Loss of Consciousness Is Related to White Matter Injury in Mild Traumatic Brain Injury

Effects of Mild Closed-Head Injury and Subanesthetic Ketamine Infusion on Microglia, Axonal Injury, and Synaptic Density in Sprague-Dawley Rats

Mild traumatic brain injury (mTBI) affects millions of people in the U.S. Approximately 20-30% of those individuals develop adverse symptoms lasting at least 3 months. In a rat mTBI study, the closed-head impact model of engineered rotational acceleration (CHIMERA) produced significant axonal injury in the optic tract (OT), indicating white-matter damage. Because retinal ganglion cells project to the lateral geniculate nucleus (LGN) in the thalamus through the OT, we hypothesized that synaptic density may be reduced in the LGN of rats following CHIMERA injury. A modified SEQUIN (synaptic evaluation and quantification by imaging nanostructure) method, combined with immunofluorescent double-labeling of pre-synaptic (synapsin) and post-synaptic (PSD-95) markers, was used to quantify synaptic density in the LGN. Microglial activation at the CHIMERA injury site was determined using Iba-1 immunohistochemistry. Additionally, the effects of ketamine, a potential neuroprotective drug, were evaluated in CHIMERA-induced mTBI. A single-session repetitive (ssr-) CHIMERA (3 impacts, 1.5 joule/impact) produced mild effects on microglial activation at the injury site, which was significantly enhanced by post-injury intravenous ketamine (10 mg/kg) infusion. However, ssr-CHIMERA did not alter synaptic density in the LGN, although ketamine produced a trend of reduction in synaptic density at post-injury day 4. Further research is necessary to characterize the effects of ssr-CHIMERA and subanesthetic doses of intravenous ketamine on different brain regions and multiple time points post-injury. The current study demonstrates the utility of the ssr-CHIMERA as a rodent model of mTBI, which researchers can use to identify biological mechanisms of mTBI and to develop improved treatment strategies for individuals suffering from head trauma.

Serial changes in diffusion tensor imaging metrics and therapeutic effects of repetitive transcranial magnetic stimulation in post-traumatic headache and depression: A case report

BACKGROUND

Mild traumatic brain injury patients commonly complain headache and central pain, and the pain accompanies depressive mood change. This case study reports the therapeutic effect of repetitive transcranial magnetic stimulation (rTMS) in mild traumatic brain injury patient with headache and depression through objective serial changes of diffusion tensor imaging (DTI).

METHODS

The 51-year-old man complained of headache and depression despite conventional treatment for 13 months. We applied 15 times rTMS on the left dorsolateral prefrontal cortex. We checked the pain and depression through numeric rating scale (NRS) and Beck depression inventory (BDI) when admission, discharged, and 1 month after discharge. DTI was performed 3 times; before, during-day of rTMS 6th stimulation, and after-day of rTMS 15th stimulation. Then the reconstructed White matter related to pain and depression was obtained.

RESULTS

NRS and BDI showed significant improvement and it was maintained 1 year after discharge. DTI-based metrics of the White matters related to pain and depression gradually increased before - during - after rTMS.

CONCLUSION

Studies focused on examining changes in pain, depression and DTI-based metrics of White matter are rare. This case is significant in that not only pain and depression improved after the rTMS, but also serial changes in White matter were observed in DTI.

Associations of prior concussion severity with brain microstructure using mean apparent propagator magnetic resonance imaging

Magnetic resonance imaging (MRI) diffusion studies have shown chronic microstructural tissue abnormalities in athletes with history of concussion, but with inconsistent findings. Concussions with post-traumatic amnesia (PTA) and/or loss of consciousness (LOC) have been connected to greater physiological injury. The novel mean apparent propagator (MAP) MRI is expected to be more sensitive to such tissue injury than the conventional diffusion tensor imaging. This study examined effects of prior concussion severity on microstructure with MAP-MRI. Collegiate-aged athletes (N = 111, 38 females; ≥6 months since most recent concussion, if present) completed semistructured interviews to determine the presence of prior concussion and associated injury characteristics, including PTA and LOC. MAP-MRI metrics (mean non-Gaussian diffusion [NG Mean], return-to-origin probability [RTOP], and mean square displacement [MSD]) were calculated from multi-shell diffusion data, then evaluated for associations with concussion severity through group comparisons in a primary model (athletes with/without prior concussion) and two secondary models (athletes with/without prior concussion with PTA and/or LOC, and athletes with/without prior concussion with LOC only). Bayesian multilevel modeling estimated models in regions of interest (ROI) in white matter and subcortical gray matter, separately. In gray matter, the primary model showed decreased NG Mean and RTOP in the bilateral pallidum and decreased NG Mean in the left putamen with prior concussion. In white matter, lower NG Mean with prior concussion was present in all ROI across all models and was further decreased with LOC. However, only prior concussion with LOC was associated with decreased RTOP and increased MSD across ROI. Exploratory analyses conducted separately in male and female athletes indicate associations in the primary model may differ by sex. Results suggest microstructural measures in gray matter are associated with a general history of concussion, while a severity-dependent association of prior concussion may exist in white matter.

The biomechanical signature of loss of consciousness: computational modelling of elite athlete head injuries

Sports related head injuries can cause transient neurological events including loss of consciousness and dystonic posturing. However, it is unknown why head impacts that appear similar produce distinct neurological effects. The biomechanical effect of impacts can be estimated using computational models of strain within the brain. Here, we investigate the strain and strain rates produced by professional American football impacts that led to loss of consciousness, posturing or no neurological signs. We reviewed 1280 National Football League American football games and selected cases where the team's medical personnel made a diagnosis of concussion. Videos were then analysed for signs of neurological events. We identified 20 head impacts that showed clear video signs of loss of consciousness and 21 showing clear abnormal posturing. Forty-one control impacts were selected where there was no observable evidence of neurological signs, resulting in 82 videos of impacts for analysis. Video analysis was used to guide physical reconstructions of these impacts, allowing us to estimate the impact kinematics. These were then used as input to a detailed 3D high-fidelity finite element model of brain injury biomechanics to estimate strain and strain rate within the brain. We tested the hypotheses that impacts producing loss of consciousness would be associated with the highest biomechanical forces, that loss of consciousness would be associated with high forces in brainstem nuclei involved in arousal and that dystonic posturing would be associated with high forces in motor regions. Impacts leading to loss of consciousness compared to controls produced higher head acceleration (linear acceleration; 81.5 g ± 39.8 versus 47.9 ± 21.4; P = 0.004, rotational acceleration; 5.9 krad/s2 ± 2.4 versus 3.5 ± 1.6; P < 0.001) and in voxel-wise analysis produced larger brain deformation in many brain regions, including parts of the brainstem and cerebellum. Dystonic posturing was also associated with higher deformation compared to controls, with brain deformation observed in cortical regions that included the motor cortex. Loss of consciousness was specifically associated with higher strain rates in brainstem regions implicated in maintenance of consciousness, including following correction for the overall severity of impact. These included brainstem nuclei including the locus coeruleus, dorsal raphé and parabrachial complex. The results show that in head impacts producing loss of consciousness, brain deformation is disproportionately seen in brainstem regions containing nuclei involved in arousal, suggesting that head impacts produce loss of consciousness through a biomechanical effect on key brainstem nuclei involved in the maintenance of consciousness.

