Cortical structural changes after subcortical stroke: Patterns and correlates

Altered effective connectivity within brain lesioned regions and cognitive impairment after stroke

Poststroke cognitive impairments (PSCI) reflect widespread network dysfunction due to structural damage, abnormal neural activity, or abnormal connections in affected brain regions. The exact influence of these lesioned regions on the related functional network and their role in PSCI remains unclear. We recruited 35 first-time stroke patients who had basal ganglia infarcts and PSCI, along with 29 age-matched healthy controls. We utilized T1-weighted imaging to inspect structural damage with regional gray matter volume (GMV). Resting-state fMRI data were utilized to examine spontaneous activities with regional Wavelet-ALFF metric, investigate dynamic functional connectivity (dFC) by seeding the region with damaged GMV, and further study effective connectivity within the abnormal dFC network and its impact on PSCI. In comparison to HC, patients showed significant reduced GMV in the bilateral Rolandic operculum (ROL), along with notable abnormal Wavelet-ALFF values in the right Precuneus (PCUN) and left Cerebellum_9 (CER9). Particularly, an abnormal dFC network seeded in the left ROL, demonstrating significantly differential between PSCI and HC groups and remaining consistent across all time windows, was observed. This abnormal dFC network comprised the left ROL as the seed region, the right ROL, bilateral PCUN, bilateral CER9, right Superior Temporal Gyrus (STG), and right Parahippocampal Gyrus (PHG). Notably, in patients, impaired functions across various cognitive domains significantly influenced the altered effective connections among the abnormal regions, particularly impacting the connections between structurally damaged regions and those with abnormal spontaneous activity. These findings suggest that altered effective connectivity networks within lesioned regions may contribute to deficits in various cognitive domains in PSCI.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-024-10209-7.

Alterations of static and dynamic changes in intrinsic brain activity and its relation to behavioral outcomes in subcortical ischemic stroke after one-month intervention

Ischemic stroke is a prominent contributor to cognitive dysfunction and disability. Gaining a comprehensive understanding of the neuronal activity and longitudinal changes underlying stroke is crucial for designing effective rehabilitative strategies. However, the neural mechanisms responsible for the longitudinal reorganization of neuronal activity following stroke remain unclear. The objective of this study was to comprehensively investigate potential abnormalities in brain activity among stroke patients before and after one month of intervention (antiplatelet therapy, as well as intravenous citicoline). To achieve this goal, we combined static and dynamic functional imaging indicators for the comprehensive analysis. Twenty ischemic stroke patients at the subacute stage and seventeen age-matched healthy controls were included in the final analysis of this study from one center. Additionally, resting-state functional magnetic imaging scans were conducted on all patients twice with a one-month interval between scans. Four static intrinsic brain activity indicators (static amplitude of low-frequency fluctuation (sALFF), static fractional amplitude of low-frequency fluctuation (sfALFF), static regional homogeneity (sReHo), and static degree centrality (sDC)), along with their corresponding dynamic indicators, were calculated to detect longitudinal alterations in brain activity following stroke onset. Correlation analyses were also performed between these indicators within areas exhibiting group differences as well as clinical scale scores and disease duration. Significant variations in these static and dynamic image indicators were observed among patients with ischemic stroke. There was substantial overlap among the abnormal brain regions detected, primarily including decreased sALFF/sfALFF/dALFF in the bilateral central precuneus, increased sfALFF/sReHo/sDC/dReHo in the left superior precuneus, increased sALFF/sReHo/dfALFF in the left inferior temporal gyrus, decreased sReHo/sDC in the anterior cingulate cortex, increased sReHo/dfALFF in the right inferior parietal lobe, increased sfALFF/sDC in the right fusiform gyrus, as well as decreased sALFF/dALFF and increased sReHo/sDC in the right angular gyrus. Furthermore, these disrupted image indicators in some regions exhibited only partial recovery at the second time point. The percentage changes of these image indicators (sfALFF in the bilateral central precuneus, sDC in the left fusiform and dALFF in the right central precuneus) between the two time points were positively correlated with the percentage changes of clinical scores (FMA and MBI). In combination, this study demonstrates that a comprehensive understanding of abnormal activity and its longitudinal changes in ischemic stroke can be achieved by integrating static and dynamic imaging methods. Regions showing significant overlap among different brain activity indicators and exhibiting consistent image-behavior relationships may have some potential values for predicting clinical outcomes.

The Optimized Transcranial Direct Current Stimulation With Simulation Using MRI

Transcranial direct current stimulation (tDCS) has emerged as a valuable neuromodulation technique. Many clinical conditions are associated with brain damage, and in severe cases, structural changes such as skull defects are common. These clinical characteristics result in distinct electrical flow patterns during tDCS application compared to cases without brain damage. Recently, notable advancements have been made in both the medical and engineering fields pertaining to the use of in silico modelling and simulation with the aid of magnetic resonance imaging (MRI). As a result, it is now possible to conduct simulations tailored to the unique structural anatomy of an individual's brain, using their own MRI data, to provide targeted tDCS. We have developed software that performs both segmentation and simulation, and have conducted randomized controlled trials using optimized tDCS for stroke and disorders of consciousness. Additionally, we have carried out simulation-related research on stroke and burr hole surgery. This review examines various articles related to simulation and optimized tDCS, evaluating their clinical implications. We believe that these insights will provide valuable guidance for both current and future applications of tDCS.

Cortical structure reorganization and correlation with attention deficit in subcortical stroke: An underlying pattern analysis

BACKGROUND

Subcortical stroke may significantly alter the cerebral cortical structure and affect attention function, but the details of this process remain unclear. The study aimed to investigate the neural substrates underlying attention impairment in patients with subcortical stroke.

