Diaschisis: past, present, future

Resting-State Beta-Band Recovery Network Related to Cognitive Improvement After Stroke

Background

Stroke is the second leading cause of death worldwide and it causes important long-term cognitive and physical deficits that hamper patients' daily activity. Neuropsychological rehabilitation (NR) has increasingly become more important to recover from cognitive disability and to improve the functionality and quality of life of these patients. Since in most stroke cases, restoration of functional connectivity (FC) precedes or accompanies cognitive and behavioral recovery, understanding the electrophysiological signatures underlying stroke recovery mechanisms is a crucial scientific and clinical goal.

Methods

For this purpose, a longitudinal study was carried out with a sample of 10 stroke patients, who underwent two neuropsychological assessments and two resting-state magnetoencephalographic (MEG) recordings, before and after undergoing a NR program. Moreover, to understand the degree of cognitive and neurophysiological impairment after stroke and the mechanisms of recovery after cognitive rehabilitation, stroke patients were compared to 10 healthy controls matched for age, sex, and educational level.

Findings

After intra and inter group comparisons, we found the following results: (1) Within the stroke group who received cognitive rehabilitation, almost all cognitive domains improved relatively or totally; (2) They exhibit a pattern of widespread increased in FC within the beta band that was related to the recovery process (there were no significant differences between patients who underwent rehabilitation and controls); (3) These FC recovery changes were related with the enhanced of cognitive performance. Furthermore, we explored the capacity of the neuropsychological scores before rehabilitation, to predict the FC changes in the brain network. Significant correlations were found in global indexes from the WAIS-III: Performance IQ (PIQ) and Perceptual Organization index (POI) (i.e., Picture Completion, Matrix Reasoning, and Block Design).

Lateropulsion Prevalence after Stroke: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

Lateropulsion is a deficit of active body orientation with respect to gravity in the frontal plane, mostly observed after a stroke. It magnifies mobility limitations and so represents an emerging target in rehabilitation. Efforts to design specific interventional studies require some basic knowledge of epidemiology, which is insufficient today because many studies focused on a few severe forms in individuals called pushers. The objectives of this study were to bridge this gap.

METHODS

We systematically searched MEDLINE, EMBASE, CINAHL, and Cochrane Clinical Trials up to 31 May 2021 for original research reporting a prevalence or incidence of post-stroke lateropulsion. We followed MOOSE and PRISMA guidelines. Eligibility for inclusion, data extraction, and study quality (Joanna Briggs Institute guidelines) were evaluated by two reviewers who used a standardized protocol: PROSPERO (CRD42020175037). A random-effects meta-analysis was used to obtain the pooled prevalence, whose heterogeneity was investigated by subgroup analysis (stroke locations and post-stroke phases) and meta-regression.

RESULTS

We identified 22 studies (5125 individuals; mean age 68.5 years; 42.6% female; assessed 24 days, on average, after stroke), most published after 2000. The studies' quality was adequate, with only 8 (36.4%) showing risk of bias. The pooled lateropulsion prevalence was 55.1% (95% confidence interval [CI] [35.9-74.2]) and was consistent across assessment tools. After supratentorial stroke, lateropulsion prevalence was 41% (95%CI [33.5-48.5]), and only 12.5% (95%CI [9.2-15.9]) in individuals with severe lateropulsion, called pushers. Meta-regression did not reveal any effect of age, sex, geographic region, publication year, or study quality. Lateropulsion prevalence progressively decreased from 52.8% (95%CI [40.7-65]) in the acute phase to 37% (95%CI [26.3-47.7]) in the early subacute phase and 22.8% (95%CI [0-46.3]) in the late subacute phase. The ratio of right- to left-hemispheric stroke with lateropulsion increased as a function of time: 1.7 in the acute phase to 7.7 in the late subacute phase. After infratentorial stroke, lateropulsion prevalence was very high, reaching 83.2% (95%CI [63.9-100.3]).

CONCLUSIONS

Post-stroke lateropulsion prevalence is high, which appeals for its systematic detection to guide early interventions. Uprightness is predominantly controlled from the right hemisphere.

Natural recovery and regeneration of the central nervous system

The diagnosis and management of CNS injuries comprises a large portion of psychiatric practice. Many clinical and preclinical studies have demonstrated the benefit of treating CNS injuries using various regenerative techniques and materials such as stem cells, biomaterials and genetic modification. Therefore it is the goal of this review article to briefly summarize the pathogenesis of CNS injuries, including traumatic brain injuries, spinal cord injuries and cerebrovascular accidents. Next, we discuss the role of natural recovery and regeneration of the CNS, explore the relevance in clinical practice and discuss emerging and cutting-edge treatments and current barriers in the field of regenerative medicine.

Understanding Language Reorganization With Neuroimaging: How Language Adapts to Different Focal Lesions and Insights Into Clinical Applications

When the language-dominant hemisphere is damaged by a focal lesion, the brain may reorganize the language network through functional and structural changes known as adaptive plasticity. Adaptive plasticity is documented for triggers including ischemic, tumoral, and epileptic focal lesions, with effects in clinical practice. Many questions remain regarding language plasticity. Different lesions may induce different patterns of reorganization depending on pathologic features, location in the brain, and timing of onset. Neuroimaging provides insights into language plasticity due to its non-invasiveness, ability to image the whole brain, and large-scale implementation. This review provides an overview of language plasticity on MRI with insights for patient care. First, we describe the structural and functional language network as depicted by neuroimaging. Second, we explore language reorganization triggered by stroke, brain tumors, and epileptic lesions and analyze applications in clinical diagnosis and treatment planning. By comparing different focal lesions, we investigate determinants of language plasticity including lesion location and timing of onset, longitudinal evolution of reorganization, and the relationship between structural and functional changes.

Resolution of diaschisis contributes to early recovery from post-stroke aphasia

Diaschisis is a phenomenon observed in stroke that is defined as neuronal dysfunction in regions spared by the infarction but connected to the lesion site. We combined lesion network mapping and task-based functional MRI in 71 patients with post-stroke aphasia to investigate, whether diaschisis and its resolution contribute to early loss and recovery of language functions. Language activation acquired in the acute, subacute and chronic phase was analyzed in compartments with high and low normative resting-state functional connectivity to the lesion site on an individual basis. Regions with high compared to regions with low lesion connectivity showed a steeper increase in language reactivation from the acute to the subacute phase. This finding is compatible with the assumption of resolution of diaschisis. Additionally, language performance in the subacute phase and improvement from the subacute to the chronic phase significantly correlated with the diaschisis effect and its resolution, respectively, suggesting a behavioral relevance of this effect. We therefore assume that undamaged but functionally connected regions become dysfunctional due to missing input from the lesion contributing to the aphasic deficit. Since these regions are structurally intact, dysfunction resolves over time contributing to the rapid early behavioral improvement observed in aphasic stroke patients. Our results demonstrate that diaschisis and its resolution might be a relevant mechanism of early loss and recovery of language function in acute stroke patients.

Predicting Individual Treatment Response to rTMS for Motor Recovery After Stroke: A Review and the CanStim Perspective

Background

Rehabilitation is critical for reducing stroke-related disability and improving quality-of-life post-stroke. Repetitive transcranial magnetic stimulation (rTMS), a non-invasive neuromodulation technique used as stand-alone or adjunct treatment to physiotherapy, may be of benefit for motor recovery in subgroups of stroke patients. The Canadian Platform for Trials in Non-Invasive Brain Stimulation (CanStim) seeks to advance the use of these techniques to improve post-stroke recovery through clinical trials and pre-clinical studies using standardized research protocols. Here, we review existing clinical trials for demographic, clinical, and neurobiological factors which may predict treatment response to identify knowledge gaps which need to be addressed before implementing these parameters for patient stratification in clinical trial protocols.

