ERP indices of resource allocation difficulties in mild head injury

Impaired auditory processing and neural representation of speech in noise among symptomatic post-concussion adults

Background: The purpose of the study was to examine auditory event-related potential (AERP) evidence of changes in earlier and later stages of auditory processing in individuals with long-term post-concussion problems compared to healthy controls, with a secondary aim of comparing AERPs by functional auditory behavioral outcomes. Methods: P1-N1-P2 complex and P300 components recorded to speech in quiet and background noise conditions were completed in individuals with ongoing post-concussion symptoms following mTBI and healthy controls. AERPs were also examined between sub-groups with normal or impaired auditory processing by behavioral tests. Results: Group differences were present for later stages of auditory processing (P300). Earlier components did not significantly differ by group overall but were more affected by noise in the mTBI group. P2 amplitude in noise differed between mTBI sub-groups with normal or impaired auditory processing. Conclusion: AERPs revealed differences between healthy controls and those with chronic post-concussion symptoms following mTBI at a later stage of auditory processing (P300). Neural processing at the earlier stage (P1-N1-P2) was more affected by noise in the mTBI group. Preliminary evidence suggested that it may be only the proportion of individuals with functional evidence of central auditory dysfunction with changes in AERPs at earlier stages of processing.

Longitudinal study of a NoGo-P3 event-related potential component following mild traumatic brain injury in adults

BACKGROUND

Event-related potentials have repeatedly revealed electrophysiological markers of cognitive dysfunction associated with Mild Traumatic Brain Injury (MTBI) and may represent a sensitive tool to guide cognitive rehabilitative interventions. We previously found patients with symptomatic MTBI characterized by smaller P300 (or P3) wave amplitudes in a NoGo-P3 subcomponent in the acute phase of the injury. The goal of this longitudinal study was to investigate whether this early NoGo-P3 subcomponent differs over time in symptomatic MTBI patients and healthy controls.

METHODS

We included adults with a diagnosis of MTBI and individually matched healthy controls tested at 1 week, 3 months, and 1 year after the MTBI. Symptoms were assessed by the Rivermead Post-Concussion Symptoms Questionnaire. NoGo-P3 was collected by using a cued Go/NoGo task and the relevant subcomponent was extracted by independent component analysis.

RESULTS

Among 53 adults with a diagnosis of MTBI and 53 controls, we included 35 with symptomatic MTBI and 35 matched healthy controls (18 females each group; mean age 34.06±13.15 and 34.26±12.98 years). Amplitudes for the early NoGo-P3 subcomponent were lower for symptomatic MTBI patients than controls (P<0.05) at 1 week post-injury. Furthermore, mixed ANOVA revealed a significant time by group interaction (P<0.05), so the effect of time differed for symptomatic MTBI patients and healthy controls. The amplitudes for MTBI patients normalized from 1 week to 3 months post-injury and were comparable to those of controls from 3 months to 1 year post-injury. However, amplitudes for 3 MTBI patients with particularly severe complaints 1 year post-injury did not normalize and were lower than those for the remaining MTBI sample (P<0.05).

CONCLUSIONS

Selected event-related potentials can be used as a sensitive and objective tool to illustrate the cognitive consequences of and recovery after MTBI.

Attentional Capacity Limits Gap Detection during Concurrent Sound Segregation

Detecting a brief silent interval (i.e., a gap) is more difficult when listeners perceive two concurrent sounds rather than one in a sound containing a mistuned harmonic in otherwise in-tune harmonics. This impairment in gap detection may reflect the interaction of low-level encoding or the division of attention between two sound objects, both of which could interfere with signal detection. To distinguish between these two alternatives, we compared ERPs during active and passive listening with complex harmonic tones that could include a gap, a mistuned harmonic, both features, or neither. During active listening, participants indicated whether they heard a gap irrespective of mistuning. During passive listening, participants watched a subtitled muted movie of their choice while the same sounds were presented. Gap detection was impaired when the complex sounds included a mistuned harmonic that popped out as a separate object. The ERP analysis revealed an early gap-related activity that was little affected by mistuning during the active or passive listening condition. However, during active listening, there was a marked decrease in the late positive wave that was thought to index attention and response-related processes. These results suggest that the limitation in detecting the gap is related to attentional processing, possibly divided attention induced by the concurrent sound objects, rather than deficits in preattentional sensory encoding.

