Long-term patterns of change in ERPs across repeated measurements

The use of the eye-fixation-related potential to investigate visual perception in professional domains with high attentional demand: a literature review

INTRODUCTION

Visual attention is a cognitive skill related to visual perception and neural activity, and also moderated by expertise, in time-constrained professional domains (e.g., aviation, driving, sport, surgery). However, the contribution of both perceptual and neural processes on performance has been studied separately in the literature.

DEVELOPMENT

We defend an integration of visual and neural signals to offer a more complete picture of the visual attention displayed by professionals of different skill levels when performing free-viewing tasks. Specifically, we propose to zoom the analysis in data related to the quiet eye and P300 component jointly, as a novel signal processing approach to evaluate professionals' visual attention.

CONCLUSION

This review highlights the advantages of using portable eye trackers and electroencephalogram systems altogether, as a promising technique for a better understanding of early cognitive components related to attentional processes. Altogether, the eye-fixation-related potentials method may provide a better understanding of the cognitive mechanisms employed by the participants in natural settings, revealing what visual information is of interest for participants and distinguishing the neural bases of visual attention between targets and non-targets whenever they perceive a stimulus during free viewing experiments.

Stability, change, and reliable individual differences in electroencephalography measures: a lifespan perspective on progress and opportunities

Electroencephalographic (EEG) methods have great potential to serve both basic and clinical science approaches to understand individual differences in human neural function. Importantly, the psychometric properties of EEG data, such as internal consistency and test-retest reliability, constrain their ability to differentiate individuals successfully. Rapid and recent technological and computational advancements in EEG research make it timely to revisit the topic of psychometric reliability in the context of individual difference analyses. Moreover, pediatric and clinical samples provide some of the most salient and urgent opportunities to apply individual difference approaches, but the changes these populations experience over time also provide unique challenges from a psychometric perspective. Here we take a developmental neuroscience perspective to consider progress and new opportunities for parsing the reliability and stability of individual differences in EEG measurements across the lifespan. We first conceptually map the different profiles of measurement reliability expected for different types of individual difference analyses over the lifespan. Next, we summarize and evaluate the state of the field's empirical knowledge and need for testing measurement reliability, both internal consistency and test-retest reliability, across EEG measures of power, event-related potentials, nonlinearity, and functional connectivity across ages. Finally, we highlight how standardized pre-processing software for EEG denoising and empirical metrics of individual data quality may be used to further improve EEG-based individual differences research moving forward. We also include recommendations and resources throughout that individual researchers can implement to improve the utility and reproducibility of individual differences analyses with EEG across the lifespan.

Test-Retest Reliability of Event-Related Potentials Across Three Tasks

Abstract. Event-related potentials (ERPs) constitute a useful and cost-effective method to assess the neural underpinnings of multiple cognitive processes. ERPs have been used to track changes in cognitive processes in longitudinal and clinical studies. However, few studies have assessed their test-retest reliability (i.e., their consistency across time). Therefore, in the current study, we aimed to assess the test-retest reliability of ERPs (P100, N100, P200, N200, P3b, lateralized readiness potentials) across three tasks. In two assessments separated by approximately 4 months, ERPs were recorded in 26 healthy participants, during two oddball tasks (motor and counting) and a stimulus-response compatibility paradigm. Pearson’s correlations and intraclass correlations were used to assess the test-retest reliability of ERPs. Correlations between ERPs elicited by the three tasks were assessed with Pearson’s correlations. Our analyses revealed moderate to very strong test-retest reliability for most ERP components across the three tasks. Test-retest reliability did not differ between the motor and counting oddball tasks. Most ERPs were also correlated across paradigms. Therefore, these results confirm that ERPs have the potential to be reliable markers to serve as robust assessment tools in longitudinal or clinical studies.

Habituation of P300 in the Use of P300-based Brain-Computer Interface Spellers: Individuals With Amyotrophic Lateral Sclerosis Versus Age-Matched Controls

The P300-based brain-computer interface speller can provide motor independent communication to individuals with amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder that affects the motor system. P300 amplitude stability is critical for operation of the P300 speller. The P300 has good long-term stability, but to our knowledge, short-term habituation in the P300 speller has not been studied. In the current study, 15 participants: 8 ALS patients and 7 age-matched healthy volunteers (HVs), used 2 versions of P300 spellers, Face speller and Flash speller, each for 30 minutes. The ALS group performed as well as the HVs in both spellers and HVs did better with the Face speller than Flash speller while the ALS group performed equally well in both spellers. Neither intra-run P300 habituation nor inter-run P300 habituation was found. The P300 speller could be a reliable communication device for individuals with ALS.

Effects of a five-day HD-tDCS application to the right IFG depend on current intensity: A study in children and adolescents with ADHD

Impaired executive functions in ADHD are associated with hypoactivity of the right inferior frontal gyrus (IFG). This region was targeted via repetitive applications of anodal, high-definition transcranial direct current simulation (HD-tDCS) on five consecutive days in 33 ADHD patients (10-17years) and in a healthy control group (n=13, only sham). Patients received either sham (n=13) or verum tDCS with 0.5mA (n=9) or 0.25mA (n=11) depending on individual cutaneous sensitivity. During stimulation, participants performed a combined working memory and response inhibition paradigm (n-back/nogo). At baseline, post, and a 4-month follow up, electroencephalography was recorded during this task. Moreover, interference control (flanker task) and spatial working memory (spanboard task) were assessed to explore possible transfer effects. Omission errors and reaction time variability in all tasks served as measures of attention. In the 0.25mA group increased nogo commission errors indicated a detrimental tDCS effect on response inhibition. After the 5-day stimulation, attentional improvements in the 0.5mA group were indicated by reduced omission errors and reaction time variability. Variability improvements were still evident at follow up. In all groups, nogo P3 amplitudes were reduced post-stimulation, but in the 0.5mA group this reduction was smaller than in the 0.25mA group. Results of the current study suggest distinct effects of tDCS with different current intensities demonstrating the importance of a deeper understanding on the impact of stimulation parameters and repeated tDCS applications to develop effective tDCS-based therapy approaches in ADHD.

Reliability of P3 Event-Related Potential During Working Memory Across the Spectrum of Cognitive Aging

Event-related potentials (ERPs) offer unparalleled temporal resolution in tracing distinct electrophysiological processes related to normal and pathological cognitive aging. The stability of ERPs in older individuals with a vast range of cognitive ability has not been established. In this test-retest reliability study, 39 older individuals (age 74.10 (5.4) years; 23 (59%) women; 15 non β-amyloid elevated, 16 β-amyloid elevated, 8 cognitively impaired) with scores on the Montreal Cognitive Assessment (MOCA) ranging between 3 and 30 completed a working memory (n-back) test with three levels of difficulty at baseline and 2-week follow-up. The main aim was to evaluate stability of the ERP on grand averaged task effects for both visits in the total sample (n = 39). Secondary aims were to evaluate the effect of age, group (non β-amyloid elevated; β-amyloid elevated, cognitively impaired), cognitive status (MOCA), and task difficulty on ERP reliability. P3 peak amplitude and latency were measured in predetermined channels. P3 peak amplitude at Fz, our main outcome variable, showed excellent reliability in 0-back (intraclass correlation coefficient (ICC), 95% confidence interval = 0.82 (0.67-0.90) and 1-back (ICC = 0.87 (0.76-0.93), however, only fair reliability in 2-back (ICC = 0.53 (0.09-0.75). Reliability of P3 peak latencies was substantially lower, with ICCs ranging between 0.17 for 2-back and 0.54 for 0-back. Generalized linear mixed models showed no confounding effect of age, group, or task difficulty on stability of P3 amplitude and latency of Fz. By contrast, MOCA scores tended to negatively correlate with P3 amplitude of Fz (p = 0.07). We conclude that P3 peak amplitude, and to lesser extent P3 peak latency, provide a stable measure of electrophysiological processes in older individuals.

