Attentional deficits in concussion

A Proposed Mechanism for Visual Vertigo: Post-Concussion Patients Have Higher Gain From Visual Input Into Subcortical Gaze Stabilization

Purpose

Post-concussion syndrome (PCS) is commonly associated with dizziness and visual motion sensitivity. This case-control study set out to explore altered motion processing in PCS by measuring gaze stabilization as a reflection of the capacity of the brain to integrate motion, and it aimed to uncover mechanisms of injury where invasive subcortical recordings are not feasible.

Methods

A total of 554 eye movements were analyzed in 10 PCS patients and nine healthy controls across 171 trials. Optokinetic and vestibulo-ocular reflexes were recorded using a head-mounted eye tracker while participants were exposed to visual, vestibular, and visuo-vestibular motion stimulations in the roll plane. Torsional and vergence eye movements were analyzed in terms of slow-phase velocities, gain, nystagmus frequency, and sensory-specific contributions toward gaze stabilization.

Results

Participants expressed eye-movement responses consistent with expected gaze stabilization; slow phases were fastest for visuo-vestibular trials and slowest for visual stimulations (P < 0.001) and increased with stimulus acceleration (P < 0.001). Concussed patients demonstrated increased gain from visual input to gaze stabilization (P = 0.005), faster slow phases (P = 0.013), earlier nystagmus beats (P = 0.003), and higher relative visual influence over the gaze-stabilizing response (P = 0.001), presenting robust effect sizes despite the limited population size.

Conclusions

The enhanced neural responsiveness to visual motion in PCS, combined with semi-intact visuo-vestibular integration, presented a subcortical hierarchy for altered gaze stabilization. Drawing on comparable animal trials, findings suggest that concussed patients may suffer from diffuse injuries to inhibiting pathways for optokinetic information, likely early in the visuo-vestibular hierarchy of sensorimotor integration. These findings offer context for common but elusive symptoms, presenting a neurological explanation for motion sensitivity and visual vertigo in PCS.

Deficits in visuospatial attentional cueing following mild traumatic brain injury

Visual attentional deficits are frequently reported in patients with mild traumatic brain injury (TBI). In the present study, the ability to orient visual attention (i.e., the use of endogenous and exogenous visual cues) was investigated using a modified Posner visual search task, in which the participant was required to search for a target shape (radial frequency patterns) amongst distractor shapes. Participants were required to determine whether a target radial frequency pattern was present or absent from an array of distractors. Attention to the target location was cued using central or peripheral cueing procedures to investigate endogenous or exogenous attention allocation. Predictability was not manipulated between central and peripheral cues. Search difficulty was varied by systematically changing the radial frequency difference between target and distractors (and thereby shape difference), and cues could be valid or invalid in that they correctly or incorrectly indicated the position of the target shape. Both target discriminability (i.e., identifying the presence or absence of the target) and reaction times were measured. Thirteen patients with chronic mild TBI and 21 age-, sex-, and IQ -matched healthy controls participated in the study. For control participants, both discrimination accuracy and reaction times improved with visual search efficiency, and they were sensitive to the type of cue, with performance worst for cue invalid conditions than valid conditions. However, the results for TBI patients were strikingly different; we find that discrimination accuracy slightly improved with visual search difficulty (compared to controls), but not reaction times, and TBI patients were largely insensitive to the type of visual cue, and did not show a selective deficit for central or peripheral cues, suggesting an impairment in both endogenous and exogenous visual attention. In conclusion, patients with mild TBI exhibit a poor ability to orient visual attention.

Visual-Spatial Attentional Performance Identifies Lower Extremity Injury Risk in Adolescent Athletes

OBJECTIVE

Strategies to identify lower extremity musculoskeletal (LEMSK) injury risk have been informed by prospectively identified biomechanical and neuromuscular risk factors. Emergent evidence suggests that cognitive and oculomotor performance may also contribute to LEMSK injury. The purpose of this study was to determine whether prospective cognitive and oculomotor measures identify adolescent athletes who sustain an in-season LEMSK injury.

DESIGN

Prospective longitudinal study.

SETTINGS

Controlled laboratory and athletic event settings.

PARTICIPANTS

Four hundred eighty-eight adolescent male football and female soccer athletes aged 13 to 18 years.

ASSESSMENT OF RISK FACTORS

Preseason baseline cognitive and oculomotor performance: Attention Network Task (ANT), cued task switching, King-Devick test, and near point of convergence.

MAIN OUTCOME MEASURE

Incidence of LEMSK sprains and strains during a single competitive season.

RESULTS

Attention Network Task-orienting network reaction time (RT) was the only cognitive or oculomotor measure significantly associated with LEMSK injury [B = 1.015, 95% confidence interval (CI): 1.01-1.024, P < 0.01]. Every 10 milliseconds increase in orienting network RT was associated with a 15% increased risk for LEMSK injury. Athletes demonstrating an orienting network RT ≥ 32.8 milliseconds had a higher risk for LEMSK injury relative to athletes below the cut-point (relative risk, 2.62; 95% CI, 1.52-4.52; odds ratio, 3.00; 95% CI, 1.63-5.52).

CONCLUSIONS

Deficits in visual-spatial components of attention were associated with 2.62 times greater risk for LEMSK injury in adolescent athletes. The present results add evidence to suggest that visual-spatial attentional processing contributes to LEMSK injury and may supplement previously established LEMSK injury risk assessments.