Objective

To provide a review of clinical rTMS trials of stroke recovery identifying factors associated with rTMS response in stroke patients with motor deficits and develop research perspectives for pre-clinical and clinical studies.

Methods

A literature search was performed in PubMed, using the Boolean search terms stroke AND repetitive transcranial magnetic stimulation OR rTMS AND motor for studies investigating the use of rTMS for motor recovery in stroke patients at any recovery phase. A total of 1,676 articles were screened by two blinded raters, with 26 papers identified for inclusion in this review.

Results

Multiple possible factors associated with rTMS response were identified, including stroke location, cortical thickness, brain-derived neurotrophic factor (BDNF) genotype, initial stroke severity, and several imaging and clinical factors associated with a relatively preserved functional motor network of the ipsilesional hemisphere. Age, sex, and time post-stroke were generally not related to rTMS response. Factors associated with greater response were identified in studies of both excitatory ipsilesional and inhibitory contralesional rTMS. Heterogeneous study designs and contradictory data exemplify the need for greater protocol standardization and high-quality controlled trials.

Conclusion

Clinical, brain structural and neurobiological factors have been identified as potential predictors for rTMS response in stroke patients with motor impairment. These factors can inform the design of future clinical trials, before being considered for optimization of individual rehabilitation therapy for stroke patients. Pre-clinical models for stroke recovery, specifically developed in a clinical context, may accelerate this process.

Imaging and Electrophysiology for Degenerative Cervical Myelopathy [AO Spine RECODE-DCM Research Priority Number 9]

STUDY DESIGN

Narrative review.

OBJECTIVE

The current review aimed to describe the role of existing techniques and emerging methods of imaging and electrophysiology for the management of degenerative cervical myelopathy (DCM), a common and often progressive condition that causes spinal cord dysfunction and significant morbidity globally.

METHODS

A narrative review was conducted to summarize the existing literature and highlight future directions.

RESULTS

Anatomical magnetic resonance imaging (MRI) is well established in the literature as the key imaging tool to identify spinal cord compression, disc herniation/bulging, and inbuckling of the ligamentum flavum, thus facilitating surgical planning, while radiographs and computed tomography (CT) provide complimentary information. Electrophysiology techniques are primarily used to rule out competing diagnoses. However, signal change and measures of cord compression on conventional MRI have limited utility to characterize the degree of tissue injury, which may be helpful for diagnosis, prognostication, and repeated assessments to identify deterioration. Early translational studies of quantitative imaging and electrophysiology techniques show potential of these methods to more accurately reflect changes in spinal cord microstructure and function.

CONCLUSION

Currently, clinical management of DCM relies heavily on anatomical MRI, with additional contributions from radiographs, CT, and electrophysiology. Novel quantitative assessments of microstructure, perfusion, and function have the potential to transform clinical practice, but require robust validation, automation, and standardization prior to uptake.

The role of disrupted structural connectivity in aphasia

Lesion-based studies are among the most informative approaches to determine a critical relationship between a particular brain region and specific function. Importantly, brain lesions cause disconnection of other brain areas that appear to be intact and may cause functional deficits in these regions due to a lack of afferent projections. If only the location of necrosis and gliosis after the stroke is considered to be the lesion, the full spectrum of brain dysfunction is only partly assessed, and there is a high probability that incomplete region-to-function inferences are made. In this chapter we (1) outline how structural connectivity can be measured in individuals with stroke, and (2) provide an overview of the importance of disrupted structural connectivity in aphasia. We conclude that connection-based and region/voxel-based symptom mapping yield complementary information and together provide an in-depth picture of brain and function relationships.

Functional neuroanatomy of mania

Mania, the diagnostic hallmark of bipolar disorder, is an episodic disturbance of mood, sleep, behavior, and perception. Improved understanding of the neurobiology of mania is expected to allow for novel avenues to address current challenges in its diagnosis and treatment. Previous research focusing on the impairment of functional neuronal circuits and brain networks has resulted in heterogenous findings, possibly due to a focus on bipolar disorder and its several phases, rather than on the unique context of mania. Here we present a comprehensive overview of the evidence regarding the functional neuroanatomy of mania. Our interpretation of the best available evidence is consistent with a convergent model of lateralized circuit dysfunction in mania, with hypoactivity of the ventral prefrontal cortex in the right hemisphere, and hyperactivity of the amygdala, basal ganglia, and anterior cingulate cortex in the left hemisphere of the brain. Clarification of dysfunctional neuroanatomic substrates of mania may contribute not only to improve understanding of the neurobiology of bipolar disorder overall, but also highlights potential avenues for new circuit-based therapeutic approaches in the treatment of mania.

Validating atlas-based lesion disconnectomics in multiple sclerosis: A retrospective multi-centric study

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Structural disconnectomes can be modelled without diffusion using tractography atlases.

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Atlas-based and DTI-derived disconnectome topological metrics correlate strongly.

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MS patient disconnectomes relate to clinical scores.

The translational potential of MR-based connectivity modelling is limited by the need for advanced diffusion imaging, which is not part of clinical protocols for many diseases. In addition, where diffusion data is available, brain connectivity analyses rely on tractography algorithms which imply two major limitations. First, tracking algorithms are known to be sensitive to the presence of white matter lesions and therefore leading to interpretation pitfalls and poor inter-subject comparability in clinical applications such as multiple sclerosis. Second, tractography quality is highly dependent on the acquisition parameters of diffusion sequences, leading to a trade-off between acquisition time and tractography precision.

Here, we propose an atlas-based approach to study the interplay between structural disconnectivity and lesions without requiring individual diffusion imaging. In a multi-centric setting involving three distinct multiple sclerosis datasets (containing both 1.5 T and 3 T data), we compare our atlas-based structural disconnectome computation pipeline to disconnectomes extracted from individual tractography and explore its clinical utility for reducing the gap between radiological findings and clinical symptoms in multiple sclerosis. Results using topological graph properties showed that overall, our atlas-based disconnectomes were suitable approximations of individual disconnectomes from diffusion imaging. Small-worldness was found to decrease for larger total lesion volumes thereby suggesting a loss of efficiency in brain connectivity of MS patients. Finally, the global efficiency of the created brain graph, combined with total lesion volume, allowed to stratify patients into subgroups with different clinical scores in all three cohorts.

New tools for shaping plasticity to enhance recovery after stroke

Stroke is the second most common cause of death worldwide and its prevalence is projected to increase in the coming years in parallel with the increase of life expectancy. Despite the great improvements in the management of the acute phase of stroke, some residual disability persists in most patients thus requiring rehabilitation. One third of patients do not reach the maximal recovery potential and different approaches have been explored with the aim to boost up recovery. In this regard, noninvasive brain stimulation techniques have been widely used to induce neuroplasticity phenomena. Different protocols of repetitive transcranial magnetic stimulation (rTMS) and transcranial electrical stimulation (tES) can induce short- and long-term changes of synaptic excitability and are promising tools for enhancing recovery in stroke patients. New options for neuromodulation are currently under investigation. They include: vagal nerve stimulation (VNS) that can be delivered invasively, with implanted stimulators and noninvasively with transcutaneous VNS (tVNS); and extremely low-frequency (1-300Hz) magnetic fields. This chapter will provide an overview on the new techniques that are used for neuroprotection and for enhancing recovery after stroke.

