High-density recording and topographic analysis of the auditory oddball event-related potential in patients with schizophrenia

Altered attentional processing of happy prosody in schizophrenia

BACKGROUND

Abnormalities in emotional prosody processing have been consistently reported in schizophrenia. Emotionally salient changes in vocal expressions attract attention in social interactions. However, it remains to be clarified how attention and emotion interact during voice processing in schizophrenia. The current study addressed this question by examining the P3b event-related potential (ERP) component.

METHOD

The P3b was elicited with a modified oddball task, in which frequent (p = .84) neutral stimuli were intermixed with infrequent (p = .16) task-relevant emotional (happy or angry) targets. Prosodic speech was presented in two conditions - with intelligible (semantic content condition - SCC) or unintelligible semantic content (prosody-only condition - POC). Fifteen chronic schizophrenia patients and 15 healthy controls were instructed to silently count the target vocal sounds.

RESULTS

Compared to controls, P3b amplitude was specifically reduced for happy prosodic stimuli in schizophrenia, irrespective of semantic status. Groups did not differ in the processing of neutral standards or angry targets.

DISCUSSION

The selectively reduced P3b for happy prosody in schizophrenia suggests top-down attentional resources were less strongly engaged by positive relative to negative prosody, reflecting alterations in the evaluation of the emotional salience of the voice. These results highlight the role played by higher-order processes in emotional prosody dysfunction in schizophrenia.

Classification of Movement Preparation Between Attended and Distracted Self-Paced Motor Tasks

OBJECTIVE

Brain-computer interface (BCI) systems aim to control external devices by using brain signals. The performance of these systems is influenced by the user's mental state, such as attention. In this study, we classified two attention states to a target task (attended and distracted task level) while attention to the task is altered by one of three types of distractors.

METHODS

A total of 27 participants were allocated into three experimental groups and exposed to one type of distractor. An attended condition that was the same across the three groups comprised only the main task execution (self-paced dorsiflexion) while the distracted condition was concurrent execution of the main task and an oddball task (dual-task condition). Electroencephalography signals were recorded from 28 electrodes to classify the two attention states of attended or distracted task conditions by extracting temporal and spectral features.

RESULTS

The results showed that the ensemble classification accuracy using the combination of temporal and spectral features (spectro-temporal features, 82.3 ± 2.7%) was greater than using temporal (69 ± 2.2%) and spectral (80.3 ± 2.6%) features separately. The classification accuracy was computed using a combination of different channel locations, and it was demonstrated that a combination of parietal and centrally located channels was superior for classification of two attention states during movement preparation (parietal channels: 84.6 ± 1.3%, central and parietal channels: 87.2 ± 1.5%).

CONCLUSION

It is possible to monitor the users' attention to the task for different types of distractors.

SIGNIFICANCE

It has implications for online BCI systems where the requirement is for high accuracy of intention detection.

Background Suppression and its Relation to Foreground Processing of Speech Versus Non-speech Streams

Since sound perception takes place against a background with a certain amount of noise, both speech and non-speech processing involve extraction of target signals and suppression of background noise. Previous works on early processing of speech phonemes largely neglected how background noise is encoded and suppressed. This study aimed to fill in this gap. We adopted an oddball paradigm where speech (vowels) or non-speech stimuli (complex tones) were presented with or without a background of amplitude-modulated noise and analyzed cortical responses related to foreground stimulus processing, including mismatch negativity (MMN), N2b, and P300, as well as neural representations of the background noise, that is, auditory steady-state response (ASSR). We found that speech deviants elicited later and weaker MMN, later N2b, and later P300 than non-speech ones, but N2b and P300 had similar strength, suggesting more complex processing of certain acoustic features in speech. Only for vowels, background noise enhanced N2b strength relative to silence, suggesting an attention-related speech-specific process to improve perception of foreground targets. In addition, noise suppression in speech contexts, quantified by ASSR amplitude reduction after stimulus onset, was lateralized towards the left hemisphere. The left-lateralized suppression following N2b was associated with the N2b enhancement in noise for speech, indicating that foreground processing may interact with background suppression, particularly during speech processing. Together, our findings indicate that the differences between perception of speech and non-speech sounds involve not only the processing of target information in the foreground but also the suppression of irrelevant aspects in the background.

Using concurrent EEG and fMRI to probe the state of the brain in schizophrenia

Perceptional abnormalities in schizophrenia are associated with hallucinations and delusions, but also with negative symptoms and poor functional outcome. Perception can be studied using EEG-derived event related potentials (ERPs). Because of their excellent temporal resolution, ERPs have been used to ask when perception is affected by schizophrenia. Because of its excellent spatial resolution, functional magnetic resonance imaging (fMRI) has been used to ask where in the brain these effects are seen. We acquired EEG and fMRI data simultaneously to explore when and where auditory perception is affected by schizophrenia. Thirty schizophrenia (SZ) patients and 23 healthy comparison subjects (HC) listened to 1000 Hz tones occurring about every second. We used joint independent components analysis (jICA) to combine EEG-based event-related potential (ERP) and fMRI responses to tones. Five ERP-fMRI joint independent components (JIC) were extracted. The "N100" JIC had temporal weights during N100 (peaking at 100 ms post-tone onset) and fMRI spatial weights in superior and middle temporal gyri (STG/MTG); however, it did not differ between groups. The "P200" JIC had temporal weights during P200 and positive fMRI spatial weights in STG/MTG and frontal areas, and negative spatial weights in the nodes of the default mode network (DMN) and visual cortex. Groups differed on the "P200" JIC: SZ had smaller "P200" JIC, especially those with more severe avolition/apathy. This is consistent with negative symptoms being related to perceptual deficits, and suggests patients with avolition/apathy may allocate too few resources to processing external auditory events and too many to processing internal events.

