Electrophysiologic Abnormalities of Auditory and Visual Information Processing in Patients with Traumatic Brain Injury

Criterion-Related Validation of a Music-Based Attention Assessment for Individuals with Traumatic Brain Injury

The music-based attention assessment (MAA) is a melody contour identification task that evaluates different types of attention. Previous studies have examined the psychometric and physiological validity of the MAA across various age groups in clinical and typical populations. The purpose of this study was to confirm the MAA's criterion validity in individuals with traumatic brain injury (TBI) and to correlate this with standardized neuropsychological measurements. The MAA and various neurocognitive tests (i.e., the Wechsler adult intelligence scale DST, Delis-Kaplan executive functioning scale color-word interference test, and Conner's continuous performance test) were administered to 38 patients within two weeks prior to or post to the MAA administration. Significant correlations between MAA and neurocognitive batteries were found, indicating the potential of MAA as a valid measure of different types of attention deficits. An additional multiple regression analysis revealed that MAA was a significant factor in predicting attention ability.

Acquired Central Auditory Processing Disorder in Service Members and Veterans

Purpose A growing body of evidence suggests that military service members and military veterans are at risk for deficits in central auditory processing. Risk factors include exposure to blast, neurotrauma, hazardous noise, and ototoxicants. We overview these risk factors and comorbidities, address implications for clinical assessment and care of central auditory processing deficits in service members and veterans, and specify knowledge gaps that warrant research. Method We reviewed the literature to identify studies of risk factors, assessment, and care of central auditory processing deficits in service members and veterans. We also assessed the current state of the science for knowledge gaps that warrant additional study. This literature review describes key findings relating to military risk factors and clinical considerations for the assessment and care of those exposed. Conclusions Central auditory processing deficits are associated with exposure to known military risk factors. Research is needed to characterize mechanisms, sources of variance, and differential diagnosis in this population. Existing best practices do not explicitly consider confounds faced by military personnel. Assessment and rehabilitation strategies that account for these challenges are needed. Finally, investment is critical to ensure that Veterans Affairs and Department of Defense clinical staff are informed, trained, and equipped to implement effective patient care.

Amelioration of visual deficits and visual system pathology after mild TBI with the cannabinoid type-2 receptor inverse agonist SMM-189

Mild TBI is often accompanied by visual system dysfunction and injury, which is at least partly caused by microglial neuroinflammatory processes initiated by the injury. Using our focal cranial blast mouse model of closed-skull mild TBI, we evaluated the ability of the cannabinoid type-2 (CB2) receptor inverse agonist SMM-189, which biases microglia from the harmful M1 state to the beneficial M2 state, to mitigate visual system dysfunction and injury after TBI. Male C57BL/6 or Thy1-EYFP reporter mice received a closed-head blast of either 0-psi (sham) or 50-psi to the left side of the cranium. Blast mice received vehicle or 6 mg/kg SMM-189 daily beginning 2 h after blast. Sham mice received vehicle. In some mice, retina and optic nerve/tract were assessed morphologically at 3-7 days after blast, while other mice were assessed functionally by Optomotry 30 days after blast and morphologically at ≥30 days after blast. Mice sacrificed at 3-7 days were treated daily until sacrificed, while those assessed ≥30 days after blast were treated daily for 2 weeks post blast. Axon damage was evident in the left optic nerve and its continuation as the right optic tract at 3 days post blast in vehicle-treated blast mice in the form of swollen axon bulbs, and was accompanied by a significant increase in the abundance of microglia. Testing at 30 days post blast revealed that the contrast sensitivity function was significantly reduced in both eyes in vehicle-treated blast mice compared to vehicle-treated sham blast mice, and axon counts at ≥30 days after blast revealed a ∼10% loss in left optic nerve in vehicle-treated blast mice. Left optic nerve axon loss was highly correlated with the left eye deficit in contrast sensitivity. Immunolabeling at 30 days post blast showed a significant increase in the abundance of microglia in the retinas of both eyes and in GFAP + Müller cell processes traversing the inner plexiform layer in the left eye of vehicle-treated blast mice. SMM-189 treatment reduced axon injury and microglial abundance at 3 days, and mitigated axon loss, contrast sensitivity deficits, microglial abundance, and Müller cell GFAP upregulation at ≥30 days after blast injury. Analysis of right optic tract microglia at 3 days post blast for M1 versus M2 markers revealed that SMM-189 biased microglia toward the M2 state, with this action of SMM-189 being linked to reduced axonal injury. Taken together, our results show that focal left side cranial blast resulted in impaired contrast sensitivity and retinal pathology bilaterally and optic nerve loss ipsilaterally. The novel cannabinoid drug SMM-189 significantly mitigated the functional deficit and the associated pathologies. Our findings suggest the value of combatting visual system injury after TBI by using CB2 inverse agonists such as SMM-189, which appear to target microglia and bias them away from the pro-inflammatory M1 state, toward the protective M2 state.