Local sleep: A new concept in brain plasticity

Traditionally, sleep and wakefulness have been considered as two global, mutually exclusive states. However, this view has been challenged by the discovery that sleep and wakefulness are actually locally regulated and that islands of these two states may often coexist in the same individual. Importantly, such a local regulation seems to be the key for many essential functions of sleep, including the maintenance of cognitive efficiency and the consolidation of new skills and memories. Indeed, local changes in sleep-related oscillations occur in brain areas that are used and involved in learning during wakefulness. In turn, these changes directly modulate experience-dependent brain adaptations and the consolidation of newly acquired memories. In line with these observations, alterations in the regional balance between wake- and sleep-like activity have been shown to accompany many pathologic conditions, including psychiatric and neurologic disorders. In the last decade, experimental research has started to shed light on the mechanisms involved in the local regulation of sleep and wakefulness. The results of this research have opened new avenues of investigation regarding the function of sleep and have revealed novel potential targets for the treatment of several pathologic conditions.

Contribution of the medial eye field network to the voluntary deployment of visuospatial attention

Historically, the study of patients with spatial neglect has provided fundamental insights into the neural basis of spatial attention. However, lesion mapping studies have been unsuccessful in establishing the potential role of associative networks spreading on the dorsal-medial axis, mainly because they are uncommonly targeted by vascular injuries. Here we combine machine learning-based lesion-symptom mapping, disconnection analyses and the longitudinal behavioral data of 128 patients with well-delineated surgical resections. The analyses show that surgical resections in a location compatible with both the supplementary and the cingulate eye fields, and disrupting the dorsal-medial fiber network, are specifically associated with severely diminished performance on a visual search task (i.e., visuo-motor exploratory neglect) with intact performance on a task probing the perceptual component of neglect. This general finding provides causal evidence for a role of the frontal-medial network in the voluntary deployment of visuo-spatial attention.

Excitatory-Inhibitory Homeostasis and Diaschisis: Tying the Local and Global Scales in the Post-stroke Cortex

Maintaining a balance between excitatory and inhibitory activity is an essential feature of neural networks of the neocortex. In the face of perturbations in the levels of excitation to cortical neurons, synapses adjust to maintain excitatory-inhibitory (EI) balance. In this review, we summarize research on this EI homeostasis in the neocortex, using stroke as our case study, and in particular the loss of excitation to distant cortical regions after focal lesions. Widespread changes following a localized lesion, a phenomenon known as diaschisis, are not only related to excitability, but also observed with respect to functional connectivity. Here, we highlight the main findings regarding the evolution of excitability and functional cortical networks during the process of post-stroke recovery, and how both are related to functional recovery. We show that cortical reorganization at a global scale can be explained from the perspective of EI homeostasis. Indeed, recovery of functional networks is paralleled by increases in excitability across the cortex. These adaptive changes likely result from plasticity mechanisms such as synaptic scaling and are linked to EI homeostasis, providing a possible target for future therapeutic strategies in the process of rehabilitation. In addition, we address the difficulty of simultaneously studying these multiscale processes by presenting recent advances in large-scale modeling of the human cortex in the contexts of stroke and EI homeostasis, suggesting computational modeling as a powerful tool to tie the meso- and macro-scale processes of recovery in stroke patients.

Bipolar spectrum disorders in neurologic disorders

Psychiatric symptoms frequently predate or complicate neurological disorders, such as neurodegenerative diseases. Symptoms of bipolar spectrum disorders (BSD), like mood, behavioral, and psychotic alterations, are known to occur - individually or as a syndromic cluster - in Parkinson's disease and in the behavioral variant of frontotemporal dementia (FTD). Nonetheless, due to shared pathophysiological mechanisms, or genetic predisposition, several other neurological disorders show significant, yet neglected, clinical and biological overlaps with BSD like neuroinflammation, ion channel dysfunctions, neurotransmission imbalance, or neurodegeneration. BSD pathophysiology is still largely unclear, but large-scale network dysfunctions are known to participate in the onset of mood disorders and psychotic symptoms. Thus, functional alterations can unleash BSD symptoms years before the evidence of an organic disease of the central nervous system. The aim of our narrative review was to illustrate the numerous intersections between BSD and neurological disorders from a clinical-biological point of view and the underlying predisposing factors, to guide future diagnostic and therapeutical research in the field.

OUP accepted manuscript

Analyses of alterations of brain networks have gained an increasing interest in stroke rehabilitation research. Compared with functional networks derived from resting-state analyses, there is limited knowledge of how structural network topology might undergo changes after stroke and, more importantly, if structural network information obtained early after stroke could enhance recovery models to infer later outcomes. The present work re-analysed cross-sectional structural imaging data, obtained within the first 2 weeks, of 45 acute stroke patients (22 females, 24 right-sided strokes, age 68 ± 13 years). Whole-brain tractography was performed to reconstruct structural connectomes and graph-theoretical analyses were employed to quantify global network organization with a focus on parameters of network integration and modular processing. Graph measures were compared between stroke patients and 34 healthy controls (15 females, aged 69 ± 10 years) and they were integrated with four clinical scores of the late subacute stage, covering neurological symptom burden (National Institutes of Health Stroke Scale), global disability (modified Rankin Scale), activity-related disability (Barthel Index) and motor functions (Upper-Extremity Score of the Fugl-Meyer Assessment). The analyses were employed across the complete cohort and, based on clustering analysis, separately within subgroups stratified in mild to moderate (n = 21) and severe (n = 24) initial deficits. The main findings were (i) a significant reduction of network’s global efficiency, specifically in patients with severe deficits compared with controls (P = 0.010) and (ii) a significant negative correlation of network efficiency with the extent of persistent functional deficits at follow-up after 3–6 months (P ≤ 0.032). Specifically, regression models revealed that this measure was capable to increase the explained variance in future deficits by 18% for the modified Rankin Scale, up to 24% for National Institutes of Health Stroke Scale, and 16% for Barthel Index when compared with models including the initial deficits and the lesion volume. Patients with mild to moderate deficits did not exhibit a similar impact of network efficiency on outcome inference. Clustering coefficient and modularity, measures of segregation and modular processing, did not exhibit comparable structure–outcome relationships, neither in severely nor in mildly affected patients. This study provides empirical evidence that structural network efficiency as a graph-theoretical marker of large-scale network topology, quantified early after stroke, relates to recovery. Notably, this contribution was only evident in severely but not mildly affected stroke patients. This suggests that the initial clinical deficit might shape the dependency of recovery on global network topology after stroke.

Neuronal activity reorganization in motor cortex for successful locomotion after a lesion in the ventrolateral thalamus

Thalamic stroke leads to ataxia if the cerebellum-receiving ventrolateral thalamus (VL) is affected. The compensation mechanisms for this deficit are not well understood, particularly the roles that single neurons and specific neuronal subpopulations outside the thalamus play in recovery. The goal of this study was to clarify neuronal mechanisms of the motor cortex involved in mitigation of ataxia during locomotion when part of the VL is inactivated or lesioned. In freely ambulating cats, we recorded the activity of neurons in layer V of the motor cortex as the cats walked on a flat surface and horizontally placed ladder. We first reversibly inactivated ∼10% of the VL unilaterally using glutamatergic transmission antagonist CNQX and analyzed how the activity of motor cortex reorganized to support successful locomotion. We next lesioned 50%-75% of the VL bilaterally using kainic acid and analyzed how the activity of motor cortex reorganized when locomotion recovered. When a small part of the VL was inactivated, the discharge rates of motor cortex neurons decreased, but otherwise the activity was near normal, and the cats walked fairly well. Individual neurons retained their ability to respond to the demand for accuracy during ladder locomotion; however, most changed their response. When the VL was lesioned, the cat walked normally on the flat surface but was ataxic on the ladder for several days after lesion. When ladder locomotion normalized, neuronal discharge rates on the ladder were normal, and the shoulder-related group was preferentially active during the stride's swing phase.NEW & NOTEWORTHY This is the first analysis of reorganization of the activity of single neurons and subpopulations of neurons related to the shoulder, elbow, or wrist, as well as fast- and slow-conducting pyramidal tract neurons in the motor cortex of animals walking before and after inactivation or lesion in the thalamus. The results offer unique insights into the mechanisms of spontaneous recovery after thalamic stroke, potentially providing guidance for new strategies to alleviate locomotor deficits after stroke.