Frequency-specific disruptions of neuronal oscillations reveal aberrant auditory processing in schizophrenia

Individuals with schizophrenia exhibit abnormalities in evoked brain responses in oddball paradigms. These could result from (a) insufficient salience-related cortical signaling (P300), (b) insufficient suppression of irrelevant aspects of the auditory environment, or (c) excessive neural noise. We tested whether disruption of ongoing auditory steady-state responses at predetermined frequencies informed which of these issues contribute to auditory stimulus relevance processing abnormalities in schizophrenia. Magnetoencephalography data were collected for 15 schizophrenia and 15 healthy subjects during an auditory oddball paradigm (25% targets; 1-s interstimulus interval). Auditory stimuli (pure tones: 1 kHz standards, 2 kHz targets) were administered during four continuous background (auditory steady-state) stimulation conditions: (1) no stimulation, (2) 24 Hz, (3) 40 Hz, and (4) 88 Hz. The modulation of the auditory steady-state response (aSSR) and the evoked responses to the transient stimuli were quantified and compared across groups. In comparison to healthy participants, the schizophrenia group showed greater disruption of the ongoing aSSR by targets regardless of steady-state frequency, and reduced amplitude of both M100 and M300 event-related field components. During the no-stimulation condition, schizophrenia patients showed accentuation of left hemisphere 40 Hz response to both standard and target stimuli, indicating an effort to enhance local stimulus processing. Together, these findings suggest abnormalities in auditory stimulus relevance processing in schizophrenia patients stem from insufficient amplification of salient stimuli.

Disruptions in small-world cortical functional connectivity network during an auditory oddball paradigm task in patients with schizophrenia

P300 deficits in patients with schizophrenia have previously been investigated using EEGs recorded during auditory oddball tasks. However, small-world cortical functional networks during auditory oddball tasks and their relationships with symptom severity scores in schizophrenia have not yet been investigated. In this study, the small-world characteristics of source-level functional connectivity networks of EEG responses elicited by an auditory oddball paradigm were evaluated using two representative graph-theoretical measures, clustering coefficient and path length. EEG signals from 34 patients with schizophrenia and 34 healthy controls were recorded while each subject was asked to attend to oddball tones. The results showed reduced clustering coefficients and increased path lengths in patients with schizophrenia, suggesting that the small-world functional network is disrupted in patients with schizophrenia. In addition, the negative and cognitive symptom components of positive and negative symptom scales were negatively correlated with the clustering coefficient and positively correlated with path length, demonstrating that both indices are indicators of symptom severity in patients with schizophrenia. Our study results suggest that disrupted small-world characteristics are potential biomarkers for patients with schizophrenia.

Dexamphetamine reduces auditory P3 delta power and phase-locking while increasing gamma power

Auditory P3 amplitude reduction is one of the most robust and replicated findings in schizophrenia. Recent evidence suggests that these reductions are due to reductions in both power and phase-locking at delta and theta frequencies. We have previously shown that the auditory, but not visual, P3 is reduced in healthy participants given the catecholamine releasing agent dexamphetamine. Our aim was to determine whether the auditory P3 amplitude reduction induced by dexamphetamine has similar power and phase locking characteristics to that seen in schizophrenia. Forty-four healthy participants were given 0.45 mg/kg dexamphetamine and placebo, in a double-blinded, placebo-controlled, cross-over design. The task was a three-stimulus auditory odd-ball task, target stimuli were the major stimuli of interest. Individual target trials underwent wavelet analysis to give power and phase-locking of delta (3 Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz) and gamma (30-50 Hz) frequencies for a 50 ms time window centred around the peak of the target P3. Delta power around the P3 peak was significantly reduced when participants were given dexamphetamine. Delta phase-locking was also reduced but only when analysis was targeted at the location of the peak P3 amplitude. In contrast, theta power and phase-locking were not affected by dexamphetamine. These findings suggest that increased catecholamine activity may be responsible for the power and phase-locking reductions of the auditory P3 delta component in patients with schizophrenia. Interestingly, dexamphetamine significantly increased gamma power around the P3 peak. We attempt to link this finding with the gamma alterations that have been found in patients with schizophrenia.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

The N1 auditory evoked potential component as an endophenotype for schizophrenia: high-density electrical mapping in clinically unaffected first-degree relatives, first-episode, and chronic schizophrenia patients

The N1 component of the auditory evoked potential (AEP) is a robust and easily recorded metric of auditory sensory-perceptual processing. In patients with schizophrenia, a diminution in the amplitude of this component is a near-ubiquitous finding. A pair of recent studies has also shown this N1 deficit in first-degree relatives of schizophrenia probands, suggesting that the deficit may be linked to the underlying genetic risk of the disease rather than to the disease state itself. However, in both these studies, a significant proportion of the relatives had other psychiatric conditions. As such, although the N1 deficit represents an intriguing candidate endophenotype for schizophrenia, it remains to be shown whether it is present in a group of clinically unaffected first-degree relatives. In addition to testing first-degree relatives, we also sought to replicate the N1 deficit in a group of first-episode patients and in a group of chronic schizophrenia probands. Subject groups consisted of 35 patients with schizophrenia, 30 unaffected first-degree relatives, 13 first-episode patients, and 22 healthy controls. Subjects sat in a dimly lit room and listened to a series of simple 1,000-Hz tones, indicating with a button press whenever they heard a deviant tone (1,500 Hz; 17% probability), while the AEP was recorded from 72 scalp electrodes. Both chronic and first-episode patients showed clear N1 amplitude decrements relative to healthy control subjects. Crucially, unaffected first-degree relatives also showed a clear N1 deficit. This study provides further support for the proposal that the auditory N1 deficit in schizophrenia is linked to the underlying genetic risk of developing this disorder. In light of recent studies, these results point to the N1 deficit as an endophenotypic marker for schizophrenia. The potential future utility of this metric as one element of a multivariate endophenotype is discussed.