Long-Term Test-Retest Reliability of Auditory Gamma Oscillations Between Different Clinical EEG Systems

OBJECTIVE

There is increasing interest in the utility of gamma-band activity for assessing various brain functions, including perception, language, memory, and cognition. The auditory steady-state response (ASSR) involves neural activity in the brain elicited by trains of a click sound, and its maximum response is obtained at 40 Hz (40-Hz ASSR). Abnormalities of the 40-Hz ASSR are also widely reported in patients with schizophrenia. Thus, the test-retest reliability of the ASSR is important for its clinical and translational application. However, there are only limited studies reporting the short-term reliability between acquisitions at two time points made using the same electroencephalogram (EEG) system. Furthermore, the long-term reliability between multiple EEG systems and the reliability of spontaneous gamma activity are unknown but are crucial for multicenter collaborative research.

METHODS

We examined the long-term test-retest reliability of 40-Hz ASSR oscillatory activities indexed by the phase locking factor (PLF), evoked power, and (non-phase-locked) induced power between two clinical 19-electrode EEG systems [recorded twice for EEG-1 (time1 and time2) and EEG-2 (time3 and time4)] at four time points from 14 healthy controls over a duration of 5 months. Test-retest reliability was examined using intraclass correlation coefficients (ICCs).

RESULTS

Both PLF and evoked power showed good to excellent ICCs (>0.60), mainly in the Fz-electrode, both within each EEG system-EEG-1 [(time1 vs. time2) PLF: ICC = 0.66, evoked power: ICC = 0.88] and EEG-2 [(time3 vs. time4) PLF: ICC = 0.82, evoked power: ICC = 0.77]-and between the two EEG systems [(EEG-1 vs. EEG-2) PLF: ICC = 0.73, evoked power: ICC = 0.84]. In contrast, induced power showed the highest (excellent) ICC between the two EEG systems (ICC = 0.95) mainly in the Cz-electrode. For PLF, the Fz-electrode showed better test-retest reliability across all EEG recordings than the Cz-electrode (Fz: ICC = 0.67, Cz: ICC = 0.63), whereas we found similar excellent reproducibility across all EEG recordings from both electrodes for evoked power (Fz: ICC = 0.79, Cz: ICC = 0.77) and induced power (Fz: ICC = 0.79, Cz: ICC = 0.80).

CONCLUSION

The 40-Hz ASSR oscillatory activities, including induced power, showed excellent test-retest reliability, even when using different EEG systems over a duration of 5 months. These findings confirm the utility of the 40-Hz ASSR as a reliable clinical and translatable biomarker for multicenter collaborative research.

Markers of Novelty Processing in Older Adults Are Stable and Reliable

Exploratory behavior and responsiveness to novelty play an important role in maintaining cognitive function in older adults. Inferences about age- or disease-related differences in neural and behavioral responses to novelty are most often based on results from single experimental testing sessions. There has been very limited research on whether such findings represent stable characteristics of populations studied, which is essential if investigators are to determine the result of interventions aimed at promoting exploratory behaviors or draw appropriate conclusions about differences in the processing of novelty across diverse clinical groups. The goal of the current study was to investigate the short-term test-retest reliability of event-related potential (ERP) and behavioral responses to novel stimuli in cognitively normal older adults. ERPs and viewing durations were recorded in 70 healthy older adults participating in a subject-controlled visual novelty oddball task during two sessions occurring 7 weeks apart. Mean midline P3 amplitude and latency, mean midline amplitude during successive 50 ms intervals, temporospatial factors derived from principal component analysis (PCA), and viewing duration in response to novel stimuli were measured during each session. Analysis of variance (ANOVA) revealed no reliable differences in the value of any measurements between Time 1 and 2. Intraclass correlation coefficients (ICCs) between Time 1 and 2 were excellent for mean P3 amplitude (ICC = 0.86), the two temporospatial factors consistent with the P3 components (ICC of 0.88 and 0.76) and viewing duration of novel stimuli (ICC = 0.81). Reliability was only fair for P3 peak latency (ICC = 0.56). Successive 50 ms mean amplitude measures from 100 to 1,000 ms yielded fair to excellent reliabilities, and all but one of the 12 temporospatial factors identified demonstrated ICCs in the good to excellent range. We conclude that older adults demonstrate substantial stability in ERP and behavioral responses to novel visual stimuli over a 7-week period. These results suggest that older adults may have a characteristic way of processing novelty that appears resistant to transient changes in their environment or internal states, which can be indexed during a single testing session. The establishment of reliable measures of novelty processing will allow investigators to determine whether proposed interventions have an impact on this important aspect of behavior.

Long-term test-retest reliability of event-related potential (ERP) recordings during treadmill walking using the mobile brain/body imaging (MoBI) approach

Advancements in acquisition technology and signal-processing techniques have spurred numerous recent investigations on the electro-cortical signals generated during whole-body motion. This approach, termed Mobile Brain/Body Imaging (MoBI), has the potential to elucidate the neural correlates of perceptual and cognitive processes during real-life activities, such as locomotion. However, as of yet, no one has assessed the long-term stability of event-related potentials (ERPs) recorded under these conditions. Therefore, the objective of the current study was to evaluate the test-retest reliability of cognitive ERPs recorded while walking. High-density EEG was acquired from 12 young adults on two occasions, separated by an average of 2.3years, as they performed a Go/No-Go response inhibition paradigm. During each testing session, participants performed the task while walking on a treadmill and seated. Using the intraclass correlation coefficient (ICC) as a measure of agreement, we focused on two well-established neurophysiological correlates of cognitive control, the N2 and P3 ERPs. Following ICA-based artifact rejection, the earlier N2 yielded good to excellent levels of reliability for both amplitude and latency, while measurements for the later P3 component were generally less robust but still indicative of adequate to good levels of stability. Interestingly, the N2 was more consistent between walking sessions, compared to sitting, for both hits and correct rejection trials. In contrast, the P3 waveform tended to have a higher degree of consistency during sitting conditions. Overall, these results suggest that the electro-cortical signals obtained during active walking are representative of stable indices of neurophysiological function.