Thalamic Aphasia: a Review

PURPOSE OF REVIEW

Thalamic aphasia is a rare language disorder resulting from lesions to the thalamus. While most patients exhibit mild symptoms with a predominance of lexical-semantic difficulties, variations in phenotype have been described. Overall, the exact mechanisms of thalamic aphasia await empirical research. The article reviews recent findings regarding phenotypes and possible underlying mechanisms of thalamic aphasia.

RECENT FINDINGS

Variations in phenotype of thalamic aphasia may be related to different lesion locations. Overall, the thalamus' role in language is thought to be due to its involvement in cortico-thalamic language networks with lesioning of certain nuclei resulting in the diachisis of otherwise interconnected areas. Its possible monitoring function in such a network might be due to its different cellular firing modes. However, no specific evidence has been collected to date. While recent findings show a more distinct understanding of thalamic aphasia phenotypes and possible underlying mechanisms, further research is needed. Additionally, as standard language testing might oftentimes not pick up on its subtle symptoms, thalamic aphasia might be underdiagnosed.

Voxelwise structural disconnection mapping: Methodological validation and recommendations

Voxelwise disconnection mapping is a novel approach to disclose lesion-symptom relationships for symptoms caused by white matter disconnection. It uses MRI-based fiber tracking in healthy subjects seeded from patient’s focal brain lesions. Resulting individual disconnection maps can then be statistically associated with symptoms. Despite increasing use in the recent years, the validity of this approach remains to be investigated. In this study, we validated both, our own implementation and the implementation provided within BCBtoolkit. For technical validation, we used simulated symptoms based on overlap of 70 real stroke lesions with tracts from a white matter atlas. For clinical validation, paresis scores and lesions from 316 patients with stroke were used. We found that voxelwise disconnection mapping is technically valid and outperforms the standard voxel-based lesion-symptom mapping approach for symptoms caused by white matter disconnection. Supporting its clinical validity and utility, we were able to reproduce the known association between corticospinal tract damage and contralateral hemiparesis. In addition, we demonstrate that the validity can be substantially diminished by relatively minor methodological changes. Based on these results, we derive methodological recommendations for the future use of voxelwise disconnection mapping. Our study highlights the importance of validating novel methodological approaches in the rapidly evolving field of neuroimaging.

Plasticity of the language system in children and adults

The language system is perhaps the most unique feature of the human brain's cognitive architecture. It has long been a quest of cognitive neuroscience to understand the neural components that contribute to the hierarchical pattern processing and advanced rule learning required for language. The most important goal of this research is to understand how language becomes impaired when these neural components malfunction or are lost to stroke, and ultimately how we might recover language abilities under these circumstances. Additionally, understanding how the language system develops and how it can reorganize in the face of brain injury or dysfunction could help us to understand brain plasticity in cognitive networks more broadly. In this chapter we will discuss the earliest features of language organization in infants, and how deviations in typical development can-but in some cases, do not-lead to disordered language. We will then survey findings from adult stroke and aphasia research on the potential for recovering language processing in both the remaining left hemisphere tissue and in the non-dominant right hemisphere. Altogether, we hope to present a clear picture of what is known about the capacity for plastic change in the neurobiology of the human language system.

Cortical Hyper-Connectivity in a Stroke Patient with Rotated Drawing

In the present case report, we investigated the cortical networks of a patient (DDA) affected by right parietal stroke who showed a constructional phenomenon, in which when coping and recalling from memory a complex figure, the model was reproduced rotated of 90° along the vertical axis. Previous studies suggested that rotation on copy is associated with visuospatial impairments and abnormalities in parietal cortex, whereas rotation on recall might be related to executive deficits and dysfunction of frontal regions. Here, we computed the DDA's resting-state functional connectivity (FC) derived from cortical regions of the dorsal attention (DAN) and the frontal portion of the executive-control network (fECN), which are involved in the control of visuospatial attention and multiple executive functions, respectively. We observed that, as compared to a control group of right stroke patients without drawing rotation, DDA exhibited selective increased FC of the DAN and fECN, but not of task-irrelevant language network, within the undamaged hemisphere. These patterns might reflect a pathological communication in such networks leading to impaired attentional and executive operations required to reproduce the model in the correct orientation. Notably, such enhancement of FC was not detected in a patient with a comparable neuropsychological profile as DDA, yet without rotated drawing, suggesting that network-specific modulations in DDA might be ascribed to the constructional phenomenon of rotated drawing.

Spatio-temporal analysis of EEG features during consciousness recovery in patients with disorders of consciousness

OBJECTIVE

As consciousness recovery is not only dynamic but also involves interactions between various brain regions, elucidating the mechanism of recovery requires tracking cortical activity in spatio-temporal dimensions.

METHODS

We tracked the cortical activities of 40 patients (mean age: 54.38 years; 28 males; 21 patients with minimally conscious states) with disorders of consciousness, and collected a total of 156 electroencephalographic signals. We investigated the longitudinal changes in EEG nonlinear dynamic features (i.e., approximate entropy, sample entropy, and Lempel-Ziv complexity) and relative wavelet energy along with consciousness recovery.

RESULTS

Global EEG features showed a non-monotonic trend during consciousness recovery (P < 0.05). When the level of consciousness of patients was transferred to a minimally conscious state from an unresponsive wakefulness syndrome/ vegetative state, an inflection point appeared in the EEG features. The EEG feature change trends between the injured and uninjured areas were dissimilar (P < 0.05). Importantly, the degree of dissimilarity increased non-monotonically across the levels of consciousness (P < 0.05).

CONCLUSIONS

EEG recovery was non-monotonic and dissimilar in spatio-temporal dimensions, with an inflection point.

SIGNIFICANCE

These findings further clarify the process of consciousness recovery and provide assistance in exploring the mechanism of consciousness recovery.

Clinical applications of magnetic resonance imaging based functional and structural connectivity

Advances in computational neuroimaging techniques have expanded the armamentarium of imaging tools available for clinical applications in clinical neuroscience. Non-invasive, in vivo brain MRI structural and functional network mapping has been used to identify therapeutic targets, define eloquent brain regions to preserve, and gain insight into pathological processes and treatments as well as prognostic biomarkers. These tools have the real potential to inform patient-specific treatment strategies. Nevertheless, a realistic appraisal of clinical utility is needed that balances the growing excitement and interest in the field with important limitations associated with these techniques. Quality of the raw data, minutiae of the processing methodology, and the statistical models applied can all impact on the results and their interpretation. A lack of standardization in data acquisition and processing has also resulted in issues with reproducibility. This limitation has had a direct impact on the reliability of these tools and ultimately, confidence in their clinical use. Advances in MRI technology and computational power as well as automation and standardization of processing methods, including machine learning approaches, may help address some of these issues and make these tools more reliable in clinical use. In this review, we will highlight the current clinical uses of MRI connectomics in the diagnosis and treatment of neurological disorders; balancing emerging applications and technologies with limitations of connectivity analytic approaches to present an encompassing and appropriate perspective.