Altered longitudinal structural connectome in paediatric mild traumatic brain injury: an Advancing Concussion Assessment in Paediatrics study

Advanced diffusion-weighted imaging techniques have increased understanding of the neuropathology of paediatric mild traumatic brain injury (i.e. concussion). Most studies have examined discrete white-matter pathways, which may not capture the characteristically subtle, diffuse and heterogenous effects of paediatric concussion on brain microstructure. This study compared the structural connectome of children with concussion to those with mild orthopaedic injury to determine whether network metrics and their trajectories across time post-injury differentiate paediatric concussion from mild traumatic injury more generally. Data were drawn from of a large study of outcomes in paediatric concussion. Children aged 8-16.99 years were recruited from five paediatric emergency departments within 48 h of sustaining a concussion (n = 360; 56% male) or mild orthopaedic injury (n = 196; 62% male). A reliable change score was used to classify children with concussion into two groups: concussion with or without persistent symptoms. Children completed 3 T MRI at post-acute (2-33 days) and/or chronic (3 or 6 months, via random assignment) post-injury follow-ups. Diffusion-weighted images were used to calculate the diffusion tensor, conduct deterministic whole-brain fibre tractography and compute connectivity matrices in native (diffusion) space for 90 supratentorial regions. Weighted adjacency matrices were constructed using average fractional anisotropy and used to calculate global and local (regional) graph theory metrics. Linear mixed effects modelling was performed to compare groups, correcting for multiple comparisons. Groups did not differ in global network metrics. However, the clustering coefficient, betweenness centrality and efficiency of the insula, cingulate, parietal, occipital and subcortical regions differed among groups, with differences moderated by time (days) post-injury, biological sex and age at time of injury. Post-acute differences were minimal, whereas more robust alterations emerged at 3 and especially 6 months in children with concussion with persistent symptoms, albeit differently by sex and age. In the largest neuroimaging study to date, post-acute regional network metrics distinguished concussion from mild orthopaedic injury and predicted symptom recovery 1-month post-injury. Regional network parameters alterations were more robust and widespread at chronic timepoints than post-acutely after concussion. Results suggest that increased regional and local subnetwork segregation (modularity) and inefficiency occurs across time after concussion, emerging after post-concussive symptom resolve in most children. These differences persist up to 6 months after concussion, especially in children who showed persistent symptoms. While prognostic, the small to modest effect size of group differences and the moderating effects of sex likely would preclude effective clinical application in individual patients.

Diffusion-Weighted Imaging in Mild Traumatic Brain Injury: A Systematic Review of the Literature

There is evidence that diffusion-weighted imaging (DWI) is able to detect tissue alterations following mild traumatic brain injury (mTBI) that may not be observed on conventional neuroimaging; however, findings are often inconsistent between studies. This systematic review assesses patterns of differences in DWI metrics between those with and without a history of mTBI. A PubMed literature search was performed using relevant indexing terms for articles published prior to May 14, 2020. Findings were limited to human studies using DWI in mTBI. Articles were excluded if they were not full-length, did not contain original data, if they were case studies, pertained to military populations, had inadequate injury severity classification, or did not report post-injury interval. Findings were reported independently for four subgroups: acute/subacute pediatric mTBI, acute/subacute adult mTBI, chronic adult mTBI, and sport-related concussion, and all DWI acquisition and analysis methods used were included. Patterns of findings between studies were reported, along with strengths and weaknesses of the current state of the literature. Although heterogeneity of sample characteristics and study methods limited the consistency of findings, alterations in DWI metrics were most commonly reported in the corpus callosum, corona radiata, internal capsule, and long association pathways. Many acute/subacute pediatric studies reported higher FA and lower ADC or MD in various regions. In contrast, acute/subacute adult studies most commonly indicate lower FA within the context of higher MD and RD. In the chronic phase of recovery, FA may remain low, possibly indicating overall demyelination or Wallerian degeneration over time. Longitudinal studies, though limited, generally indicate at least a partial normalization of DWI metrics over time, which is often associated with functional improvement. We conclude that DWI is able to detect structural mTBI-related abnormalities that may persist over time, although future DWI research will benefit from larger samples, improved data analysis methods, standardized reporting, and increasing transparency.

Diffusion Tensor and Kurtosis Imaging Findings the First Year following Mild Traumatic Brain Injury

Despite enormous research interest in diffusion tensor imaging and diffusion kurtosis imaging (DTI; DKI) following mild traumatic brain injury (MTBI), it remains unknown how diffusion in white matter evolves post-injury and relates to acute MTBI characteristics. This prospective cohort study aimed to characterize diffusion changes in white matter the first year after MTBI. Patients with MTBI (n = 193) and matched controls (n = 83) underwent 3T magnetic resonance imaging (MRI) within 72 h and 3- and 12-months post-injury. Diffusion data were analyzed in three steps: 1) voxel-wise comparisons between the MTBI and control group were performed with tract-based spatial statistics at each time-point; 2) clusters of significant voxels identified in step 1 above were evaluated longitudinally with mixed-effect models; 3) the MTBI group was divided into: (A) complicated (with macrostructural findings on MRI) and uncomplicated MTBI; (B) long (1-24 h) and short (< 1 h) post-traumatic amnesia (PTA); and (C) other and no other concurrent injuries to investigate if findings in step 1 were driven mainly by aberrant diffusion in patients with a more severe injury. At 72 h, voxel-wise comparisons revealed significantly lower fractional anisotropy (FA) in one tract and significantly lower mean kurtosis (Kmean) in 11 tracts in the MTBI compared with control group. At 3 months, the MTBI group had significantly higher mean diffusivity in eight tracts compared with controls. At 12 months, FA was significantly lower in four tracts and Kmean in 10 tracts in patients with MTBI compared with controls. There was considerable overlap in affected tracts across time, including the corpus callosum, corona radiata, internal and external capsule, and cerebellar peduncles. Longitudinal analyses revealed that the diffusion metrics remained relatively stable throughout the first year after MTBI. The significant group*time interactions identified were driven by changes in the control rather than the MTBI group. Further, differences identified in step 1 did not result from greater diffusion abnormalities in patients with complicated MTBI, long PTA, or other concurrent injuries, as standardized mean differences in diffusion metrics between the groups were small (0.07 ± 0.11) and non-significant. However, follow-up voxel-wise analyses revealed that other concurrent injuries had effects on diffusion metrics, but predominantly in other metrics and at other time-points than the effects observed in the MTBI versus control group analysis. In conclusion, patients with MTBI differed from controls in white matter integrity already 72 h after injury. Diffusion metrics remained relatively stable throughout the first year after MTBI and were not driven by deviating diffusion in patients with a more severe MTBI.

