution produced differential combinations of autonomy traits and adaptations. These processes are described as modifications in relative autonomy because numerous interconnections with the environment and dependencies upon it were retained. Also, it is not a linear trend, but rather an outcome of all the diverse processes which have been involved during evolutionary changes. Since the principle of regulation is a core element of physiology, the concept of autonomy is suitable to build a bridge from physiology to evolutionary research.

Ventricular Netrin-1 deficiency leads to defective pyramidal decussation and mirror movement in mice

The corticospinal tract (CST) is the principal neural pathway responsible for conducting voluntary movement in the vertebrate nervous system. Netrin-1 is a well-known guidance molecule for midline crossing of commissural axons during embryonic development. Families with inherited Netrin-1 mutations display congenital mirror movements (CMM), which are associated with malformations of pyramidal decussation in most cases. Here, we investigated the role of Netrin-1 in CST formation by generating conditional knockout (CKO) mice using a Gfap-driven Cre line. A large proportion of CST axons spread laterally in the ventral medulla oblongata, failed to decussate and descended in the ipsilateral spinal white matter of Ntn1Gfap CKO mice. Netrin-1 mRNA was expressed in the ventral ventricular zone (VZ) and midline, while Netrin-1 protein was transported by radial glial cells to the ventral medulla, through which CST axons pass. The level of transported Netrin-1 protein was significantly reduced in Ntn1Gfap CKO mice. In addition, Ntn1Gfap CKO mice displayed increased symmetric movements. Our findings indicate that VZ-derived Netrin-1 deletion leads to an abnormal trajectory of the CST in the spinal cord due to the failure of CST midline crossing and provides novel evidence supporting the idea that the Netrin-1 signalling pathway is involved in the pathogenesis of CMM.

Diffusion tensor imaging in photosensitive and nonphotosensitive juvenile myoclonic epilepsy

INTRODUCTION/BACKGROUND

Juvenile myoclonic epilepsy (JME) syndrome is known to cause alterations in brain structure and white matter integrity. The study aimed to determine structural white matter changes in patients with JME and to reveal the differences between the photosensitive (PS) and nonphotosensitive (NPS) subgroups by diffusion tensor imaging (DTI) using the tract-based spatial statistics (TBSS) method.

METHODS

This study included data from 16 PS, 15 NPS patients with JME, and 41 healthy participants. The mean fractional anisotropy (FA) values of these groups were calculated, and comparisons were made via the TBSS method over FA values in the whole-brain and 81 regions of interest (ROI) obtained from the John Hopkins University White Matter Atlas.

RESULTS

In the whole-brain TBSS analysis, no significant differences in FA values were observed in pairwise comparisons of JME patient group and subgroups with healthy controls (HCs) and in comparison between JME subgroups. In ROI-based TBSS analysis, an increase in FA values of right anterior corona radiata and left corticospinal pathways was found in JME patient group compared with HC group. When comparing JME-PS patients with HCs, an FA increase was observed in the bilateral anterior corona radiata region, whereas when comparing JME-NPS patients with HCs, an FA increase was observed in bilateral corticospinal pathway. Moreover, in subgroup comparison, an increase in FA values was noted in corpus callosum genu region in JME-PS compared with JME-NPS.

CONCLUSIONS

Our results support the disruption in thalamofrontal white matter integrity in JME, and subgroups and highlight the importance of using different analysis methods to show the underlying microstructural changes.

Progressive white matter degeneration in patients with spinocerebellar ataxia type 2

PURPOSE

Spinocerebellar ataxia type 2 (SCA2) is a progressive neurodegenerative disorder characterized by cerebellar atrophy. However, studies to elucidate the longitudinal progression of the neuropathology are limited. We sought to identify brain macrostructural and microstructural alterations in patients with SCA2 using fixel-based analysis (FBA) to better understand its distribution patterns and progression.