A CBF decrease in the left supplementary motor areas: New insight into postoperative pediatric cerebellar mutism syndrome using arterial spin labeling perfusion MRI

Postoperative pediatric cerebellar mutism syndrome (pCMS), characterized mainly by delayed onset transient mutism is a poorly understood complication that may occur after pediatric medulloblastoma (MB) resection. Our aim was to investigate postoperative changes in whole-brain cerebral blood flow (CBF) at rest in pCMS patients using arterial spin labeling (ASL) perfusion imaging. This study compared preoperative and postoperative T2-weighted signal abnormalities and CBF using a voxel-wise, whole-brain analysis in 27 children undergoing MB resection, including 11 patients who developed mutism and 16 who did not. Comparison of postoperative T2 signal abnormalities between patients who developed pCMS (mean age 7.0 years) and those who did not showed that pCMS (mean age 8.9 years) patients were significantly more likely to present with T2-weighted hyperintensities in the right dentate nucleus (DN) (p = 0.02). Comparison of preoperative and postoperative CBF in patients with pCMS showed a significant postoperative CBF decrease in the left pre-supplementary motor area (pre-SMA) (p = 0.007) and SMA (p = 0.009). In patients who did not develop pCMS, no significant differences were observed. Findings provide evidence of an association between pCMS, injury to the right DN, and left pre-SMA/SMA hypoperfusion, areas responsible for speech. This supports the relevance of CBF investigations in pCMS.

Independent contributions of structural and functional connectivity: Evidence from a stroke model

Altered functional connectivity is related to severity of language impairment in poststroke aphasia. However, it is not clear whether this finding specifically reflects loss of functional coherence, or more generally, is related to decreased structural connectivity due to cortical necrosis. The aim of the current study was to investigate this issue by factoring out structural connectivity from functional connectivity measures and then relating the residual data to language performance poststroke. Ninety-seven participants with a history of stroke were assessed using language impairment measures (Auditory Verbal Comprehension and Spontaneous Speech scores from the Western Aphasia Battery-Revised) and MRI (structural, diffusion tensor imaging, and resting-state functional connectivity). We analyzed the association between functional connectivity and language and controlled for multiple potential neuroanatomical confounders, namely structural connectivity. We identified functional connections within the left hemisphere ventral stream where decreased functional connectivity, independent of structural connectivity, was associated with speech comprehension impairment. These connections exist in frontotemporal and temporoparietal regions. Our results suggest poor speech comprehension in aphasia is at least partially caused by loss of cortical synchrony in a left hemisphere ventral stream network and is not only reflective of localized necrosis or structural connectivity.

Neurophysiological Examinations as Adjunctive Tool to Imaging Techniques in Spontaneous Intracerebral Hemorrhage: IRONHEART Study

Introduction: Intracerebral hemorrhage (ICH) is a devastating disease, which may lead to severe disability or even death. Although many factors may influence the outcome, neurophysiological examinations might also play a role in its course. Our aim was to examine whether the findings of electroencephalography (EEG) and transcranial magnetic stimulation (TMS) can predict the prognosis of these patients.

Methods: Between June 1 2017 and June 15 2021, 116 consecutive patients with ICH were enrolled prospectively in our observational study. Clinical examinations and non-Contrast computed tomography (NCCT) scan were done on admission for ICH; follow-up NCCT scans were taken at 14 ± 2 days and at 3 months ± 7 days after stroke onset. EEG and TMS examinations were also carried out.

Results: Of the patients in the study, 65.5% were male, and the mean age of the study population was 70 years. Most patients had a history of hypertension, 50.8% of whom had been untreated. In almost 20% of the cases, excessive hypertension was measured on admission, accompanied with >10 mmol/L blood glucose level, whereas their Glasgow Coma Scale was 12 on average. Presence of blood in the ventricles or subarachnoid space and high blood and perihematomal volumes meant poor prognosis. Pathological EEG was prognostic of a worse outcome. With TMS examination at 14 days, it might be possible to estimate outcome in a univariate model and the absence, or reduction of the amplitude of the motor evoked potentials was associated with poor prognosis.

Conclusion: Together with the clinical symptoms, the volume of bleeding, perihematomal edema (or their combined volume), and neurophysiological examinations like EEG and TMS play an important role in the neurological outcome of patients with ICH. This might affect the patients' rehabilitation plans in the future, since with the help of the examinations the subset of patients with potential for recovery could be identified.

The functional characterization of callosal connections

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The functional characterization of callosal connections is informed by anatomical data.

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Callosal connections play a conditional driving role depending on the brain state and behavioral demands.

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Callosal connections play a modulatory function, in addition to a driving role.

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The corpus callosum participates in learning and interhemispheric transfer of sensorimotor habits.

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The corpus callosum contributes to language processing and cognitive functions.

The brain operates through the synaptic interaction of distant neurons within flexible, often heterogeneous, distributed systems. Histological studies have detailed the connections between distant neurons, but their functional characterization deserves further exploration. Studies performed on the corpus callosum in animals and humans are unique in that they capitalize on results obtained from several neuroscience disciplines. Such data inspire a new interpretation of the function of callosal connections and delineate a novel road map, thus paving the way toward a general theory of cortico-cortical connectivity. Here we suggest that callosal axons can drive their post-synaptic targets preferentially when coupled to other inputs endowing the cortical network with a high degree of conditionality. This might depend on several factors, such as their pattern of convergence-divergence, the excitatory and inhibitory operation mode, the range of conduction velocities, the variety of homotopic and heterotopic projections and, finally, the state-dependency of their firing. We propose that, in addition to direct stimulation of post-synaptic targets, callosal axons often play a conditional driving or modulatory role, which depends on task contingencies, as documented by several recent studies.

Effective connectivity extracts clinically relevant prognostic information from resting state activity in stroke

Recent resting-state functional MRI studies in stroke patients have identified two robust biomarkers of acute brain dysfunction: a reduction of inter-hemispheric functional connectivity between homotopic regions of the same network, and an abnormal increase of ipsi-lesional functional connectivity between task-negative and task-positive resting-state networks. Whole-brain computational modelling studies, at the individual subject level, using undirected effective connectivity derived from empirically measured functional connectivity, have shown a reduction of measures of integration and segregation in stroke as compared to healthy brains. Here we employ a novel method, first, to infer whole-brain directional effective connectivity from zero-lagged and lagged covariance matrices, then, to compare it to empirically measured functional connectivity for predicting stroke versus healthy status, and patient performance (zero, one, multiple deficits) across neuropsychological tests. We also investigated the accuracy of functional connectivity versus model effective connectivity in predicting the long-term outcome from acute measures. Both functional and effective connectivity predicted healthy from stroke individuals significantly better than the chance-level; however, accuracy for the effective connectivity was significantly higher than for functional connectivity at 1- to 2-week, 3-month and 1-year post-stroke. Predictive functional connections mainly included those reported in previous studies (within-network inter-hemispheric and between task-positive and -negative networks intra-hemispherically). Predictive effective connections included additional between-network links. Effective connectivity was a better predictor than functional connectivity of the number of behavioural domains in which patients suffered deficits, both at 2-week and 1-year post-onset of stroke. Interestingly, patient deficits at 1-year time-point were better predicted by effective connectivity values at 2 weeks rather than at 1-year time-point. Our results thus demonstrate that the second-order statistics of functional MRI resting-state activity at an early stage of stroke, derived from a whole-brain effective connectivity, estimated in a model fitted to reproduce the propagation of neuronal activity, has pertinent information for clinical prognosis.