Effects of White-Matter Tract Length in Sport-Related Concussion: A Tractography Study from the NCAA-DoD CARE Consortium

Sport-related concussion (SRC) is an important public health issue. White-matter alterations after SRC are widely studied by neuroimaging approaches, such as diffusion magnetic resonance imaging (MRI). Although the exact anatomical location of the alterations may differ, significant white-matter alterations are commonly observed in long fiber tracts, but are never proven. In the present study, we performed streamline tractography to characterize the association between tract length and white-matter microstructural alterations after SRC. Sixty-eight collegiate athletes diagnosed with acute concussion (24-48 h post-injury) and 64 matched contact-sport controls were included in this study. The athletes underwent diffusion tensor imaging (DTI) in 3.0 T MRI scanners across three study sites. DTI metrics were used for tract-based spatial statistics to map white-matter regions-of-interest (ROIs) with significant group differences. Whole-brain white-mater streamline tractography was performed to extract "affected" white-matter streamlines (i.e., streamlines passing through the identified ROIs). In the concussed athletes, streamline counts and DTI metrics of the affected white-matter fiber tracts were summarized and compared with unaffected white-matter tracts across tract length in the same participant. The affected white-matter tracts had a high streamline count at length of 80-100 mm and high length-adjusted affected ratio for streamline length longer than 80 mm. DTI mean diffusivity was higher in the affected streamlines longer than 100 mm with significant associations with the Brief Symptom Inventory score. Our findings suggest that long fibers in the brains of collegiate athletes are more vulnerable to acute SRC with higher mean diffusivity and a higher affected ratio compared with the whole distribution.

White Matter Abnormalities and Cognitive Deficit After Mild Traumatic Brain Injury: Comparing DTI, DKI, and NODDI

White matter (WM) disruption is an important determinant of cognitive impairment after mild traumatic brain injury (mTBI), but traditional diffusion tensor imaging (DTI) shows some limitations in assessing WM damage. Diffusion kurtosis imaging (DKI) and neurite orientation dispersion and density imaging (NODDI) show advantages over DTI in this respect. Therefore, we used these three diffusion models to investigate complex WM changes in the acute stage after mTBI. From 32 mTBI patients and 31 age-, sex-, and education-matched healthy controls, we calculated eight diffusion metrics based on DTI (fractional anisotropy, axial diffusivity, radial diffusivity, and mean diffusivity), DKI (mean kurtosis), and NODDI (orientation dispersion index, volume fraction of intracellular water (Vic), and volume fraction of the isotropic diffusion compartment). We used tract-based spatial statistics to identify group differences at the voxel level, and we then assessed the correlation between diffusion metrics and cognitive function. We also performed subgroup comparisons based on loss of consciousness. Patients showed WM abnormalities and cognitive deficit. And these two changes showed positive correlation. The correlation between Vic of the splenium of the corpus callosum and Digit Symbol Substitution Test scores showed the smallest p-value (p = 0.000, r = 0.481). We concluded that WM changes, especially in the splenium of the corpus callosum, correlate to cognitive deficit in this study. Furthermore, the high voxel count of NODDI results and the consistency of mean kurtosis and the volume fraction of intracellular water in previous studies and our study showed the functional complementarity of DKI and NODDI to DTI.

A systematic review and data synthesis of longitudinal changes in white matter integrity after mild traumatic brain injury assessed by diffusion tensor imaging in adults

PURPOSE

This study aimed to review diffusion tensor imaging studies of mild traumatic brain injury (mTBI) in adults with longitudinal acquisition of data and investigate the variability of findings in association with related factors, such as the time post-injury.

METHODS

Eligible studies from PubMed and EMBASE were searched to identify relevant studies for review. Of the 540 studies, 23 observational studies without intervention and with the following characteristics were included: original research in which adults with mTBI were examined, diffusion tensor imaging was acquired at least twice, white matter integrity was investigated by estimating diffusion metrics, and mode of injury was not restricted to sport- or blast-related mTBI.

RESULTS

Baseline scans were acquired within 3 weeks post-injury, followed by longitudinal scans within 3 months and at 12 months post-injury. During the acute/subacute period, mixed results (increase, decrease, or no significant change) of fractional anisotropy (FA) were observed compared to those in controls. Some studies reported increased FA during the acute/subacute period compared to controls, followed by normalization of FA. Decreased FA was also reported during the acute/subacute period, which lasted long into the chronic phase. In the acute phase, the mean diffusivity (MD) was greater than that in the controls. Compared to the early phase of injury, MD was reduced in the follow-up phase in most studies in the mTBI group. Insignificant differences in FA and MD have been reported in several studies. Such variability limits the clinical usefulness of diffusion tensor metrics.

CONCLUSIONS

There was a high variability in reported changes in white matter integrity. Decreased FA not only in acute/subacute but also in long-term period after injury may indicate long-term neurodegenerative processes after mTBI. Nevertheless, longitudinal changes in MD towards normalization suggest possible recovery. Long-term cohort studies with research initiatives should be considered to elucidate brain changes after mTBI.