Altered Brain Functional Connectivity in Female Athletes Over the Course of a Season of Collision or Contact Sports

University athletes are exposed to numerous impacts to the body and head, though the potential cumulative effects of such hits remain elusive. This study examined resting-state functional connectivity (rsFC) of brain networks in female varsity athletes over the course of a season. Nineteen female university athletes involved in collision (N = 12) and contact (N = 7) sports underwent functional magnetic resonance imaging scans at both pre- and post-season. A group-level independent component analysis (ICA) was used to investigate differences in rsFC over the course of a season and differences between contact and collision sport athletes. Decreased rsFC was observed over the course of the season between the default mode network (DMN) and regions in the frontal, parietal, and occipital lobe (p false discovery rate, ≤0.05) driven by differences in the contact group. There was also a main effect of group in the dorsal attention network (DAN) driven by differences between contact and collision groups at pre-season. Differences identified over the course of a season of play indicate largely decreased rsFC within the DMN, and level of contact was associated with differences in rsFC of the DAN. The association between exposure to repetitive head impacts (RHIs) and observed changes in network rsFC supplements the growing literature suggesting that even non-concussed athletes may be at risk for changes in brain functioning. However, the complexity of examining the direct effects of RHIs highlights the need to consider multiple factors, including mental health and sport-specific training and expertise, that may potentially be associated with neural changes.

Deficits in multiple object-tracking and visual attention following mild traumatic brain injury

Difficulty in the ability to allocate and maintain visual attention is frequently reported by patients with traumatic brain injury (TBI). In the present study, we used a multiple object tracking (MOT) task to investigate the degree to which TBI affects the allocation and maintenance of visual attention to multiple moving targets. Fifteen adults with mild TBI and 20 control participants took part in this study. All participants were matched for age, gender, and IQ. The sensitivity and time taken to perform the MOT task were measured for different conditions in which the duration of the tracking, number of target, and distractor dots were systematically varied. When the number of target dots required to be tracked increased, sensitivity in correctly detecting them decreased for both groups but was significantly greater for patients with mild TBI. Similarly, increasing the number of distractor dots had a greater effect on reducing task sensitivity for patients with mild TBI than control participants. Finally, across all conditions, poorer detection performance was observed for patients with mild TBI when the tracking duration was longer compared to control participants. The present study showed that patients with mild TBI have greater deficits (compared to control participants) in their ability to maintain visual attention on tracking multiple moving objects, which was particularly hindered by increased tracking load and distraction.

Changes in the components of visual attention following traumatic brain injury: A systematic review and meta-analysis

Purpose

We conducted a systematic review and meta-analysis to understand the impact of traumatic brain injury (TBI) on visual attention and whether different components and processes of visual attention (such as selective, sustained, divided, and covert orientation of visual attention) are affected following brain injury.

Methods

A literature search between January 1980 to May 2021 was conducted using Medline, Scopus, PubMed, and Google Scholar databases was undertaken for studies that assessed visual attention using different tasks that target specific or multiple components of visual attention. Three hundred twenty-nine potentially relevant articles were identified, and 20 studies met our inclusion criteria.

Results

A total of 123 effect sizes (ES) were estimated from 20 studies that included 519 patients with TBI and 530 normal participants. The overall combined ES was statistically significant and large (ES = 0.92), but with high heterogeneity (Q = 614.83, p < 0.0001, I² = 80.32%). Subgroup analysis showed that the impact of TBI severity, with the ES for moderate-severe TBI significantly higher than mild TBI (t (112) = 3.11, p = 0.002). Additionally, the component of visual attention was differentially affected by TBI (F (2, 120) = 10.25, p<0.0001); the ES for selective attention (ES = 1.13) and covert orientation of visual attention (ES = 1.14) were large, whilst for sustained attention, the ES was medium at 0.43. A subgroup analysis comparing outcome measures showed that reaction time (ES = 1.12) was significantly more affected compared to performance accuracy (ES = 0.43), F (1, 96) = 25.98, p<0.0001).

Conclusion

Large and significant deficits in visual attention was found following TBI which can last for years after the initial injury. However, different components of visual attention were not affected to the same extent, with selective visual attention and orientation of visual attention most affected following TBI.

Altered Attention Network in Paratroopers Exposed to Repetitive Subconcussion: Evidence Based on Behavioral and Event-Related Potential Results

Cognitive impairment caused by repetitive subconcussion has received increasing attention in recent years. Although the dysfunction of attention has been confirmed by neuropsychological research using scales, there is no event-related potentials (ERPs) research. The Attention Network Test (ANT) has been widely used to evaluate the three separate components of attention processing (alerting, orienting, and executive control). Twenty-seven paratroopers exposed to repetitive subconcussion (subconcussion group) and 25 matched healthy control participants (HCs group) were enrolled, and all of them performed the ANT test while continuous scalp electroencephalography data were recorded. On the behavioral performance level, the subconcussion group showed a slower task response, with an especially significant slower reaction time in alerting. Concerning ERP results, reduction amplitudes of cue-N1 in the alerting network were observed, indicating that this group was less able to make efficient use of cues and maintain an alerting state for incoming information. For the orienting network, no difference in N1 amplitude was observed between the two groups. Moreover, there was a reduced P3 amplitude in the executive control network in the subconcussion group compared with the HCs group, suggesting a dysfunction of attentional resource allocation and inhibition control in the former group. This study is, to our knowledge, the first analysis of the altered attention network caused by repetitive subconcussion from the perspectives of behavioral and neuropsychology levels. These preliminary results revealed the possible damage of the alerting and executive control networks and provided a reference for further research on subconcussion cognitive impairment.

Visuospatial Attention Allocation as an Indicator of Cognitive Deficit in Traumatic Brain Injury: A Systematic Review and Meta-Analysis

Traumatic Brain Injury (TBI) is defined by changes in brain function resulting from external forces acting on the brain and is typically characterized by a host of physiological and functional changes such as cognitive deficits including attention problems. In the present study, we focused on the effect of TBI on the ability to allocate attention in vision (i.e., the use of endogenous and exogenous visual cues) by systematically reviewing previous literature on the topic. We conducted quantitative synthesis of 16 selected studies of visual attention following TBI, calculating 80 effect size estimates. The combined effect size was large (g = 0.79, p < 0.0001) with medium heterogeneity (I² = 68.39%). Subgroup analyses revealed an increase in deficit with moderate-to-severe and severe TBI as compared to mild TBI [F_{(2, 76)} = 24.14, p < 0.0001]. Task type was another key source of variability and subgroup analyses indicated that higher order attention processes were severely affected by TBI [F_{(2, 77)} = 5.66, p = 0.0051). Meta-regression analyses revealed significant improvement in visual attention deficit with time [p(mild) = 0.031, p(moderate-to-severe) = 0.002, p(severe) < 0.0001]. Taken together, these results demonstrate that visual attention is affected by TBI and that regular assessment of visual attention, using a systematic attention allocation task, may provide a useful clinical measure of cognitive impairment and change after TBI.