Long-term effects of mild traumatic brain injuries to oculomotor tracking performances and reaction times to simple environmental stimuli

Understanding the long-term effects of concussive events remains a challenge for the development of modern medical practices and the prevention of recurrent traumas. In this study, we utilized indices of oculomotor performance and the ability to react to simple environmental stimuli to assess the long-term motor effects of traumatic brain injury in its mildest form (mTBI). We performed analysis of eye movement accuracy, investigated the presence of abnormal eye movements, and quantified time to react to simple environmental stimuli on long-term mTBI survivors. Results indicated the presence of impairments to basic neural functions used to explore and respond to environmental demands long after the occurrence of mTBIs. Specifically, the result revealed the presence of abnormal saccadic eye movements while performing horizontal smooth pursuit, diminished accuracy of primary saccadic horizontal eye movement, and a widespread slower reaction to both visual and auditory stimuli. The methodology used in this study indicated to be potentially useful in aiding future investigations of neural circuitry impaired by mTBI and provide indices of recovery in future clinical trials testing mTBI-related clinical interventions.

Visual problems associated with traumatic brain injury

Traumatic brain injury (TBI) and its associated concussion are major causes of disability and death. All ages can be affected but children, young adults and the elderly are particularly susceptible. A decline in mortality has resulted in many more individuals living with a disability caused by TBI including those affecting vision. This review describes: (1) the major clinical and pathological features of TBI; (2) the visual signs and symptoms associated with the disorder; and (3) discusses the assessment of quality of life and visual rehabilitation of the patient. Defects in primary vision such as visual acuity and visual fields, eye movement including vergence, saccadic and smooth pursuit movements, and in more complex aspects of vision involving visual perception, motion vision ('akinopsia'), and visuo-spatial function have all been reported in TBI. Eye movement dysfunction may be an early sign of TBI. Hence, TBI can result in a variety of visual problems, many patients exhibiting multiple visual defects in combination with a decline in overall health. Patients with chronic dysfunction following TBI may require occupational, vestibular, cognitive and other forms of physical therapy. Such patients may also benefit from visual rehabilitation, including reading-related oculomotor training and the prescribing of spectacles with a variety of tints and prism combinations.

Concussion Alters the Functional Brain Processes of Visual Attention and Working Memory

Millions of North Americans sustain a concussion or a mild traumatic brain injury annually, and are at risk of cognitive, emotional, and physical sequelae. Although functional MRI (fMRI) studies have provided an initial framework for examining functional deficits induced by concussion, particularly working memory and attention, the temporal dynamics underlying these deficits are not well understood. We used magnetoencephalography (MEG), a modality with millisecond temporal resolution, in conjunction with a 1-back visual working memory (VWM) paradigm using scenes from everyday life to characterize spatiotemporal functional differences at specific VWM stages, in adults had had or had not had a recent concussion. MEG source-level differences between groups were determined by whole-brain analyses during encoding and recognition phases. Despite comparable behavioral performance, abnormal hypo- and hyperactivation patterns were found in brain areas involving frontoparietal, ventral occipitotemporal, temporal, and subcortical areas in concussed patients. These patterns and their timing varied as a function of VWM stagewise processing, linked to early attentional control, visuoperceptual scene processing, and VWM maintenance and retrieval processes. Parietal hypoactivation, starting at 60 ms during encoding, was correlated with symptom severity, possibly linked to impaired top-down attentional processing. Hyperactivation in the scene-selective occipitotemporal areas, the medial temporal complex, specifically the right hippocampus and orbitofrontal areas during encoding and/or recognition, lead us to posit inefficient but compensatory visuoperceptual, relational, and retrieval processing. Although injuries sustained after the concussion were considered "mild," these data suggest that they can have prolonged effects on early attentional and VWM processes.

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.