Dynamic changes in white matter following traumatic brain injury and how diffuse axonal injury relates to cognitive domain

Objective: The goal is to evaluate longitudinally with diffusion tensor imaging (DTI) the integrity of cerebral white matter in patients with moderate and severe DAI and to correlate the DTI findings with cognitive deficits.Methods: Patients with DAI (n = 20) were scanned at three timepoints (2, 6 and 12 months) after trauma. A healthy control group (n = 20) was evaluated once with the same high-field MRI scanner. The corpus callosum (CC) and the bilateral superior longitudinal fascicles (SLFs) were assessed by deterministic tractography with ExploreDTI. A neuropschychological evaluation was also performed.Results: The CC and both SLFs demonstrated various microstructural abnormalities in between-groups comparisons. All DTI parameters demonstrated changes across time in the body of the CC, while FA (fractional anisotropy) increases were seen on both SLFs. In the splenium of the CC, progressive changes in the mean diffusivity (MD) and axial diffusivity (AD) were also observed. There was an improvement in attention and memory along time. Remarkably, DTI parameters demonstrated several correlations with the cognitive domains.Conclusions: Our findings suggest that microstructural changes in the white matter are dynamic and may be detectable by DTI throughout the first year after trauma. Likewise, patients also demonstrated improvement in some cognitive skills.

Evaluation of diffusion measurements reveals radial diffusivity indicative of microstructural damage following acute, mild traumatic brain injury

PURPOSE

Mild TBI, characterized by microstructural damage, often undetectable on conventional imaging techniques, is a pervasive condition that disturbs brain function and can potentially result in long-term deficits. Deciphering the underlying microstructural damage in mild TBI is crucial for establishing a reliable diagnosis and enabling effective therapeutics. Efforts to capture this damage have been extensive, but results have been inconsistent and incomplete.

METHODS

To that effect, we set out to examine the shape of the diffusion tensor in mild TBI during the acute phase of injury. We inspected diffusivity and geometric measurements describing the diffusion tensor's shape and compared mild TBI (N = 34, 20.4-66.6 yo) measurements with those from healthy control (N = 42, 20.7-67.2 yo) participants using voxelwise tract-based spatial statistics. Subsequently, to explore associations between the diffusion measurements in mild TBI, we performed nonparametric statistics and machine learning techniques.

RESULTS

Overall, mild TBI displayed a diffuse increase in D_λ2, D_λ3, D_radial, D_mean, and C_spherical, with a diffuse decrease in A_fractional, A_mode, and C_linear, in addition to no change in D_axial or C_planar. Most notably, our results provide evidence for D_radial as a potential biomarker for microstructural damage, specifically its main component D_λ2, based on their performance in discriminating between mild TBI and control groups. A_fractional was also found to be important for discriminating between groups.

CONCLUSION

Our results revealed the importance of a diffusion measurement often overlooked, D_radial, in assessing TBI and suggest differentiating diffusion measurements has the potential utility to detect variations in the underlying pathophysiology after injury.

Interval-censored survival analysis of mild traumatic brain injury with outcome based neuroimaging clinical applications

Objective

The purpose of this study was to assess the relationship between MRI findings and clinical presentation and outcomes in patients following mild traumatic brain injury (mTBI). We hypothesize that imaging findings other than hemorrhages and contusions may be used to predict symptom presentation and longevity following mTBI.

Methods

Patients (n = 250) diagnosed with mTBI and in litigation for brain injury underwent 3T magnetic resonance imaging (MRI). A retrospective chart review was performed to assess symptom presentation and improvement/resolution. To account for variable times of clinical presentation, nonuniform follow-up, and uncertainty in the dates of symptom resolution, a right censored, interval censored statistical analysis was performed. Incidence and resolution of headache, balance, cognitive deficit, fatigue, anxiety, depression, and emotional lability were compared among patients. Image findings analyzed included white matter hyperintensities (WMH), Diffusion Tensor Imaging (DTI) fractional anisotropy (FA) values, MR perfusion, auditory functional MRI (fMRI) activation, hippocampal atrophy (HA) and hippocampal asymmetry as defined by NeuroQuant ® volumetric software.

Results

Patients who reported LOC were significantly more likely to present with balance problems (p < 0.001), cognitive deficits (p = 0.010), fatigue (p = 0.025), depression (p = 0.002), and emotional lability (p = 0.002). Patients with LOC also demonstrated significantly slower recovery of cognitive function than those who did not lose consciousness (p = 0.044). Patients over the age of 40 had significantly higher odds of presenting with balance problems (p = 0.006). Additionally, these older patients were slower to recover cognitive function (p = 0.001) and less likely to experience improvement of headaches (p = 0.007). Abnormal MRI did not correlate significantly with symptom presentation, but was a strong indicator of symptom progression, with slower recovery of balance (p = 0.009) and cognitive deficits (p < 0.001).

Conclusion

This analysis demonstrates the utility of clinical data analysis using interval-censored survival statistical technique in head trauma patients. Strong statistical associations between neuroimaging findings and aggregate clinical outcomes were identified in patients with mTBI.

Tractography in Neurosurgery: A Systematic Review of Current Applications

The ability to visualize the brain's fiber connections noninvasively in vivo is relatively young compared with other possibilities of functional magnetic resonance imaging. Although many studies showed tractography to be of promising value for neurosurgical care, the implications remain inconclusive. An overview of current applications is presented in this systematic review. A search was conducted for (("tractography" or "fiber tracking" or "fibre tracking") and "neurosurgery") that produced 751 results. We identified 260 relevant articles and added 20 more from other sources. Most publications concerned surgical planning for resection of tumors (n = 193) and vascular lesions (n = 15). Preoperative use of transcranial magnetic stimulation was discussed in 22 of these articles. Tractography in skull base surgery presents a special challenge (n = 29). Fewer publications evaluated traumatic brain injury (TBI) (n = 25) and spontaneous intracranial bleeding (n = 22). Twenty-three articles focused on tractography in pediatric neurosurgery. Most authors found tractography to be a valuable addition in neurosurgical care. The accuracy of the technique has increased over time. There are articles suggesting that tractography improves patient outcome after tumor resection. However, no reliable biomarkers have yet been described. The better rehabilitation potential after TBI and spontaneous intracranial bleeding compared with brain tumors offers an insight into the process of neurorehabilitation. Tractography and diffusion measurements in some studies showed a correlation with patient outcome that might help uncover the neuroanatomical principles of rehabilitation itself. Alternative corticofugal and cortico-cortical networks have been implicated in motor recovery after ischemic stroke, suggesting more complex mechanisms in neurorehabilitation that go beyond current models. Hence tractography may potentially be able to predict clinical deficits and rehabilitation potential, as well as finding possible explanations for neurologic disorders in retrospect. However, large variations of the results indicate a lack of data to establish robust diagnostical concepts at this point. Therefore, in vivo tractography should still be interpreted with caution and by experienced surgeons.