MATERIALS AND METHODS

In this prospective observational study, two distinct datasets were acquired to identify imaging biomarkers underlying attention deficit. The first dataset consisted of 86 patients with subcortical stroke, providing a cross-sectional perspective, whereas the second comprised 108 patients with stroke, offering longitudinal insights. All statistical analyses were subjected to false discovery rate correction upon P < 0.05.

RESULTS

In the chronic-stage data, the stroke group exhibited significantly poorer attention function compared with that of the control group. The cortical structure analysis showed that patients with stroke exhibited decreased cortical thickness of the precentral gyrus and surface area of the cuneus, along with an increase in various frontal, occipital, and parietal cortices regions. The declined attention function positively correlated with the superior frontal gyrus cortical thickness and supramarginal gyrus surface area. In the longitudinal dataset, patients with stroke showed gradually increasing cortical thickness and surface area within regions of obvious structural reorganization. Furthermore, deficient attention positively correlated with supramarginal gyrus surface area both at the subacute and chronic stages post-stroke.

CONCLUSIONS

Subcortical stroke can elicit dynamic reorganization of cortical areas associated with attention impairment. Moreover, the altered surface area of the supramarginal gyrus is a potential neuroimaging biomarker for attention deficits.

Electric field simulation and appropriate electrode positioning for optimized transcranial direct current stimulation of stroke patients: an in Silico model

Transcranial Direct Current Stimulation (tDCS) has benefits for motor rehabilitation in stroke patients, but its clinical application is limited due to inter-individual heterogeneous effects. Recently, optimized tDCS that considers individual brain structure has been proposed, but the utility thereof has not been studied in detail. We explored whether optimized tDCS provides unique electrode positions for each patient and creates a higher target electric field than the conventional approach. A comparative within-subject simulation study was conducted using data collected for a randomized controlled study evaluating the effect of optimized tDCS on upper extremity function in stroke patients. Using Neurophet tES LAB 3.0 software, individual brain models were created based on magnetic resonance images and tDCS simulations were performed for each of the conventional and optimized configurations. A comparison of electrode positions between conventional tDCS and optimized tDCS was quantified by calculation of Euclidean distances. A total of 21 stroke patients were studied. Optimized tDCS produced a higher electric field in the hand motor region than conventional tDCS, with an average improvement of 20% and a maximum of 52%. The electrode montage for optimized tDCS was unique to each patient and exhibited various configurations that differed from electrode placement of conventional tDCS. Optimized tDCS afforded a higher electric field in the target of a stroke patient compared to conventional tDCS, which was made possible by appropriately positioning the electrodes. Our findings may encourage further trials on optimized tDCS for motor rehabilitation after stroke.

Dynamic brain activity states of memory impairment in stroke patients with varying motor outcomes

Introduction

The objective of this study was to characterize the alteration patterns of dynamic spatiotemporal activity in chronic subcortical stroke patients with varying motor outcomes, while investigating the imaging indicators relevant to the assessment of potential cognitive deficits in these patients.

Methods

A total of 136 patients and 88 normal controls were included in the analysis of static and dynamic intrinsic brain activity, determined by amplitude of low-frequency fluctuations.

Results

The findings unveiled that subcortical stroke patients exhibited significantly aberrant temporal dynamics of intrinsic brain activity, involving regions within multiple brain networks. These spatiotemporal patterns were found to be contingent upon the side of the lesion. In addition, these aberrant metrics demonstrated potential in discerning cognitive deficits in stroke patients with memory impairment, with the dynamic indices exerting more influence than the static ones. The observe findings may indicate that subcortical stroke can trigger imbalances in the segregation and integration of spatiotemporal patterns across the entire brain with multi-domain networks, especially in patients with poor motor outcomes.

Conclusion

It suggests that the temporal dynamics indices of intrinsic brain activity could serve as potential imaging indicators for assessing cognitive impairment in patients with chronic subcortical stroke, which may be associated with the motor outcomes.

Morphological alterations of contralesional hemisphere relate to functional outcomes after stroke

The present study aimed to investigate poststroke morphological alterations contralesionally and correlations with functional outcomes. Structural magnetic resonance images were obtained from 27 poststroke patients (24 males, 50.21 ± 10.97 years) and 20 healthy controls (13 males, 46.63 ± 12.18 years). Voxel-based and surface-based morphometry analysis were conducted to detect alterations of contralesional grey matter volume (GMV), cortical thickness (CT), gyrification index (GI), sulcus depth (SD), and fractal dimension (FD) in poststroke patients. Partial correlation analysis was used to explore the relationship between regions with significant structural differences and scores of clinical assessments, including Modified Barthel Index (MBI), Berg Balance Scale (BBS), Fugl-Meyer Assessment of Upper Extremity (FMA-UE), Mini-Mental State Examination (MMSE), and Montreal Cognitive Assessment (MoCA). Correction for multiplicity was conducted within each parameter and for all tests. GMV significantly decreased in the contralesional motor-related, occipital and temporal cortex, limbic system, and cerebellum lobe (P < 0.01, family-wise error [FWE] correction). Lower CT was found in the contralesional precentral and lingual gyrus (P < 0.01, FWE correction), while lower GI found in the contralesional superior temporal gyrus and insula (P < 0.01, FWE correction). There were significant correlations between GMV of contralesional lingual gyrus and MBI (P = 0.031, r = 0.441), and BBS (P = 0.047, r = 0.409) scores, and GMV of contralesional hippocampus and FMA-UE scores (P = 0.048, r = 0.408). In conclusion, stroke patients exhibited wide grey matter loss and cortical morphological changes in the contralesional hemisphere, which correlated with sensorimotor functions and the ability of daily living.