Disruption of Network Synchrony and Cognitive Dysfunction After Traumatic Brain Injury

Traumatic brain injury (TBI) is a heterogeneous disorder with many factors contributing to a spectrum of severity, leading to cognitive dysfunction that may last for many years after injury. Injury to axons in the white matter, which are preferentially vulnerable to biomechanical forces, is prevalent in many TBIs. Unlike focal injury to a discrete brain region, axonal injury is fundamentally an injury to the substrate by which networks of the brain communicate with one another. The brain is envisioned as a series of dynamic, interconnected networks that communicate via long axonal conduits termed the "connectome". Ensembles of neurons communicate via these pathways and encode information within and between brain regions in ways that are timing dependent. Our central hypothesis is that traumatic injury to axons may disrupt the exquisite timing of neuronal communication within and between brain networks, and that this may underlie aspects of post-TBI cognitive dysfunction. With a better understanding of how highly interconnected networks of neurons communicate with one another in important cognitive regions such as the limbic system, and how disruption of this communication occurs during injury, we can identify new therapeutic targets to restore lost function. This requires the tools of systems neuroscience, including electrophysiological analysis of ensemble neuronal activity and circuitry changes in awake animals after TBI, as well as computational modeling of the effects of TBI on these networks. As more is revealed about how inter-regional neuronal interactions are disrupted, treatments directly targeting these dysfunctional pathways using neuromodulation can be developed.

Differential susceptibility of cortical and subcortical inhibitory neurons and astrocytes in the long term following diffuse traumatic brain injury

Long-term diffuse traumatic brain injury (dTBI) causes neuronal hyperexcitation in supragranular layers in sensory cortex, likely through reduced inhibition. Other forms of TBI affect inhibitory interneurons in subcortical areas but it is unknown if this occurs in cortex, or in any brain area in dTBI. We investigated dTBI effects on inhibitory neurons and astrocytes in somatosensory and motor cortex, and hippocampus, 8 weeks post-TBI. Brains were labeled with antibodies against calbindin (CB), parvalbumin (PV), calretinin (CR) and neuropeptide Y (NPY), and somatostatin (SOM) and glial fibrillary acidic protein (GFAP), a marker for astrogliosis during neurodegeneration. Despite persistent behavioral deficits in rotarod performance up to the time of brain extraction (TBI = 73.13 ± 5.23% mean ± SEM, Sham = 92.29 ± 5.56%, P < 0.01), motor cortex showed only a significant increase, in NPY neurons in supragranular layers (mean cells/mm² ± SEM, Sham = 16 ± 0.971, TBI = 25 ± 1.51, P = 0.001). In somatosensory cortex, only CR⁺ neurons showed changes, being decreased in supragranular (TBI = 19 ± 1.18, Sham = 25 ± 1.10, P < 0.01) and increased in infragranular (TBI = 28 ± 1.35, Sham = 24 ± 1.07, P < 0.05) layers. Heterogeneous changes were seen in hippocampal staining: CB⁺ decreased in dentate gyrus (TBI = 2 ± 0.382, Sham = 4 ± 0.383, P < 0.01), PV⁺ increased in CA1 (TBI = 39 ± 1.26, Sham = 33 ± 1.69, P < 0.05) and CA2/3 (TBI = 26 ± 2.10, Sham = 20 ± 1.49, P < 0.05), and CR⁺ decreased in CA1 (TBI = 10 ± 1.02, Sham = 14 ± 1.14, P < 0.05). Astrogliosis significantly increased in corpus callosum (TBI = 6.7 ± 0.69, Sham = 2.5 ± 0.38; P = 0.007). While dTBI effects on inhibitory neurons appear region- and type-specific, a common feature in all cases of decrease was that changes occurred in dendrite targeting interneurons involved in neuronal integration. J. Comp. Neurol. 524:3530-3560, 2016. © 2016 Wiley Periodicals, Inc.

Characterizing common workplace communication skills for disorders associated with traumatic brain injury: A qualitative study

BACKGROUND

Interpersonal skill deficits are the primary reason for workplace separation after traumatic brain injury (TBI). Communication is integral to interpersonal skills, but workplace communication demands are inadequately described in the rehabilitation literature.

OBJECTIVE

This study describes inter-stakeholder examples of workplace communication behaviors for a level of employment to which people with TBI commonly attempt to return.

METHODS

Setting: Mid-level workplaces.Design: Semi-structured interviews were audio recorded, transcribed verbatim, then analyzed using thematic content analysis. Findings were linked to common communication deficits in persons with TBI.Participants: A volunteer sample of twenty healthy individuals employed in the mid-level workplaces, ten employees and ten supervisors.Main Outcome Measure(s): Taxonomy of communication skill deficits common in persons with TBI and associated with mid-level workplaces.

RESULTS

Interviews revealed seven communication-related skills associated with mid-level employment: 1) spoken language processing; 2) verbal memory; 3) reading and writing; 4) verbal reasoning; 5) expressive pragmatics; 6) multi-tasking; and 7) social cognition.

CONCLUSION

Workers and supervisors from an assortment of mid-level jobs with differing job contents all identified similarly common and important cross-occupational communication-related skills. Findings provide a preliminary guide to assess and treat communication skills for patients who have work re-entry as a goal.