Brain-computer interfaces for patients with disorders of consciousness

The disorders of consciousness refer to clinical conditions that follow a severe head injury. Patients diagnosed as in a vegetative state lack awareness, while patients diagnosed as in a minimally conscious state retain fluctuating awareness. However, it is a challenge to accurately diagnose these disorders with clinical assessments of behavior. To improve diagnostic accuracy, neuroimaging-based approaches have been developed to detect the presence or absence of awareness in patients who lack overt responsiveness. For the small subset of patients who retain awareness, brain-computer interfaces could serve as tools for communication and environmental control. Here we review the existing literature concerning the sensory and cognitive abilities of patients with disorders of consciousness with respect to existing brain-computer interface designs. We highlight the challenges of device development for this special population and address some of the most promising approaches for future investigations.

A Brain Signature to Differentiate Acute and Chronic Pain in Rats

The transition from acute pain to chronic pain entails considerable changes of patients at multiple levels of the nervous system and in psychological states. An accurate differentiation between acute and chronic pain is essential in pain management as it may help optimize analgesic treatments according to the pain state of patients. Given that acute and chronic pain could modulate brain states in different ways and that brain states could greatly shape the neural processing of external inputs, we hypothesized that acute and chronic pain would show differential effects on cortical responses to non-nociceptive sensory information. Here by analyzing auditory-evoked potentials (AEPs) to pure tones in rats with acute or chronic pain, we found opposite influences of acute and chronic pain on cortical responses to auditory inputs. In particular, compared to no-pain controls, the N100 wave of rat AEPs was significantly enhanced in rats with acute pain but significantly reduced in rats with chronic pain, indicating that acute pain facilitated cortical processing of auditory information while chronic pain exerted an inhibitory effect. These findings could be justified by the fact that individuals suffering from acute or chronic pain would have different vigilance states, i.e., the vigilance level to external sensory stimuli would be increased with acute pain, but decreased with chronic pain. Therefore, this auditory response holds promise of being a brain signature to differentiate acute and chronic pain. Instead of investigating the pain system per se, the study of pain-induced influences on cortical processing of non-nocicpetive sensory information might represent a potential strategy to monitor the progress of pain chronification in clinical applications.

Test-Retest of Long Latency Auditory Evoked Potentials (P300) with Pure Tone and Speech Stimuli

Introduction Long latency auditory evoked potentials, especially P300, have been used for clinical evaluation of mental processing. Many factors can interfere with Auditory Evoked Potential - P300 results, suggesting large intra and inter-subject variations.

Objective The objective of the study was to identify the reliability of P3 components (latency and amplitude) over 4–6 weeks and the most stable auditory stimulus with the best test-retest agreement.

Methods Ten normal-hearing women participated in the study. Only subjects without auditory processing problems were included. To determine the P3 components, we elicited long latency auditory evoked potential (P300) by pure tone and speech stimuli, and retested after 4–6 weeks using the same parameters. We identified P300 latency and amplitude by waveform subtraction.

Results We found lower coefficient of variation values in latency than in amplitude, with less variability analysis when speech stimulus was used. There was no significant correlation in latency measures between pure tone and speech stimuli, and sessions. There was a significant intrasubject correlation between measures of latency and amplitude.

Conclusion These findings show that amplitude responses are more robust for the speech stimulus when compared with its pure tone counterpart. The P300 indicated stability for latency and amplitude measures when the test-retest was applied. Reliability was higher for amplitude than for latency, with better agreement when the pure tone stimulus was used. However, further research with speech stimulus is needed to clarify how these stimuli are processed by the nervous system.

Test-retest reliability of N400 event-related brain potential measures in a word-pair semantic priming paradigm in patients with schizophrenia

The N400 event-related brain potential (ERP), a negative voltage deflection occurring approximately 400ms after onset of any meaningful stimulus, is reduced in amplitude when the stimulus is preceded by related context. Previous work has found this N400 semantic priming effect to be decreased in schizophrenia, suggesting impairment in using meaningful context to activate related concepts in semantic memory. Thus, N400 amplitude may be a useful biomarker of abnormal semantic processing and its response to treatment in schizophrenia. To help assess the validity of N400 amplitude as a longitudinal measure in schizophrenia, we evaluated its test-retest reliability. ERPs were recorded in sixteen schizophrenia patients who viewed prime words, each followed at 300- or 750-ms stimulus-onset asynchrony (SOA) by a target that was either a related or unrelated word, or nonword. Participants' task was to indicate whether or not the target was a real word. They were retested on the same procedure one week later. Test-retest reliability was assessed by calculating Pearson's r and intraclass correlation coefficients (ICCs) across timepoints for N400 amplitudes for related and unrelated targets, at each SOA. Consistent with previous results, there were no significant differences between patients' N400 amplitudes for related and unrelated targets, at any SOA/timepoint combination. Pearson's r and ICCs for N400 amplitudes at Fz across timepoints were significant for both target types at each SOA (ranges: r 0.52-0.64, ICC 0.52-0.63; all p<.04). The results suggest potential utility of N400 amplitude as a longitudinal neurophysiological biomarker of semantic processing abnormalities in schizophrenia.

Retest reliability of individual p3 topography assessed by high density electroencephalography

BACKGROUND

Some controversy remains about the potential applicability of cognitive potentials for evaluating the cerebral activity associated with cognitive capacity. A fundamental requirement is that these neurophysiological parameters show a high level of stability over time. Previous studies have shown that the reliability of diverse parameters of the P3 component (latency and amplitude) ranges between moderate and high. However, few studies have paid attention to the retest reliability of the P3 topography in groups or individuals. Considering that changes in P3 topography have been related to different pathologies and healthy aging, the main objective of this article was to evaluate in a longitudinal study (two sessions) the reliability of P3 topography in a group and at the individual level.

RESULTS

The correlation between sessions for P3 topography in the grand average of groups was high (r = 0.977, p<0.001). The within-subject correlation values ranged from 0.626 to 0.981 (mean: 0.888). In the between-subjects topography comparisons, the correlation was always lower for comparisons between different subjects than for within-subjects correlations in the first session but not in the second session.

CONCLUSIONS

The present study shows that P3 topography is highly reliable for group analysis (comprising the same subjects) in different sessions. The results also confirmed that retest reliability for individual P3 maps is suitable for follow-up studies for a particular subject. Moreover, P3 topography appears to be a specific marker considering that the between-subjects correlations were lower than the within-subject correlations. However, P3 topography appears more similar between subjects in the second session, demonstrating that is modulated by experience. Possible clinical applications of all these results are discussed.

Test-retest reliability and stability of N400 effects in a word-pair semantic priming paradigm

OBJECTIVE

Elicited by any meaningful stimulus, the N400 event-related potential (ERP) component is reduced when the stimulus is related to a preceding one. This N400 semantic priming effect has been used to probe abnormal semantic relationship processing in clinical disorders, and suggested as a possible biomarker for treatment studies. Validating N400 semantic priming effects as a clinical biomarker requires characterizing their test-retest reliability.

