Time-dependent differences in cortical measures and their associations with behavioral measures following mild traumatic brain injury

Acute limbic system connectivity predicts chronic cognitive function in mild traumatic brain injury: An individualized differential structural covariance network study

Mild traumatic brain injury (mTBI) is a known risk factor for neurodegenerative diseases, yet the precise pathophysiological mechanisms remain poorly understand, often obscured by group-level analysis in non-invasive neuroimaging studies. Individual-based method is critical to exploring heterogeneity in mTBI. We recruited 80 mTBI patients and 40 matched healthy controls, obtaining high-resolution structural MRI for constructing Individual Differential Structural Covariance Networks (IDSCN). Comparisons were conducted at both the individual and group levels. Connectome-based Predictive Modeling (CPM) was applied to predict cognitive performance based on whole-brain connectivity. During the acute stage of mTBI, patients exhibited significant heterogeneity in the count and direction of altered edges, obscured by group-level analysis. In the chronic stage, the number of altered edges decreased and became more consistent, aligning with clinical observations of acute cognitive impairment and gradual improvement. Subgroup analysis based on loss of consciousness/post-traumatic amnesia revealed distinct patterns of alterations. The temporal lobe, particularly regions related to the limbic system, significantly predicted cognitive function from acute to chronic stage. The use of IDSCN and CPM has provided valuable individual-level insights, reconciling discrepancies from previous studies. Additionally, the limbic system may be an appropriate target for future intervention efforts.

Neuroanatomical restoration of salience network links reduced headache impact to cognitive function improvement in mild traumatic brain injury with posttraumatic headache

BACKGROUND

Neuroanatomical alterations have been associated with cognitive deficits in mild traumatic brain injury (MTBI). However, most studies have focused on the abnormal gray matter volume in widespread brain regions using a cross-sectional design in MTBI. This study investigated the neuroanatomical restoration of key regions in salience network and the outcomes in MTBI.

METHODS

Thirty-six MTBI patients with posttraumatic headache (PTH) and 34 matched healthy controls were enrolled in this study. All participants underwent magnetic resonance imaging scans and were assessed with clinical measures during the acute and subacute phases. Surface-based morphometry was conducted to get cortical thickness (CT) and cortical surface area (CSA) of neuroanatomical regions which were defined by the Desikan atlas. Then mixed analysis of variance models were performed to examine CT and CSA restoration in patients from acute to subacute phase related to controls. Finally, mediation effects models were built to explore the relationships between neuroanatomical restoration and symptomatic improvement in patients.

RESULTS

MTBI patients with PTH showed reduced headache impact and improved cognitive function from the acute to subacute phase. Moreover, patients experienced restoration of CT of the left caudal anterior cingulate cortex (ACC) and left insula and cortical surface area of the right superior frontal gyrus from acute to subacute phase. Further mediation analysis found that CT restoration of the ACC and insula mediated the relationship between reduced headache impact and improved cognitive function in patients.

CONCLUSIONS

These results showed that neuroanatomical restoration of key regions in salience network correlated reduced headache impact with cognitive function improvement in MTBI with PTH, which further substantiated the vital role of salience network and provided an alternative clinical target for cognitive improvement in MTBI patients with PTH.

Cortical Gyrification Morphology in Adult Males with Mild Traumatic Brain Injury

Cortical gyrification, as a specific measure derived from magnetic resonance imaging, remains understudied in mild traumatic brain injury (mTBI). Local gyrification index (lGI) and mean curvature are related measures indexing the patterned folding of the cortex,ml which reflect distinct properties of cortical morphology and geometry. Using both metrics, we examined cortical gyrification morphology in 59 adult males with mTBI (n = 29) versus those without (n = 30) mTBI in the subacute phase of injury (between 2 weeks and 3 months). The effect of IQ on lGI and brain-symptom relations were also examined. General linear models revealed greater lGI in mTBI versus controls in the frontal lobes bilaterally, but reduced lGI in mTBI of the left temporal lobe. An age-related decrease in lGI was found in numerous areas, with no significant group-by-age interaction effects observed. Including other factors (i.e., mTBI severity, symptoms, and IQ) in the lGI model yielded similar results with few exceptions. Mean curvature analyses depicted a significant group-by-age interaction with the absence of significant main effects of group or age. Our results suggest that cortical gyrification morphology is adversely affected by mTBI in both frontal and temporal lobes, which are thought of as highly susceptible regions to mTBI. These findings contribute to understanding the effects of mTBI on neuromorphological properties, such as alterations in cortical gyrification, which reflect underlying microstructural changes (i.e., apoptosis, neuronal number, or white matter alterations). Future studies are needed to infer causal relationships between micro- and macrostructural changes after an mTBI and investigate potential sex differences.