Paired cognitive flexibility task with symptom factors improves detection of sports-related concussion in high school and collegiate athletes

Determining the sensitivity and specificity of short neurocognitive assessments to objectively detect concussion will help clinicians more confidently integrate such tools in clinical management decisions. This study quantified the sensitivity and specificity of a computerized cognitive flexibility task isolating shifts of visuospatial attention in combination with clinical symptoms acutely (< 72 h) following concussion. A total of 100 athletes (53 concussed; 47 non-injured control; 42% female) completed computerized neurocognitive testing and clinical symptom reports (Sport Concussion Assessment Tool 3rd edition: SCAT3). Separate discriminant function analyses were performed for individual, combination, and stepwise inclusion of neurocognitive and clinical symptomology assessments. Findings revealed the combination of neurocognitive outcomes (i.e., mean reaction time, response accuracy, and response accuracy cost) with clinical symptom factor scores exhibited the greatest sensitivity (95.7%) and specificity (88.7%) as well as the highest positive predictive value (95.9%) and negative predictive value (88%) relative to other approaches. Further, a stepwise approach predicting concussion status using the discriminant functions improved detection of concussion (98.2% sensitivity, 95.7% specificity, 96.4% positive predictive value, and 97.8% negative predictive value) when clinical symptom factors failed to indicate the presence of a concussion. Incorporating a cognitive flexibility task involving shifts of visuospatial attention combined with clinical symptom factor scores may improve clinical decision-making as this approach exceeds the sensitivity and specificity of widely popular neurocognitive test batteries and takes less than 10 min to administer.

Evidence of residual cognitive deficits in young adults with a concussion history from adolescence

The present study investigated executive function and sustained attention of non-athlete, young adults (ages 18-23) with a history of concussion beyond ten months post incident. Cognitive functioning was examined in 24 non-athletic, college students with a concussion history (mean age 21 yrs.; mean time and range post-injury: 4 years, 10-90 months) and 24 non-athletic controls with no history (NH) of concussion. Computerized versions of two cognitive assessment techniques were utilized to examine executive functioning (Stroop) and sustained attention capacity (D2). Primary dependent variables were response time, error score, and sustained attention score. Relationships between dependent variables and concussion metrics were also analyzed. ANOVA's revealed a significantly higher error rate in concussion history (CH) participants when performing the Stroop task (p < 0.05), including a trend for greater errors in the incongruent task condition (p < 0.05). Group measures did not differ in the sustained attention test (all p > 0.05). Nevertheless, there was a significant relationship between D2 error rate and time since concussion (p < 0.01), showing that D2 error rate was greater for participants with more time since concussion sustainment. Our findings indicate the potential for prolonged cognitive dysfunction linked to decision-making, but not to processing speed, in young adult non-athletes with a CH averaging four years post-injury. These findings may provide evidence of residual cognitive deficits in young adults with a concussion history over time.

Changes in attentional processing following neurofeedback in patients with persistent post-concussive symptoms: a pilot study

OBJECTIVE

Persistent post-concussive symptoms (PPCS) often include attention deficits, particularly orienting and executive attention. Research in other clinical populations has demonstrated that neurofeedback therapy (NFT) is effective at improving orienting and executive attention, although its effects on attentional networks in patients with PPCS are unknown.

METHOD

In this single-group pilot study, we examined attention-related event-related potentials (ERPs) - N1 and P3 - and cognitive outcomes following Live Z-score training (LZT), a variant of NFT.

RESULTS

No changes in early selective attention, as indexed by N1 amplitude, were observed; however, P3 amplitude, which indexes neural resource allocation, increased following LZT and returned to baseline by 3 months. Cognitive performance improved following treatment, which was sustained at 3 months. The magnitude of change in P3 and ANT performance did not differ between orienting or executive attention, suggesting LZT improved general attentional processing efficiency.

CONCLUSION

Our results suggest that LZT may positively affect attention globally, but does not target specific attention networks. These pilot data warrant the initiation of a clinical trial evaluating the effectiveness of LZT for treating attention deficits in patients with PPCS.

Perceptual Cognitive Training Does Not Improve Clinical Outcomes at 4 and 12 Weeks Following Concussion in Children and Adolescents: A Randomized Controlled Trial

OBJECTIVE

To determine whether a perceptual-cognitive training program using 3D-multiple object tracking (3D-MOT) can improve symptoms following acute pediatric concussion.

SETTING

Research laboratory within a pediatric trauma center.

PARTICIPANTS

Children and adolescents (n = 62, age= 13.27 ± 2.50) with diagnosed concussion.

DESIGN

Randomized controlled trial. Children were randomized into either 3D-MOT, 2048 game, or standard care-only groups. Participants and parents completed the Post-Concussion Symptom Inventory (PCSI) at baseline, 4, 8, and 12 weeks postinjury. Intervention participants completed either the 3D-MOT protocol or the 2048 game at 6 sessions between the baseline and 4-week assessment.

MAIN MEASURES

A 3 (group) × 10 (time) mixed-model analysis of variance evaluated PCSI total scores. The rate of persistent postconcussive symptom (PPCS) was evaluated at 4 weeks using χ2 analysis.

RESULTS

Symptoms decreased throughout the study using both child-reported (F(9,374) = 22.03, P < .001) and parent-reported scores (F(9,370) = 28.06, P < .001). Twenty-four (44.4%) children met the study definition for PPCS using the child-reported PCSI, while 20 (37.7%) children had PPCS using parent reports. The intervention did not significantly affect symptom resolution or PPCS rates.

