Middle cerebral artery occlusive disease: the New England Medical Center Stroke Registry

Effects of long-term exposure to high altitude on brain structure in healthy people: an MRI-based systematic review and meta-analysis

Purpose

To conduct a systematic review and meta-analysis of observational studies of brain MRI, this paper assesses the effects of long-term exposure to high-altitude on brain structures in healthy people.

Methods

Observational studies related to high-altitude, brain and MRI were systematically searched based on data retrieved from PubMed, Embase and Cochrane Library. The timescale for collecting literature was from the establishment of the databases to 2023. NoteExpress 3.2 was used to manage the literature. Two investigators performed literature screening and data extraction based on inclusion criteria, exclusion criteria, and literature quality. The quality of the literature was assessed using the NOS Scale. Finally, meta-analysis of included studies was performed using Reviewer Manager 5.3.

Results

Initially, 3,626 articles were retrieved. After screening, 16 articles (n = 756 participants) were included in the systematic review, and meta-analysis was performed on 6 articles (n = 350 participants). The overall quality of the included articles was at medium level, with a mean NOS score of 5.62. The results of meta-analysis showed that the differences between the HA group and LA group were not statistically significant, in total GM volume (MD: -0.60, 95% CI: -16.78 to 15.58, P = 0.94), WM volume (MD: 3.05, 95% CI: -15.72 to 21.81, P = 0.75) and CSF volume (MD: 5.00, 95% CI: -11.10 to 21.09, P = 0.54).The differences between HA and LA in FA values of frontotemporal lobes were not statistically significant: right frontal lobe (MD: -0.02, 95% CI: -0.07 to 0.03, P = 0.38), left frontal lobe (MD: 0.01, 95% CI: -0.02 to 0.04, P = 0.65), right temporal lobe (MD: -0.00, 95% CI: -0.03 to 0.02, P = 0.78) and left temporal lobe (MD: -0.01, 95% CI: -0.04 to 0.02, P = 0.62). However, there were significant differences in GM volume, GM density and FA values in local brain regions between HA group and LA group.

Conclusion

Compared with LA area, there were no significant differences in total GM, WM and CSF volumes in healthy people living at high-altitude area for long-term, while there were significant differences in GM volume and FA values in local brain regions. Long-term exposure to high-altitude area caused the adaptive structural changes in local brain regions. Since heterogeneity existed between the studies, further studies are needed to uncover the effects of high-altitude on brain of healthy people.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier: CRD42023403491.

Altered resting-state networks may explain the executive impairment in young health immigrants into high-altitude area

Executive function is a complex involving multiple advanced brain functions like planning, working memory, mental flexibility and psychomotor. Previous researches indicated that executive function may be impaired after acute or chronic high-altitude exposure, while the underlying neurobiological mechanism has not been totally clarified. In the present study, based on 69 young healthy volunteers immigrating to high-altitude, Stroop test was utilized to identify the potential impairment of executive function after two-year high-altitude exposure while resting-state functional MRI (rs-fMRI) technology was employed to observe the alteration of resting-state networks. Stroop test indicated that the subjects experienced significantly lower accuracies and prolonged responding time after two-year exposure. Resting-state network analysis displayed a significantly decreased degree of co-activation within the left/right frontoparietal network, sensorimotor network, and auditory network after exposure. In the frontoparietal network, decreased co-activation intensity was found in left angular gyrus, while in the right frontoparietal network, decreased co-activation intensity was found in left precentral gyrus and postcentral gyrus. Similarly, as for sensorimotor and auditory network, left middle frontal gyrus and left superior temporal gyrus was identified to have decreased co-activation, respectively. Moreover, the responding delays in ST (part II) were negatively correlated with the signal intensity alteration of the right frontoparietal network. All these evidences indicated that the high-altitude exposure induced alteration in above resting state networks may be the functional basis of executive control impairment.

Alteration in topological properties of brain functional network after 2-year high altitude exposure: A panel study

INTRODUCTION

High altitude (HA) exposure leads to cognitive impairment while the underlying mechanism is still unclear. Brain functional network is crucial for advanced functions, and its alteration is implicated in cognitive decline in multiple diseases. The aim of current study was to investigate the topological changes in HA-exposed brain functional network.

METHODS

Based on Shaanxi-Tibet immigrant cohort, neuropsychological tests and resting-state functional MRI were applied to evaluate the participants' cognitive function and functional connection (FC) changes, respectively. GRETNA toolbox was used to construct the brain functional network. The gray matter was parcellated into 116 anatomically defined regions according to Automated Anatomical Labeling atlas. Subsequently, the mean time series for each of the 116 regions were extracted and computed for Pearson's correlation coefficients. The relation matrix was further processed and seen as brain functional network. Correlation between functional network changes and neuropsychological results was also examined.