METHODS

We enrolled 9 patients with SCA2 and 16 age- and gender-matched controls. Longitudinal clinical and imaging data were collected at baseline, and 3.5 years later. Fiber density (FD), fiber-bundle cross-section (FC), and a combination of FD and FC (FDC) were calculated. The paired t-test was used to examine longitudinal differences. The associations between fixel-based metrics and clinical variables were explored in SCA2 patients.

RESULTS

At baseline, patients with SCA2 displayed multiple white matter tracts with significantly decreased FD, FC, and FDC in the corticospinal tract, cerebellar peduncles, brainstem, corpus callosum, thalamus, striatum, and prefrontal cortex, compared to controls. Over time, many of these macrostructural and microstructural alterations progressed, manifesting lower FD, FC, and FDC in corticospinal tract, middle cerebellar peduncle, brainstem, striatum, fornix, and cingulum. No significant brain white matter alterations were found in the healthy controls over time. There was no association between the FBA-derived metrics and clinical variables in SCA2.

CONCLUSION

This study provides evidence of brain macrostructural and microstructural alterations and of progression over time in SCA2. The FBA-derived metrics may serve as potential biomarkers of SCA2 progression.

Betz cells of the primary motor cortex

Betz cells, named in honor of Volodymyr Betz (1834-1894), who described them as "giant pyramids" in the primary motor cortex of primates and other mammalian species, are layer V extratelencephalic projection (ETP) neurons that directly innervate α-motoneurons of the brainstem and spinal cord. Despite their large volume and circumferential dendritic architecture, to date, no single molecular criterion has been established that unequivocally distinguishes adult Betz cells from other layer V ETP neurons. In primates, transcriptional signatures suggest the presence of at least two ETP neuron clusters that contain mature Betz cells; these are characterized by an abundance of axon guidance and oxidative phosphorylation transcripts. How neurodevelopmental programs drive the distinct positional and morphological features of Betz cells in humans remains unknown. Betz cells display a distinct biphasic firing pattern involving early cessation of firing followed by delayed sustained acceleration in spike frequency and magnitude. Few cell type-specific transcripts and electrophysiological characteristics are conserved between rodent layer V ETP neurons of the motor cortex and primate Betz cells. This has implications for the modeling of disorders that affect the motor cortex in humans, such as amyotrophic lateral sclerosis (ALS). Perhaps vulnerability to ALS is linked to the evolution of neural networks for fine motor control reflected in the distinct morphomolecular architecture of the human motor cortex, including Betz cells. Here, we discuss histological, molecular, and functional data concerning the position of Betz cells in the emerging taxonomy of neurons across diverse species and their role in neurological disorders.

Reversible deactivation of motor cortex reveals that areas in parietal cortex are differentially dependent on motor cortex for the generation of movement

Primates are characterized by specializations for manual manipulation, including expansion of posterior parietal cortex (PPC) and, in Catarrhines, evolution of a dexterous hand and opposable thumb. Previous studies examined functional interactions between motor cortex and PPC in New World monkeys and galagos, by inactivating M1 and evoking movements from PPC. These studies found that portions of PPC depend on M1 to generate movements. We now add a species that more closely resembles humans in hand morphology and PPC: macaques. Inactivating portions of M1 resulted in all evoked movements being reduced (28%) or completely abolished (72%) at the PPC sites tested (in areas 5L, PF, and PFG). Anterior parietal area 2 was similarly affected (26% reduced and 74% abolished) and area 1 was the least affected (12% no effect, 54% reduced, and 34% abolished). Unlike previous studies in New World monkeys and galagos, interactions between both nonanalogous (heterotopic) and analogous (homotopic) M1 and parietal movement domains were commonly found in most areas. These experiments demonstrate that there may be two parallel networks involved in motor control: a posterior parietal network dependent on M1 and a network that includes area 1 that is relatively independent of M1. Furthermore, it appears that the relative size and number of cortical fields in parietal cortex in different species correlates with homotopic and heterotopic effect prevalence. These functional differences in macaques could contribute to more numerous and varied muscle synergies across major muscle groups, supporting the expansion of the primate manual behavioral repertoire observed in Old World monkeys.NEW & NOTEWORTHY Motor cortex and anterior and posterior parietal cortex form a sensorimotor integration network. We tested the extent to which parietal areas could initiate movements independent of M1. Our findings support the contention that, although areas 2, 5L, PF, and PFG are highly dependent on M1 to produce movement, area 1 may constitute a parallel corticospinal pathway that can function somewhat independently of M1. A similar functional architecture may underlie dexterous tool use in humans.