METHODS

We assessed test-retest reliability of N400 semantic priming in 16 healthy adults who viewed the same related and unrelated prime-target word pairs in two sessions one week apart.

RESULTS

As expected, N400 amplitudes were smaller for related versus unrelated targets across sessions. N400 priming effects (amplitude differences between unrelated and related targets) were highly correlated across sessions (r=0.85, P<0.0001), but smaller in the second session due to larger N400s to related targets.

CONCLUSIONS

N400 priming effects have high reliability over a one-week interval. They may decrease with repeat testing, possibly because of motivational changes.

SIGNIFICANCE

Use of N400 priming effects in treatment studies should account for possible magnitude decreases with repeat testing. Further research is needed to delineate N400 priming effects' test-retest reliability and stability in different age and clinical groups, and with different stimulus types.

Effects of GSM signals during exposure to event related potentials (ERPs)

OBJECTIVES

The primary aim of this work was to assess the effect of electromagnetic field (EMF) from the GSM mobile phone system on human brain function. The assessment was based on the assay of event related potentials (ERPs).

MATERIAL AND METHODS

The study group consisted of 15 volunteers, including 7 men and 8 women. The test protocol comprised determination of P300 wave in each volunteer during exposure to the EMF. To eliminate possible effects of the applied test procedure on the final result, the test was repeated without EMF exposure. P300 latency, amplitude, and latency of the N1, N2, P2 waves were analysed.

RESULTS

The statistical analysis revealed an effect of EMF on P300 amplitude. In the experiment with EMF exposure, lower P300 amplitudes were observed only at the time in which the volunteers were exposed to EMF; when the exposure was discontinued, the values of the amplitude were the same as those observed before EMF application. No such change was observed when the experiment was repeated with sham exposure, which may be considered as an indirect proof that lower P300 amplitude values were due to EMF exposure. No statistically significant changes were noted in the latencies of the N1, N2, P2 waves that precede the P300 wave, nor in the latency of the P300 itself.

CONCLUSIONS

The results suggest that exposure to GSM EMF exerts some effects on CNS, including effects on long latency ERPs.

Characteristics of exploratory eye movements in elderly people: possibility of early diagnosis of dementia

BACKGROUND

Visual cognitive dysfunction is one of the most important signs indicating the early stage of dementia. Thus, visual testing could be used as an aid to the clinical diagnosis of dementia. In the present study, exploratory eye movement was measured to evaluate visual cognitive function in elderly subjects, including those with dementia.

METHODS

We analyzed responsive search scores (RSS) from exploratory eye movements of 300 subjects who were examined with an eye mark recorder while viewing S shaped figures. Subjects were divided into three groups (dementia, intermediate, healthy) from the values of the Revised Hasegawa Dementia Scale (HDS-R), the Mini-Mental State Examination (MMSE) and the Clinical Dementia Rating. We further divided the intermediate groups into two subgroups, the high score and low score groups, based on RSS. In 202 subjects, Z-scores of voxel-based specific regional analysis system for Alzheimer's disease (VSRAD) were obtained from magnetic resonance imaging (MRI).

RESULTS

RSS of the dementia group were significantly lower than those in the intermediate and healthy groups, in order: dementia < intermediate < healthy groups. RSS of the low score intermediate group was significantly lower than that of the high score intermediate group. There was no significant difference between the low score intermediate and dementia groups, or between the high score intermediate and healthy groups. No significant differences of either HSD-R or MMSE were observed between the low score and the high score intermediate groups. The Z-score of VSRAD using MRI in the low score intermediate group was significantly higher than that in the high score intermediate group.

CONCLUSIONS

These findings suggest that RSS using an eye mark recorder is a useful psychophysiological marker to evaluate the early stage of dementia as well as at-risk elderly people.

Suicide risk markers in major depressive disorder: a study of electrodermal activity and event-related potentials

BACKGROUND

Globally approximately 1 million people die annually by suicide. We studied both Electrodermal Activity (EDA) and Event-Related Potential (ERP) P3, together with an assessment of expressed anger as potential suicide risk predictors in Major Depressive Disorder (MDD) patients.

METHODS

In this controlled cross-sectional study, MDD inpatients were allocated to one of three groups: 1. history of 'hard attempted suicide' (e.g., hanging, stabbing; HAS), 2. 'soft attempted suicide' (poisoning; SAS) or 3. no attempted suicide (NAS), respectively. Patients were tested using both an auditory habituation paradigm (study 1) and an 'oddball task' (study 2). EDA Habituation Rate (HabR) and P3 amplitude differences evoked by both 'novel' and 'target' stimuli were computed between the first and second halves of the two studies. 'Anger' was assessed using State Trait Anger Expression Inventory (STAXI) subscales.

RESULTS

HabRs in both HAS (n=16) and SAS (n=16) were significantly lower than in NAS (n=18), in both study 1 and study 2, condition 'novel'. Decreases in P3 were also more pronounced in the HAS and SAS groups in study 1 and in the HAS group in study 2, 'novel' and 'target' condition. STAXI Anger In score was higher in HAS than in NAS.

LIMITATIONS

The sample size is small; medication may influence EDA.

CONCLUSIONS

Both EDA and P3 habituated faster in MDD patients with a history of attempted suicide, and were associated with higher 'anger' scores. Our data is a starting point for developing further neurobiological assessments of suicide risk in clinical practice.

Repeated stimulus exposure alters the way sound is encoded in the human brain

Auditory training programs are being developed to remediate various types of communication disorders. Biological changes have been shown to coincide with improved perception following auditory training so there is interest in determining if these changes represent biologic markers of auditory learning. Here we examine the role of stimulus exposure and listening tasks, in the absence of training, on the modulation of evoked brain activity. Twenty adults were divided into two groups and exposed to two similar sounding speech syllables during four electrophysiological recording sessions (24 hours, one week, and up to one year later). In between each session, members of one group were asked to identify each stimulus. Both groups showed enhanced neural activity from session-to-session, in the same P2 latency range previously identified as being responsive to auditory training. The enhancement effect was most pronounced over temporal-occipital scalp regions and largest for the group who participated in the identification task. The effects were rapid and long-lasting with enhanced synchronous activity persisting months after the last auditory experience. Physiological changes did not coincide with perceptual changes so results are interpreted to mean stimulus exposure, with and without being paired with an identification task, alters the way sound is processed in the brain. The cumulative effect likely involves auditory memory; however, in the absence of training, the observed physiological changes are insufficient to result in changes in learned behavior.

Neurophysiological measures of sensory registration, stimulus discrimination, and selection in schizophrenia patients

Cortical Neurophysiological event related potentials (ERPs) are multidimensional measures of information processing that are well suited to efficiently parse automatic and controlled components of cognition that span the range of deficits exhibited in schizophrenia patients. Components following a stimulus reflect the sequence of neural processes triggered by the stimulus, beginning with early automatic sensory processes and proceeding through controlled decision and response related processes. Previous studies employing ERP paradigms have reported deficits of information processing in schizophrenia across automatic through attention dependent processes including sensory registration (N1), automatic change detection (MMN), the orienting or covert shift of attention towards novel or infrequent stimuli (P3a), and attentional allocation following successful target detection processes (P3b). These automatic and attention dependent information components are beginning to be recognized as valid targets for intervention in the context of novel treatment development for schizophrenia and related neuropsychiatric disorders. In this review, we describe three extensively studied ERP components (N1, mismatch negativity, P300) that are consistently deficient in schizophrenia patients and may serve as genetic endophenotypes and as quantitative biological markers of response outcome.