In Patients Over 50 Years, Increased Age Is Associated With Decreased Odds of Documented Loss of Consciousness After a Concussion

Background: Advanced aged adults have the highest rate of traumatic brain injury (TBI) related hospital admissions, compared to younger age groups. Data were published in 2014 indicating differential injury and neurological responses to a TBI by age categories. In a recent article examining patients with mTBI and isolated subdural hematoma, it was found that older patients had a decreased risk of documented loss of consciousness (LOC). The primary objective was to determine the extent to which the odds of documented LOC changes with increasing age in a population of older adults suffering an isolated concussion and uncomplicated mTBI.

Methods: This was a retrospective study utilizing 6 years (2010–2015) of National Trauma Data Bank data. This study included patients with (1) diagnosis of concussion; (2) positive or negative loss of consciousness; (3) loss of consciousness durations no longer than 59 min or undefined; (4) age ≥50 years; (5) had a “fall” mechanism of injury; and (6) a valid emergency department Glasgow coma scale 13–15. We excluded patients (1) with any intracranial hemorrhage or intracranial injury of other and unspecified nature; (2) skull fracture; (3) an injury severity scale score >17; (4) a concussion with “unspecified” LOC (ICD-9: 850.9).

Results: There were 7,466 patients included in the study; the median (IQR) age was 70 (60–80) years. The risk of documented LOC was 71% (n = 5,319). An 80-year-old had 72% decreased odds of having a documented LOC, compared to a 50-year-old (OR = 0.28, 99.5%CI [0.23–0.34], P < 0.001). This association held when controlling for multiple demographic, comorbid, and clinical variables, and in sensitivity analyses.

Conclusion: These nationwide data suggest that in patients aged ≥50 years, a significant inverse association exists between age and odds of documented LOC after sustaining a fall-related concussion. Additional studies are needed to validate these findings and to investigate the triad of age, documented LOC, and intracranial hemorrhage. Clinical diagnostic criteria relying on LOC might be at risk of being modified by the association between increasing age and decreasing odds of LOC.

Optimizing Outcome Assessment in Multicenter TBI Trials: Perspectives From TRACK-TBI and the TBI Endpoints Development Initiative

Traumatic brain injury (TBI) is a global public health problem that affects the long-term cognitive, physical, and psychological health of patients, while also having a major impact on family and caregivers. In stark contrast to the effective trials that have been conducted in other neurological diseases, nearly 30 studies of interventions employed during acute hospital care for TBI have failed to identify treatments that improve outcome. Many factors may confound the ability to detect true and meaningful treatment effects. One promising area for improving the precision of intervention studies is to optimize the validity of the outcome assessment battery by using well-designed tools and data collection strategies to reduce variability in the outcome data. The Transforming Research and Clinical Knowledge in TBI (TRACK-TBI) study, conducted at 18 sites across the United States, implemented a multidimensional outcome assessment battery with 22 measures aimed at characterizing TBI outcome up to 1 year postinjury. In parallel, through the TBI Endpoints Development (TED) Initiative, federal agencies and investigators have partnered to identify the most valid, reliable, and sensitive outcome assessments for TBI. Here, we present lessons learned from the TRACK-TBI and TED initiatives aimed at optimizing the validity of outcome assessment in TBI.

Persistent Disruption of Brain Connectivity after Sports-Related Concussion in a Female Athlete

Structural and functional connectivity (FC) after sports-related concussion (SRC) may remain altered in adolescent athletes despite symptom resolution. Little is known, however, about how alterations in structural connectivity and FC co-present in female athletes whose symptom recovery tends to be prolonged. Despite resolution of symptoms, one month after her second SRC, an 18-year-old female athlete had decreased structural connectivity in the corpus callosum and cingulum, with altered FC near those regions, compared with other SRC and orthopedically injured athletes. Findings show persistent effects of SRC on advanced brain imaging and the possibility of greater vulnerability of white matter tracts in females.

Diffusion tensor imaging changes following mild, moderate and severe adult traumatic brain injury: a meta-analysis

Diffusion tensor imaging quantifies the asymmetry (fractional anisotropy; FA) and amount of water diffusion (mean diffusivity/apparent diffusion coefficient; MD/ADC) and has been used to assess white matter damage following traumatic brain injury (TBI). In healthy brains, diffusion is constrained by the organization of axons, resulting in high FA and low MD/ADC. Following a TBI, diffusion may be altered; however the exact nature of these changes has yet to be determined. A meta-analysis was therefore conducted to determine the location and extent of changes in DTI following adult TBI. The data from 44 studies that compared the FA and/or MD/ADC data from TBI and Control participants in different regions of interest (ROIs) were analyzed. The impact of injury severity, post-injury interval (acute: ≤ 1 week, subacute: 1 week-3 months, chronic: > 3 months), scanner details and acquisition parameters were investigated in subgroup analyses, with the findings indicating that mild TBI should be examined separately to that of moderate to severe injuries. Lower FA values were found in 88% of brain regions following mild TBI and 92% following moderate-severe TBI, compared to Controls. MD/ADC was higher in 95% and 100% of brain regions following mild and moderate-severe TBI, respectively. Moderate to severe TBI resulted in larger changes in FA and MD/ADC than mild TBI. Overall, changes to FA and MD/ADC were widespread, reflecting more symmetric and a higher amount of diffusion, indicative of white matter damage.

A preliminary report of cerebral white matter microstructural changes associated with adolescent sports concussion acutely and subacutely using diffusion tensor imaging

Diffusion tensor imaging (DTI) has demonstrated its utility in detecting microscopic post-concussion cerebral white matter structural changes, which are not routinely evident on conventional neuroimaging modalities. In this study, we compared 10 adolescents with sports concussion (SC) to 12 orthopedically-injured (OI) individuals within 96 h and three months post injury to 12 typically-developing (TD) participants using DTI and volumetric analyses. In terms of volume, no group differences were noted between SC, OI and TD groups at both 96 h and three months post concussion. Results did not show significant differences between SC, OI, and TD groups for both fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in all regions of interest within 96 h post concussion. However, at three months post-injury, the SC group exhibited significantly lower FA than the TD group in various regions of interest. In terms of ADC, significant group differences between SC and TD groups were found in some regions, with SC group having higher ADC than TD. No group differences for FA and ADC were noted between SC and OI groups at three months post-injury. However, several moderate effect sizes on between-group analyses were noted such that FA was lower and ADC was higher in SC relative to OI. Longitudinally, the SC group demonstrated decreased FA and increased ADC in some areas. The findings highlight the fact that the brain continues to change during the post-injury recovery period, and raises the possibility that adverse changes may result from the neurometabolic cascade that purportedly ensues following SC. DTI may potentially be used to characterize the nature of brain changes that occur following sports-related concussions.