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.

Progesterone Exacerbates Short-Term Effects of Traumatic Brain Injury on Supragranular Responses in Sensory Cortex and Over-Excites Infragranular Responses in the Long Term

Progesterone (P4) has been suggested as a neuroprotective agent for traumatic brain injury (TBI) because it ameliorates many post-TBI sequelae. We examined the effects of P4 treatment on the short-term (4 days post-TBI) and long-term (8 weeks post-TBI) aftermath on neuronal processing in the rodent sensory cortex of impact acceleration-induced diffuse TBI. We have previously reported that in sensory cortex, diffuse TBI induces a short-term hypoexcitation that is greatest in the supragranular layers and decreases with depth, but a long-term hyperexcitation that is exclusive to the supragranular layers. Now, adult male TBI-treated rats administered P4 showed, in the short term, even greater suppression in neural responses in supragranular layers but a reversal of the TBI-induced suppression in granular and infragranular layers. In long-term TBI there were only inconsistent effects of P4 on the TBI-induced hyperexcitation in supragranular responses but infragranular responses, which were not affected by TBI alone, were elevated by P4 treatment. Intriguingly, the effects in the injured brain were almost identical to P4 effects in the normal brain, as seen in sham control animals treated with P4: in the short term, P4 effects in the normal brain were identical to those exercised in the injured brain and in the long term, P4 effects in the normal brain were rather similar to what was seen in the TBI brain. Overall, these results provide no support for any protective effects of P4 treatment on neuronal encoding in diffuse TBI, and this was reflected in sensorimotor and other behavior tasks also tested here. Additionally, the effects suggest that mechanisms used for P4 effects in the normal brain are also intact in the injured brain.

Traumatic brain injury detection using electrophysiological methods

Measuring neuronal activity with electrophysiological methods may be useful in detecting neurological dysfunctions, such as mild traumatic brain injury (mTBI). This approach may be particularly valuable for rapid detection in at-risk populations including military service members and athletes. Electrophysiological methods, such as quantitative electroencephalography (qEEG) and recording event-related potentials (ERPs) may be promising; however, the field is nascent and significant controversy exists on the efficacy and accuracy of the approaches as diagnostic tools. For example, the specific measures derived from an electroencephalogram (EEG) that are most suitable as markers of dysfunction have not been clearly established. A study was conducted to summarize and evaluate the statistical rigor of evidence on the overall utility of qEEG as an mTBI detection tool. The analysis evaluated qEEG measures/parameters that may be most suitable as fieldable diagnostic tools, identified other types of EEG measures and analysis methods of promise, recommended specific measures and analysis methods for further development as mTBI detection tools, identified research gaps in the field, and recommended future research and development thrust areas. The qEEG study group formed the following conclusions: (1) Individual qEEG measures provide limited diagnostic utility for mTBI. However, many measures can be important features of qEEG discriminant functions, which do show significant promise as mTBI detection tools. (2) ERPs offer utility in mTBI detection. In fact, evidence indicates that ERPs can identify abnormalities in cases where EEGs alone are non-disclosing. (3) The standard mathematical procedures used in the characterization of mTBI EEGs should be expanded to incorporate newer methods of analysis including non-linear dynamical analysis, complexity measures, analysis of causal interactions, graph theory, and information dynamics. (4) Reports of high specificity in qEEG evaluations of TBI must be interpreted with care. High specificities have been reported in carefully constructed clinical studies in which healthy controls were compared against a carefully selected TBI population. The published literature indicates, however, that similar abnormalities in qEEG measures are observed in other neuropsychiatric disorders. While it may be possible to distinguish a clinical patient from a healthy control participant with this technology, these measures are unlikely to discriminate between, for example, major depressive disorder, bipolar disorder, or TBI. The specificities observed in these clinical studies may well be lost in real world clinical practice. (5) The absence of specificity does not preclude clinical utility. The possibility of use as a longitudinal measure of treatment response remains. However, efficacy as a longitudinal clinical measure does require acceptable test-retest reliability. To date, very few test-retest reliability studies have been published with qEEG data obtained from TBI patients or from healthy controls. This is a particular concern because high variability is a known characteristic of the injured central nervous system.

Diffuse traumatic brain injury and the sensory brain

In this review we discuss the consequences to the brain's cortex, specifically to the sensory cortex, of traumatic brain injury. The thesis underlying this approach is that long-term deficits in cognition seen after brain damage in humans are likely underpinned by an impaired cortical processing of the sensory information needed to drive cognition or to be used by cognitive processes to produce a response. We take it here that the impairment to sensory processing does not arise from damage to peripheral sensory systems, but from disordered brain processing of sensory input.