The effects of immediate and short-term retest on the latencies and amplitudes of the auditory event-related potentials in healthy adults

OBJECTIVE

To evaluate the immediate and short-term effects of repeated within session trials on N1, P2, N2 and P3 latencies and P2, N2 and P3 amplitudes in healthy adults.

MATERIALS AND METHODS

ERPs were elicited by the auditory oddball paradigm and recorded over Fz, Cz and Pz in 18 healthy adults over two sessions, one to three days apart, and two within session trials with one to three minutes trial-retrial interval. The ERPs' latencies and amplitudes were blindly calculated and were analyzed by Analysis of Variance (ANOVA) with repeated measures.

RESULTS

Significant decreases of N2 amplitude at Fz, P3 amplitude at Cz and P3 latency at Pz were recorded in the second-compared to the first within session trial (p=0.034, 0.041, 0.046, respectively). There were no significant inter-session differences regarding N1, P2, N2 and P3 latencies or amplitudes. There was no significant interaction between session and trial. A statistically significant difference was found between the first session's mental count errors (p=0.039) but there were no significant differences between the second session's trials (p=0.581) or between sessions (p=0.328).

CONCLUSIONS

N1, P2, N2 and P3 latencies and amplitudes are stable at short-term intervals of one to three days, but one to three minutes' retrial interval may affect P3 latency and N2 and P3 amplitudes. We suggest that when primary novelty-induced cognitive processes are evaluated, single trial sessions or more than three-minute inter-trials interval should be employed in order to mitigate habituation.

Stimulus experience modifies auditory neuromagnetic responses in young and older listeners

Experiencing repeatedly presented auditory stimuli during magnetoencephalographic (MEG) recording may affect how the sound is processed in the listener's brain and may modify auditory evoked responses over the time course of the experiment. Amplitudes of N1 and P2 responses have been proposed as indicators for the outcome of training and learning studies. In this context the effect of merely sound experience on N1 and P2 responses was studied during two experimental sessions on different days with young, middle-aged, and older participants passively listening to speech stimuli and a noise sound. N1 and P2 were characterized as functionally distinct responses with P2 sources located more anterior than N1 in auditory cortices. N1 amplitudes decreased continuously during each recording session, but completely recovered between sessions. In contrast, P2 amplitudes were fairly constant within a session but increased from the first to the second day of MEG recording. Whereas N1 decrease was independent of age, the amount of P2 amplitude increase diminished with age. Temporal dynamics of N1 and P2 amplitudes were interpreted as reflecting neuroplastic changes along different time scales. The long lasting increase in P2 amplitude indicates that the auditory P2 response is potentially an important physiological correlate of perceptual learning, memory, and training.

Evaluation of cognitive performance by using P300 auditory event related potentials (ERPs) in patients with growth hormone (GH) deficiency and acromegaly

CONTEXT

Impaired cognitive performance has been demonstrated in adults with GH deficiency and acromegaly by using different neuropsychological tests. P300 event related potential (ERP) application is a well established neurophysiological approach in the assessment of cognitive performance.

OBJECTIVES

Evaluation of cognitive performance by using P300 ERPs has not been reported in acromegaly, and the comparisons of the P300 ERPs between the patients with GH deficiency and GH excess have not been done yet. Therefore present study was designed to investigate the effects of GH deficiency and GH excess on cognitive performance by using P300 ERPs.

DESIGN AND METHODS

The study comprised 19 patients with severe GH deficiency, 18 acromegalic patients and 16 age, education and sex matched healthy controls. Baseline auditory ERPs were obtained at Fz (frontal), Cz (central), Pz (parietal) and Oz (occipital) electrode sites in GH deficient group, GH excess group and control group.

RESULTS

There was a significant difference between mean serum IGF-I levels in the GH deficient and acromegalic patients (48+/-38 ng/ml and 742+/-272 ng/ml, respectively) (P=0.01). The mean P300 latency of the patients with GH deficiency was significantly (P=0.0001) prolonged when compared with that of normal controls and acromegalic patients at all electrode sites. The mean P300 amplitude of the patients with acromegaly was significantly (P=0.005) lower when compared with that of normal controls and GH deficient patients at all electrode sites.

CONCLUSIONS

Using ERPs recordings, the present study indicates the prolongation of P300 latencies in patients with severe GH deficiency and reduction of P300 amplitudes in patients with acromegaly. This study provides the electrophysiological evidence for the presence of cognitive dysfunction in both GH deficiency and GH excess, and different components of the cognitive performance are impaired in these conditions.

Preliminary Feasibility and Efficacy of a Brief Motivational Intervention with Psychophysiological Feedback for Cocaine Abuse

Motivational interviewing (MI) with personalized feedback, particularly related to biological markers of risk or harm, has been found effective for alcohol use disorders, but has not been fully investigated in cocaine use disorders. A randomized, controlled pilot study evaluating the feasibility and preliminary efficacy of a brief MI intervention using EEG/ERP graphical feedback for cocaine abusers was conducted. Treatment-seeking cocaine abusers (N = 31) were randomly assigned to a two-session MI intervention or a minimal control condition. All participants received EEG assessments at intake and post-treatment. Results indicated that the MI intervention was feasible and the subjective impact of the EEG feedback was positive. Significant group differences in percentage of cocaine positive urine screens across the study were found, favoring the MI group; 84.9% for the control group and 62.6% in the MI group, p < .05. Further research must determine the specific conditions under which MI is most appropriate and efficacious.

Long-term stability of N1 sources using low-resolution electromagnetic tomography

The purpose of this study was to investigate the long-term stability of auditory N1 sources using low-resolution electromagnetic tomography (LORETA). Data collected from 72 electrodes in ten young adult female participants were analyzed. For each participant, N1 peak amplitude and latency values at Cz (referred to M2) were compared for right, left, and bilateral stimulation across three separate recording sessions. Further, sources calculated by LORETA were analyzed in three regions of interest: right temporal, left temporal, and frontal. Peak amplitude and latency measurements were stable across session and ear of stimulation. Three-way RM-ANOVAs revealed relatively stable source amplitudes and stable three-dimensional locations of the sources in each region of interest with shifts of up to 2 cm around the mean locations. The 2 cm variability may be attributable both to normal hemispheric asymmetries and electrode placement variability. These results suggest that N1 scalp activity and its underlying sources are stable.