Rapid and Bihemispheric Reorganization of Neuronal Activity in Premotor Cortex after Brain Injury

Brain injuries cause hemodynamic changes in several distant, spared areas from the lesion. Our objective was to better understand the neuronal correlates of this reorganization in awake, behaving female monkeys. We used reversible inactivation techniques to “injure” the primary motor cortex, while continuously recording neuronal activity of the ventral premotor cortex in the two hemispheres, before and after the onset of behavioral impairments. Inactivation rapidly induced profound alterations of neuronal discharges that were heterogeneous within each and across the two hemispheres, occurred during movements of either the affected or nonaffected arm, and varied during different phases of grasping. Our results support that extensive, and much more complex than expected, neuronal reorganization takes place in spared areas of the bihemispheric cortical network involved in the control of hand movements. This broad pattern of reorganization offers potential targets that should be considered for the development of neuromodulation protocols applied early after brain injury.

SIGNIFICANCE STATEMENT It is well known that brain injuries cause changes in several distant, spared areas of the network, often in the premotor cortex. This reorganization is greater early after the injury and the magnitude of early changes correlates with impairments. However, studies to date have used noninvasive brain imaging approaches or have been conducted in sedated animals. Therefore, we do not know how brain injuries specifically affect the activity of neurons during the generation of movements. Our study clearly shows how a lesion rapidly impacts neurons in the premotor cortex of both hemispheres. A better understanding of these complex changes can help formulate hypotheses for the development of new treatments that specifically target neuronal reorganization induced by lesions in the brain.

Cortical Thickness of Brain Areas Beyond Stroke Lesions and Sensory-Motor Recovery: A Systematic Review

Background: The clinical outcome of patients suffering from stroke is dependent on multiple factors. The features of the lesion itself play an important role but clinical recovery is remarkably influenced by the plasticity mechanisms triggered by the stroke and occurring at a distance from the lesion. The latter translate into functional and structural changes of which cortical thickness might be easy to quantify one of the main players. However, studies on the changes of cortical thickness in brain areas beyond stroke lesion and their relationship to sensory-motor recovery are sparse. Objectives: To evaluate the effects of cerebral stroke on cortical thickness (CT) beyond the stroke lesion and its association with sensory-motor recovery. Materials and Methods: Five electronic databases (PubMed, Embase, Web of Science, Scopus and the Cochrane Library) were searched. Methodological quality of the included studies was assessed with the Newcastle-Ottawa Scale for non-randomized controlled trials and the Risk of Bias Cochrane tool for randomized controlled trials. Results: The search strategy retrieved 821 records, 12 studies were included and risk of bias assessed. In most of the included studies, cortical thinning was seen at the ipsilesional motor area (M1). Cortical thinning can occur beyond the stroke lesion, typically in regions anatomically connected because of anterograde degeneration. Nonetheless, studies also reported cortical thickening of regions of the unaffected hemisphere, likely related to compensatory plasticity. Some studies revealed a significant correlation between changes in cortical thickness of M1 or somatosensory (S1) cortical areas and motor function recovery. Discussion and Conclusions: Following a stroke, changes in cortical thickness occur both in regions directly connected to the stroke lesion and in contralateral hemisphere areas as well as in the cerebellum. The underlying mechanisms leading to these changes in cortical thickness are still to be fully understood and further research in the field is needed. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020200539; PROSPERO 2020, identifier: CRD42020200539.

Immediate Plasticity of Parietal-Frontocentral Functional Connections in Music-Reality based Post-Stroke Rehabilitation

Post-stroke neuronal plasticity was always viewed as a localized gain-of-functionality. The reorganization of neurons neighboring the lesioned brain tissues is able to compensate for the function of damaged neurons. However, it was also proposed that distant interconnected brain regions could be affected by stroke. Changes in functional connections across the brain were found associated with motor deficiency and recovery. Parietal-frontocentral functional connectivity was found related to the performance of motor imagery. This study aims to evaluate the EEG-based parietal-frontocentral functional connectivity in post-stroke patients, and to investigate the immediate effect of rehabilitation training toward these connections. Pairwise functional connectivity was extracted from healthy subjects and post-stroke patients during standing and walking. Significant reductions in P3-FC4 and P3-C4 connectivity strengths were found in post-stroke patients during both standing and walking conditions. Immediate improvement in the reduced connections was observed with the intervention of a previously proposed, motivation-based rehabilitation system, which was known as the mixed-reality music rehabilitation (MR²) system. This indicates the relationship between left parietal functional connectivity and stroke-related motor performance. These findings suggest the feasibility to evaluate the immediate plasticity of functional connectivity during post-stroke rehabilitation.

Correlations between cognitive function and gray matter alterations in patients with acute lacunar stroke

Researchers emphasized acute lacunar stroke (ALS) patients suffer from poor social/physical outcomes, cognitive decline, and decreased quality of life. We hypothesized brain abnormalities may occur in ALS during this particular stage and may be associated with cognitive deficits upon evaluation. We investigated structural abnormalities in ALS using magnetic resonance imaging and voxel-based morphometry conducted on 28 healthy controls (HC) and 29 patients with ALS and proximal anterior circulation occlusion within 12 hours of symptom onset. Mini-Mental State Examination (MMSE) scores were used to evaluate cognitive dysfunction. Decreased gray matter (GM) in ALS vs. HC was predominantly in the superior frontal gyrus, inferior frontal gyrus, insula, superior temporal gyrus (STG), heschl gyrus, middle temporal gyrus (MTG), posterior cingulate cortex (PCC), hippocampus (HIP), and others. Positive correlation was found between GM density and MMSE scores in STG ( r = 0.59, p = 0.0007), MTG ( r = 0.46, p = 0.01), PCC ( r = 0.42, p = 0.02), HIP ( r = 0.4, p = 0.03), and medial prefrontal cortex ( r = 0.5, p = 0.005). This study provided further information on pathophysiological/morphological mechanisms related to cognitive impairment in ALS and is the basis for further studies in aging-related diseases.

Chemogenetic sensory fMRI reveals behaviorally relevant bidirectional changes in primate somatosensory network

Concurrent genetic neuromodulation and functional magnetic resonance imaging (fMRI) in primates has provided a valuable opportunity to assess the modified brain-wide operation in the resting state. However, its application to link the network operation with behavior still remains challenging. Here, we combined chemogenetic silencing of the primary somatosensory cortex (SI) with tactile fMRI and related behaviors in macaques. Focal chemogenetic silencing of functionally identified SI hand region impaired grasping behavior. The same silencing also attenuated hand stimulation-evoked fMRI signal at both the local silencing site and the anatomically and/or functionally connected downstream grasping network, suggesting altered network operation underlying the induced behavioral impairment. Furthermore, the hand region silencing unexpectedly disinhibited foot representation with accompanying behavioral hypersensitization. These results demonstrate that focal chemogenetic silencing with sensory fMRI in macaques unveils bidirectional network changes to generate multifaceted behavioral impairments, thereby opening a pivotal window toward elucidating the causal network operation underpinning higher brain functions in primates.

Post-Stroke Cognitive Impairment: Pathophysiological Insights into Brain Disconnectome from Advanced Neuroimaging Analysis Techniques

The neurological symptoms of stroke have traditionally provided the foundation for functional mapping of the brain. However, there are many unresolved aspects in our understanding of cerebral activity, especially regarding high-level cognitive functions. This review provides a comprehensive look at the pathophysiology of post-stroke cognitive impairment in light of recent findings from advanced imaging techniques. Combining network neuroscience and clinical neurology, our research focuses on how changes in brain networks correlate with post-stroke cognitive prognosis. More specifically, we first discuss the general consequences of stroke lesions due to damage of canonical resting-state large-scale networks or changes in the composition of the entire brain. We also review emerging methods, such as lesion-network mapping and gradient analysis, used to study the aforementioned events caused by stroke lesions. Lastly, we examine other patient vulnerabilities, such as superimposed amyloid pathology and blood-brain barrier leakage, which potentially lead to different outcomes for the brain network compositions even in the presence of similar stroke lesions. This knowledge will allow a better understanding of the pathophysiology of post-stroke cognitive impairment and provide a theoretical basis for the development of new treatments, such as neuromodulation.