RESULTS

The cognitive performance was impaired by HA exposure as indicated by neuropsychological test. HA exposure led to alterations of degree centrality and nodal efficiency in multiple brain regions. Moreover, two subnetworks were extracted in which the FCs significantly decreased after exposure. In addition, the alterations in FCs within above two subnetworks were significantly correlated with changes of memory and reaction time.

CONCLUSIONS

Our results suggest that HA exposure modulates the topological property of functional network and FCs of some important regions, which may impair the attention, perception, memory, motion ignition, and modulation processes, finally decreasing cognitive performance in neuropsychological tests.

Cognitive and neuroimaging changes in healthy immigrants upon relocation to a high altitude: A panel study

BACKGROUND

Cognitive and neuroimaging changes under chronic high-altitude exposure have never been followed up and dynamically assessed.

OBJECTIVES

To investigate the cognitive and brain structural/functional alterations associated with chronic high-altitude exposure.

METHODS

Sixty-nine college freshmen that were immigrating to Tibet were enrolled and followed up for two years. Neuropsychological tests, including verbal/visual memory and simple/recognition reaction time, were utilized to determine whether the subjects' cognitive function had changed in response to chronic high-altitude exposure. Structural magnetic resonance imaging (MRI) and resting-state functional MRI (rs-fMRI) were used to quantify brain gray matter (GM) volumes, regional homogeneity (ReHo) and functional connectivity (FC) alterations before and after exposure. Areas with changes in both GM and ReHo were used as seeds in the inter-regional FC analysis.

RESULTS

The subjects showed significantly lower accuracy in memory tests and longer reaction times after exposure, and neuroimaging analysis showed markedly decreased GM volumes and ReHo in the left putamen. FC analysis seeding of the left putamen showed significantly weakened FC with the superior temporal gyrus, anterior/middle cingulate gyrus and other brain regions. In addition, decreased ReHo was found in the superior temporal gyrus, superior parietal lobule, anterior cingulate gyrus and medial frontal gyrus, while increased ReHo was found in the hippocampus. Differences in ReHo/FC before and after high-altitude exposure in multiple regions were significantly correlated with the cognitive changes.

CONCLUSION

Cognitive functions such as working memory and psychomotor function are impaired during chronic high-altitude exposure. The putamen may play an important role in chronic hypoxia-induced cognitive impairment. Hum Brain Mapp 38:3865-3877, 2017. © 2017 Wiley Periodicals, Inc.

Sensorimotor cortex injury effects on recovery of contralesional dexterous movements in Macaca mulatta

The effects of primary somatosensory cortex (S1) injury on recovery of contralateral upper limb reaching and grasping were studied by comparing the consequences of isolated lesions to the arm/hand region of primary motor cortex (M1) and lateral premotor cortex (LPMC) to lesions of these same areas plus anterior parietal cortex (S1 and rostral area PE). We used multiple linear regression to assess the effects of gray and white matter lesion volumes on deficits in reaching and fine motor performance during the first month after the lesion, and during recovery of function over 3, 6 and 12months post-injury in 13 monkeys. Subjects with frontoparietal lesions exhibited larger deficits and poorer recovery as predicted, including one subject with extensive peri-Rolandic injury developing learned nonuse after showing signs of recovery. Regression analyses showed that total white matter lesion volume was strongly associated with initial post-lesion deficits in motor performance and with recovery of skill in reaching and manipulation. Multiple regression analyses using percent damage to caudal M1 (M1c), rostral S1 (S1r), LPMC and area PE as predictor variables showed that S1r lesion volumes were closely related to delayed post-lesion recovery of upper limb function, as well as lower skill level of recovery. In contrast, M1c lesion volume was related primarily to initial post-lesion deficits in hand motor performance. Overall, these findings demonstrate that frontoparietal injury impairs hand motor function more so than frontal motor injury alone, and results in slower and poorer recovery than lesions limited to frontal motor cortex.

Frontal and frontoparietal injury differentially affect the ipsilateral corticospinal projection from the nonlesioned hemisphere in monkey (Macaca mulatta)

Upper extremity hemiplegia is a common consequence of unilateral cortical stroke. Understanding the role of the unaffected cerebral hemisphere in the motor recovery process has been encouraged, in part, by the presence of ipsilateral corticospinal projections (iCSP). We examined the neuroplastic response of the iCSP from the contralesional primary motor cortex (cM1) hand/arm area to spinal levels C5-T1 after spontaneous long-term recovery from isolated frontal lobe injury and isolated frontoparietal injury. High-resolution tract tracing, stereological, and behavioral methodologies were applied. Recovery from frontal motor injury resulted in enhanced numbers of terminal labeled boutons in the iCSP from cM1 compared with controls. Increases occurred in lamina VIII and the adjacent ventral sectors of lamina VII, which are involved in axial/proximal limb sensorimotor processing. Larger frontal lobe lesions were associated with greater numbers of terminal boutons than smaller frontal lobe lesions. In contrast, frontoparietal injury blocked this response; total bouton number was similar to controls, demonstrating that disruption of somatosensory input to one hemisphere has a suppressive effect on the iCSP from the nonlesioned hemisphere. However, compared with controls, elevated bouton numbers occurred in lamina VIII, at the expense of lamina VII bouton labeling. Lamina IX boutons were also elevated in two frontoparietal lesion cases with extensive cortical injury. Because laminae VIII and IX collectively harbor axial, proximal, and distal motoneurons, therapeutic intervention targeting the ipsilateral corticospinal linkage from cM1 may promote proximal, and possibly distal, upper-limb motor recovery following frontal and frontoparietal injury.