CONCLUSION

There is no benefit to prescribing 3D-MOT training for acute rehabilitation in pediatric patients with concussion and clinicians should instead focus on more effective programs.

Persistent alterations of cortical hemodynamic response in asymptomatic concussed patients

Aim:

The underlying neurophysiological effects of concussion often result in attenuated cognitive and cortical function. To understand the relation between cognition and brain injury, we investigated the effects of concussion on attentional networks using functional near-infrared spectroscopy (fNIRS).

Materials & methods:

Healthy controls and concussed patients, tested within 72 h from injury (T1) and after symptoms resolved (T2) completed a computerized attention task during fNIRS imaging.

Results:

T1 patients exhibited slower reaction times and reduced brain activation pattern relative to healthy controls. Interestingly, the cortical oxygenation hemoglobin response at T2 was greater relative to T1 and healthy controls, while reaction time was normative.

Conclusion:

The exploratory findings of this study suggest once asymptomatic, a compensatory hemodynamic response may support the restoration of reaction time despite ongoing physiological recovery.

Noninvasive Brain Stimulation and Noninvasive Peripheral Stimulation for Neglect Syndrome Following Acquired Brain Injury

OBJECTIVE

Hemispatial neglect is a frequent condition usually following nondominant hemispheric brain injury. It strongly affects rehabilitation strategies and everyday life activities. It is associated with behavioral and cognitive disability with a strong impact on patient's life.

METHODS

We reviewed the published literature on the use of noninvasive brain stimulation, including repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), and of noninvasive peripheral muscle stimulation, as therapeutic strategies for rehabilitation of neglect after acquired brain injury, such as in stroke or in traumatic injuries. The studies were grouped as controlled or uncontrolled studies in each stimulation techniques.

RESULTS

Thirty-four studies were identified and 16 on rTMS, 10 on tDCS, and 8 on vibration. All studies were conducted in adult patients who suffered a stroke, except for one that was conducted in a patient suffering traumatic acquired brain injury and another that was conducted in a patient with brain tumor. In spite of significant variability in treatment protocols, patients' features and assessment of neglect, improvement was reported in almost all studies with no side-effects.

CONCLUSIONS

Noninvasive brain stimulation and neuromuscular vibration are promising therapeutic neuromodulatory approaches for neglect. Further randomized-controlled studies are needed to corroborate their effectiveness as separate and combined techniques.

Sport-Related Concussion Evaluation and Management

Concussion is a challenging and controversial medical diagnosis that can test even the most seasoned practitioner. Knowledge on this topic is ever evolving. It was not so long ago that grading guidelines were based on loss of consciousness and amnesia. Medicine has seen a renaissance of discovery over the past 20 years in concussion evaluation and management. A PubMed search for "concussion" between 1990 and 2000 produced just over 1000 articles and that same search including the last 18 years expands to over 10,000 publications. The most recent knowledge and recommendations are discussed based on the published evidence.

Exploring changes in processing speed and intraindividual variability in youth following sports-related concussion

Background

Concussion represents a growing concern in sports participation for adults and youth alike. Studies exploring the neurocognitive sequelae of concussion, such as speed of processing typically compare mean reaction time scores to a control group. Intraindividual variability measures the consistency of reaction times between trials and has been previously explored in adults post-concussion. Some adult studies show increased variability following injury. Developmentally youth show higher intraindividual variability than adults, which may put them at higher risk of increased intraindividual variability change post-concussion. Exploring intraindividual variability may provide additional insight into fluctuating performance reported following injury. Despite preliminary findings of slowed reaction time in youth, a pre-/post-concussion comparison of intraindividual variability of reaction time has not been explored.

Objective

To describe and compare pre- and post-concussion measures of processing speed and intraindividual variability in youth.

Methods

A pre-/post-concussion design was used to compare mean reaction time and the coefficient of variation before and after sports-related concussion in 18 youth athletes aged 10–14 years using verbal and nonverbal working memory tasks. Pre-/post-concussion reaction time and coefficient of variation were compared using t-tests.

Results

The coefficient of variation for nonverbal working memory was significantly higher following concussion, but no changes in average reaction time were found.

Conclusions

Preliminary findings suggest that average response times are unchanged following concussion, but the fluctuation across response times is more variable during a nonverbal working memory task in youth. Increased variability in speed of reaction times could have implications for safe return to sports and reduced academic performance.

Effects of concussions on visually guided motor actions: A literature review

Athletes must be able to successfully navigate the soccer pitch or hockey rink to win the game, requiring maximal cognitive resources to successfully compete. Concussions potentially deplete these resources, and the long-term impact of concussions on an individual's goal-directed visually guided behavior continues to elude the scientific community. While the acute effects on cognition and the motor system have been elucidated elsewhere, long-term effects on performance have been less clear. Additionally, most investigations into long-term postinjury motor behaviors have focused on balance and gait, with little focus on functional upper extremity movements. These arm movements require both cognitive and motor functions to successfully complete the task, such as visually guided reaching, and have received little attention. This review examines the current state of the literature to date on the long-term effects of concussions on cognitive and motor deficits affecting visuomotor behavior.

Diagnostic accuracy of tablet-based software for the detection of concussion

Despite the high prevalence of traumatic brain injuries (TBI), there are few rapid and straightforward tests to improve its assessment. To this end, we developed a tablet-based software battery ("BrainCheck") for concussion detection that is well suited to sports, emergency department, and clinical settings. This article is a study of the diagnostic accuracy of BrainCheck. We administered BrainCheck to 30 TBI patients and 30 pain-matched controls at a hospital Emergency Department (ED), and 538 healthy individuals at 10 control test sites. We compared the results of the tablet-based assessment against physician diagnoses derived from brain scans, clinical examination, and the SCAT3 test, a traditional measure of TBI. We found consistent distributions of normative data and high test-retest reliability. Based on these assessments, we defined a composite score that distinguishes TBI from non-TBI individuals with high sensitivity (83%) and specificity (87%). We conclude that our testing application provides a rapid, portable testing method for TBI.