Artifacts, habituation and p300-based brain machine interfaces

We investigated to what degree the detection rate of the P300 in single trial event-related potentials is affected by short-term and long-term habituation effects, and we present an algorithm to eliminate eye-movement artifacts. Data from 26 subjects were collected using a visual oddball paradigm. P300 components were detected using a threshold algorithm operating on the delta band (0-4 Hz). Using data from four subjects, collected over a 7 to 12 week period, it was observed that the P300 amplitude tended to decrease within a session, and also between successive sessions. However, this decrease did not affect the detection rate. The eye-movement removal algorithm was tested on simulated and actual data, and resulted in a significant increase in detection rate.

Neurophysiological endophenotypes of schizophrenia: the viability of selected candidate measures

In an effort to reveal susceptibility genes, schizophrenia research has turned to the endophenotype strategy. Endophenotypes are characteristics that reflect the actions of genes predisposing an individual to a disorder, even in the absence of diagnosable pathology. Individual endophenotypes are presumably determined by fewer genes than the more complex phenotype of schizophrenia and would, therefore, reduce the complexity of genetic analyses. Unfortunately, despite there being rational criteria to define a viable endophenotype, the term is sometimes applied indiscriminately to characteristics that are deviant in affected individuals. Schizophrenia patients exhibit deficits in several neurophysiological measures of information processing that have been proposed as candidate endophenotypes. Successful processing of sensory inputs requires the ability to inhibit intrinsic responses to redundant stimuli and, reciprocally, to facilitate responses to less frequent salient stimuli. There is evidence to suggest that both these processes are "impaired" in schizophrenia. Measures of inhibitory failure include prepulse inhibition of the startle reflex, P50 auditory evoked potential suppression, and antisaccade eye movements. Measures of impaired deviance detection include mismatch negativity and the P300 event-related potential. The purpose of this review is to systematically evaluate the endophenotype candidacy of these key neurophysiological abilities. For each candidate, we describe typical experimental procedures, the current understanding of the underlying neurobiology, the nature of the abnormality in schizophrenia, the reliability, stability and heritability of the measure, and any reported gene associations. We conclude with a discussion of the few studies thus far that have employed a multivariate approach with these candidates.

Habituation and Dishabituation of P300

OBJECTIVE

We aimed to see the consequences of habituation and posthabituation by means of repeatedly measuring the effects over a longer period.

METHOD

The study was performed on 27 healthy volunteers. The event-related potentials were recorded from the Fz, the Cz, and the Pz electrode sites. The rare tone-frequent tone probability ratio was 20%. All subjects were asked to press a button when they heard a rare tone. The test was continued until 20 artifact-free rare tones were averaged, which was accepted as 1 trial block. After 10 trial blocks were obtained in a sequential manner, the test was completed.

RESULT

This study has indicated that P300 amplitudes decrease with repeated stimulations, that is, there is a habituation period. As the test continues, the speed of amplitude decrease slows down and after a while it even starts to increase: that is, a dishabituation occurs.

CONCLUSIONS

It is very likely that this habituation relates to a period of learning and dishabituation relates to a period of mental fatigue. In these processes, changes of amplitude and latency values reflect changes in amount of neuronal activation.

A P300 event-related potential brain-computer interface (BCI): the effects of matrix size and inter stimulus interval on performance

We describe a study designed to assess properties of a P300 brain-computer interface (BCI). The BCI presents the user with a matrix containing letters and numbers. The user attends to a character to be communicated and the rows and columns of the matrix briefly intensify. Each time the attended character is intensified it serves as a rare event in an oddball sequence and it elicits a P300 response. The BCI works by detecting which character elicited a P300 response. We manipulated the size of the character matrix (either 3 x 3 or 6 x 6) and the duration of the inter stimulus interval (ISI) between intensifications (either 175 or 350 ms). Online accuracy was highest for the 3 x 3 matrix 175-ms ISI condition, while bit rate was highest for the 6 x 6 matrix 175-ms ISI condition. Average accuracy in the best condition for each subject was 88%. P300 amplitude was significantly greater for the attended stimulus and for the 6 x 6 matrix. This work demonstrates that matrix size and ISI are important variables to consider when optimizing a BCI system for individual users and that a P300-BCI can be used for effective communication.

A P300-based brain–computer interface: Initial tests by ALS patients

OBJECTIVE

The current study evaluates the effectiveness of a brain-computer interface (BCI) system that operates by detecting a P300 elicited by one of four randomly presented stimuli (i.e. YES, NO, PASS, END).

METHODS

Two groups of participants were tested. The first group included three amyotrophic lateral sclerosis (ALS) patients that varied in degree of disability, but all retained the ability to communicate; the second group included three non-ALS controls. Each participant participated in ten experimental sessions during a period of approximately 6 weeks. During each run the participant's task was to attend to one stimulus and disregard the other three. Stimuli were presented auditorily, visually, or in both modes.

RESULTS

Two of the 3 ALS patient's classification rates were equal to those achieved by the non-ALS participants. Waveform morphology varied as a function of the presentation mode, but not in a similar pattern for each participant.

CONCLUSIONS

The event-related potentials elicited by the target stimuli could be discriminated from the non-target stimuli for the non-ALS and the ALS groups. Future studies will begin to examine online classification.

SIGNIFICANCE

The results of offline classification suggest that a P300-based BCI can serve as a non-muscular communication device in both ALS, and non-ALS control groups.

The test-retest reliability of a standardized neurocognitive and neurophysiological test battery: "neuromarker"

NeuroMarker combines EEG and ERP measures with neurocognitive tests in a fully computerized and standardized testing system. It is designed for use across the lifespan and has a large normative database of over 1,000 subjects. This study was a preliminary evaluation of "NeuroMarker" in subjects spanning four decades. Twenty-one healthy subjects (12-57 years) were tested at baseline and four weeks later. From the "Neuromarker" battery, the authors analyzed EEG data (eyes open and closed) and ERPs elicited during auditory oddball (N100, P200, N200, P300) and working memory (P150, P300) tasks. Concomitant neuropsychological data, acquired using a touch-screen system, comprised measures of sensori-motor, attention, verbal, executive, and memory function. Test-retest data were examined using analyses of variance and correlational procedures (corrected for multiple comparisons), with parallel analyses of age. EEG data did not differ across sessions, and showed high test-retest reliability (.71-.95), particularly for theta and delta (>.85). ERP components also showed sound reliability, particularly for sites where components are maximal: fronto-central N100 (.76-.77), centro-parietal P300 (.78-.81) to oddball targets, N100 and P200 (.74-.86) to oddball non-targets, and P150 amplitude and latency (.84-.93) to working memory stimuli. Neuropsychological tests showed a similarly sound level of consistency (on average, .70), with the most consistent tests tapping simple motor function, estimated intelligence, switching of attention (Part 2), verbal interference response time and memory intrusions (.71-.89). Age and sex did not have a differential impact on reliability for EEG, ERP, or neuropsychology measures. These findings provide preliminary evidence that the "NeuroMarker" battery is reliable for test-retest assessments. The results suggest that the standardized approach has utility for providing sensitive clinical and treatment evaluations across age groups.