Changes in brain structure in subjects with resistance to thyroid hormone due to THRB mutations

BACKGROUND

Being critical for brain development and neurocognitive function thyroid hormones may have an effect on behaviour and brain structure. Our exploratory study aimed to delineate the influence of mutations in the thyroid hormone receptor (TR) ß gene on brain structure.

METHODS

High-resolution 3D T1-weighted images were acquired in 21 patients with a resistance to thyroid hormone ß (RTHß) in comparison to 21 healthy matched-controls. Changes in grey and white matter, as well as cortical thickness were evaluated using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI).

RESULTS

RTHß patients showed elevated circulating fT4 & fT3 with normal TSH concentrations, whereas controls showed normal thyroid hormone levels. RTHß patients revealed significantly higher scores in a self-rating questionnaire for attention deficit hyperactivity disorder (ADHD). Imaging revealed alterations of the corticospinal tract, increased cortical thickness in bilateral superior parietal cortex and decreased grey matter volume in bilateral inferior temporal cortex and thalamus.

CONCLUSION

RTHb patients exhibited structural changes in multiple brain areas. Whether these structural changes are causally linked to the abnormal behavioral profile of RTHß which is similar to ADHD, remains to be determined.

Longitudinal Trajectories of White Matter Development in Attention-Deficit/Hyperactivity Disorder

BACKGROUND

Few longitudinal studies have investigated whether white matter development reflects differential outcomes for children with and without attention-deficit/hyperactivity disorder (ADHD). To examine whether deviations from typical trajectories of white matter development were associated with the persistence or remission of ADHD symptoms, this study examined microstructural and morphological properties of 71 white matter tracts from 390 high angular diffusion scans acquired prospectively for 62 children with persistent ADHD, 37 children remitted from ADHD, and 85 children without ADHD.

METHODS

Participants (mean age at wave 1 = 10.39 years, scan interval = 18 months) underwent up to 3 magnetic resonance imaging assessments. White matter tracts were reconstructed using TractSeg, a semiautomated method. For each tract, we derived measures of fiber density (microstructure) and fiber bundle cross-section (morphology) using fixel-based analysis. Linear mixed models were used to compare trajectories of fiber development between the persistent ADHD, remitted ADHD, and non-ADHD groups.

RESULTS

Compared with the non-ADHD group, the remitted and persistent ADHD groups showed accelerated fiber development in thalamic pathways, striatal pathways, and the superior longitudinal fasciculus. In the remitted ADHD group, accelerated fiber development in corticospinal, frontopontine, striatal-premotor, and thalamo-premotor pathways was associated with greater reductions in ADHD symptom severity. The persistent ADHD group showed ongoing white matter alterations along sensorimotor pathways.

CONCLUSIONS

These results suggest that variations in white matter development are associated with different clinical trajectories in ADHD. The findings advance our understanding of the neurobiological mechanisms underpinning ADHD symptom progression and provide novel evidence in support of developmental models of ADHD.

Corticospinal fibers with different origins impair in amyotrophic lateral sclerosis: A neurite orientation dispersion and density imaging study

AIMS

To investigate microstructural impairments of corticospinal tracts (CSTs) with different origins in amyotrophic lateral sclerosis (ALS) using neurite orientation dispersion and density imaging (NODDI).