Retinal ganglion cell damage in an experimental rodent model of blast-mediated traumatic brain injury

PURPOSE

To evaluate retina and optic nerve damage following experimental blast injury.

METHODS

Healthy adult mice were exposed to an overpressure blast wave using a custom-built blast chamber. The effects of blast exposure on retina and optic nerve function and structure were evaluated using the pattern electroretinogram (pERG), spectral domain optical coherence tomography (OCT), and the chromatic pupil light reflex.

RESULTS

Assessment of the pupil response to light demonstrated decreased maximum pupil constriction diameter in blast-injured mice using red light or blue light stimuli 24 hours after injury compared with baseline in the eye exposed to direct blast injury. A decrease in the pupil light reflex was not observed chronically following blast exposure. We observed a biphasic pERG decrease with the acute injury recovering by 24 hours postblast and the chronic injury appearing at 4 months postblast injury. Furthermore, at 3 months following injury, a significant decrease in the retinal nerve fiber layer was observed using OCT compared with controls. Histologic analysis of the retina and optic nerve revealed punctate regions of reduced cellularity in the ganglion cell layer and damage to optic nerves. Additionally, a significant upregulation of proteins associated with oxidative stress was observed acutely following blast exposure compared with control mice.

CONCLUSIONS

Our study demonstrates that decrements in retinal ganglion cell responses can be detected after blast injury using noninvasive functional and structural tests. These objective responses may serve as surrogate tests for higher CNS functions following traumatic brain injury that are difficult to quantify.

Cortical hypoexcitation defines neuronal responses in the immediate aftermath of traumatic brain injury

Traumatic brain injury (TBI) from a blow to the head is often associated with complex patterns of brain abnormalities that accompany deficits in cognitive and motor function. Previously we reported that a long-term consequence of TBI, induced with a closed-head injury method modelling human car and sporting accidents, is neuronal hyper-excitation in the rat sensory barrel cortex that receives tactile input from the face whiskers. Hyper-excitation occurred only in supra-granular layers and was stronger to complex than simple stimuli. We now examine changes in the immediate aftermath of TBI induced with same injury method. At 24 hours post-trauma significant sensorimotor deficits were observed and characterisation of the cortical population neuronal responses at that time revealed a depth-dependent suppression of neuronal responses, with reduced responses from supragranular layers through to input layer IV, but not in infragranular layers. In addition, increased spontaneous firing rate was recorded in cortical layers IV and V. We postulate that this early post-injury suppression of cortical processing of sensory input accounts for immediate post-trauma sensory morbidity and sets into train events that resolve into long-term cortical hyper-excitability in upper sensory cortex layers that may account for long-term sensory hyper-sensitivity in humans with TBI.

Growth hormone deficiency due to sports-related head trauma is associated with impaired cognitive performance in amateur boxers and kickboxers as revealed by P300 auditory event-related potentials

OBJECTIVES

It has been recently reported that boxing and kickboxing may cause pituitary dysfunction, GH deficiency in particular. The strong link between poor cognitive performance and GH deficiency due to causes other than head trauma and the improvement of cognitive function after GH replacement therapy have been previously shown. P300 auditory event-related potential (ERP) measure is widely used to evaluate cognitive performance. In this study, we investigated the relation between the GH-IGF-I axis and cognitive performance in boxers and kickboxers.

DESIGN AND PATIENTS

Forty-one actively competing or retired male boxers (n: 27) and kickboxers (n: 14) with a mean age of 29·04 ± 9·30 year and 14 age- and education-matched healthy male controls were included in the study. For neuropsychological tests, the mini-mental state examination (MMSE) and Quality of Life Assessment of GH Deficiency in Adults (QoL-AGHDA) questionnaires were administered. Moreover, cognitive performance was evaluated according to P300 ERPs.

RESULTS

Nine of 41 (21·9%) athletes had GH deficiency. P300 amplitudes were lower at all electrode sites in the GH-deficient group than in controls, and the differences were statistically significant at Fz and Oz electrode sites (P < 0·05). When GH-deficient athletes were compared with GH-sufficient athletes, the P300 amplitudes were lower at all electrode sites in the GH-deficient group; these differences were statistically significant at Fz, Pz and Cz electrode sites (P < 0·05). In all athletes, there were significant negative correlations between IGF-I levels vs P300 latencies, and there were significant positive correlations between IGF-I levels vs P300 amplitudes (P < 0·05).

CONCLUSION

This study provides the first electrophysiological evidence for the close relation between the P300 ERPs and the GH-IGF-I axis in boxers and kickboxers.