Increased risk for age-related impairment in visual attention associated with mild traumatic brain injury: Evidence from saccadic response times

It was hypothesized that risk for age-related impairment in attention would be greater among those with remote history of mild TBI than individuals without history of head injury. Twenty-seven adults with remote history of mild TBI and a well-matched comparison group of 54 uninjured controls completed a computerized test of visual attention while saccadic and manual response times were recorded. Within the mild TBI group only, older age was associated with slower saccadic responses and poorer saccadic inhibition. Saccadic slowing was mitigated in situations where the timing and location of attention targets was fully predictable. Mild TBI was not associated with age-related increases in risk for neuropsychological impairment or neurobehavioral symptoms. These results provide preliminary evidence that risk for age-related impairment in visual attention may be higher among those with a history of mild TBI. Saccadic measures may provide enhanced sensitivity to this subtle form of cognitive impairment.

Executive attention deficits after traumatic brain injury reflect impaired recruitment of resources

Deficits in attention are a common and devastating consequence of traumatic brain injury (TBI), leading to functional impairments, rehabilitation barriers, and long-term disability. While such deficits are well documented, little is known about their underlying pathophysiology hindering development of effective and targeted interventions. Here we evaluate the integrity of brain systems specific to attentional functions using quantitative assessments of electroencephalography recorded during performance of the Attention Network Test (ANT), a behavioral paradigm that separates alerting, orienting, and executive components of attention. We studied 13 patients, at least 6 months post-TBI with cognitive impairments, and 24 control subjects. Based on performance on the ANT, TBI subjects showed selective impairment in executive attention. In TBI subjects, principal component analysis combined with spectral analysis of the EEG after target appearance extracted a pattern of increased frontal midline theta power (2.5–7.5 Hz) and suppression of frontal beta power (12.5–22.5 Hz). Individual expression of this pattern correlated (r = − 0.67, p < 0.001) with executive attention impairment. The grading of this pattern of spatiotemporal dynamics with executive attention deficits reflects impaired recruitment of anterior forebrain resources following TBI; specifically, deafferentation and variable disfacilitation of medial frontal neuronal populations is proposed as the basis of our findings.

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Electrophysiological correlate of impaired executive attention after Traumatic Brain Injury is derived.

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Theta increases in medial frontal and beta suppression in frontal regions is linked to behavioral performance.

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Individual-specific pathophysiology allows for tracking of recovery/interventions and studies of function-structure.

Reduced P3b brain response during sustained visual attention is associated with remote blast mTBI and current PTSD in U.S. military veterans

Approximately 275,000 American service members deployed to Iraq or Afghanistan have sustained a mild traumatic brain injury (mTBI), with 75% of these incidents involving an explosive blast. Combat-related mTBI is frequently associated with comorbid mental health disorders, especially posttraumatic stress disorder (PTSD). Attention problems, including sustained attention, are common cognitive complaints of veterans with TBI and PTSD. The present study sought to examine neural correlates of sustained attention in veterans with blast mTBI and/or current PTSD. In 124 veterans of Operations Enduring and Iraqi Freedom (OEF/OIF), we examined event-related potentials (ERPs) elicited by targets and non-targets during performance of a degraded-stimulus continuous performance task (DS-CPT). Four groups, consisting of veterans with blast-related mTBI only, current PTSD only, both blast mTBI and PTSD, and a control group, were studied. Compared to all other groups, blast mTBI only participants were more likely to respond regardless of stimulus type during the DS-CPT. During target detection, the three mTBI/PTSD groups showed reduced amplitude of the P3b (i.e., P300) ERP at Pz compared to the control group. P3b of the three affected groups did not differ from each other. These results suggest that parietal P3b amplitude reduction during target detection in the DS-CPT task may be an index of brain pathology after combat trauma, yet the diminished brain response fails to differentiate independent effects of blast-related mTBI or severity of PTSD symptomatology.

Callosal dysfunction explains injury sequelae in a computational network model of axonal injury

Mild traumatic brain injury (mTBI) often results in neurobehavioral aberrations such as impaired attention and increased reaction time. Diffusion imaging and postmortem analysis studies suggest that mTBI primarily affects myelinated axons in white matter tracts. In particular, corpus callosum, mediating interhemispheric information exchange, has been shown to be affected in mTBI. Yet little is known about the mechanisms linking the injury of myelinated callosal axons to the neurobehavioral sequelae of mTBI. To address this issue, we devised and studied a large, biologically plausible neuronal network model of cortical tissue. Importantly, the model architecture incorporated intra- and interhemispheric organization, including myelinated callosal axons and distance-dependent axonal conduction delays. In the resting state, the intact model network exhibited several salient features, including alpha-band (8-12 Hz) collective activity with low-frequency irregular spiking of individual neurons. The network model of callosal injury captured several clinical observations, including 1) "slowing down" of the network rhythms, manifested as an increased resting-state theta-to-alpha power ratio, 2) reduced response to attention-like network stimulation, manifested as a reduced spectral power of collective activity, and 3) increased population response time in response to stimulation. Importantly, these changes were positively correlated with injury severity, supporting proposals to use neurobehavioral indices as biomarkers for determining the severity of injury. Our modeling effort helps to understand the role played by the injury of callosal myelinated axons in defining the neurobehavioral sequelae of mTBI.

Novel computer tests for identification of mental fatigue after traumatic brain injury

BACKGROUND

Mental fatigue is one of the most significant post-traumatic brain injury symptoms. It is currently not possible to objectively identify.

OBJECTIVE

This study investigated whether a complex computer cognitive test with load on endurance, processing speed and attention were more demanding for participants suffering from mental fatigue after brain injury compared with a control group.