METHODS

Diffusion-weighted imaging data acquired from 39 patients with ALS and 50 controls were used to estimate NODDI and diffusion tensor imaging (DTI) models. Fine maps of CST subfibers originating from the primary motor area (M1), premotor cortex, primary sensory area, and supplementary motor area (SMA) were segmented. NODDI metrics (neurite density index [NDI] and orientation dispersion index [ODI]) and DTI metrics (fractional anisotropy [FA] and mean/axial/radial diffusivity [MD/AD/RD]) were computed.

RESULTS

The patients with ALS showed microstructural impairments (reflected by NDI, ODI, and FA reductions and MD, AD, and RD increases) in CST subfibers, especially in M1 fibers, which correlated with disease severity. Compared with other diffusion metrics, NDI yielded a higher effect size and detected the greatest extent of CST subfibers damage. Logistic regression analyses based on NDI in M1 subfiber yielded the best diagnostic performance compared with other subfibers and the whole CST.

CONCLUSIONS

Microstructural impairment of CST subfibers (especially those originating from M1) is the key feature of ALS. The combination of NODDI and CST subfibers analysis may improve diagnosing performance for ALS.

Adolescents with ADHD and co-occurring motor difficulties show a distinct pattern of maturation within the corticospinal tract from those without: A longitudinal fixel-based study

It is well documented that attention-deficit hyperactivity disorder (ADHD) often presents with co-occurring motor difficulties. However, little is known about the biological mechanisms that explain compromised motor skills in approximately half of those with ADHD. To provide insight into the neurobiological basis of poor motor outcomes in ADHD, this study profiled the development of white matter organization within the cortico-spinal tract (CST) in adolescents with ADHD with and without co-occurring motor problems, as well as non-ADHD control children with and without motor problems. Participants were 60 children aged 9-14 years, 27 with a history of ADHD and 33 controls. All underwent high-angular resolution diffusion MRI data at up to three time points (115 in scans total). We screened for motor impairment in all participants at the third time point (≈14 years) using the Developmental Coordination Disorder Questionnaire (DCD-Q). Following pre-processing of diffusion MRI scans, fixel-based analysis was performed, and the bilateral CST was delineated using TractSeg. Mean fiber density (FD) and fiber cross-section (FC) were extracted for each tract at each time-point. To investigate longitudinal trajectories of fiber development, linear mixed models were performed separately for the left and right CST, controlling for nuisance variables. To examine possible variations in fiber development between groups, we tested whether the inclusion of group and the interaction between age and group improved model fit. At ≈10 years, those with ADHD presented with lower FD within the bilateral CST relative to controls, irrespective of their prospective motor status. While these microstructural abnormalities persisted into adolescence for individuals with ADHD and co-occurring motor problems, they resolved for those with ADHD alone. Divergent maturational pathways of motor networks (i.e., the CST) may, at least partly, explain motor problems individuals with ADHD.

Functional Anatomy of the Spinal Tracts Based on Evolutionary Perspectives

The development of spinal cord represents evolutionary progression. The primitive tract is responsible for functions related to basic survival such as locomotion. In contrast, the developed tracts are involved in perceiving the external environment and controlling conscious movements. There are also differences in the arrangement of spinal tracts between the 2 categories. Tracts serving developed functions are located in the deep layer of the lateral funiculus, whereas primitive tracts occupy other areas. Decussation correlates with tract pathways, with primitive tracts projecting ipsilaterally and developing tracts decussating early. Understanding these principles provides insights into spinal tract organization.

Non-human primate models of focal cortical ischemia for neuronal replacement therapy

Despite the high prevalence, stroke remains incurable due to the limited regeneration capacity in the central nervous system. Neuronal replacement strategies are highly diverse biomedical fields that attempt to replace lost neurons by utilizing exogenous stem cell transplants, biomaterials, and direct neuronal reprogramming. Although these approaches have achieved encouraging outcomes mostly in the rodent stroke model, further preclinical validation in non-human primates (NHP) is still needed prior to clinical trials. In this paper, we briefly review the recent progress of promising neuronal replacement therapy in NHP stroke studies. Moreover, we summarize the key characteristics of the NHP as highly valuable translational tools and discuss (1) NHP species and their advantages in terms of genetics, physiology, neuroanatomy, immunology, and behavior; (2) various methods for establishing NHP focal ischemic models to study the regenerative and plastic changes associated with motor functional recovery; and (3) a comprehensive analysis of experimentally and clinically accessible outcomes and a potential adaptive mechanism. Our review specifically aims to facilitate the selection of the appropriate NHP cortical ischemic models and efficient prognostic evaluation methods in preclinical stroke research design of neuronal replacement strategies.