Restoration of aberrant shape of caudate sub-regions associated with cognitive function improvement in mild traumatic brain injury

Mild traumatic brain injury (mTBI) is an important but less recognized public health concern. Research shows that altered subcortical structures mediate cognitive impairment in patients with mTBI. This has been performed mostly using voxel-based morphometry methods and traditional volume measurement methods, which have certain limitations. In this study, we conducted a vertex-wise shape analysis to understand the aberrant patterns of caudate sub-regions and recovery from mTBI. The study involved 36 mTBI patients and 34 matched healthy controls (HCs) observed at seven-days (acute phase) and followed-up for one-month (subacute phase) post-injury. Different aberrant shapes of the caudate sub-regions were observed at acute phase, which revealed atrophy in the bilateral dorsal medial caudate, and increase in the size of the right ventral anterior caudate in mTBI patients related to HCs. Moreover, specific and significant shape restoration of right dorsal medial caudate in mTBI was observed at subacute phase, which significantly associated with the cognitive function improvement of the patients. These findings suggest that the restoration of the aberrant shape atrophy of right dorsal medial caudate plays a vital role in the improvement of cognitive function of mTBI patients, providing an alternative clinical target for these patients.

Morphometric changes in the cortex following acute mild traumatic brain injury

Morphometric changes in cortical thickness (CT), cortical surface area (CSA), and cortical volume (CV) can reflect pathological changes after acute mild traumatic brain injury (mTBI). Most previous studies focused on changes in CT, CSA, and CV in subacute or chronic mTBI, and few studies have examined changes in CT, CSA, and CV in acute mTBI. Furthermore, acute mTBI patients typically show transient cognitive impairment, and few studies have reported on the relationship between cerebral morphological changes and cognitive function in patients with mTBI. This prospective cohort study included 30 patients with acute mTBI (15 males, 15 females, mean age 33.7 years) and 27 matched healthy controls (12 males, 15 females, mean age 37.7 years) who were recruited from the Second Xiangya Hospital of Central South University between September and December 2019. High-resolution T1-weighted images were acquired within 7 days after the onset of mTBI. The results of analyses using FreeSurfer software revealed significantly increased CSA and CV in the right lateral occipital gyrus of acute-stage mTBI patients compared with healthy controls, but no significant changes in CT. The acute-stage mTBI patients also showed reduced executive function and processing speed indicated by a lower score in the Digital Symbol Substitution Test, and reduced cognitive ability indicated by a longer time to complete the Trail Making Test-B. Both increased CSA and CV in the right lateral occipital gyrus were negatively correlated with performance in the Trail Making Test part A. These findings suggest that cognitive deficits and cortical alterations in CSA and CV can be detected in the acute stage of mTBI, and that increased CSA and CV in the right lateral occipital gyrus may be a compensatory mechanism for cognitive dysfunction in acute-stage mTBI patients. This study was approved by the Ethics Committee of the Second Xiangya Hospital of Central South University, China (approval No. 086) on February 9, 2019.

Network-wise surface-based morphometric insight into the cortical neural circuitry underlying irritability in adolescents

Previous studies examining structural brain correlates of irritability have taken a region-specific approach and have been relatively inconsistent. In a sample of adolescents with and without clinically impairing irritability, the current study examines: (i) cortical volume (CV) in canonical functional networks; (ii) the association between the CV of functional networks and severity of irritability; and (iii) the extent to which IQ mediates the association between structural abnormalities and severity of irritability. Structural MRI and IQ data were collected from 130 adolescents with high irritability (mean age = 15.54±1.83 years, 58 females, self-reported Affective Reactivity Index [ARI] ≥ 4) and 119 adolescents with low irritability (mean age = 15.10±1.93 years, 39 females, self-reported ARI < 4). Subject-specific network-wise CV was estimated after parcellating the whole brain into 17 previously reported functional networks. Our Multivariate Analysis of Covariance (MANCOVA) revealed that adolescents with high irritability had significantly reduced CV of the bilateral control and default-mode networks (p < 0.05) relative to adolescents with low irritability. Multiple regression analyses showed a significant negative association between the control network CV and the severity of irritability. Mediation analysis showed that IQ partially mediated the association between the control network CV and the severity of irritability. Follow-up analysis on subcortical volume (SCV) showed that adolescents with high irritability had reduced bilateral SCV within the amygdala relative to adolescents with low irritability. Reduced CV within bilateral control and default networks and reduced SCV within bilateral amygdala may represent core features of the pathophysiology of irritability. The current data also indicate the potential importance of a patient's IQ in determining how pathophysiology related to the control network is expressed.