Comparing Region of Interest versus Voxel-Wise Diffusion Tensor Imaging Analytic Methods in Mild and Moderate Traumatic Brain Injury: A Systematic Review and Meta-Analysis

Diffusion tensor imaging is a magnetic resonance imaging technique that is uniquely capable of detecting microstructural tissue damage in mild and moderate traumatic brain injuries (TBIs). To date, it remains unknown if two common analytic techniques, region of interest (ROI) versus voxel-wise (VW) analyses, detect injury in similar locations. The purpose of this systematic review and meta-analysis was to directly compare the regions of abnormality elucidated by each method. Twenty-seven ROI and 11 VW studies met our inclusion criteria. Our ROI meta-analysis identified 11 regions, including the splenium of the corpus callosum, where fractional anisotropy (FA) was significantly decreased in TBI patients, compared with controls. Likewise, we identified higher mean diffusivity/apparent diffusivity constant in the genu, body, and splenium of the corpus callosum. Alternatively, our VW analysis identified one region of high FA in the right superior longitudinal fasciculus and seven regions of low FA, with the two largest located in the corpus callosum. High mean diffusivity and high radial diffusivity, both in the right inferior longitudinal fasciculus, also was revealed by our VW analysis. Moreover, we have shown that the magnitude of damage in the corpus callosum revealed by ROI analysis (z = -3.15) is greater than that demonstrated by VW analysis (z = -1.41). Overall, this study indicates that both ROI and VW analytic methods are sensitive to low FA in the corpus callosum; however, the ROI method has more power to detect the full extent of tissue abnormality in the corpus callosum. More research utilizing standardized methods and reporting is essential to fully characterize the extent to which ROI and VW analyses can concordantly detect other locations of pathology in mild and moderate TBI patients.

Orthopedic Injured versus Uninjured Comparison Groups for Neuroimaging Research in Mild Traumatic Brain Injury

To address controversy surrounding the most appropriate comparison group for mild traumatic brain injury (mTBI) research, mTBI patients 12-30 years of age were compared with an extracranial orthopedic injury (OI) patient group and an uninjured, typically developing (TD) participant group with comparable demographic backgrounds. Injured participants underwent subacute (within 96 h) and late (3 months) diffusion tensor imaging (DTI); TD controls underwent DTI once. Group differences in fractional anisotropy (FA) and mean diffusivity (MD) of commonly studied white matter tracts were assessed. For FA, subacute group differences occurred in the bilateral inferior frontal occipital fasciculus (IFOF) and right inferior longitudinal fasciculus (ILF), and for MD, differences were found in the total corpus callosum, right uncinate fasciculus, IFOF, ILF, and bilateral cingulum bundle (CB). In these analyses, differences (lower FA and higher MD) were generally observed between the mTBI and TD groups but not between the mTBI and OI groups. After a 3 month interval, groups significantly differed in left IFOF FA and in right IFOF and CB MD; the TD group had significantly higher FA and lower MD than both injury groups, which did not differ. There was one exception to this pattern, in which the OI group demonstrated significantly lower FA in the left ILF than the TD group, although neither group differed from the mTBI group. The mTBI and OI groups had generally similar longitudinal results. Findings suggest that different conclusions about group-level DTI analyses could be drawn, depending on the selected comparison group, highlighting the need for additional research in this area. Where possible, mTBI studies may benefit from the inclusion of both OI and TD controls.

The Microtubule-Modulating Drug Epothilone D Alters Dendritic Spine Morphology in a Mouse Model of Mild Traumatic Brain Injury

Microtubule dynamics underpin a plethora of roles involved in the intricate development, structure, function, and maintenance of the central nervous system. Within the injured brain, microtubules are vulnerable to misalignment and dissolution in neurons and have been implicated in injury-induced glial responses and adaptive neuroplasticity in the aftermath of injury. Unfortunately, there is a current lack of therapeutic options for treating traumatic brain injury (TBI). Thus, using a clinically relevant model of mild TBI, lateral fluid percussion injury (FPI) in adult male Thy1-YFPH mice, we investigated the potential therapeutic effects of the brain-penetrant microtubule-stabilizing agent, epothilone D. At 7 days following a single mild lateral FPI the ipsilateral hemisphere was characterized by mild astroglial activation and a stereotypical and widespread pattern of axonal damage in the internal and external capsule white matter tracts. These alterations occurred in the absence of other overt signs of trauma: there were no alterations in cortical thickness or in the number of cortical projection neurons, axons or dendrites expressing YFP. Interestingly, a single low dose of epothilone D administered immediately following FPI (and sham-operation) caused significant alterations in the dendritic spines of layer 5 cortical projection neurons, while the astroglial response and axonal pathology were unaffected. Specifically, spine length was significantly decreased, whereas the density of mushroom spines was significantly increased following epothilone D treatment. Together, these findings have implications for the use of microtubule stabilizing agents in manipulating injury-induced synaptic plasticity and indicate that further study into the viability of microtubule stabilization as a therapeutic strategy in combating TBI is warranted.

Diffusion Tensor Imaging (DTI) Correlates of Self-Reported Sleep Quality and Depression Following Mild Traumatic Brain Injury

Background: Mild traumatic brain injuries (mTBIs) are a significant social, sport, and military health issue. In spite of advances in the clinical management of these injuries, the underlying pathophysiology is not well-understood. There is a critical need to advance objective biomarkers, allowing the identification and tracking of the long-term evolution of changes resulting from mTBI. Diffusion-weighted imaging (DWI) allows for the assessment of white-matter properties in the brain and shows promise as a suitable biomarker of mTBI pathophysiology. Methods: 34 individuals within a year of an mTBI (age: 24.4 ± 7.4) and 18 individuals with no history of mTBI (age: 23.2 ± 3.4) participated in this study. Participants completed self-report measures related to functional outcomes, psychological health, post-injury symptoms, and sleep, and underwent a neuroimaging session that included DWI. Whole-brain white matter was skeletonized using tract-based spatial statistics (TBSS) and compared between groups as well as correlated within-group with the self-report measures. Results: There were no statistically significant anatomical differences between the two groups. After controlling for time since injury, fractional anisotropy (FA) demonstrated a negative correlation with sleep quality scores (higher FA was associated with better sleep quality) and increasing depressive symptoms in the mTBI participants. Conversely, mean (MD) and radial diffusivity (RD) demonstrated positive correlations with sleep quality scores (higher RD was associated with worse sleep quality) and increasing depressive symptoms. These correlations were observed bilaterally in the internal capsule (anterior and posterior limbs), corona radiata (anterior and superior), fornix, and superior fronto-occipital fasciculi. Conclusion: The results of this study indicate that the clinical presentation of mTBI, particularly with respect to depression and sleep, is associated with reduced white-matter integrity in multiple areas of the brain, even after controlling for time since injury. These areas are generally associated not only with sleep and emotion regulation but also cognition. Consequently, the onset of depression and sleep dysfunction as well as cognitive impairments following mTBI may be closely related to each other and to white-matter integrity throughout the brain.