Auditory ERP components before and after transition to a first psychotic episode

We investigated the course of Event Related Potentials (ERP) from prior to until shortly after a first psychotic episode in subjects at Ultra High Risk (UHR) for psychosis. N1, N2, N2b, P2 and P3 amplitudes were assessed using an auditory active oddball paradigm in 15 UHR subjects who made a transition to psychosis (UHR+T) at follow up, 23 subjects without a transition (UHR+NT) and 17 matched healthy controls at inclusion and again after approximately 18 months. Repeated-measures analyses revealed no significant time effects for any of the ERP components. However, an interaction effect was found for N1 amplitudes. Post-hoc analyses showed that N1 amplitudes were smaller at follow up compared to baseline only in UHR+T subjects. P3 amplitudes showed no further reduction after psychotic onset. These findings suggest that discernable ERP components behave differently during progression from the prodromal phase to the first psychotic episode. These findings may give insight in pathophysiological mechanisms underlying the genesis of psychosis.

Reduced parietal P300 amplitude is associated with an increased risk for a first psychotic episode

BACKGROUND

P300 abnormalities indicate changes in information processing and are one of the most reliable biological markers of schizophrenia. We sought to investigate whether abnormalities in P300 (P3) or other event-related potentials are also present in subjects at ultra high risk (UHR) for developing psychosis and whether they are helpful in predicting transition to psychosis.

METHODS

The N1, N2, N2b, P2, and P3 amplitudes were assessed in 61 UHR subjects, of whom 18 subjects (30%) made a transition to psychosis over a 3-year follow-up period (UHR + T: age 20.4 years) and 43 (70%) did not (UHR + NT: age 19.3 years), and 28 age- and intelligence-matched healthy control subjects (age 20.0 years). Psychopathology was also assessed.

RESULTS

The UHR + T subjects showed smaller parietal P3 amplitudes, compared with control subjects and UHR + NT subjects. Moreover, the N2b was higher in control subjects compared with both UHR groups. We found no differences in N1 or P2 components between the groups, and our UHR subjects did not exhibit bilateral P3 asymmetry. Reduced P3 amplitudes were the best predictor for subsequent psychosis in the UHR group. The P3 reduction was related to increased social anhedonia and withdrawal and a lower global assessment of social functioning and social personal adjustment.

CONCLUSIONS

The UHR + T subjects showed reduced parietal P3 amplitudes. In addition, a reduced P3 amplitude was the best predictor for subsequent psychosis. If replicated, these findings might contribute to a more accurate prediction of a first psychotic episode. Furthermore, reduced social functioning might be related to information processing deficits in UHR subjects.

How much does phase resetting contribute to event-related EEG abnormalities in schizophrenia?

OBJECTIVE

Patients suffering from schizophrenia demonstrate impaired low frequency electrophysiological responses to stimuli, but it remains unclear whether these abnormalities arise from phase resetting of ongoing oscillations, new phase-locked (evoked) activity or non-phase-locked (induced) activity. Our goal is to clarify the contribution of each of these three processes to the impairment of neural activity during information processing in schizophrenia, by using statistics that do not confound increases in the mean post-stimulus signal with phase resetting.

METHODS

Thirty-four male schizophrenia patients and 34 healthy matched controls performed an auditory oddball task. We applied the analysis procedure developed by Martinez-Montes et al. based on complex-valued wavelet transform to event-related signal elicited by target stimuli.

RESULTS

The largest abnormalities were found for phase-locked delta (1-4 Hz) and non-phase-locked theta (4-8 Hz). Delta phase resetting was moderately impaired and related to symptoms of disorganization. It also predicted evoked theta signal.

CONCLUSION

The substantial reduction of both evoked and induced oscillatory activity in schizophrenia indicates diminished recruitment of brain circuits engaged not only in stimulus-locked perceptual processing but also in more extensive processing less tightly time locked to the stimulus. Although reduced phase resetting makes a lesser contribution, it indicates a deficit in the ability to harness ongoing electrical activity.

Time and frequency domain event-related electrical activity associated with response control in schizophrenia

OBJECTIVE

To confirm previously reported abnormalities in time domain EEG components during a go/no-go task in schizophrenia, and to test the hypothesis that patients exhibit abnormalities in frequency domain components reflecting indices of behavioural impairment.

METHODS

EEG data were recorded from 17 male schizophrenia patients in a stable phase of illness and 17 healthy controls.

RESULTS

As compared with controls, patients displayed smaller N200 amplitudes and less evoked theta for correct hit trials; and smaller N200 and P300 amplitudes and less evoked delta and theta for correct reject trials. Effect sizes were largest for evoked delta. Source localisation revealed reduced activation in schizophrenia patients during the N200 and P300 time windows in anterior and posterior cingulate, medial frontal gyrus and precuneus. Evoked delta and theta oscillations were significantly correlated with the variability of reaction times and the performance level statistic d-prime.