Functional connectome reorganization relates to post-stroke motor recovery and structural and functional disconnection

Motor recovery following ischemic stroke is contingent on the ability of surviving brain networks to compensate for damaged tissue. In rodent models, sensory and motor cortical representations have been shown to remap onto intact tissue around the lesion site, but remapping to more distal sites (e.g. in the contralesional hemisphere) has also been observed. Resting state functional connectivity (FC) analysis has been employed to study compensatory network adaptations in humans, but mechanisms and time course of motor recovery are not well understood. Here, we examine longitudinal FC in 23 first-episode ischemic pontine stroke patients and utilize a graph matching approach to identify patterns of functional connectivity reorganization during recovery. We quantified functional reorganization between several intervals ranging from 1 week to 6 months following stroke, and demonstrated that the areas that undergo functional reorganization most frequently are in cerebellar/subcortical networks. Brain regions with more structural and functional connectome disruption due to the stroke also had more remapping over time. Finally, we show that functional reorganization is correlated with the extent of motor recovery in the early to late subacute phases, and furthermore, individuals with greater baseline motor impairment demonstrate more extensive early subacute functional reorganization (from one to two weeks post-stroke) and this reorganization correlates with better motor recovery at 6 months. Taken together, these results suggest that our graph matching approach can quantify recovery-relevant, whole-brain functional connectivity network reorganization after stroke.

A New Environmental Dependency Syndrome Occurring With Frontotemporal Lobe Degeneration: Hypervisual Illusory Spread Syndrome

A 59-year-old man presented with non-fluent aphasia and behavioral variant frontotemporal lobe degeneration (FTD), volunteered unusual visual symptoms that were best described as illusory visual spread (the image spreading over a larger area). This type of visual hyperfunction, related to the palinopsia syndromes, has not been reported in association with FTD. The syndrome may be best understood in terms of a visual variant of the environmental dependency syndrome, akin to the verbal variant of forced hyperphasia syndrome.

The spatiotemporal organization of experience dictates hippocampal involvement in primary visual cortical plasticity

The hippocampus and neocortex are theorized to be crucial partners in the formation of long-term memories. Here, we assess hippocampal involvement in two related forms of experience-dependent plasticity in the primary visual cortex (V1) of mice. Like control animals, those with hippocampal lesions exhibit potentiation of visually evoked potentials after passive daily exposure to a phase-reversing oriented grating stimulus, which is accompanied by long-term habituation of a reflexive behavioral response. Thus, low-level recognition memory is formed independently of the hippocampus. However, response potentiation resulting from daily exposure to a fixed sequence of four oriented gratings is severely impaired in mice with hippocampal damage. A feature of sequence plasticity in V1 of controls, which is absent in lesioned mice, is the generation of predictive responses to an anticipated stimulus element when it is withheld or delayed. Thus, the hippocampus is involved in encoding temporally structured experience, even within the primary sensory cortex.

From competition to cooperation: Visual neglect across the hemispheres

Visuospatial neglect is a frequent and disabling consequence of injuries to the right hemisphere. Patients with neglect show signs of impaired attention for left-sided events, which depends on dysfunction of fronto-parietal networks. After unilateral injury, such as stroke, these networks and their contralateral homologs can reorganize following multiple potential trajectories, which can be either adaptive or maladaptive. This article presents possible factors influencing the profile of evolution of neglect towards recovery or chronicity, and highlights potential mechanisms that may constrain these processes in time and space. The integrity of white matter pathways within and between the hemisphere appears to pose crucial connectivity constraints for compensatory brain plasticity from remote brain regions. Specifically, the availability of a sufficient degree of inter-hemispheric connectivity might be critical to shift the role of the undamaged left hemisphere in spatial neglect, from exerting maladaptive effects, to promoting compensatory activity.

Periinfarct rewiring supports recovery after primary motor cortex stroke

After stroke restricted to the primary motor cortex (M1), it is uncertain whether network reorganization associated with recovery involves the periinfarct or more remote regions. We studied 16 patients with focal M1 stroke and hand paresis. Motor function and resting-state MRI functional connectivity (FC) were assessed at three time points: acute (<10 days), early subacute (3 weeks), and late subacute (3 months). FC correlates of recovery were investigated at three spatial scales, (i) ipsilesional non-infarcted M1, (ii) core motor network (M1, premotor cortex (PMC), supplementary motor area (SMA), and primary somatosensory cortex), and (iii) extended motor network including all regions structurally connected to the upper limb representation of M1. Hand dexterity was impaired only in the acute phase (P = 0.036). At a small spatial scale, clinical recovery was more frequently associated with connections involving ipsilesional non-infarcted M1 (Odds Ratio = 6.29; P = 0.036). At a larger scale, recovery correlated with increased FC strength in the core network compared to the extended motor network (rho = 0.71;P = 0.006). These results suggest that FC changes associated with motor improvement involve the perilesional M1 and do not extend beyond the core motor network. Core motor regions, and more specifically ipsilesional non-infarcted M1, could hence become primary targets for restorative therapies.

Effect of Stroke on Contralateral Functional Connectivity

Introduction: Stroke can induce large-scale functional reorganization of the brain; however, the spatial patterns of this reorganization remain largely unknown. Methods: Using a large (N = 116) sample of participants who were in the chronic stages of stroke, we present a systematic study of the association between brain damage and functional connectivity (FC) within the intact hemisphere. We computed correlations between regional cortical damage and contralateral FC. Results: We identified left-hemisphere regions that had the most pronounced effect on the right-hemisphere FC, and, conversely, right-hemisphere connections where the effect of damage was particularly strong. Notably, the vast majority of significant correlations were positive: damage was associated with an increase in regional contralateral connectivity. Discussion: These findings lend evidence of the reorganization of contralateral cortical networks as a response to brain damage, which is more pronounced in a set of well-connected regions where connectivity increases with the amount of damage. Impact statement The relatively large sample size combined with our best-of-breed analysis methods provides us with sufficient statistical power and spatial sensitivity to identify a set of brain regions where damage has the strongest impact on contralateral networks, and a set of contralateral functional connections that increase in strength in response to brain damage. Our results demonstrate that the brain's ability to reorganize itself after extensive damage is not distributed equally in space, but is more likely to occur in specific core regions. We believe that the associations between brain damage and increased connectivity in the "intact" hemisphere provide novel, and important, insight into the plasticity of the adult brain.

