Prolonged latencies of the N2 and P3 of the auditory event-related potential in children at risk for schizophrenia. A preliminary report

A Meta-analytic Review of Auditory Event-Related Potential Components as Endophenotypes for Schizophrenia: Perspectives From First-Degree Relatives

INTRODUCTION

As endophenotypes bridge the gap between genetics and phenotypic disease expression, identifying reliable markers is important for fostering understanding of pathophysiology. The present aim was to conduct current meta-analyses of 3 key auditory event-related potential (ERP) components that have been held as potential endophenotypes for schizophrenia: P50, P300 amplitude and latency, and mismatch negativity (MMN), reflective of sensory gating, attention and classification speed, and perceptual discrimination ability, respectively. In order to assess endophenotype viability, these components were examined in unaffected relatives of patients with schizophrenia and healthy controls.

METHODS

Effect sizes (ES) were examined between relatives and controls for P50 suppression (10 studies, n = 360 relatives, 473 controls), P300 amplitude (20 studies, n = 868 relatives, 961 controls), P300 latency (17 studies, n = 674 relatives, 792 controls), and MMN (11 studies, n = 377 relatives, 552 controls).

RESULTS

Reliable differences in P50 suppression (ES = 0.86, P < .001), P300 amplitude (ES = -0.52, P < .001), and P300 latency (ES = 0.44, P < .05) were found between unaffected relatives and controls. A trend was found between relatives and controls for MMN (ES = 0.21, P = 0.06), and the use of extraneous channels was found to be a significant moderator (P = 0.01). When MMN was analyzed using frontocentral channel Fz, a significant difference was found (ES = 0.26, P < 0.01).

DISCUSSION

The results indicate that P50 suppression, P300 amplitude and P300 latency, and MMN may serve as viable endophenotypes for schizophrenia.

In search of biomarkers in psychiatry: EEG-based measures of brain function

Current clinical parameters used for diagnosis and phenotypic definitions of psychopathology are both highly variable and subjective. Intensive research efforts for specific and sensitive biological markers, or biomarkers, for psychopathology as objective alternatives to the current paradigm are ongoing. While biomarker research in psychiatry has focused largely on functional neuroimaging methods for identifying the neural functions that associate with psychopathology, scalp electroencephalography (EEG) has been viewed, historically, as offering little specific brain source information, as scalp appearance is only loosely correlated to its brain source dynamics. However, ongoing advances in signal processing of EEG data can now deliver functional EEG brain-imaging with distinctly improved spatial, as well as fine temporal, resolution. One computational approach proving particularly useful for EEG cortical brain imaging is independent component analysis (ICA). ICA decomposition can be used to identify distinct cortical source activities that are sensitive and specific to the pathophysiology of psychiatric disorders. Given its practical research advantages, relatively low cost, and ease of use, EEG-imaging is now both feasible and attractive, in particular for studies involving the large samples required by genetically informative designs to characterize causal pathways to psychopathology. The completely non-invasive nature of EEG data acquisition, coupled with ongoing advances in dry, wireless, and wearable EEG technology, makes EEG-imaging increasingly attractive and appropriate for psychiatric research, including the study of developmentally young samples. Applied to large genetically and developmentally informative samples, EEG imaging can advance the search for robust diagnostic biomarkers and phenotypes in psychiatry.

Premorbid indicators and risk for schizophrenia: a selective review and update

Prospective studies of young relatives at risk for schizophrenia (high-risk studies, HR) can shed light on premorbid precursors of schizophrenia. Early HR studies pointed to a wide prevalence of schizophrenia spectrum psychopathology among young relatives at increased genetic risk. Recent studies suggest that young HR relatives have neurobehavioral deficits and structural, physiological, and neurochemical brain abnormalities that may date back to childhood or earlier. In this paper, we provide a selected overview of the lessons and limitations of early "first generation" studies and the beginning insights from recent "second generation" studies. We also provide an interim summary of data from the ongoing studies of young relatives at risk for schizophrenia in Pittsburgh. Collectively, such data may help us to predict the eventual emergence of schizophrenia, and schizophrenia spectrum or non-spectrum psychopathology.

Approaches for adolescents with an affected family member with schizophrenia

Prospective studies of adolescents at risk for schizophrenia (high-risk studies) can shed light on the possible premorbid precursors of schizophrenia. Recent studies have provided evidence of neurobehavioral, brain structural, physiologic, and neurochemical deficits in adolescent nonpsychotic high-risk relatives that may date back to childhood or earlier. These results are collectively providing a critical window into the inter-relationships between genetic predisposition, neurodevelopment, and premorbid indicators of risk in schizophrenia. Convergent approaches are inherently powerful in mutually informing each other in enriching the knowledge of the risk factors that predict the eventual onset of schizophrenia. Defining such reliable predictors of the onset of schizophrenia may provide us with the tools to better understand the etiology and pathophysiology of the illness, and may pave the way for innovative methods of treatment and possibly prevention. The authors review the relevant literature in this promising field of inquiry and summarize recent findings from high-risk studies.