CONCLUSIONS

The results demonstrate impairment of frontal and parietal brain areas involved in response control in schizophrenia. They also suggest that the timing of oscillations in patients is less precise leading to smaller evoked amplitudes and more variable reaction times.

SIGNIFICANCE

These findings add to the evidence that abnormal EEG oscillations contribute to impaired behavioural control in schizophrenia.

Auditory evoked potential variability in healthy and schizophrenia subjects

OBJECTIVES

To investigate if the reduced P50, N100 and P200 auditory evoked potential (EP) components and gating deficits seen in schizophrenia can be explained in terms of response incompleteness.

METHODS

Twenty-five healthy and schizophrenia participants were studied using pairs of 1000Hz tones (S1 and S2, 0.5s apart) separated by 8.0s. A correlation-based clustering method identified the responses containing P50, N100, and/or P200 related-activity.

RESULTS

Schizophrenia participants produced fewer S1 and S2 responses containing all three EP components than healthy participants. Healthy participants, but not the patient population, produced fewer and smaller S2 than S1 responses containing all three EP components. However, the S2 responses following complete S1 responses were smaller than the complete S1 responses in both populations.

CONCLUSIONS

The gating deficits observed in schizophrenia are due to two mechanisms. First, the S1 response consistency is less in schizophrenia than in health. Second, the S2 responses are attenuated less in schizophrenia.

SIGNIFICANCE

This research contributes to the understanding of response variability and sensory gating in health and schizophrenia. It also extends previous reports that fewer and smaller P300 components are produced in schizophrenia than in health to the mid-latency component range.

Reduced auditory evoked potential component N100 in schizophrenia--a critical review

The role of a reduced N100 (or N1) component of the auditory event related potential as a potential trait marker of schizophrenia is critically discussed in this review. We suggest that the extent of the N100 amplitude reduction in schizophrenia depends on experimental and subject factors, as well as on clinical variables: N100 is more consistently reduced in studies using interstimulus intervals (ISIs) >1 s than in studies using shorter ISIs. An increase of the N100 amplitude by allocation of attention is often lacking in schizophrenia patients. A reduction of the N100 amplitude is nevertheless also observed when such an allocation is not required, proposing that both endogenous and exogenous constituents of the N100 are affected by schizophrenia. N100 is more consistently reduced in medicated than unmedicated patients, but a reduction of the N100 amplitude as a consequence of antipsychotic medication was shown in only two of seven studies. In line with that, the association between the N100 reduction and degree of psychopathology of patients appears to be weak overall. A reduced N100 amplitude is found in first degree relatives of schizophrenia patients, but the risk of developing schizophrenia is not reflected in the N100 amplitude reduction.

An auditory processing abnormality specific to liability for schizophrenia

Abnormal brain activity during the processing of simple sounds is evident in individuals with increased genetic liability for schizophrenia; however, the diagnostic specificity of these abnormalities has yet to be fully examined. Because recent evidence suggests that schizophrenia and bipolar disorder may share aspects of genetic etiology the present study was conducted to determine whether individuals with heightened genetic liability for each disorder manifested distinct neural abnormalities during auditory processing. Utilizing a dichotic listening paradigm, we assessed target tone discrimination and electrophysiological responses in schizophrenia patients, first-degree biological relatives of schizophrenia patients, bipolar disorder patients, first-degree biological relatives of bipolar patients and nonpsychiatric control participants. Schizophrenia patients and relatives of schizophrenia patients demonstrated reductions in an early neural response (i.e. N1) suggestive of deficient sensory registration of auditory stimuli. Bipolar patients and relatives of bipolar patients demonstrated no such abnormality. Both schizophrenia and bipolar patients failed to significantly augment N1 amplitude with attention. Schizophrenia patients also failed to show sensitivity of longer-latency neural processes (N2) to stimulus frequency suggesting a disorder specific deficit in stimulus classification. Only schizophrenia patients exhibited reduced target tone discrimination accuracy. Reduced N1 responses reflective of early auditory processing abnormalities are suggestive of a marker of genetic liability for schizophrenia and may serve as an endophenotype for the disorder.

Differentiating cortical patterns of cognitive dysfunction in schizophrenia and posttraumatic stress disorder

Comparative studies are needed to determine whether the cognitive impairments found in various psychiatric disorders are specific to those disorders, or are a more universal consequence of mental illness. This study compares the patterns of cognitive dysfunction in two conditions characterized by working memory dysfunction, schizophrenia and posttraumatic stress disorder (PTSD). Three matched groups (Schizophrenia, PTSD, Control) of 16 subjects had event related potentials recorded, using a 27 electrode array, while they performed a working memory auditory target detection task. Both disorders were associated with impaired task performance, with greater impairment in schizophrenia. Reduction in N1 amplitude was found only in schizophrenia, and an increase in target N2 amplitude and latency was found only in PTSD. Both patient groups showed a reduction in the amplitude of the non-target and target P3, but the groups were distinguished by a reduction in non-target parietal P3 amplitude in the schizophrenia group and a reduction in target P3 amplitude over the left posterior parietal region in the PTSD Group. This study demonstrates that there are specific patterns of cognitive dysfunction associated with schizophrenia and with PTSD.