Sensory cortex underpinnings of traumatic brain injury deficits

Traumatic brain injury (TBI) can result in persistent sensorimotor and cognitive deficits including long-term altered sensory processing. The few animal models of sensory cortical processing effects of TBI have been limited to examination of effects immediately after TBI and only in some layers of cortex. We have now used the rat whisker tactile system and the cortex processing whisker-derived input to provide a highly detailed description of TBI-induced long-term changes in neuronal responses across the entire columnar network in primary sensory cortex. Brain injury (n = 19) was induced using an impact acceleration method and sham controls received surgery only (n = 15). Animals were tested in a range of sensorimotor behaviour tasks prior to and up to 6 weeks post-injury when there were still significant sensorimotor behaviour deficits. At 8–10 weeks post-trauma, in terminal experiments, extracellular recordings were obtained from barrel cortex neurons in response to whisker motion, including motion that mimicked whisker motion observed in awake animals undertaking different tasks. In cortex, there were lamina-specific neuronal response alterations that appeared to reflect local circuit changes. Hyper-excitation was found only in supragranular layers involved in intra-areal processing and long-range integration, and only for stimulation with complex, naturalistic whisker motion patterns and not for stimulation with simple trapezoidal whisker motion. Thus TBI induces long-term directional changes in integrative sensory cortical layers that depend on the complexity of the incoming sensory information. The nature of these changes allow predictions as to what types of sensory processes may be affected in TBI and contribute to post-trauma sensorimotor deficits.

Avaliação eletrofisiológica da audição em indivíduos após traumatismo cranioencefálico

OBJETIVO: caracterizar o potencial evocado auditivo de tronco encefálico e de longa latência em pacientes pós traumatismo cranioencefálico, comparando-os com indivíduos normais. MÉTODO: estudo clínico transversal realizado com 20 indivíduos audiologicamente normais divididos em dois grupos pareados por idade e sexo: a) 10 indivíduos que sofreram traumatismo cranioencefálico (grupo pesquisa); b) 10 indivíduos sem qualquer tipo de alteração neurológica (grupo controle). Foram submetidos à avaliação audiológica básica, ao potencial evocado auditivo de tronco encefálico e ao potencial evocado auditivo de longa latência (P300). RESULTADOS: observou-se no potencial evocado auditivo de tronco encefálico, latências absolutas das ondas I, III e V e intervalo interpico I-III mais prolongados no grupo pesquisa do que no grupo controle, sendo estatisticamente significante para as latências absolutas das ondas I e III à direita e para a onda III e intervalo interpico I-III à esquerda. A amplitude das ondas I, III e V na orelha direita e das ondas III e V na orelha esquerda foram maiores no grupo controle. Em relação ao P300, o grupo pesquisa apresentou maior latência e menor amplitude em ambas as orelhas, sem significância estatística, quando comparado ao grupo controle. CONCLUSÃO: indivíduos que sofreram traumatismo cranioencefálico apresentam alterações no potencial evocado auditivo de tronco encefálico e não apresentam diferenças significantes no potencial evocado auditivo de longa latência (P300) quando comparados a indivíduos sem lesões cerebrais.

Visual attention study in youth with spastic cerebral palsy using the event-related potential method

Youth with mild spastic cerebral palsy (n = 14) and a peer control group were compared on an oddball paradigm. Here, visual stimuli were presented with low and high probability and participants were instructed to count in silence the number of rare stimuli. The infrequent stimulus typically elicits an enhanced frontal central N2 and a centroparietal P300 event-related brain potential, reflecting orientation and evaluation of stimulus novelty. No differences in latency and amplitude of the N2-P300 complex were found between the 2 groups, indicating that some fundamental attention processes are intact in youth with mild spastic cerebral palsy.

Electrophysiological assessments of cognition and sensory processing in TBI: applications for diagnosis, prognosis and rehabilitation

Traumatic brain injuries are often associated with damage to sensory and cognitive processing pathways. Because evoked potentials (EPs) and event-related potentials (ERPs) are generated by neuronal activity, they are useful for assessing the integrity of neural processing capabilities in patients with traumatic brain injury (TBI). This review of somatosensory, auditory and visual ERPs in assessments of TBI patients is provided with the hope that it will be of interest to clinicians and researchers who conduct or interpret electrophysiological evaluations of this population. Because this article reviews ERP studies conducted in three different sensory modalities, involving patients with a wide range of TBI severity ratings and circumstances, it is difficult to provide a coherent summary of findings. However, some general trends emerge that give rise to the following observations and recommendations: 1) bilateral absence of somatosensory evoked potentials (SEPs) is often associated with poor clinical prognosis and outcome; 2) the presence of normal ERPs does not guarantee favorable outcome; 3) ERPs evoked by a variety of sensory stimuli should be used to evaluate TBI patients, especially those with severe injuries; 4) time since onset of injury should be taken into account when conducting ERP evaluations of TBI patients or interpreting results; 5) because sensory deficits (e.g., vision impairment or hearing loss) affect ERP results, tests of peripheral sensory integrity should be conducted in conjunction with ERP recordings; and 6) patients' state of consciousness, physical and cognitive abilities to respond and follow directions should be considered when conducting or interpreting ERP evaluations.