[The p300 cognitive event-related potential. II. Individual variability and clinical application in psychopathology]

The P300 wave is one of the cognitive components of the event-related potential (ERP) that is used to investigate the cognitive processes, and which can be used to study patient populations with a variety of psychiatric disorders. Its clinical utility has been increased by the identification of factors that contribute to the variability in its amplitude and latency. However, its value as a diagnostic index has not been entirely established. It can provide a useful recording of patients' information processing, and indicate the severity of the clinical state and its possible evolution. It can also assist in determining what therapeutic approach to adopt. In the present review, the findings in the literature concerning interindividual variation in the P300 wave are first described; several variables significantly influence the amplitude and latency of this wave, such as age, gender, intelligence and personality. Following this, the relevance of the data in the literature on the clinical applications of P300 in psychopathology is examined, including the studies undertaken to obtain an objective diagnostic index for mental disorders and also those carried out to assess the problems concerning the interpretation of information connected with the mental pathologies examined. P300-associated findings on dementia, schizophrenia, depression, alcoholism, drug addiction, anxiety disorders (panic disorder, obsessive-compulsive disorder, and post-traumatic stress syndrome) and on personality disorders (schizoid, antisocial or borderline personality disorder) have been examined in detail.

P300 subcomponent abnormalities in schizophrenia: III. Deficits In unaffected siblings of schizophrenic probands

BACKGROUND

Reduced P300 amplitude is a robust finding in patients with schizophrenia. In previous investigations, we reported reductions of specific subcomponents of the auditory oddball P300 that were independent of acute symptomatology and persistent over time, consistent with a trait abnormality. To clarify whether these stable deficits represented genetic markers of vulnerability to schizophrenia, event-related brain potentials (ERPs) from patients were compared to those from their own healthy siblings and unrelated control subjects.

METHODS

Auditory P300 ERPs were acquired from 11 schizophrenic patients, 12 healthy siblings and 23 matched control subjects. Five P300 subcomponents were identified using current source density measures: frontal, bilateral parietal, and bilateral temporal.

RESULTS

Consistent with previous reports, patients had reduced parietal and frontal P300 amplitudes. The healthy siblings of the schizophrenic probands had an isolated reduction of the frontal P300.

CONCLUSIONS

Frontal P300 amplitude is a potential endophenotypic marker of genetic vulnerability to schizophrenia in individuals who otherwise show no evidence of clinical symptomatology. Given the functional interpretation of the frontal P300 as a physiological correlate of cognitive orienting, this supports the hypothesis that impairments of the neural substrate underlying attentional mechanisms are selective indicators of genetic susceptibility to schizophrenia in high-risk individuals.

Alteration of event related potentials in siblings discordant for schizophrenia

This study was aimed at confirming that auditory event related potential (ERP) abnormalities are indicators of vulnerability to schizophrenia. Auditory ERP performances were assessed at Fz, Cz, and Pz, with an oddball paradigm, in 21 clinically stable patients with schizophrenia, 21 of their healthy biological full siblings and 21 control subjects. The evoked response did not differ between the three groups on N200 waves. Compared to controls, patients with schizophrenia exhibited reduced amplitudes of N100 and P300, and prolonged latency of P300, while their siblings showed prolonged latency of P200 and P300. Among the patients with schizophrenia, ERP abnormalities did not correlate with age, clinical state, duration of illness or antipsychotic treatments. Although other conditions also accounted for alterations of the same type, ERP abnormalities may represent a neurobiological marker of the genetic vulnerability to schizophrenia, independent of phenotypic expression.

N2 and P3b components of the event-related potential in students at risk for psychosis

The N2 and P3b components of event-related potentials (ERPs) were studied in students who were identified as being at high risk for psychosis on the basis of their scores on the Chapman Psychosis Proneness Scales (PPS). The Magical Ideation subscale (MIS), the Perceptual Aberration subscale (PABS), and the Social Anhedonia subscale (SAS) were administered to 2,022 undergraduate university students. To determine if there were any relationships between these psychometric instruments and electrophysiological measures, 40 high-risk students were compared with 40 age- and gender-matched control students using auditory ERPs obtained from three midline electrodes (Fz, Cz, Pz) in a standard oddball paradigm. N2 (rare stimuli) and N2b latencies were significantly longer in the high-risk than in the control subjects, and the high-risk group also evidenced significantly smaller amplitude of the P3b component. No significant correlations between scores on the PPS or its three subscales and the amplitudes or latencies of the P3b or N200 component were found. These findings suggest that the N2 and P3b ERP components might serve as trait markers for psychosis and that individuals psychometrically identified as being at high risk for psychosis have deficits in the maintenance of attention and in decision-making.