Electrophysiological correlates of selective attention: a lifespan comparison

Background

To study how event-related brain potentials (ERPs) and underlying cortical mechanisms of selective attention change from childhood to old age, we investigated lifespan age differences in ERPs during an auditory oddball task in four age groups including 24 younger children (9–10 years), 28 older children (11–12 years), 31 younger adults (18–25), and 28 older adults (63–74 years). In the Unattend condition, participants were asked to simply listen to the tones. In the Attend condition, participants were asked to count the deviant stimuli. Five primary ERP components (N1, P2, N2, P3 and N3) were extracted for deviant stimuli under Attend conditions for lifespan comparison. Furthermore, Mismatch Negativity (MMN) and Late Discriminative Negativity (LDN) were computed as difference waves between deviant and standard tones, whereas Early and Late Processing Negativity (EPN and LPN) were calculated as difference waves between tones processed under Attend and Unattend conditions. These four secondary ERP-derived measures were taken as indicators for change detection (MMN and LDN) and selective attention (EPN and LPN), respectively. To examine lifespan age differences, the derived difference-wave components for attended (MMN and LDN) and deviant (EPN and LPN) stimuli were specifically compared across the four age groups.

Results

Both primary and secondary ERP components showed age-related differences in peak amplitude, peak latency, and topological distribution. The P2 amplitude was higher in adults compared to children, whereas N2 showed the opposite effect. P3 peak amplitude was higher in older children and younger adults than in older adults. The amplitudes of N3, LDN, and LPN were higher in older children compared with both of the adult groups. In addition, both P3 and N3 peak latencies were significantly longer in older than in younger adults. Interestingly, in the young adult sample P3 peak amplitude correlated positively and P3 peak latency correlated negatively with performance in the Identical Picture test, a marker measure of fluid intelligence.

Conclusion

The present findings suggest that patterns of event-related brain potentials are highly malleable within individuals and undergo profound reorganization from childhood to adulthood and old age.

Disruption of auditory and visual attention in schizophrenia

Disruption of attention is a hallmark symptom of schizophrenia, and event-related potentials have been instrumental in studying this cognitive deficit. Event-related potentials (ERPs) have been used to study attention and its disruption in schizophrenia, with the most common finding of a reduced P300 component in auditory tasks. Some studies have found sparing of the P300 in visual attention, but reduction of an earlier attention-sensitive N2b, suggesting that the N2b may be a more sensitive index of attention disruption in schizophrenia. The current study compared visual and auditory attention using both unimodal and bimodal stimulus presentation in the same participants to examine the impact of schizophrenia on attention at both the early N2b and later P300 stages. Both N2b and P300 showed attention effects, being larger to targets than non-targets in all tasks. The N2b was reduced in the patient group in all tasks except the bimodal attend visual task, while the P300 was not reduced in the patients in any condition. This indicates that early attention, as indexed by the N2b, is differentially impaired in patients with schizophrenia, even when later attention, indexed by the P300, is intact.

Event-related potentials to auditory and visual selective attention in schizophrenia

BACKGROUND

Prior studies have shown a consistent reduction of the auditory P300 in schizophrenia, while the visual attention findings have been mixed. Both the auditory and visual N2b, an earlier, modality-specific attention index, are reduced in schizophrenia, sometimes despite sparing of the visual P300. Thus there may be a dissociation between the N2b and P300 attention effects in auditory and visual modalities in schizophrenia.

METHODS

Thirteen patients and thirteen controls observed symbols appearing on a screen, paired with simultaneous tones. In some blocks subjects responded to one of the symbols, in others to one of the tones. The N2b was predicted to be reduced in the patient group in both auditory and visual attention but the P300 reduced only while attending to tones.

RESULTS

Results showed a reduction of the N1 component in the patient group in the auditory condition but not in the visual. There was a reduction of the N2b target-minus-non-target difference wave in the patients in both auditory and visual target conditions. The P300 component was larger overall in the control group in both modalities, but did not show the usual enhancement to auditory targets in the control group.

CONCLUSIONS

These findings suggest that the ability to selectively attend to a target in one modality while ignoring the other is compromised in patients with schizophrenia. Perceptual processing appears to be impacted in the auditory modality while remaining intact in the visual. The N2b appears more vulnerable than the P300 in both auditory and visual attention in schizophrenia.

Clozapine improves working memory updating in schizophrenia

This study investigated the effect of clozapine on working memory in 15 subjects with schizophrenia, using an event related potential paradigm designed to separate components reflecting working memory updating from components related to target detection and response. Compared to matched controls and prior to treatment with clozapine, subjects with schizophrenia had N1, P3 and Late Slow Wave abnormalities indicating impairment in early stimulus evaluation and subsequent working memory functions. Treatment with clozapine was associated with normalization of the P3 and Late Slow Waves, indicating improvement in working memory updating and executive processing. There was also a partial normalization of N1 amplitude, suggesting improvement in early stimulus evaluation.

Stimulus sequence affects schizophrenia-normal differences in event processing during an auditory oddball task

Schizophrenia patients have difficulty distinguishing relevant from irrelevant auditory information. Auditory oddball paradigms are commonly used to investigate the processing of stimulus relevance. The present study used dense-array EEG and distributed source reconstructions to examine schizophrenia-normal differences in the processing of targets and standards as a function of the temporal sequence of stimuli. Brain responses were evaluated separately for early and late standards (standards 1-3 and 4-6 following a target, respectively) and early and late targets (those following 2-3 standards and 4-6 standards, respectively). The latencies of peaks (N1, P2, P3) in the event-related potential (ERP) waveforms did not differ between schizophrenia and normal subjects. However, schizophrenia-normal differences in neural activity, derived from minimum norm estimation, occurred at specific times during stimulus processing as a function of stimulus sequence. Schizophrenia patients displayed smaller activity than normals in early ERPs (left hemispheric N1, right frontal P2) to late targets, and they produced P3-like responses to late standards. Furthermore, during the P2/N2 time interval, opposite patterns of brain activity were elicited in schizophrenia and normal subjects in response to standards, indicating different neural responses to the same stimulus events. These results suggest attention allocation to task-irrelevant stimuli in schizophrenia, consequent upon insufficient representation of stimulus significance and context. Thus, schizophrenia compromises the ability to properly use context to solve even simple cognitive problems.