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.

An exploratory analysis of Go/Nogo event-related potentials in major depression and depression following traumatic brain injury

Rates of major depressive disorder (MDD) following traumatic brain injury (TBI) are estimated to be between 20% and 45%, a higher prevalence than that seen in the general population. These increased rates may be due to specific changes in brain function following TBI. Event related potentials (ERPs) are well suited for measuring the electrophysiological differences between groups in areas of cognitive processing impaired in both MDD and TBI, such as response inhibition. The current study presented an emotional Go/Nogo task (with schematic emotional faces as stimuli) to participants with TBI, participants with MDD, and participants with both TBI and MDD (TBI-MDD). Topographical distribution of activity and global field power comparisons were made across stimulus-locked epochs between these groups and healthy controls. The results indicated that ERPs were not altered by TBI alone. Both MDD and TBI-MDD groups showed similar alterations in topographical distribution and global field power in the N2 window, as well as late epoch alterations. The MDD and TBI-MDD groups showed significantly less fronto-central negativity during the N2 window in Nogo trials compared with the control group. The MDD and TBI-MDD groups also showed significantly less global field power in Nogo trials than Go trials during the N2 window while the control group showed the opposite pattern. The MDD and TBI-MDD groups showed no mood-congruent bias in behavioural or ERP measures. The results suggest that TBI-MDD displays similar electrophysiological changes to those found in the MDD group without TBI.

Enhanced attention capture by emotional stimuli in mild traumatic brain injury

Mild traumatic brain injury (mTBI) may be associated with compromised executive functioning and altered emotional reactivity. Despite frequent affective and cognitive symptoms in mTBI, objective evidence for brain dysfunction is often lacking. Previously we have reported compromised performance in symptomatic mTBI patients in an executive reaction time (RT) test, a computer-based RT test engaging several executive functions simultaneously. Here, we investigated the cognitive control processes in mTBI in context of threat-related stimuli. We used behavioral measures and event-related potentials (ERP) to investigate attentional capture by task-relevant and task-irrelevant emotional stimuli during a Go-NoGo task requiring cognitive control. We also assessed subjective cognitive, somatic, and emotional symptoms with questionnaires. Twenty-seven subjects with previous mTBI and 17 controls with previous ankle injury participated in the study over 9 months post-injury. Electroencephalogram (EEG) was recorded while patients performed a modified executive RT-test. N2-P3 ERP component was used as a general measure of allocated attentional and executive processing resources. Although at the time of the testing, the mTBI and the control groups did not differ in symptom endorsement, mTBI patients reported having had more emotional symptoms overall since the injury than controls. The overall RT-test performance levels did not differ between groups. However, when threat-related emotional stimuli were used as Go-signals, the mTBI group was faster than the control group. In comparison to neutral stimuli, threat-related stimuli were associated with increased N2-P3 amplitude in all conditions. This threat-related enhancement of the N2-P3 complex was greater in mTBI patients than in controls in response to Go signals and NoGo signals, independent of relevance. We conclude that mTBI may be associated with enhanced attentional and executive resource allocation to threat-related stimuli. Along with behavioral evidence for enhanced attention allocation to threat stimuli, increased brain responses to threat were observed in mTBI. Enhanced attention capture by threat-related emotional stimuli may reflect inefficient top-down control of bottom-up influences of emotion, and might contribute to affective symptoms in mTBI.