Vulnerability of the medial frontal corticospinal projection accompanies combined lateral frontal and parietal cortex injury in rhesus monkey

Concurrent damage to the lateral frontal and parietal cortex is common following middle cerebral artery infarction, leading to upper extremity paresis, paresthesia, and sensory loss. Motor recovery is often poor, and the mechanisms that support or impede this process are unclear. Since the medial wall of the cerebral hemisphere is commonly spared following stroke, we investigated the spontaneous long-term (6 and 12 month) effects of lateral frontoparietal injury (F2P2 lesion) on the terminal distribution of the corticospinal projection (CSP) from intact, ipsilesional supplementary motor cortex (M2) at spinal levels C5 to T1. Isolated injury to the frontoparietal arm/hand region resulted in a significant loss of contralateral corticospinal boutons from M2 compared with controls. Specifically, reductions occurred in the medial and lateral parts of lamina VII and the dorsal quadrants of lamina IX. There were no statistical differences in the ipsilateral CSP. Contrary to isolated lateral frontal motor injury (F2 lesion), which results in substantial increases in contralateral M2 labeling in laminae VII and IX (McNeal et al. [2010] J. Comp. Neurol. 518:586-621), the added effect of adjacent parietal cortex injury to the frontal motor lesion (F2P2 lesion) not only impedes a favorable compensatory neuroplastic response but results in a substantial loss of M2 CSP terminals. This dramatic reversal of the CSP response suggests a critical trophic role for cortical somatosensory influence on spared ipsilesional frontal corticospinal projections, and that restoration of a favorable compensatory response will require therapeutic intervention.

Dysarthria in stroke: a narrative review of its description and the outcome of intervention

Dysarthria is a frequent and persisting sequel to stroke and arises from varied lesion locations. Although the presence of dysarthria is well documented, for stroke there are scant data on presentation and intervention outcome. A literature search was undertaken to evaluate (a) the features of dysarthria in adult stroke populations relative to the conventional Mayo system for classification, which was developed from diverse pathological groups, and (b) the current status of evidence for the effectiveness of intervention in dysarthria caused by stroke. A narrative review of results is presented. The limited data available indicate that, regardless of stroke location, imprecise articulation and slow speaking rate are consistent features, and voice disturbances, especially harshness, and reduced prosodic variation are also common. Dysarthria is more prevalent in left than in right hemisphere lesions. There is a need for comprehensive, thorough analysis of dysarthria features, involving larger populations, with stroke and other variables controlled and with appropriate age-referenced control data. There is low level evidence for benefits arising from intervention in stroke-related dysarthria. Because studies involve few participants, without external control, and sometimes include stroke with other aetiologies, their results lack the required weight for confident evidence-based practice.

Ischemic stroke of the cortical "hand knob" area: stroke mechanisms and prognosis

Cortical ischemic stroke affecting the precentral "hand knob" area is a rare but well known stroke entity. To date, little is known about the underlying stroke mechanisms and the prognosis. Twenty-nine patients admitted to our service between 2003 and 2007 were included in the study on the basis of an acute ischemic infarct of the cortical "hand knob" area confirmed by diffusion-weighted magnetic resonance imaging with contralateral hand paresis. For all patients clinical, epidemiological as well as imaging data at the time point of admission were analysed retrospectively and follow-up data on all patients was obtained. The majority (n = 21/72%) had an isolated infarct of the cortical "hand knob" area. In 23 (79%) patients it was a first ever stroke. Ten patients (34%) had ipsilateral extracranial stenosis of the internal carotid artery (ICA), whereas potential cardiac embolic sources were less frequent (n = 4/14%). No patient exhibited ipsilateral MCA stenosis. All but two patients (93%) had marked atherosclerotic alterations of the ICA. Hypertension was the most prevalent vascular risk factor (n = 23/79%). At follow-up (mean 25.0 months, range 0.4-47.4 months) no patient had died and only one (3%) experienced a recurrent stroke. The majority of patients (79%) reported improvement of hand paresis, 17 (59%) were asymptomatic (modified Rankin score = 0). Only one patient was significantly disabled due to a recurrent stroke. In conclusion, ischemic infarcts affecting the cortical "hand knob" area are frequently associated with atherosclerotic changes of the carotid artery, suggesting an arterio-arterial thrombembolic stroke mechanism. It mostly reflects first ever ischemic stroke, and follow-up data suggest a rather benign course.