Comparison of [11C]UCB-J and [18F]FDG PET in Alzheimer's disease: A tracer kinetic modeling study

[11C]UCB-J PET for synaptic vesicle glycoprotein 2 A (SV2A) has been proposed as a suitable marker for synaptic density in Alzheimer's disease (AD). We compared [11C]UCB-J binding for synaptic density and [18F]FDG uptake for metabolism (correlated with neuronal activity) in 14 AD and 11 cognitively normal (CN) participants. We assessed both absolute and relative outcome measures in brain regions of interest, i.e., K1 or R1 for [11C]UCB-J perfusion, VT (volume of distribution) or DVR to cerebellum for [11C]UCB-J binding to SV2A; and Ki or KiR to cerebellum for [18F]FDG metabolism. [11C]UCB-J binding and [18F]FDG metabolism showed a similar magnitude of reduction in the medial temporal lobe of AD -compared to CN participants. However, the magnitude of reduction of [11C]UCB-J binding in neocortical regions was less than that observed with [18F]FDG metabolism. Inter-tracer correlations were also higher in the medial temporal regions between synaptic density and metabolism, with lower correlations in neocortical regions. [11C]UCB-J perfusion showed a similar pattern to [18F]FDG metabolism, with high inter-tracer regional correlations. In summary, we conducted the first in vivo PET imaging of synaptic density and metabolism in the same AD participants and reported a concordant reduction in medial temporal regions but a discordant reduction in neocortical regions.

Superlative Artistic Abilities in a Patient With Post-traumatic Brain Injury

This case describes a patient who exhibits newfound superlative abilities in painting, music, philosophy, culinary, and performing arts after a traumatic brain injury (TBI) involving the frontal and temporal lobes. Such a dramatic change in de novo artistic behavior after brain injury is rare but has been reported in other patients with frontotemporal dementia, as well as other neurological diseases. Previous studies have shown that mild frontal cortical dysfunction likely plays a role in facilitating creative endeavors and that artistic circuitry is distributed throughout the brain. The neuronal reorganization which occurs after injuries enhances synapse formation and neural plasticity, which may contribute to the acceleration of artistic output after brain injury. This is likely an underdiagnosed phenomenon and a deeper understanding is required to allow clinicians to more effectively recognize and nurture newfound creativity in the setting of brain damage.

Rodent models used in preclinical studies of deep brain stimulation to rescue memory deficits

Deep brain stimulation paradigms might be used to treat memory disorders in patients with stroke or traumatic brain injury. However, proof of concept studies in animal models are needed before clinical translation. We propose here a comprehensive review of rodent models for Traumatic Brain Injury and Stroke. We systematically review the histological, behavioral and electrophysiological features of each model and identify those that are the most relevant for translational research.

Adaptive Mechanisms of Somatostatin-Positive Interneurons after Traumatic Brain Injury through a Switch of α Subunits in L-Type Voltage-Gated Calcium Channels

Unilateral traumatic brain injury (TBI) causes cortical dysfunctions spreading to the primarily undamaged hemisphere. This phenomenon, called transhemispheric diaschisis, is mediated by an imbalance of glutamatergic versus GABAergic neurotransmission. This study investigated the role of GABAergic, somatostatin-positive (SST) interneurons in the contralateral hemisphere 72 h after unilateral TBI. The brain injury was induced to the primary motor/somatosensory cortex of glutamate decarboxylase 67-green fluorescent protein (GAD67-GFP) knock-in mice at postnatal days 19-21 under anesthesia in vivo. Single GFP+ interneurons of the undamaged, contralateral cortex were isolated by fluorescence-activated cell sorting and analyzed by mass spectrometry. TBI caused a switch of 2 α subunits of pore-forming L-type voltage-gated calcium channels (VGCC) in GABAergic interneurons, an increased expression of CaV1.3, and simultaneous ablation of CaV1.2. This switch was associated with 1) increased excitability of single SST interneurons in patch-clamp recordings and (2) a recovery from early network hyperactivity in the contralateral hemisphere in microelectrode array recordings of acute slices. The electrophysiological changes were sensitive to pharmacological blockade of CaV1.3 (isradipine, 100 nM). These data identify a switch of 2 α subunits of VGCCs in SST interneurons early after TBI as a mechanism to counterbalance post-traumatic hyperexcitability.

Neuropsychological rehabilitation, neuroimaging and neuroplasticity: A clinical commentary

Initial brain imaging studies on recovery of motor functioning after stroke suggested their potential prognostic value in neurorehabilitation. However, the value of brain imaging in documenting brain changes associated with cognitive and behavioral treatment effects seem less likely. Also, neuroimaging studies at that time seem to have little, if any, value for treatment planning. Advances in neuroimaging technology are beginning to challenge these initial impressions. In this clinical commentary, we propose that advances in the field of neuroimaging have relevance for the future development of neuropsychological rehabilitation. Neuropsychological rehabilitation is entering a new era that involves collaboration with neuroimaging and associated studies on neuroplasticity. We recognize that this may seem “aspirational” rather than practical in most rehabilitation settings. However, we provide examples of how this can be achieved as illustrated by collaborative efforts of clinicians and scientists in the SARAH Network of Rehabilitation Hospitals in Brazil. We also review selective papers on neuroplasticity, spontaneous recovery and diaschisis that have relevance for research which will expand and further develop the field of neuropsychological rehabilitation.

Brain network hubs and cognitive performance of survivors of childhood infratentorial tumors

BACKGROUND

Childhood infratentorial tumor patients frequently suffer from long-term cognitive deficits. As each constituent of their treatment can lead to neurotoxicity, cascade effects can lead to profound reorganization of the underlying brain network, the so-called 'connectome'. However, to date, few studies have assessed the relationship between brain network topology, the functional role of network hubs (i.e. highly connected regions), and neurocognitive outcomes in adult survivors of childhood infratentorial tumors.

METHODS

In this cross-sectional study, childhood infratentorial tumor survivors (n = 21: pilocytic astrocytoma (n = 8), ependymoma (n = 1) and medulloblastoma (n = 12)) and healthy controls (n = 21) were recruited. Using multishell diffusion-weighted MRI, microstructural organization and topology of supratentorial white matter was investigated; using a voxel-based approach, a fixel-based analysis, and a graph theoretical approach. In addition, neurocognitive subscales of the WAIS-IV intelligence test, and their relationship with nodal strength and network efficiency metrics were assessed.

RESULTS

Similar to earlier studies, we observed widespread decreases in fractional anisotropy (FA) in patients compared to controls, based on voxel-based analyses. In addition, the fixel-based analyses dissociated macro- from microstructural changes, which were encountered in in infratentorial versus supratentorial brain areas, respectively. Finally, regional reorganization (i.e. differences in local efficiency) occurred mainly in hubs, which suggests a specific vulnerability of these areas. These hubs were not only mostly affected, but also most strongly correlated with the intelligence subscales.

CONCLUSION

This study suggests that network hubs are functionally important for intellectual outcomes in infratentorial tumor survivors. Furthermore, these regions could be the primary targets of treatment toxicity. Validation of this specific hypothesis in larger samples is required.

The computational neurology of movement under active inference

We propose a computational neurology of movement based on the convergence of theoretical neurobiology and clinical neurology. A significant development in the former is the idea that we can frame brain function as a process of (active) inference, in which the nervous system makes predictions about its sensory data. These predictions depend upon an implicit predictive (generative) model used by the brain. This means neural dynamics can be framed as generating actions to ensure sensations are consistent with these predictions-and adjusting predictions when they are not. We illustrate the significance of this formulation for clinical neurology by simulating a clinical examination of the motor system using an upper limb coordination task. Specifically, we show how tendon reflexes emerge naturally under the right kind of generative model. Through simulated perturbations, pertaining to prior probabilities of this model's variables, we illustrate the emergence of hyperreflexia and pendular reflexes, reminiscent of neurological lesions in the corticospinal tract and cerebellum. We then turn to the computational lesions causing hypokinesia and deficits of coordination. This in silico lesion-deficit analysis provides an opportunity to revisit classic neurological dichotomies (e.g. pyramidal versus extrapyramidal systems) from the perspective of modern approaches to theoretical neurobiology-and our understanding of the neurocomputational architecture of movement control based on first principles.