Attentional training in elderly subjects affects voluntarily oriented, but not automatic attention: A neurophysiological study

OBJECTIVES

Our study aimed at investigating the effect of repetitive recordings on somatosensory evoked potentials (SEPs) related to spatial attention in a population of healthy elderly subjects.

METHODS

Fifteen healthy elderly subjects were tested for six consecutive days using a somatosensory oddball paradigm, in which target stimuli were applied above the elbow and the non-target stimuli on the ipsilateral shoulder. Brain electrical activity was recorded from six scalp electrodes (Fz, Cz, F3, F4, T3 and T4).

RESULTS

The N140 response to target stimuli showed a significantly decreased amplitude across the sessions with the lowest value during the fourth day of recording and with a partial recovery at the sixth day. On the contrary, the amplitude of the N140 response to non-target stimuli and that of the P300 potential to target stimuli were not significantly modified.

CONCLUSIONS

The significant amplitude reduction of the N140 potential in target, but not in non-target recordings across sessions, suggests that the voluntarily oriented attention is reduced by stimulus repetition, while the automatic attention is not.

Eliminating the P300 rebound in short oddball paradigms

In short oddball paradigms, the P3 (or P300) amplitude often shows a curvilinear "rebound" pattern, such that an initial drop during the first few trials is followed by an increase in later trials. While the initial attenuation has been attributed to habituation, no explanation has been offered for the later increase. Our hypothesis was that this curvilinear pattern is due to anticipation of the end of each fixed-length block. In study 1, a series of 16 short, fixed-length auditory oddball tests (with six targets each) replicated the rebound effect. In study 2, a further set of 16 variable-length blocks (7-10 targets) eliminated the rebound, and the P300 amplitude decreased linearly as expected. Results are interpreted in light of various constructs related to the P3: habituation, attentional salience, and updating in working memory.

Prolonged P300 latency in thyroid failure: a paradox. P300 latency recovers later in mild hypothyroidism than in severe hypothyroidism

This study was performed to analyze quantitatively the cognitive functions of patients with mild and severe hypothyroidism by measuring P300 event-related evoked potentials before and after euthyroidism was established. Patients diagnosed as having Hashimato's thyroiditis with thyroid stimulating hormone (TSH) levels between 5 and 10 mU/L (mild thyroid failure; n = 24) and those with severe hypothyroidism (n = 13) were enrolled randomly to the study protocol. P300-event related potentials were recorded during thyroid insufficiency, and in the first and sixth month of euthyroidism. P300 latencies were prolonged in both the mild and severe hypothyroid patients compared to controls (p = 0.042, p < 0.001, respectively). The overt hypothyroid patients showed significant decrease in their P300 latencies after the first month of euthyroidism (p = 0.001). These P300 latency values did not differ in the subsequent 6-month period. The mild hypothyroid group, however, displayed no improvement of P300 latency in the first month but normalized at the sixth month of euthyroidism. In conclusion, both the overt and the mild hypothyroid patients revealed prolonged P300 latencies. Unexpectedly, P300 latencies in the patients with mild thyroid failure required more time to recover compared to the overt hypothyroid patients. This finding indicates different clinical outcomes of various thyroid insufficiency states on the brain.

An Exploratory Study of Factors Affecting Single Trial P300 Detection

A threshold detector for single-trial P300 detection has been evaluated. The detector operates on the 0-4 Hz band, isolated from the raw electroencephalogram using low-pass filtering, wavelet transforms, or the piecewise prony method (PPM). A detection rate around 70% was found, irregardless of stimulus type, interstimulus interval (ISI), probability of occurrence (Pr) of the target stimuli, intrasession and intersession effects, or filtering method. This suggests that P300-based brain-machine interfaces can use an ISI as short as 1 s and a Pr of 45%, to increase throughput.

Brain maturation and subtypes of conduct disorder: interactive effects on p300 amplitude and topography in male adolescents

OBJECTIVE

Adolescents with conduct disorder problems are, on average, at increased risk for a variety of unfortunate adult outcomes, including substance dependence. This study was designed to identify the neurophysiological correlates of different categories of conduct disorder problems as well as the relationship between these correlates and the maturational status of the brain.

METHOD

The subjects were 94 males, aged 14-19 years, recruited from the community. None were recruited from treatment or juvenile justice programs. The subjects varied in the type and number of conduct problem behaviors exhibited prior to age 15. Groups were operationally defined by the relative number (0 versus > or =1) of DSM-IV conduct disorder diagnostic criteria within each of four categories: rules violations, aggression, deceitfulness/theft, and destructiveness. Age was included as an additional grouping factor. P300 electroencephalographic potentials were recorded while subjects performed a task in which rare auditory stimuli were used to signal a change in stimulus-response mapping during a succeeding set of trials.

RESULTS

Analyses revealed that boys with a history of rules violations failed to exhibit the normal maturational increase in P300 amplitude found in boys without a history of rules violations. Topographic analyses of current source densities suggest that the source of the maturational deficit involved P300 generators within the frontal brain. Parietal generators of P300 matured normally.

CONCLUSIONS

The present results are interpreted as reflecting a decrement in frontal brain maturation among boys potentially at risk for substance dependence, antisocial personality disorder, or other forms of adult psychopathology.

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.

Auditory novelty oddball allows reliable distinction of top-down and bottom-up processes of attention

An auditory novelty-oddball task, which is known to evoke a P3 event-related potential (ERP) in a target condition and a novelty-P3 ERP in response to task-irrelevant unique environmental sounds, was repeatedly applied to healthy participants (n = 14) on two separate recording sessions, 7 days apart. Both target-P3 and novelty-P3 were internally consistent and test-retest reliable. Interestingly, novelty-P3 amplitude declined from the first to the second half of each recording session, whereas no systematic alteration between both sessions occurred. The target-P3 showed the opposite pattern, i.e. a reduced amplitude from the first to the second session, but no systematic change within each session. These findings suggest that novelty-P3 amplitude changes reflect habituation, whereas target-P3 session effects may indicate the adjusted amount of processing resources invested into the task. In general, the results support the interpretation of the novelty-P3 as indicating automatic, bottom-up related aspects of attention, whereas the target-P3, in the present paradigm, seems to reflect voluntary, top-down related aspects of attention.

Long-term reliability of electrophysiologic response control parameters

The execution (Go) and the inhibition (NoGo) of a motor response are basic cognitive processes that can be assessed by means of a simple neuropsychological Go-NoGo task: the Continuous Performance Test (CPT). Simultaneous electrophysiologic investigations revealed that the NoGo condition of the CPT is associated with a clearly more anterior brain electrical activity compared with the Go condition. Recently, it has been shown that this NoGo anteriorization effect during a response control paradigm can be measured quantitatively with the electrophysiologic centroid method. The objective of the current study, therefore, was to determine the long-term reliability of the topographic measures of cognitive response control (i.e., location of the Go and the NoGo centroid and the NoGo anteriorization). For this purpose, a 21-channel EEG was recorded twice from 13 healthy volunteers during their execution of a cued CPT (O-X version). The time interval between test and retest was 2.74 years (range, 2.41 to 2.97 years). Statistical analysis of the event-related Go and NoGo potentials revealed an excellent test-retest reliability, as expressed by Pearson's product moment correlation coefficients of more than 0.85 (P < or = 0.0005) and intraclass correlation coefficients of more than 0.90 (P </= 0.0005) for all three topographic measures. These results indicate that these electrophysiologic parameters present with superior long-term reliability and that they may be applied as electrophysiologic trait markers of response control mechanisms in the human brain.