METHOD

Seventy-six subjects of mild traumatic brain injury (mTBI) and 45 healthy controls were included in the study. All subjects with mTBI had been suffering from mental fatigue for six months or more. Mental fatigue was screened using the Mental Fatigue Scale (MFS). Cognitive function was measured for information processing speed and working memory, and with a novel computer test.

RESULTS

The mTBI group rated MFS significantly higher than the control group. The results revealed a significantly slower information processing speed for the mTBI subjects and a poorer performance on the working memory test. The computer test revealed a less efficient performance over time for the TBI subjects compared to the control group.

CONCLUSIONS

The results indicate a less efficient performance over time in complex and demanding cognitive tasks for individuals experiencing from mental fatigue after brain injury.

Visuospatial attention after traumatic brain injury: The role of hemispheric specialization

PRIMARY OBJECTIVE

To evaluate the behavioural and neural effects of TBI on the hemispheric integrity of three components of visuospatial attention: alerting, orienting and executive control.

METHOD

Behavioural performance and high density event-related potentials (ERPs) were acquired while a sample of 12 patients with chronic moderate-to-severe TBI and 12 controls performed the Lateralized Attention Network Test (LANT). Neural indices of attention (posterior N1 amplitude to alerting and orienting cues, midline P3 amplitude during conflict resolution) were examined.

RESULTS

Patients with TBI exhibited smaller N1 amplitude to alerting cues, but comparable behavioural performance to controls. Participants with TBI also demonstrated poorer orienting performance to the left hemispace relative to the right. A corresponding reduction in right hemisphere N1 was found during left orienting to spatial cues in the TBI group. No group differences were observed on behavioural measures of executive control; however, patients with TBI exhibited reduced P3 amplitude overall.

CONCLUSIONS

TBI may have an enduring effect on the orienting system at both neural and behavioural levels. Assessment of attention in chronic TBI can be improved by the integration of hemispheric findings that suggest disproportionate vulnerability in leftward orienting. Results may enhance clinical sensitivity to detection of subtle signs of neglect.

Developmental and gender influences on executive function following concussion in youth hockey players

BACKGROUND

Concussion is the most common athletic injury in youth who are simultaneously undergoing rapid developmental changes in the brain, specifically the development of executive functions (EF). The developing brain is more vulnerable to concussive injury with a protracted and different trajectory of recovery than that of adults. Thus, there is a critical need to enhance understanding of how concussion affects EF in youth.

OBJECTIVE

To investigate the effects of age, gender and concussion history (i.e. concussion incidence, recency, severity) on EF in youth hockey players.

METHODS

This 3-year cross-sectional and longitudinal multiple cohort study examined data from 211 hockey players of 8-15 years of age. Mixed-effects modelling was used to examine the influence of age, gender and concussion on EF in youth athletes.

FINDINGS

Baseline analyses revealed significant age and gender effects on measures of EF. Multiple effects of concussion history on measures of cognitive flexibility (F = 2.48, p = 0.03) and psychomotor speed (F = 2.59, p = 0.04) were found.

IMPLICATIONS

This study highlights the impact of age, gender and concussion on EF in youth. These findings provide foundational knowledge to better manage cognitive sequelae following sports-related concussion.

Reliable Attention Network Scores and Mutually Inhibited Inter-network Relationships Revealed by Mixed Design and Non-orthogonal Method

The attention system can be divided into alerting, orienting, and executive control networks. The efficiency and independence of attention networks have been widely tested with the attention network test (ANT) and its revised versions. However, many studies have failed to find effects of attention network scores (ANSs) and inter-network relationships (INRs). Moreover, the low reliability of ANSs can not meet the demands of theoretical and empirical investigations. Two methodological factors (the inter-trial influence in the event-related design and the inter-network interference in orthogonal contrast) may be responsible for the unreliability of ANT. In this study, we combined the mixed design and non-orthogonal method to explore ANSs and directional INRs. With a small number of trials, we obtained reliable and independent ANSs (split-half reliability of alerting: 0.684; orienting: 0.588; and executive control: 0.616), suggesting an individual and specific attention system. Furthermore, mutual inhibition was observed when two networks were operated simultaneously, indicating a differentiated but integrated attention system. Overall, the reliable and individual specific ANSs and mutually inhibited INRs provide novel insight into the understanding of the developmental, physiological and pathological mechanisms of attention networks, and can benefit future experimental and clinical investigations of attention using ANT.

High School Athletes' Perceptions of Concussion

BACKGROUND

The perception high school athletes have regarding concussions may influence their injury-reporting behavior, and if their perceptions are based on incorrect or incomplete information, they may be at risk for subsequent head injuries.

PURPOSE

To determine whether the recent influx of concussion information has had a positive impact on high school athletes' knowledge of concussions, to determine their perceptions regarding the severity of a concussion injury, and to determine whether receiving correct information will potentially alter their future reporting behavior.

STUDY DESIGN

Cross-sectional study; Level of evidence, 4.

METHODS

A total of 454 high school athletes (212 females, 242 males; mean age, 15.7 ± 1.15 years) from 6 different schools participated in an anonymous survey. The researchers met with teams individually at their high schools to collect data and provide an educational intervention regarding sports-related concussions. The survey questions assessed the athletes' personal injury histories and perceptions and knowledge of the severity of concussion injuries.

RESULTS

There was a difference in the number of athletes who reported having their "bell rung" (n = 297) versus the number of athletes reporting at least 1 concussion (n = 172) (t (453) = -11.60, P = .000, d = -0.54). There was also a difference in the number of athletes who reported a history of at least 1 concussion at the beginning of the study session (n = 172) versus the number of athletes who reported at least 1 concussion at the end of the session (n = 292) (t (453) = -12.018, P = .000, d = 0.732). Fifty percent of athletes also stated that the importance of a game/event should dictate when they return to play.

CONCLUSION

High school athletes continue to fail to realize when they have sustained a concussion. Additionally, athletes lack understanding regarding the severity and seriousness of a concussion. A better effort at formalized education must be made if the culture of sports is to change.