Astroglial exosome HepaCAM signaling and ApoE antagonization coordinates early postnatal cortical pyramidal neuronal axon growth and dendritic spine formation

Developing astroglia play important roles in regulating synaptogenesis through secreted and contact signals. Whether they regulate postnatal axon growth is unknown. By selectively isolating exosomes using size-exclusion chromatography (SEC) and employing cell-type specific exosome reporter mice, our current results define a secreted astroglial exosome pathway that can spread long-range in vivo and stimulate axon growth of cortical pyramidal neurons. Subsequent biochemical and genetic studies found that surface expression of glial HepaCAM protein essentially and sufficiently mediates the axon-stimulating effect of astroglial exosomes. Interestingly, apolipoprotein E (ApoE), a major astroglia-secreted cholesterol carrier to promote synaptogenesis, strongly inhibits the stimulatory effect of astroglial exosomes on axon growth. Developmental ApoE deficiency also significantly reduces spine density of cortical pyramidal neurons. Together, our study suggests a surface contact mechanism of astroglial exosomes in regulating axon growth and its antagonization by ApoE, which collectively coordinates early postnatal pyramidal neuronal axon growth and dendritic spine formation.

Assessment of corticospinal tract remodeling based on diffusion tensor imaging in the treatment of motor dysfunction after ischemic stroke by acupuncture: A meta-analysis

BACKGROUND

To investigate the efficacy of acupuncture in improving motor dysfunction after ischemic stroke (IS) and to investigate the effect of acupuncture on corticospinal tract (CST) remodeling using diffusion tensor imaging.

METHODS

Published literature on the effect of acupuncture on CST remodeling after IS using diffusion tensor imaging in the form of randomized controlled trials (RCTs) were systematically retrieved and screened from Cochrane Library, Web of Science, PubMed, Embase, CNKI, CBM, VIP, and Wanfang databases from inception to December 2022. The methodological quality of the included studies was critically and independently evaluated by 2 reviewers using the Cochrane Risk of Bias Assessment Tool for RCTs. The correlated data were extracted using the pre-designed form, and all analyses were performed using Reviewer Manager version 5.4.

RESULTS

Eleven eligible RCTs involving 459 patients were eventually included. The combined evidence results showed that the acupuncture group significantly improved patients' National Institute of Health stroke scale, Fugl-Meyer Assessment Scale, and Barthel index compared with conventional medical treatment. The acupuncture group significantly promoted remodeling of the CST, as reflected by an increase in fractional anisotropy (FA) throughout the CST [MD = 0.04, 95% CI (0.02, 0.07), P = .001], and in addition, subgroup analysis showed that the acupuncture group significantly improved FA in the infarct area compared with conventional medical treatment at around 4 weeks [MD = 0.04, 95% CI (0.02, 0.06), P = .0002] and FA of the affected cerebral peduncle [MD = 0.03, 95% CI (0.00, 0.07), P = .02]. Also, compared with conventional medical treatment, the acupuncture group significantly increased average diffusion coefficient of the affected cerebral peduncle [MD = -0.21, 95% CI (-0.28, -0.13), P < .00001].

CONCLUSION

The results of the meta-analysis suggest that acupuncture therapy can improve the clinical manifestations of motor dysfunction in patients after IS and advance a possibly beneficial effect on CST remodeling. However, due to the number and quality of eligible studies, these findings need to be further validated in more standardized, rigorous, high-quality clinical trials.