ERP correlates of malingered executive dysfunction

Assessment of malingering has become an integral part of many neuropsychological evaluations, particularly in forensic settings. However, traditional malingering measures are known to be vulnerable to both manipulation and coaching. Consequently, recent research has attempted to identify physiological indices of cognitive functioning that are less susceptible to overt manipulation. While prior studies have explored the validity of physiological assessment of memory deficits, this study evaluates the effectiveness of a physiological measure of executive functioning. This study used EEG recording in conjunction with a three-stimulus oddball design to compare neural responses in simulated malingerers feigning cognitive deficits associated with traumatic brain injury (TBI) and controls. Specifically, the study explored the efficacy of an event-related potential (ERP) known as P3a, which is believed to be an index of frontal lobe executive processes, specifically the attentional orienting response. The results of this study demonstrated that simulated malingerers did not produce a P3a response that was significantly different from control participants. Furthermore, the P3a in simulated malingerers did not demonstrate any of the properties reported in prior studies with TBI patients. Not only were malingerers unable to produce a significant change in their basic orienting response, but the very process of attempting to employ additional strategies to appear impaired produced other physiological markers of deception. Therefore, the P3a component appeared to be unaffected by an individual's motivation or overt performance, which suggests that it may have potential for development as a physiological measure for differentiating between malingerers and those with genuine TBI.

Decreased prefrontal cortex activity in mild traumatic brain injury during performance of an auditory oddball task

Up to one-third of patients with mild traumatic brain injury (TBI) demonstrate persistent cognitive deficits in the 'executive' function domain. Mild TBI patients have shown prefrontal cortex activity deficits during the performance of executive tasks requiring active information maintenance and manipulation. However, it is unclear whether these deficits are related to the executive processes themselves, or to the degree of mental effort. To determine whether prefrontal deficits also would be found during less effortful forms of executive ability, fMRI images were obtained on 31 mild TBI patients and 31 control participants during three-stimulus auditory oddball task performance. Although patients and controls had similar topographical patterns of brain activity, region-of-interest analysis revealed significantly decreased activity in right dorsolateral prefrontal cortex for mild TBI patients during target stimulus detection. Between-group analyses found evidence for potential compensatory brain activity during target detection and default-mode network dysfunction only during the detection of novel stimuli.

Electrophysiological abnormalities in well functioning multiple concussed athletes

OBJECTIVE

The present study was aimed at characterizing the short- and long-term effects of multiple concussions using an electrophysiological approach.

METHOD

Participants for this study were recruited from college football teams. They included athletes who never sustained concussions compared to two groups of asymptomatic multiple concussed athletes, one that sustained their last concussion within the year and the other more than 2 years prior to testing. All participants were submitted to an auditory three-tone Oddball paradigm while event-related potentials (ERP) were recorded.

RESULTS

Results from ERP recordings reveal significantly reduced P3a and P3b amplitudes in the recent concussed group in the three-tone task compared to control athletes. In contrast, athletes who sustained their concussions more than 2 years prior to testing had equivalent P3a and P3b amplitude to that of controls.

CONCLUSION

These findings suggest that, despite functioning normally in their daily lives, concussed athletes still show subtle neuronal changes in information processing. Thus, the persistence of sub-clinical abnormalities on ERP components despite normal overt functioning may indicate sub-optimal compensation in multiple concussed athletes and leave them vulnerable to subsequent concussions.

Long-term electrophysiological changes in athletes with a history of multiple concussions

PRIMARY OBJECTIVE

This event-related potentials study investigated the long-term effects associated with a history of one or multiple concussions on the N2pc and P3 components using a visual search oddball paradigm.

METHODS AND PROCEDURE

A total of 47 university football players were assigned to three experimental groups based on prior concussion history: Athletes with a history of one concussion (single-concussion group); Athletes with two or more concussions (multi-concussion group); non-concussed athletic controls. The average post-concussion period was 31 months for athletes in the multi-concussion group and 59 months for the single-concussion group.

RESULTS

This study found significantly suppressed P3 amplitude in the multi-concussed athletes group compared to the single-concussion and non-concussed athletes even when using the time since the latest concussion as a covariate.

CONCLUSION

This finding suggests that the multi-concussed athletes group showed long-lasting P3 amplitude suppression when compared with single-concussion or non-concussed athletes despite equivalent neuropsychological test scores and post-concussion symptoms self-reports. This pattern of results is important because it shows that 'old' concussions do not cause general or ubiquitous electrophysiological suppression. The specificity of the long-term effects of previous concussions to the P3, along with an intact N2pc response, suggests that further work may allow one to pinpoint the cognitive system that is specifically affected by multiple concussions.