Mild Traumatic Brain Injury and Aggression, Impulsivity, and History of Other- and Self-Directed Aggression

Mild traumatic brain injury (mTBI) is highly prevalent, with an estimated occurrence in the United States of more than 1.3 million per year. While one consequence of mTBI is impulsive aggressive behavior, very few studies have examined the relationship between history of mTBI and aggressive behavior in impulsively aggressive individuals. The authors examined the relationship between history of mTBI in a healthy control group (HC; N=453), a control group with psychiatric disorders (PC; N=486), and individuals with intermittent explosive disorder (IED; N=695), a disorder of primary impulsive aggression. Results demonstrated that IED study participants were significantly more likely to have a history of mTBI (with or without history of a brief loss of consciousness [LOC]) compared with both HC and PC participants. A similar observation was made with regard to self-directed aggression (i.e., suicidal or self-injurious behavior), although group differences were only among those with mTBI with LOC. For both other- and self-directed aggression variables, the authors observed a stepwise increase in dimensional aggression and impulsivity scores across participants as a function of mTBI history. Given that impulsive aggressive behavior begins very early in life, these data are consistent with the hypothesis that lifelong presence of an impulsive aggressive temperament places impulsive aggressive individuals in circumstances that put them at greater risk for mTBI compared with other individuals with and without nonimpulsive aggressive psychopathology.

White matter microstructure predicts longitudinal social cognitive outcomes after paediatric traumatic brain injury: a diffusion tensor imaging study

BACKGROUND

Deficits in social cognition may be among the most profound and disabling sequelae of paediatric traumatic brain injury (TBI); however, the neuroanatomical correlates of longitudinal outcomes in this domain remain unexplored. This study aimed to characterize social cognitive outcomes longitudinally after paediatric TBI, and to evaluate the use of sub-acute diffusion tensor imaging (DTI) to predict these outcomes.

METHODS

The sample included 52 children with mild complex-severe TBI who were assessed on cognitive theory of mind (ToM), pragmatic language and affective ToM at 6- and 24-months post-injury. For comparison, 43 typically developing controls (TDCs) of similar age and sex were recruited. DTI data were acquired sub-acutely (mean = 5.5 weeks post-injury) in a subset of 65 children (TBI = 35; TDC = 30) to evaluate longitudinal prospective relationships between white matter microstructure assessed using Tract-Based Spatial Statistics and social cognitive outcomes.

RESULTS

Whole brain voxel-wise analysis revealed significantly higher mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) in the sub-acute TBI group compared with TDC, with differences observed predominantly in the splenium of the corpus callosum (sCC), sagittal stratum (SS), dorsal cingulum (DC), uncinate fasciculus (UF) and middle and superior cerebellar peduncles (MCP & SCP, respectively). Relative to TDCs, children with TBI showed poorer cognitive ToM, affective ToM and pragmatic language at 6-months post-insult, and those deficits were related to abnormal diffusivity of the sCC, SS, DC, UF, MCP and SCP. Moreover, children with TBI showed poorer affective ToM and pragmatic language at 24-months post-injury, and those outcomes were predicted by sub-acute alterations in diffusivity of the DC and MCP.

CONCLUSIONS

Abnormal microstructure within frontal-temporal, limbic and cerebro-cerebellar white matter may be a risk factor for long-term social difficulties observed in children with TBI. DTI may have potential to unlock early prognostic markers of long-term social outcomes.

Common Patterns of Regional Brain Injury Detectable by Diffusion Tensor Imaging in Otherwise Normal-Appearing White Matter in Patients with Early Moderate to Severe Traumatic Brain Injury

Traumatic brain injury (TBI) alters the lives of millions of people every year. Although mortality rates have improved, attributed to better pre-hospital care and reduction of secondary injury in the critical care setting, improvements in functional outcomes post-TBI have been difficult to achieve. Diffusion-tensor imaging (DTI) allows detailed measurement of microstructural damage in regional brain tissue post-TBI, thus improving our understanding of the extent and severity of TBI. Twenty subjects were recruited from a neurological intensive care unit and compared to 18 healthy control subjects. Magnetic resonance imaging (MRI) scanning was performed on a 3.0-Tesla Siemens TIM Trio Scanner (Siemens Medical Solutions, Erlangen, Germany) including T1- and T2-weighted sequences and DTI. Images were processed using DTIStudio software. SAS (SAS Institute Inc., Cary, NC) was used for statistical analysis of group differences in 14 brain regions (25 regions of interests [ROIs]). Seventeen TBI subjects completed scanning. TBI and control subjects did not differ in age or sex. All TBI subjects had visible lesions on structural MRI. TBI subjects had seven brain regions (nine ROIs) that showed significant group differences on DTI metrics (fractional anisotropy, radial diffusion, or mean diffusion) compared to noninjured subjects, including the corpus callosum (genu and splenium), superior longitudinal fasciculus, internal capsule, right retrolenticular internal capsule, posterior corona radiata, and thalamus. However, 16 ROIs showed relatively normal DTI measures. Quantitative DTI demonstrates multiple areas of microstructual injury in specific normal-appearing white matter brain regions. DTI may be useful for assessing the extent of brain injury in patients with early moderate to severe TBI.

Concussion history is negatively associated with visual-motor force complexity: evidence for persistent effects on visual-motor integration

OBJECTIVES

Long-term monitoring of concussion recovery requires time- and cost-effective methods. Physiologic complexity may be useful in evaluating visual-motor integration following concussion. The purpose of this study was to quantify the extent to which prior number of concussions influenced visual-motor tracking force complexity.

METHODS

Thirty-five individuals with a self-reported concussion history (age: 20.92 ± 1.98) and 15 without (age: 20.92 ± 2.21) performed an isometric visual-motor tracking task, using index finger force to trace a straight line across a computer screen. Finger force root mean square error (RMSE), multi-scale complexity, and average power from 0 to 12 Hertz (Hz) were calculated. Individual multiple regressions were fit to these outcomes.