CLINICAL RELEVANCE

Allied health care professionals need to continue to put forth a great effort in educating all student athletes on what a concussion is and the dangers of a concussion injury. Preseason meetings should be used as an opportunity to provide formalized education to all student athletes.

Executive dysfunction assessed with a task-switching task following concussion

Concussion frequently results in executive function deficits that can be specifically probed using task-switching tasks. The current study examined in detail the influence of concussion on task switching performance using both spatial and numerical stimuli. Individuals with concussion (n = 16) were tested within 48 hours of injury and 7, 14, and 28 days later. Healthy sex-, age-, height-, weight- and activity-matched controls (n = 16) were also tested at the same intervals. Switch costs were significantly greater in the participants with concussion than in the controls for both types of stimuli. By contrast, the global costs on non-switching trials were unaffected by concussion. We conclude that concussion has pronounced negative effects on the ability to switch task sets that generalize across task combinations (spatial or numerical) and that persist across at least a month after injury.

The effect of cognitive task complexity on gait stability in adolescents following concussion

Concussion has been reported to result in disturbances to motor and cognitive functions. One way to examine these disturbances is through a dual-task assessment. Many secondary cognitive tasks have been proposed as appropriate tools during concussion assessment; however, task complexity has not been compared within a dual-task investigation. The purpose of this study was to prospectively examine how gait balance control was affected by three secondary cognitive tasks of varying complexity following concussion. Forty-six adolescents completed a dual-task walking protocol which included walking without any cognitive task (WALK), walking while completing a single auditory Stroop (SAS), multiple auditory Stroop (MAS), and a question and answer task (Q&A). Those who sustained a concussion (n = 23, mean age 15.4 ± 1.3 years) reported to the laboratory within 72 h of injury and in the following time increments: 1 week, 2 weeks, 1 month, and 2 months post-injury. Twenty-three healthy control subjects (mean age 15.4 ± 1.3 years), individually matched to each concussion subject, completed the same protocol in similar time increments. The concussion group demonstrated greater total center of mass (COM) medial/lateral displacement in the MAS and Q&A conditions compared with the control group. The concussion group also displayed the greatest peak COM anterior velocity in the least complex condition (WALK), and a significant decrease was observed as task complexity increased (SAS > MAS > Q&A). These findings indicate that gait balance control may be affected by task complexity following concussion and represent a way to identify motor recovery following concussion.

Returning service members to duty following mild traumatic brain injury: exploring the use of dual-task and multitask assessment methods

Within the last decade, more than 220,000 service members have sustained traumatic brain injury (TBI) in support of military operations in Iraq and Afghanistan. Mild TBI may result in subtle cognitive and sensorimotor deficits that adversely affect warfighter performance, creating significant challenges for service members, commanders, and clinicians. In recent conflicts, physical therapists and occupational therapists have played an important role in evaluating service member readiness to return to duty (RTD), incorporating research and best practices from the sports concussion literature. Because premorbid (baseline) performance metrics are not typically available for deployed service members as for athletes, clinicians commonly determine duty readiness based upon the absence of postconcussive symptoms and return to "normal" performance on clinical assessments not yet validated in the military population. Although practices described in the sports concussion literature guide "return-to-play" determinations, resolution of symptoms or improvement of isolated impairments may be inadequate to predict readiness in a military operational environment. Existing clinical metrics informing RTD decision making are limited because they fail to emphasize functional, warrior task demands and they lack versatility to assess the effects of comorbid deficits. Recently, a number of complex task-oriented RTD approaches have emerged from Department of Defense laboratory and clinical settings to address this gap. Immersive virtual reality environments, field-based scenario-driven assessment programs, and militarized dual-task and multitask-based approaches have all been proposed for the evaluation of sensorimotor and cognitive function following TBI. There remains a need for clinically feasible assessment methods that can be used to verify functional performance and operational competence in a variety of practice settings. Complex and ecologically valid assessment techniques incorporating dual-task and multitask methods may prove useful in validating return-to-activity requirements in civilian and military populations.

Auditory orienting and inhibition of return in mild traumatic brain injury: a FMRI study

The semiacute phase of mild traumatic brain injury (mTBI) is associated with deficits in the cognitive domains of attention, memory, and executive function, which previous work suggests may be related to a specific deficit in disengaging attentional focus. However, to date, there have only been a few studies that have employed dynamic imaging techniques to investigate the potential neurological basis of these cognitive deficits during the semiacute stage of injury. Therefore, event-related functional magnetic resonance imaging was used to investigate the neurological correlates of attentional dysfunction in a clinically homogeneous sample of 16 patients with mTBI during the semiacute phase of injury (<3 weeks). Behaviorally, patients with mTBI exhibited deficits in disengaging and reorienting auditory attention following invalid cues as well as a failure to inhibit attentional allocation to a cued spatial location compared to a group of matched controls. Accordingly, patients with mTBI also exhibited hypoactivation within thalamus, striatum, midbrain nuclei, and cerebellum across all trials as well as hypoactivation in the right posterior parietal cortex, presupplementary motor area, bilateral frontal eye fields, and right ventrolateral prefrontal cortex during attentional disengagement. Finally, the hemodynamic response within several regions of the attentional network predicted response times better for controls than for patients with mTBI. These objective neurological findings represent a potential biomarker for the behavioral deficits in spatial attention that characterize the initial recovery phase of mTBI.

The Temporal Stability of the Effects Induced by the Cued Reaction Time Task

The temporal stability of the effects induced by the Cued Reaction Time Task (CRTT) on the orienting of attention was assessed across four weekly sessions. Benefits, costs, and validity effects were computed for each session, and the correlation coefficients between each session were calculated (interindividual stability index). Intraindividual stability indices, the percentage of individuals showing both costs and benefits or the validity effect, were also calculated. The results (based on 41 participants) show a low stability for the effects in which the neutral trials were involved (benefits and costs) but an acceptable reliability for the validity effect, especially when evaluated using the intraindividual index. To maximize the reliability of the data collected using the CRTT, the validity effect seems to be a better probe of spatial orienting of attention.