Working memory load modulates oscillatory activity and the distribution of fast frequencies across frontal theta phase during working memory maintenance

Working memory (WM) is a keystone of our cognitive abilities. Increasing load has been shown to dampen its performance and affect oscillatory neural activity in different frequency bands. Nevertheless, mixed results regarding fast frequencies activity and a lack of research on WM load modulations of cross-frequency phase-amplitude coupling mechanisms preclude a better understanding of the impact of increased WM load levels on brain activity as well as inter-regional communication and coordination supporting WM processes. Hence, we analyzed the EEG activity of 25 participants while performing a delayed-matching-to-sample (DMS) WM task with three WM load levels. Current density power and distribution at the source level for theta, beta, and gamma frequencies during the task's delay period were compared for each pair of WM load conditions. Results showed maximal increases of theta activity in frontal areas and of fast frequencies' activity in posterior regions with WM load, showing the involvement of frontal theta activity in WM maintenance and the control of attentional resources and visual processing by beta and gamma activity. To study whether WM load modulates communication between cortical areas, posterior beta and gamma amplitudes distribution across frontal theta phase was also analysed for those areas showing the largest significant WM load modulations. Higher beta activity amplitude at bilateral cuneus and right middle occipital gyrus, and higher gamma activity amplitude at bilateral posterior cingulate were observed during frontal theta phase peak in low than high memory load conditions. Moreover, greater fast beta amplitude at the right postcentral gyrus was observed during theta phase trough at right middle frontal gyrus in high than low memory load conditions. These results show that WM load modulates whether interregional communication occurs during theoretically optimal or non-optimal time windows, depending on the demands of frontal control of posterior areas required to perform the task successfully.

Visual working memory deficits in undergraduates with a history of mild traumatic brain injury

We investigated whether a history of mild traumatic brain injury (mTBI), or concussion, has any effect on visual working memory (WM) performance. In most cases, cognitive performance is thought to return to premorbid levels soon after injury, without further medical intervention. We tested this assumption in undergraduates, among whom a history of mTBI is prevalent. Notably, participants with a history of mTBI performed worse than their colleagues with no such history. Experiment 1 was based on a change detection paradigm in which we manipulated visual WM set size from one to three items, which revealed a significant deficit at set size 3. In Experiment 2 we investigated whether feedback could rescue WM performance in the mTBI group, and found that it failed. In Experiment 3 we manipulated WM maintenance duration (set size 3, 500-1,500 ms) to investigate a maintenance-related deficit. Across all durations, the mTBI group was impaired. In Experiment 4 we tested whether retrieval demands contributed to WM deficits and showed a consistent deficit across recognition and recall probes. In short, even years after an mTBI, undergraduates perform differently on visual WM tasks than their peers with no such history. Given the prevalence of mTBI, these data may benefit other researchers who see high variability in their data. Clearly, further studies will be needed to determine the breadth of the cognitive deficits in those with a history of mTBI and to identify relevant factors that contribute to positive cognitive outcomes.

Structural neuroimaging in mild traumatic brain injury: A chronic effects of neurotrauma consortium study

OBJECTIVES

The chronic effects of neurotrauma consortium (CENC) observational study is a multisite investigation designed to examine the long-term longitudinal effects of mild traumatic brain injury (mTBI). All participants in this initial CENC cohort had a history of deployment in Operation Enduring Freedom (Afghanistan), Operation Iraqi Freedom (Iraq), and/or their follow-on conflicts (Operation Freedom's Sentinel). All participants undergo extensive medical, neuropsychological, and neuroimaging assessments and either meet criteria for any lifetime mTBI or not. These assessments are integrated into six CENC core studies-Biorepository, Biostatistics, Data and Study Management, Neuroimaging, and Neuropathology.

METHODS

The current study outlines the quantitative neuroimaging methods managed by the Neuroimaging Core using FreeSurfer automated software for image quantification.

RESULTS

At this writing, 319 participants from the CENC observational study have completed all baseline assessments including the imaging protocol and tertiary data quality assurance procedures.

CONCLUSIONS/DISCUSSION

The preliminary findings of this initial cohort are reported to describe how the Neuroimaging Core manages neuroimaging quantification for CENC studies.

Time-dependent differences in cortical measures and their associations with behavioral measures following mild traumatic brain injury

There is currently a critical need to establish an improved understanding of time-dependent differences in brain structure following mild traumatic brain injury (mTBI). We compared differences in brain structure, specifically cortical thickness (CT), cortical volume (CV), and cortical surface area (CSA) in 54 individuals who sustained a recent mTBI and 33 healthy controls (HCs). Individuals with mTBI were split into three groups, depending on their time since injury. By comparing structural measures between mTBI and HC groups, differences in CT reflected cortical thickening within several areas following 0-3 (time-point, TP1) and 3-6 months (TP2) post-mTBI. Compared with the HC group, the mTBI group at TP2 showed lower CSA within several areas. Compared with the mTBI group at TP2, the mTBI group during the most chronic stage (TP3: 6-18 months post-mTBI) showed significantly higher CSA in several areas. All the above reported differences in CT and CSA were significant at a cluster-forming p < .01 (corrected for multiple comparisons). We also found that in the mTBI group at TP2, CT within two clusters (i.e., the left rostral middle frontal gyrus (L. RMFG) and the right postcentral gyrus (R. PostCG)) was negatively correlated with basic attention abilities (L. RMFG: r = -.41, p = .05 and R. PostCG: r = -.44, p = .03). Our findings suggest that alterations in CT and associated neuropsychological assessments may be more prominent during the early stages of mTBI. However, alterations in CSA may reflect compensatory structural recovery during the chronic stages of mTBI.