RESULTS

Force complexity decreased linearly with an increasing number of concussions (R² = 0.101). Males had more complex force overall (R² = 0.219) and greater 4-8 Hz average power (R² = 0.193). The 8-12 Hz average power decreased significantly for individuals with prior loss of consciousness (LOC) and increasing numbers of concussions (R² = 0.143).

CONCLUSION

Individuals exhibited linear decreases in visual-motor tracking force complexity with increasing numbers of concussions, influenced by both gender and a history of LOC. These findings indicate cumulative changes in the ways in which previously concussed individuals process and integrate visual information to guide behaviour.

Prevalence of Incomplete Functional and Symptomatic Recovery among Patients with Head Injury but Brain Injury Debatable

Head injury patients not meeting the American Congress of Rehabilitation Medicine (ACRM)'s criteria for mild traumatic brain injury (mTBI), referred to hereafter as HIBRID (Head Injury BRain Injury Debatable), are often excluded from studies. The prognostic importance of HIBRID is unclear. We investigated the differences in functional and symptomatic recovery at 1 month post-injury among TBI patients classified as: HIBRID, ACRM+ cranial computed tomography (CT)-, and cranial CT+; and trauma and healthy controls. Subjects were enrolled in an ongoing prospective cohort (Head Injury Serum Markers for Assessing Response to Trauma; HeadSMART). Outcomes measured at 1 month post-injury include: incomplete functional recovery (Glasgow Outcome Scale Extended <8); moderate/severe post-concussive symptoms (PCS), defined according to the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision definition; and moderate/severe depressive symptoms (Patient Health Questionnaire 9 ≥ 10). Between April 2014 and May 2016, 500 TBI and 100 control subjects were enrolled and 376 TBI and 78 control subjects completed outcome assessment. The HIBRID group, constituting 23.9% of study population, had a lower incidence of incomplete functional recovery (36.7% [33 of 90]) than ACRM+, CT- (60.7% [125 of 206]; p < 0.01) and CT+ (78.8% [63 of 80]; p < 0.01) groups. However, the incidence of delayed functional recovery within the HIBRID group was higher than in trauma (9.3% [5 of 54]; p < 0.01) and healthy controls (0% [0 of 24]; p < 0.01). Compared to trauma/healthy controls, the HIBRID group had a higher incidence of moderate/severe depressive symptoms and a similar incidence of moderate/severe PCS. Subjects in the HIBRID group are at high risk for adverse outcomes following head injury and warrant further investigation.

White matter changes in patients with mild traumatic brain injury: MRI perspective

This review focuses on white matter (WM) changes in mild traumatic brain injury (mTBI) as assessed by multimodal MRI. All the peer reviewed publications on WM changes in mTBI from January 2011 through September 2016 are included in this review. This review is organized as follows: introduction to mTBI, the basics of multimodal MRI techniques that are potentially useful for probing the WM integrity, summary and critical evaluation of the published literature on the application of multimodal MRI techniques to assess the changes of WM in mTBI, and correlation of MRI measures with behavioral deficits. The MRI–pathology correlation studies based on preclinical models of mTBI are also reviewed. Finally, the author's perspective of future research directions is described.

Phase II Clinical Trial of Atorvastatin in Mild Traumatic Brain Injury

Statins constitute a class of medications commonly used in the treatment of elevated cholesterol. However, in experimental studies, statins also have other non-cholesterol-mediated mechanisms of action, which may have neuroprotective effects. The aim of this study was to determine whether administration of atorvastatin for 7 days post-injury would improve neurological recovery in patients with mild traumatic brain injury (mTBI). The hypothesis was that atorvastatin administration would reduce post-concussion symptoms and also that atorvastatin administration for 1 week post-injury would be safe. One hundred forty patients with mTBI were planned to be enrolled and randomly assigned to receive atorvastatin 1 mg/kg (up to 80 mg/kg) per day or placebo for 7 days starting within 24 h of injury. Assessments of post-concussion syndrome, post-traumatic stress and depressive symptoms, cognition, memory, verbal fluency, functional, and work status were performed at baseline, 1 week, and 1 and 3 months. The result on the Rivermead Post-Concussion Symptoms Questionnaire at 3 months was the primary outcome. Enrollment in the trial was stopped early because of difficulty in recruiting sufficient numbers of subjects. Fifty-two patients with mTBI were enrolled; 28 patients received atorvastatin and 24 received placebo. The median Rivermead score was 2 for the atorvastatin group, compared to 3.5 for the placebo group, at 3 months post-injury (χ2(1) = 0.0976; p = 0.7547). The change in the Rivermead score between baseline and 3 months was also analyzed. The median decrease in score was 4 for the atorvastatin group and 10.5 for the placebo group (χ2(1) = 0.8750; p = 0.3496). No serious adverse events occurred, and there was no significant difference in the incidence of adverse events in the two treatment groups. Atorvastatin administration for 7 days post-injury was safe, but there were no significant differences in neurological recovery post-mTBI with atorvastatin.

Functional Connectivity Is Altered in Concussed Adolescent Athletes Despite Medical Clearance to Return to Play: A Preliminary Report

Recovery following sports-related concussion (SRC) is slower and often more complicated in young adolescent athletes than in collegiate players. Further, the clinical decision to return to play is currently based on symptoms and cognitive performance without direct knowledge of brain function. We tested the hypothesis that brain functional connectivity (FC) would be aberrant in recently concussed, asymptomatic athletes who had been cleared to return to play. A seed-based FC analysis measured the FC of the default mode network (DMN) (seeds = anterior cingulate cortex, posterior cingulate cortex (PCC), right lateral parietal cortex, and left lateral parietal cortex) 30 days after SRC in asymptomatic high school athletes cleared to return to play (n = 13) and was compared to the FC of high school athletes with orthopedic injury (OI) (n = 13). The SRC group demonstrated greater FC than the OI group between the PCC and the ventral lateral prefrontal cortex, as well as between the right lateral parietal cortex and lateral temporal cortex (with regions both outside of and within the DMN). Additionally, the OI group demonstrated greater FC than the SRC group between right lateral parietal cortex and supramarginal gyrus. When relating the FC results to verbal memory performance approximately 1 week and 1 month after injury, significantly different between-group relations were found for the posterior cingulate and right lateral parietal cortex seeds. However, the groups did not differ in verbal memory at 1 month. We suggest that changes in FC are apparent 1-month post-SRC despite resolution of post-concussion symptoms and recovery of cognitive performance in adolescent athletes cleared to return to play.