Attentional disengagement dysfunction following mTBI assessed with the gap saccade task

Concussion, or mild traumatic brain injury (mTBI), leads to a number of cognitive, attentional, and sensorimotor deficits that can last a surprisingly long time after the initial injury. We have previously shown that the ability to orient visuospatial attention is deficient in participants with mTBI within 2 days of their injury, but then recovers to normal levels within a week. Orienting attention requires disengagement from the point of fixation, movement of attention to the location of interest, and re-engagement at that location. Deficits in any or all of these processes could lead to the difficulties with orienting attention that we have observed in mTBI. To address this issue, we tested participants with mTBI using a gap saccade task. Because this task manipulates the temporal gap between the offset of the fixation target and the appearance of the peripheral saccade target, it isolates the contribution of the disengagement process to saccadic reaction time. We found that participants with mTBI had significantly longer saccadic reaction times than controls when the temporal gap was short but not when it was long. This gap-dependent difference in saccadic reaction time was present within 2 days of the injury and resolved within 1 week. This pattern of results suggests that as the contribution of the disengagement process is reduced, so too is the extent of the reaction time deficit in the participants with mTBI. Taken together, this is consistent with the idea that the deficits in orienting visuospatial attention in participants with mTBI are fully accounted for by difficulties with the initial disengagement process.

Cancelling planned actions following mild traumatic brain injury

Mild traumatic brain injury (mTBI) leads to a variety of attentional, cognitive, and sensorimotor deficits. An important aspect of behavior that intersects each of these functions is the ability to cancel a planned action. Thus, the purpose of this study was to determine the effects of mTBI on the ability to perform a countermanding saccade task. In this task, participants were asked to generate a saccade to a target appearing in peripheral vision, but to inhibit saccade execution if an auditory stop signal was presented. The delay between the appearance of the peripheral target and the presentation of the auditory stop signal was varied between 0 and 125ms. We found that the change in the probability of cancelling the saccade as a function of this delay was no different between participants with mTBI tested within 2 days of their injury and matched controls. However, saccadic reaction times and the stop signal reaction time were unexpectedly faster in the participants with mTBI and, furthermore, they inaccurately inhibited saccades during 15% of the trials with no stop signal. Taken together, this data suggests that the ability to cancel planned actions is subtly yet adversely affected by mTBI.

Cognitive task effects on gait stability following concussion

The purpose of this study was to determine how two different types of concurrent tasks affect gait stability in patients with concussion and how balance is maintained. Fourteen individuals suffering from a grade II concussion and 14 matched controls performed a single task of level walking and two types of concurrent tasks during level walking: a discrete reaction time task and a continuous sequential question and answer task. Common gait spatial/temporal measurements, whole-body center of mass motion, and the center of pressure trajectory were recorded. Concussed individuals demonstrated differences in gait while performing single-task level walking and while being challenged with a more difficult secondary task compared to normal controls. Concussed individuals adopted a slower, more conservative gait strategy to maintain stability, but still exhibited signs of instability with center of mass deviations in the coronal plane increasing by 13% during the question and answer dual-task and 26% more than control subjects. Trends of attentional deficits were present with the question and answer task, while the reaction time task seemed to help concussed individuals be more alert to their gait and stability. Recommendations for a sensitive testing protocol of deficits following concussion are explained.

The influence of mild traumatic brain injury on the temporal distribution of attention

The purpose of this study was to examine whether the temporal dynamics of attention was deficient in participants who have recently experienced mild traumatic brain injury (mTBI). For this purpose the rapid serial visual presentation (RSVP) task was used and the performance of participants with mTBI was compared to that of controls matched for age, gender, education, and activity type. In the RSVP task a stream of rapidly presented letters is displayed with target and probe letters separated by varying durations. The participant is required to identify the target letter and determine whether the probe letter was present or not. Previous research has shown that healthy participants display an attentional blink: they fail to detect the probe letter when it appears within approximately 500 ms of the target letter. We found that participants with mTBI had a normal attentional blink-it was neither greater in magnitude nor longer in duration than that displayed by the control participants. However, the participants with mTBI did show evidence of attentional competition-making more errors in identifying the target letter when the probe letter was presented-that was not present in the control participants. Taken together, these results suggest that the temporal constraints of attention are subtly but systematically affected by mTBI.

Attentional and Biomechanical Deficits Interact After Mild Traumatic Brain Injury

Even a mild traumatic brain injury leads to deficits in the ability to maintain gait stability that is exacerbated when a secondary cognitive task is performed at the same time. This implies that executive function is disrupted after concussion-a supposition that is confirmed when tested directly.

Tracking the recovery of visuospatial attention deficits in mild traumatic brain injury

The goal of the current investigation was to probe the deficits in the alerting, orienting and executive components of visuospatial attention in individuals who have recently suffered a mild traumatic brain injury (mTBI) and to assess the rate and degree of recovery for each of these components over a month post-injury. A group design was employed to assess and compare the performance of participants (12 males, 8 females; mean age: 21 +/- 1.74 years) identified with mTBI relative to control subjects matched for gender, age, height, weight and activity level. Participants performed the attentional network test, designed to isolate the constituents of attention into alerting, orienting and executive components. Reaction times (RTs) and response accuracy were the main dependent variables. The results showed that the orienting and executive components were significantly affected by mTBI immediately after the injury, whereas the alerting component was not. Furthermore, participants with mTBI recovered from the deficits in the orienting component of attention within a week of their injury, whereas the deficits in the executive component remained throughout the month post-injury. In addition, the RT cost to generate accurate compared with inaccurate responses was significantly larger in participants with mTBI than in controls, and this difference was maintained throughout the 1 month testing period. These findings indicate that the regions of the brain associated with the orienting and executive components of visuospatial attention may be most susceptible to neural damage resulting from mTBI. Moreover, the lack of recovery in the executive component indicates that the degree and time course for recovery may be regionally specific.