Reduced fractional anisotropy does not change the shape of the hemodynamic response in survivors of severe traumatic brain injury

The hemodynamic response (HDR) function is the basis for standard functional magnetic resonance imaging (fMRI) analysis. HDR is influenced by white matter inflammation. Traumatic brain injury (TBI) is frequently accompanied by diffuse white matter injury, but the effect of this on the HDR has not been investigated. The aims of the present study were to describe the HDR in visual cortex and examine its relationship with the microstructure of the optic radiation in severe TBI survivors and controls. Ten severe TBI survivors without visual impairments, but with known diffuse axonal injury, and 9 matched controls underwent diffusion tensor imaging (DTI) and fMRI. From the fMRI time series obtained during brief randomized visual stimuli, blood oxygenation level-dependent (BOLD) signal changes for each subject were estimated in V1, and group HDR curves were produced. Standard between-group analysis of BOLD activation in V1 + V2 was performed. For each individual the optic radiations were identified and fractional anisotropy (FA) plus mean apparent diffusion coefficient (ADC(mean)) values for these tracts were calculated. Group HDR curves from the visual cortex were fully transposable between TBI survivors and controls, despite a significant reduction in FA in the optic radiation in TBI survivors. A significant correlation between BOLD signal in the visual cortex and FA values in the optical tract was present in controls, but not in TBI survivors. Between-group comparisons showed that TBI survivors had increased areas of activation in V1 and V2. The HDR appears to be intact in traumatic white matter damage, supporting the validity of using standard fMRI methodology to study neuroplasticity in TBI.

Simultaneous measurement of perceptual and motor cortical potentials: implications for assessing information processing in traumatic brain injury

OBJECTIVE

Psychomotor slowing is a common manifestation of traumatic brain injury. Previous electrophysiological studies of traumatic brain injury have focused on abnormal attentional and perceptual responses to incoming stimuli. We hypothesize that traumatic brain injury is also associated with abnormal cortical components of motor execution.

DESIGN

To test this hypothesis, we analyzed event-related potentials of 22 subjects (11 with a history of severe traumatic brain injury and 11 age-matched healthy subjects) during oddball discrimination tasks. In addition to the usual stimulus-locked averaging of electrophysiological data to reveal cognitive components, such as the P300, we also analyzed subjects' response-locked data to reveal motor potential waveforms. To focus on generalized effects across modality, analyses were performed on composite measures from both auditory and visual event-related potentials.

RESULTS

(1) Traumatic brain injury subjects had abnormal P300 responses (with reduced amplitude and prolonged latency) in both sensory modalities. (2) Traumatic brain injury subjects' motor potential waveforms showed significantly reduced amplitude in both sensory modalities. (3) Abnormalities in P300 latency, amplitude, and motor potential amplitude (effect sizes = 1.2-1.5 SD) were greater than behavioral slowing, as measured by reaction times (0.7 SD). (4) P300 latency and motor potential amplitude together accounted for much of the reaction time prolongation (r = 0.73).

CONCLUSIONS

This study demonstrates the value of concurrently analyzing stimulus-locked and response-locked event-related potential data to evaluate cortical components of perceptual and motor processing. The present findings indicate that patients with traumatic brain injury have impairments in both the perceptual interpretation of incoming stimuli and the execution of motor responses and that both abnormalities contribute to psychomotor slowing in patients with traumatic brain injury.

Reductions in qEEG slowing over 1 year and after treatment with Cerebrolysin in patients with moderate-severe traumatic brain injury

Changes in quantitative EEG (qEEG) recordings over a 1-year period and the effects of Cerebrolysin (Cere) on qEEG slowing and cognitive performance were investigated in postacute moderate-severe traumatic brain injury (TBI) patients. Time-related changes in qEEG activity frequency bands (increases of alpha and beta, and reductions of theta and delta relative power) and in qEEG slowing (reduction of EEG power ratio) were statistically significant in patients with a disease progress of less than 2 years at baseline, but not in those patients having a longer disease progress time. Slowing of qEEG activity was also found to be significantly reduced in TBI patients after 1 month of treatment with Cere and 3 months later. Therefore, Cere seems to accelerate the time-related reduction of qEEG slowing occurring in untreated patients. The decrease of qEEG slowing induced by Cere correlated with the improvement of attention and working memory. Results of this exploratory study suggest that Cere might improve the functional recovery after brain injury and encourage the conduction of further controlled clinical trials.