Long latency evoked potential database for clinical applications: justification and examples

We summarize our experience with the clinical utility of long latency evoked potential (EP) data in clinical QEEG studies. In contrast to common wisdom, such EP data are consistent across appropriately chosen age groups. In a healthy adult population, EP data correlate consistently with independently collected psychological variables. In our pediatric referral population, EP data are of greatest and most unique value in the learning disabilities but also augment detection of abnormality in epilepsy and behavioral abnormality. Selection of subjects for a clinical database on the basis of examined medical, neurological and behavioral health, forms adequately consistent groupings for clinical utility. The use of the Z-SPM is essential for detection of EP abnormality. A minimum of three replications within a clinical study protects against chance/false positives. Also, the true data dimensionality within EP data sets is far less than the total number of variables typically collected.

An ERP index of task relevance evaluation of visual stimuli

Recently several event-related potential attention studies have described a prefrontal positivity at about the same latency as the posterior N2 (approximately 200-300 ms), variously termed the frontal selection positivity (FSP), the anterior P2 (P2a), or the frontal P3 (P3f). These components have a similar spatio-temporal distribution and similar eliciting properties, suggesting that they represent the same component. However, these components have been differentially interpreted as arising from neural systems of feature selection, stimulus evaluation, or response production. The present study employed a visual target detection (oddball) design with different response conditions: passive (no response), overt (keypress), and covert (silent count), to examine the impact of task relevance and response production on the frontal P2a. The results showed that the P2a was present to task-relevant stimuli but had the same scalp topography and estimated source-dipole locations in both overt and covert responding, indicative of an index of stimulus evaluation, rather than response production.

Electroencephalographic brain dynamics following manually responded visual targets

Scalp-recorded electroencephalographic (EEG) signals produced by partial synchronization of cortical field activity mix locally synchronous electrical activities of many cortical areas. Analysis of event-related EEG signals typically assumes that poststimulus potentials emerge out of a flat baseline. Signals associated with a particular type of cognitive event are then assessed by averaging data from each scalp channel across trials, producing averaged event-related potentials (ERPs). ERP averaging, however, filters out much of the information about cortical dynamics available in the unaveraged data trials. Here, we studied the dynamics of cortical electrical activity while subjects detected and manually responded to visual targets, viewing signals retained in ERP averages not as responses of an otherwise silent system but as resulting from event-related alterations in ongoing EEG processes. We applied infomax independent component analysis to parse the dynamics of the unaveraged 31-channel EEG signals into maximally independent processes, then clustered the resulting processes across subjects by similarities in their scalp maps and activity power spectra, identifying nine classes of EEG processes with distinct spatial distributions and event-related dynamics. Coupled two-cycle postmotor theta bursts followed button presses in frontal midline and somatomotor clusters, while the broad postmotor "P300" positivity summed distinct contributions from several classes of frontal, parietal, and occipital processes. The observed event-related changes in local field activities, within and between cortical areas, may serve to modulate the strength of spike-based communication between cortical areas to update attention, expectancy, memory, and motor preparation during and after target recognition and speeded responding.

Meta-analysis of P300 and schizophrenia: patients, paradigms, and practical implications

The goal of the present meta-analysis was to identify factors that contribute to P300 event-related brain potential (ERP) differences in patients with schizophrenia compared to unaffected controls in an attempt to characterize the clinically relevant dimensions underlying P300 deficits in patients with schizophrenia. P300 effect size (d) was smaller in amplitude and longer in latency in schizophrenic patients compared to normal controls, with the strongest effects obtained from the auditory oddball. Paranoid subtype demonstrated larger P300 amplitude effect sizes than other disease subtypes, and P300 latency effect size decreased with disease duration. Psychopathology severity and antipsychotic medications were unrelated to P300 amplitude effect size. Gender proportion, educational level, and stimulus and task variables also affected P300 amplitude and latency effect sizes. The findings are used to formulate a theoretical account of the empirical data and provide suggestions for maximizing the utility of the P300 component in the assessment of schizophrenia.

Neurophysiologic correlates of psychiatric disorders and potential applications in epilepsy

There is increasing interest in psychiatric assessment using neurophysiologic tools such as electroencephalography (EEG), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS). This is because these technologies have good temporal resolution, are relatively noninvasive, and (with the exception of MEG) are economical. Many different experimental paradigms and analysis techniques for the assessment of psychiatric patients involving these technologies are reviewed including conventional quantitative electroencephalography (QEEG), EEG cordance, low-resolution electromagnetic tomography (LORETA), frontal midline theta, midlatency auditory evoked potentials (P50, N100, P300), loudness dependency of the auditory evoked potential (LDAEP), mismatch negativity (MMN), contingent negative variation (CNV), and transcranial magnetic stimulation (TMS). Many of these neurophysiologic stimulus paradigms hold the promise of improving psychiatric patient care by improving diagnostic precision, predicting treatment response, and providing new phenotypes for genetic studies. Large cooperative multisite studies need to be designed to test and validate a few of these paradigms so that they might find use in routine clinical practice.