Mild traumatic brain injury and its sequelae: characterisation of divided attention deficits

Deficits in divided attention occur after a mild traumatic brain injury (MTBI) but many extant tasks lack sensitivity for detecting subtle cognitive difficulties. We use the Test d'Attention Partagee Informatise (TAPI), a novel dual-task paradigm, to investigate the impact of MTBI on the ability to divide attention between two stimuli sources. Individuals with MTBI (n=37) were evaluated within the first week following head trauma and at three months post-injury. A healthy control (HC) group (n=79) was also assessed. The primary outcome was reaction time and there were three different conditions that included visual target detection and auditory digit span tasks. Analyses utilised repeated measures ANOVA and ANCOVA models that adjusted for relevant variables including post-concussive and affective symptoms. Results indicated that at both baseline and follow-up, the MTBI group had significantly slower reaction time than the HC group. Also, both the MTBI and HC groups had slower reaction times as participants progressed through each of the more challenging TAPI conditions. This study supports the usefulness of this novel instrument and allows clinicians and researchers to assess for subtle divided attention deficits that may persist in those with MTBI even three months post-injury.

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.

Closed head injury-related information processing deficits: An event-related potential analysis

Event-related potentials (ERPs) can elucidate aspects of sensory and cognitive processing that have been compromised due to closed head injury. We present the results of two investigations, one previously unreported, in which we used ERPs to evaluate information processing in head-injury survivors. In the first study, we used visual and auditory reaction time tasks differing in attentional demands to assess processing after head trauma. We found numerous changes in auditory processing in survivors: longer reaction times (but normal accuracy), longer N200 and P300 latencies, and reduced N100 and N200 amplitudes. In contrast, on visual tasks, only reduced N200 amplitude distinguished survivors and controls. To increase attentional demands, in a second study, we administered the continuous performance test (CPT). Survivors performed with lower accuracy than controls on visual and auditory tasks, and their ERPs were characterized by smaller visual and auditory N200s and P300s and smaller auditory N100s. We also present a synthesis, derived from a review of the literature, of closed head-injury effects on ERPs. Our own findings are in agreement with that synthesis. Namely, cognitive ERP components are more sensitive than sensory components to the effects of trauma. Specifically, in survivors, the amplitudes of N200 and P300 are often reduced, and their latencies prolonged. In general, as compared with visual ERPs, auditory ERPs may be more susceptible to the effects of closed head injury, suggesting that the auditory processing system is more vulnerable than the visual system. We conclude by discussing the potential use of ERPs to monitor clinical course and recovery in survivors of closed head injury.

Attention to affective pictures in closed head injury: event-related brain potentials and cardiac responses

We examined whether closed head injury patients show altered patterns of selective attention to stimulus categories that naturally evoke differential responses in healthy people. Self-reported rating and electrophysiological (event-related potentials [ERPs], heart rate [HR]) responses to affective pictures were studied in patients with mild head injury (n = 20; CT/MRI negative), in patients with predominantly frontal brain lesions (n = 12; CT/MRI confirmed), and in healthy controls (n = 20). Affective valence similarly modulated HR and ERP responses in all groups, but group differences occurred that were independent of picture valence. The attenuation of P3-slow wave amplitudes in the mild head injury group indicates a reduction in the engagement of attentional resources to the task. In contrast, the general enhancement of ERP amplitudes at occipital sites in the group with primarily frontal brain injury may reflect disinhibition of input at sensory receptive areas, possibly due to a deficit in top-down modulation performed by anterior control systems.

Personality assessment without borders: adaptation of the MMPI-2 across cultures

In contemporary psychology, personality assessment knows few national or cultural boundaries. Psychological tests developed in one country are often translated and adapted into cultures that might appear to be greatly different from the country of origin. In this article, I address the factors that are important to international test adaptation and examine problems that can adversely affect cross-cultural test research programs. I address qualities important for verifying the accuracy and adequacy of cross-cultural assessment. I review the extensive adaptation of the MMPI (Hathaway & McKinley, 1940) and MMPI-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989), the most frequently used personality measure. I highlight several contemporary research trends in international personality assessment.