The Effects of Increasing Stimulus Complexity in Event-Related Potentials and Reaction Time Testing: Clinical Applications in Evaluating Patients with Traumatic Brain Injury

This study compared the effectiveness of P300 event related potentials (ERPs) and reaction time (RT) in discriminating patients with traumatic brain injury (TBI) from healthy control subjects. In particular, we examined how the use of more complex, ecologically relevant stimuli may affect the clinical utility of these tasks. We also evaluated how length of posttraumatic amnesia (PTA) and loss of consciousness (LOC) related to P300 and RT measures in our patient sample. There were 22 subjects (11 patients with TBI and 11 age-matched healthy control subjects). Four stimulus detection procedures were used: two using simple, conventional stimuli (auditory tone discrimination, AT; visual color discrimination, VC), and two using complex, ecologically relevant stimuli in the auditory and visual modalities (auditory word category discrimination, AWC; visual facial affect discrimination, VFA). Our results showed that RT measures were more effective in identifying TBI patients when complex stimuli were used (AWC and VFA). On the other hand, ERP measures were more effective in identifying TBI patients when simple stimuli were used (AT and VC). We also found a remarkably high correlation between duration of PTA and P300 amplitude.

Temporal Stability of Auditory Event-Related Potentials in Healthy Individuals and Patients With Traumatic Brain Injury

Historically, cognitive event-related potentials (ERPs) have received limited acceptance for clinical use due to lack of evidence for their reliability. However, recent advances in computer technology and artifact rejection methods have greatly enhanced the fidelity of ERP measurements. The present study examined the test-retest reliability of ERP measurement by using current data processing methods. We assessed the temporal stability of the most commonly used ERP paradigm, auditory pure-tone "odd ball" detection, and compared it with other commonly used clinical measures reported in the literature. Auditory ERPs were collected in 19 healthy subjects and 7 patients with traumatic brain injury at two time points, 2 days to 2 months apart. Test-retest reliability was calculated for four ERP components: N1, MMN (mismatch negativity), P3, and N4. In healthy subjects, temporal stabilities of these four commonly studied ERP components' amplitude measurements were moderate to high, with intraclass correlations ranging from 0.6 to 0.8. In contrast, in patients with traumatic brain injury, ERPs were stable only for the N1 component (intraclass correlation = 0.7).

Characteristics of cognitive function in patients after traumatic brain injury assessed by visual and auditory event-related potentials

OBJECTIVE

Using auditory and visual stimuli including facial affective stimuli, we analyzed the P300 components of event-related potentials (ERPs) in patients after traumatic brain injury (TBI) to assess their cognitive characteristics.

DESIGN

Twenty TBI patients and 32 age-matched control subjects were recruited. Using conventional oddball paradigms, visual ERPs were recorded using images of crying and smiling babies as visual stimuli. Auditory ERPs were obtained using 2-kHz tones as stimuli without affective stimuli. The peak amplitude and latency for P300, and the latency for N200, were recorded.

RESULTS

: In visual ERPs, the P300 amplitudes were significantly smaller in patients than in controls for the crying baby, but the amplitudes were similar between groups for the smiling baby. Controls showed smaller P300 amplitudes for the smiling baby than for the crying baby, but patients showed no difference. In patients, the P300 latency for both smiling and crying babies was longer than in the controls. Patients' auditory ERPs showed smaller P300 amplitudes but similar P300 latencies compared with controls. The N200 latency in patients was significantly longer than in controls only for the crying baby.

CONCLUSIONS

Visual ERPs are a potentially useful marker for evaluating cognitive dysfunction in patients after TBI.

Prognostic value of evoked and event-related potentials in moderate to severe brain injury

Clinicians are often expected to project patients' clinical outcomes to allow effective planning for future care. This can be a challenge in patients with moderate to severe traumatic brain injury (TBI) who are often unable to participate reliably in clinical evaluations. With recent advances in computer instrumentation and signal processing, evoked potentials and event-related potentials show increasing promise as powerful tools for prognosticating the trajectory of recovery and ultimate outcome from the TBI. Short- and middle-latency evoked potentials can now effectively predict coma outcomes in patients with acute TBI. Long-latency event-related potential components hold promise in predicting recovery of higher order cognitive abilities.