Cerebral signs of altered adaptability in females with acute psychosis

In psychosis, behavior is not guided by sensory cues from surroundings. Novel, meaningful behaviors require intact integrative functions such as short-term memory and motor planning, as well as an optimized level of arousal. In this study, we monitored markers of automatic auditory processing in 15 female never-medicated psychotic patients. Fifty-eight channels of EEG were recorded simultaneously with sympathetic skin responses while arousing auditory stimuli were delivered. Neuropsychological tests concentrating on frontal lobe functions were also performed. Prominent neurophysiological and behavioral signs of increased cortical activation were observed in psychotic patients. This widespread disinhibition may attempt to compensate for the impairment of neuronal processing of sensory input from surroundings in the earliest stages of a psychotic illness.

Reaction-times and bioelectrical brain signals of drug-naive schizophrenic first-onset patients in identification and classification tasks

OBJECTIVE

The question of the present study is whether disturbances of response-selection in schizophrenic patients are discernible only if overt motor-actions are required, or also if covert cognitive actions are necessary.

METHOD

Visual identification (digits) and classification (dot-enumeration) tasks were presented to 18 drug-naive, first-onset schizophrenic patients and healthy controls. It is assumed that enumeration of more than three dots requires additional cognitive processes as buffering and re-focusing of attention. Reaction-times and 21-channel-EEG were measured. For eye-movement artefact-elimination a new non-parametric regression approach was applied.

RESULTS

Reaction-times revealed that in the patient group response selection is lengthened in both tasks. Perception of dot numbers is not affected. Bioelectrical data depicted a left-lateralization of posterior P100 and N 100 in the patient group as well as an enhanced fronto-central P200.

CONCLUSION

Whereas in reaction-times of patients only a disturbance of response selection is discernible, bioelectrical measurements also point to an altered organization of perceptive processes.

Functional asymmetry in schizophrenic patients during auditory speech processing

In two experiments, functional laterality and interhemispheric transfer was investigated in schizophrenic patients (n=14) and healthy controls (n=17). In Experiment 1, words and pseudowords were presented either to the left or right ear (monaural condition) or simultaneously to both ears (binaural condition). In Experiment 2, subjects had to discriminate two tones differing in frequency during monaural and binaural stimulation. Healthy controls showed a right ear advantage (REA) for word stimuli, indicating left-hemispheric superiority for word processing. The same lateralization pattern was found in schizophrenic patients, indicating unimpaired functional lateralization of auditory language processing. In both groups, no REA was found for pseudowords resulting in significant WordnessxEar interactions. When presented binaurally, auditory processing of words and pseudowords did not differ significantly from any of the two monaural conditions. Tone discrimination did not lead to any ear asymmetry. The results show normal patterns of functional asymmetry during auditory language processing and tone discrimination in schizophrenic patients.

Event-related potentials and genetic risk for schizophrenia

BACKGROUND

Event-related potentials (ERPs) during an auditory oddball task were investigated in patients with schizophrenia and in their healthy siblings to explore the question of whether abnormalities of two-dimensional topographic scalp-distribution of P300 amplitude and latency relate to genetic risk for schizophrenia. We also examined the P50, N100, and P200-waves, elicited during the same task.

METHODS

We investigated 42 schizophrenic patients, 62 of their healthy siblings, and 34 unrelated normal control subjects with a standard auditory oddball paradigm and 16 electroencephalogram electrodes. Amplitudes and latencies of the ERPs P50, N100, P200, and P300 were topographically analyzed.

RESULTS

In the patients, P300 amplitude was significantly decreased in the range of 54%-58% over the left parietotemporal area. Siblings did not show decreased P300 amplitudes when compared with normal subjects. P300 latencies were unchanged in both groups. No significant group differences were observed for the other event-related potentials.

CONCLUSIONS

In line with previous studies, the P300 amplitude in schizophrenic patients was decreased over the left temporoparietal area; however, we found no evidence for a genetic trait effect in the event-related potential abnormality. Possible reasons for these largely negative findings are discussed.

The P3 auditory event-related brain potential indexes major personality traits

BACKGROUND

The amplitude of the auditory P3 event-related potential is reduced in patients with axes I and II disorders. Data regarding P3 amplitude and normal personality traits in healthy individuals have been inconsistent, however, although more extreme variants of dimensional traits such as neuroticism and extraversion are associated with psychiatric morbidity.

METHODS

Male subjects (n = 18) recruited from the community completed the NEO Five-Factor Inventory, which consists of five scales: Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness. P3 potentials were generated using an auditory discrimination paradigm to which a third, novel stimulus was added. Partial least squares analysis, a multivariate statistical procedure, was used to test the relationship, in both stimulus conditions, between P3 amplitude at six electrode sites and the five personality dimensions.

RESULTS

P3 amplitude across conditions and sites was positively related to Extraversion, Openness, Agreeableness, and Conscientiousness and negatively related to Neuroticism.

CONCLUSIONS

Previous studies have shown that both reduced P3 amplitude and a high Neuroticism/low Extraversion-Openness-Agreeableness-Conscientiousness trait pattern are associated with the presence of, and risk for, substantial psychiatric morbidity. Our results suggest that processes indexed by auditory P3 amplitude are related to these broad personality dimensions in healthy individuals.

Event-related brain potentials (ERPs) in schizophrenia for tonal and phonetic oddball tasks

BACKGROUND

Prior studies using simple target detection ("oddball") tasks with pure tones have reported asymmetric reduction of the P3 event-related potential (ERP). This study investigated the time course and topography of ERPs recorded during both tonal and phonetic oddball tasks.