Phobic anxiety changes the function of brain-gut axis in irritable bowel syndrome

OBJECTIVE

Disease severity in the irritable bowel syndrome (IBS) is highly influenced by psychiatric comorbidity. The mechanism of this influence is generally unknown, even if the brain-gut axis seems to be involved. Recent research has indicated that IBS patients have aberrant perception of visceral stimuli in the CNS. We compared IBS patients with and without comorbid phobic anxiety to see if the comorbid disorder influenced brain information processing of auditory stimuli, and looked for possible consequences with respect to visceral sensitivity thresholds and disease severity.

METHODS

Eleven female patients with IBS with comorbid phobic anxiety disorder were compared with 22 age-matched female IBS patients without such comorbidity. The groups were compared with respect to event-related potentials (ERP), auditory-presented words with emotional contents, barostat-assessed visceral sensitivity thresholds, and symptom levels the last week before assessment.

RESULTS

The comorbid group had a significantly enhanced first negative ERP wave (N1) to all stimuli, indicating increased use of brain attentional resources. It also had increased visceral threshold for the sensation of gas, and reduced gas-stool and gas-discomfort tolerances compared with the noncomorbid group. Enhanced N1 amplitude at the frontal electrode and reduced gas-stools tolerance significantly predicted subjective gas complaints, explaining 47% of the symptom variation.

CONCLUSIONS

The study suggests an association between information processing in the frontal brain and visceral sensitivity characteristics in IBS patients, and indicates that subjective disease-related symptomatology is predicted by brain perceptual characteristics. The findings indicate that an interaction between IBS-related and anxiety-related hyperreactivity in the frontal brain may constitute a psychophysiological mechanism for the contribution of psychiatric comorbidity to severity and duration of the irritable bowel syndrome.

Test-retest reliability of electrophysiological parameters related to cognitive motor control

Previously, the continuous performance test was demonstrated to elicit distinct electrophysiological correlates of cognitive response during execution (Go) and inhibition (NoGo) of an anticipated motor response. A robust method for topographical quantification of these brain electrical microstates has been established recently. Test reliability is crucial to allow application in the assessment of neuropsychiatric disorders. The present study evaluates the reliability of the Go and NoGo centroid locations as well as the NoGo anteriorisation (NGA) in 23 healthy individuals. Our results show supreme test-alternate retest reliabilities of Pearson's product moment correlations and intraclass correlation coefficients of r> or =0.63 (P< or =0.001) for these parameters which assert a quality well within the range reported for those of other electrophysiological standard paradigms. Go and NoGo centroid locations as well as the NGA are, therefore, reliable correlates of prefrontal motor control and may contribute to the understanding of disorders with allied impairments.

The auditory event-related potential is a stable and reliable measure in elderly subjects over a 3 year period

OBJECTIVES

Valid markers of psychobiological processes, including changes over the lifespan, must be reliable. This study investigated the reliability of the auditory event-related potential (ERP) over a 3 year period.

METHODS

Predictable and unpredictable rare tones were embedded in common-to-rare sequences at 3 different ratios (2:3, 2:5 and 2:8). Forty-six older (mean age 72.3 years) volunteers pressed a key to the rare tones, and ERPs (Fz, Cz and Pz) and reaction time (RT) were measured. Reliability across years was assessed using 3 methods: (1) determination of the stability of waveform components (P1, N1, P2, N2 and P3); (2) cross-correlation of successive 15 ms epochs of within-subject ERPs; and (3) cross-correlation of 15 ms epochs of between-subject ERPs.

RESULTS

With all analyses, the ERP was stable. Analysis of the scored components indicated that P3 was especially stable in the unpredictable rare (2:8) condition. Earlier components were equally stable across all conditions. Analysis of 15 ms ERP epochs indicated significant ERP stability 60 ms after stimulation, lasting over 640 ms.

CONCLUSIONS

Robust within-subject reliability of the ERP strengthens its potential use for detecting preclinical changes in at-risk elderly populations.

Auditory distraction: event-related potential and behavioral indices

OBJECTIVE

The aim of this study was to illuminate behavioral and event-related potential (ERP) effects of attentional orienting and reorienting obtained in a newly developed auditory distraction paradigm, to provide more precise indicators about the neural generators of the ERP effects using scalp current density (SCD) analysis, and to evaluate the stability of the distraction effects.

METHODS

In two sessions separated by 25 days, 10 subjects were presented with tones being of short (200 ms) and long (400 ms) duration equiprobably; tones were of high-probability standard or of low-probability deviant frequency. In Distraction condition, subjects had to behaviorally discriminate short from long tones. In Ignore condition, subjects were reading a book. Behavioral performance and multi-channel EEG were recorded.

RESULTS

Task-irrelevant frequency deviations prolonged reaction times in the duration discrimination task by more than 35 ms and elicited the MMN and P3a components of the event-related potential. The P3a was followed by a negative deflection called RON (reorienting negativity). P3a and RON were absent in Ignore condition. All effects were found to be highly stable between sessions (product-moment correlations between 0.76 and 0.90). SCD analysis suggested frontal generators for P3a and for RON.

CONCLUSIONS

It is demonstrated that small frequency deviations may yield distinct distraction effects in a tone duration discrimination task on a behavioral and on an electrophysiological level. Results support the hypothesis that frontal areas are involved in the exogenous orienting of attention (P3a) and in the reorienting of attention (RON). Due to the high stability of the deviance-related behavioral and ERP effects, this distraction paradigm may be utilized for clinical research.

Habituation of event-related potentials in patients with Parkinson's disease

Auditory event-related potential (ERP) was studied in idiopathic Parkinson's disease (PD) using our new procedures. We examined 12 non-demented patients with PD, and 9 age-matched control subjects. Ninety responses induced by rare stimulation were continuously recorded from Fz, Cz, Pz referred to linked earlobe electrode (A1A2), and were divided into nine blocks (one block = 10 responses) for statistical analysis. We assessed the habituation of auditory ERP to detect delicate changes related to the information processing in PD. N100 and P300 latencies were significantly longer in PD than in control subjects (p<0.05). P300 latency gradually increased with progression of recording blocks in both PD and control subjects, whereas N100 latency increased only in PD. Three way analysis of variance for P300 amplitude revealed significant effects of subject group, recording electrode site, and trial block. P300 amplitude was smaller in PD than in control subjects. Significant negative correlation between P300 amplitudes and block numbers were observed at Cz and Pz in PD, and at Fz in the control group. Previous reports as well as present results suggest that prolongation of N100 latency might be related to frontal lobe dysfunction, and abnormality of P300 to dysfunction in both the frontal lobe and hippocampus in PD.