Effects of auditory stimulus intensity and hearing threshold on the relationship among P300, age, and cognitive function

OBJECTIVE

Although P300 is regarded as cognitive or endogenous, studies have demonstrated that stimulus intensity influences the component. To isolate effects of hearing from cognition, two experiments were designed to compare the effects of variation in stimulus intensities with naturally occurring differences in hearing thresholds.

METHODS

In experiment 1, 18 participants were tested with 5 auditory oddball event-related potential (ERP) paradigms with different intensities. In experiment 2, an auditory oddball ERP task was completed by 3 groups of participants with different hearing thresholds (n=57). P300 was then correlated with block design and matrices from Wechsler's abbreviated scale of intelligence.

RESULTS

At Cz and Pz, manipulation of intensity had less effect on P300 than the observed differences between groups with different hearing thresholds. At Fz, however, the effect of manipulations of stimulus intensity was greater than the effect of naturally occurring differences in hearing thresholds. P300 still correlated in predicted directions with cognitive tests after correcting for the estimated effect of differences in hearing.

CONCLUSIONS

The results indicate that P300 is an index of cognitive function even when the relationship is corrected for perceptual differences, at least at posterior scalp areas.

Event-related potential assessment of information processing after closed head injury

We evaluated alterations in information processing after closed head injury as a function of task demands and stimulus modality. Visual and auditory discrimination tasks were administered to 11 survivors of a head injury and 16 matched healthy controls. In auditory tasks, compared with controls, the survivors had smaller N100s, smaller and later N200s, a more posterior scalp distribution of N200, and longer P300 and response latencies. Auditory N200 and P300 correlated highly with duration of unconsciousness. In contrast, in visual tasks, only a reduced N200 in the survivors differentiated the groups. Our results indicate that processing of auditory stimuli, including the perception and discrimination of stimulus features and the evaluation and categorization of stimuli, may be impaired after head trauma. Visual sensory processing may be spared, but higher-order visual processing involved in stimulus classification may be compromised.

One-year test-retest reliability of auditory ERPs in young and old adults

The reliability of ERP measures was investigated in a sample covering the adult life span (n = 59, age 21-92). This sample was divided into a young and an old group. ERPs to an auditory two-stimuli oddball task were recorded in the sample at two occasions separated by 12-14 months (T1 and T2). The recordings of T1 were split in half, to assess within session reliability. Correlations were calculated for N1, P2 and P3 peak latency and amplitude, for average amplitude during 50 ms epochs within the defined P3-window 250-550, and for average amplitude in successive 15 ms epochs from 1 to 705 ms. The results show that amplitude measures were more reliable than the latency measures at all electrodes. Time window/epoch amplitude measures yielded reliabilities in the same range as peak amplitude. Reliabilities peaked around the conventionally studied N1, P2 and P3, and this is seen as a validation of the components. In general, the old group exhibited weaker P3 peak latency reliabilities than the young group. However, many of these differences did not reach statistical significance. Implications of the findings are discussed.

Assessment of P3a and P3b after moderate to severe brain injury

The purpose of the study was to examine the P3a and P3b components of the event-related brain potential (ERP) in patients sustaining moderate to severe brain injury. Electrophysiological and behavioral responses were recorded in brain injured (N = 18) and healthy control (N = 21) participants performance of an auditory 3-stimulus distractor paradigm. Auditory stimuli consisted of a series of repetitive standard tones (75 ms), occasionally interrupted by equiprobable target (25 ms) and distractor sounds (white noise). Tone duration discrimination accuracy was similar in patients and controls, but patients had prolonged reaction times to targets. The reaction time delay was paralleled by a prolongation of P3b latency to targets in the patient group relative to controls. The stimulus and task dependent modulation of ERP responses in the brain injury group was similar to that of controls in terms of the spatial distribution of ERPs over the scalp. However, the brain injury group had attenuated P3a and P3b amplitudes to distractor and target stimuli, respectively. The electrophysiological data suggest a deficit in the allocation of attentional resources to the processing of deviant stimuli in the brain injury group.