METHODS

Event-related potentials of 66 patients (14 unmedicated) diagnosed with schizophrenia (n = 46) or schizoaffective disorder (n = 20) and 32 healthy adults were recorded from 30 scalp electrodes during two oddball tasks using consonant-vowel syllables or complex tones. Overlapping ERP components were identified and measured by covariance-based principal components analysis.

RESULTS

Schizophrenic patients showed marked, task-independent reductions of early negative potentials (N1, N2) but not reduced P3 amplitude or abnormal P3 asymmetry. Task-related hemispheric asymmetries of the N2/P3 complex were similar in healthy adults and schizophrenic patients. Poorer task performance in patients was related to ERP amplitudes, but could not account for reductions of early negativities.

CONCLUSIONS

The findings suggest that both patients and control subjects activated lateralized cortical networks required for pitch (right frontotemporal) and phoneme (left parietotemporal) discrimination. Task-independent reductions of negativities between 80 and 280 msec after stimulus onset suggest a deficit of automatic stimulus classification in schizophrenia, which may be partly compensated by later effortful processing.

Auditory feature conjunction in patients with schizophrenia

The neural mechanisms supporting performance during single feature and feature conjunction tasks were investigated in patients with schizophrenia and age-matched controls using event-related brain potentials. In different blocks of trials, participants responded to auditory targets defined by one of two pitches, one of two locations, or both pitch and location. All participants were faster and more accurate in detecting targets defined by a single feature than for targets defined by a conjunction of features. Compared with the single feature conditions, conjunction targets were associated with enhanced negativity between 200 and 250ms (N2) post-stimulus and showed a delayed P3b latency. Compared with controls, patients with schizophrenia showed reduced N1 and N2 amplitude elicited by single and conjunctive targets. The results are consistent with defective perceptual mechanisms in schizophrenia. The fact that both performance and P3b amplitude were similar in patients and controls suggests that controlled processes compensate for processes normally carried out by early perceptual mechanisms.

Impairment of an event-related potential correlate of memory in schizophrenia: effects of immediate and delayed word repetition

OBJECTIVE

We investigated the nature of the memory impairment in schizophrenia using an event-related potential (ERP).

METHODS

Visual ERPs were recorded while 20 schizophrenics and 20 controls performed semantic categorization tasks with incidental word repetitions. Participants responded to occasional target words. Half of the non-target words were repeated immediately after initial presentation (lag 0) or after 5 intervening words (lag 5).

RESULTS

In both groups, ERPs to words at lag 0 were more positive than those to non-repeated words, though this positive-going effect was attenuated in the schizophrenics, especially around 400-500 ms. The effect at lag 5 was smaller and shorter than that at lag 0 but was comparable between groups. Attenuation of the N400 peak occurred for word repetition at lag 0 in controls but not in schizophrenics, whereas a peak increment in the late positive component induced by word repetition at both lags was observed in both groups.

CONCLUSIONS

Findings indicate that patients with schizophrenia have a deficit in a brain process modulating ERP correlates of memory, when words are repeated immediately. This deficit might be related to an abnormal N400 priming effect in schizophrenia.

Frontal evaluation and posterior representation in target detection

This study examined the topography of the event-related potential in visual-spatial compared to visual-object target detection. The initial index of target detection in the ERP was an inferior anterior P2a accompanied by a posterior N2b. Single unit studies in the monkey indicate that the detection of task-relevant stimuli requires interaction between prefrontal cortex and perceptual representation areas in the posterior brain. The posterior brain processes the physical features of stimuli while frontal cortex performs higher-order operations, such as evaluating the task-relevance of a stimulus. Target detection requires an interaction between feature representations and relevance representations. We hypothesize that the P2a and N2b ERP indices of target detection reflect this frontal/posterior interaction. Visual-spatial feature information is processed in the dorsal posterior brain (posterior parietal cortex) and visual-object information is processed in the ventral posterior brain (inferior occipito-temporal cortex). We observed that at the peak of the P2a the N2b was located over posterior dorsal leads in visual-spatial target detection and over posterior ventral leads in visual-object target detection. The P2a was largest over inferior prefrontal leads in both tasks. We suggest that this distribution is consistent with interaction between orbitofrontal cortical areas of salience representation and posterior cortical areas of stimulus feature representation.

The neurophysiological meaning of auditory P300 in subtypes of schizophrenia

Event-related potentials are a powerful tool to investigate the real-time course of brain electrical mass activation during cognitive processing. In several psychiatric disorders, differences compared to healthy subjects have been reliably described. The specificity and the pathophysiological meaning of the findings were unclear in most studies, however. This review summarizes methodological aspects and findings, in healthy subjects and psychiatric patients, of investigations based on the auditory oddball paradigm, which evokes the P300 component of event-related potentials. Recent convergent results from P300 and brain imaging studies allowed the interpretation of P300 findings in psychotic disorders in terms of different specific and meaningful neurophysiological disturbances. Namely, core schizophrenia is characterized by a left-temporal dysfunction associated with deficits in verbal processing. Acute remitting schizophrenia-like psychoses (cycloid psychosis, ICD-10 F23), on the other hand, show normal hemispheric balance but consistent signs of cerebral hyperarousal. Recent studies further indicate that the drive for action of manic patients does not rely on over-excitation but rather on frontal disinhibition. The findings may help to further advance the understandings and sub-grouping of functional psychoses based on pathophysiological mechanisms.