Topography of the auditory P300 in schizotypal personality

BACKGROUND

Research with schizophrenic patients has demonstrated reduced amplitude of the P300b elicited with the auditory "oddball" paradigm, as well as reduced P300a amplitude following "novel" stimuli. The focus of the present study was the investigation of these components in a nonclinical sample of participants with high expressions of the schizotypal personality trait.

METHODS

By use of an acoustic oddball task, including the presentation of novel stimuli, the event-related brain potentials of 14 participants with "low" and 13 participants with "high" scores on the German adaptation of the "Schizotypal Personality Questionnaire" were investigated. Current source density (CSD) curves and spline-interpolated CSD maps were generated. Peak amplitudes and latencies of the N100, P200, P300a, and P300b were determined for the CSD data.

RESULTS

Results indicate no group differences with respect to N100, P200, and P300a amplitudes and latencies. By contrast, the P300b amplitude was significantly smaller in high- as compared to low-scoring participants. Left-temporal as compared to right-temporal P300b was significantly smaller in high- than in low-schizotypal participants.

CONCLUSIONS

Confirming results of other researchers, this present study suggests that a reduced P300b amplitude and an altered P300b topography at temporal sites may be a trait-like "marker" of the schizophrenia spectrum.

Relationship between auditory P300 amplitude and age of onset of schizophrenia in older patients

Auditory P300 amplitude reductions are well-established in young adults with schizophrenia. Little is known, however, regarding the P300 in older schizophrenia patients, especially those with late onset. We studied 28 middle-aged and elderly (mean age = 62.7 years) patients [14 with early onset schizophrenia (EOS) and 14 with late onset schizophrenia (LOS)] and 14 normal comparison (NC) participants using an auditory oddball paradigm. Event-related potentials were recorded from 15 scalp electrodes and six non-scalp sites. There were no significant differences between EOS and LOS groups in neuroleptic dosage, symptom severity, reaction times, target-detection accuracy, or N100 and N200 ERP measures. The EOS, but not the LOS, group had significantly smaller auditory oddball P300 amplitudes than the NC group. Twelve of the 14 LOS patients had P300 amplitudes in the normal range. Smaller P300 amplitudes were associated with earlier age of onset (r = 0.48), longer duration of illness (r = -0.49) and more severe alogia (r = -0.50). We conclude that P300 abnormalities in schizophrenia may be a marker for a disease subtype with early onset and more severe information-processing deficits.

Preattentive information processing as measured by backward masking and texton detection tasks in adolescents at high genetic risk for schizophrenia

Schizophrenic patients have consistently been reported to show deficits in preattentive information processing as demonstrated by impairments in visual backward masking and texton detection tasks. Texton detection refers to Julesz's texton theory, which defines a certain limited number of texton elements (e.g., one 'L' among many '+') that can be detected readily and simultaneously without attentional effort irrespective of the size of the rest of the visual field. The present study investigated whether deficits of preattentive information processing are more prevalent in a group of adolescents of high genetic risk for schizophrenia compared to matched control subjects. Although differences in the performance in visual backward masking tasks could not be detected with our experimental approach, preattentive texton detection was to a certain extent disturbed in subjects at risk. Moreover, subjects at risk did not show the advantage of the right hemisphere in processing texton elements which was found in the control group. This may point to a subtle dysfunction of the right hemisphere in the risk group. It is concluded from the present study that deficits in preattentive texton detection may represent an indicator for a schizophrenic disposition. However, further studies including other high risk groups, schizophrenics in remission and individuals with a schizotypal personality disorder are needed to confirm this hypothesis.

Deviate P200 and P300 in non-patient college students with high scores on the schizophrenia scale of the Minnesota Multiphasic Personality Inventory (MMPI)

Event-related potentials (ERPs) were examined in 16 college students who had high scores on the Schizophrenia Scale of the MMPI (HSS) but were without a hereditary disposition for major psychiatric disorders. 32 sex- and age-matched college students were used as controls. Subjects whose T scores were higher than 70 were designated the HSS subjects. ERPs were recorded during an auditory oddball task. Although neither the P300 latencies nor the P200 latencies differed between the two subject groups, the amplitudes of P300 to rare stimuli and P200 to frequent stimuli were lower in the HSS subjects than in the controls. These results suggest that deficits, both in the P300-related cognitive function to rare relevant stimuli, as well as matching and/or the comparison process for irrelevant frequent stimuli, may be present in HSS subjects. The HSS subjects, especially those with a combination of P300 and P200 deficits, even though without a hereditary diathesis for schizophrenia, may constitute one type of high-risk group.

The auditory N2 component in schizophrenia: relationship to MRI temporal lobe gray matter and to other ERP abnormalities

The N2 component of the auditory event-related potential (ERP) indexes cognitive processes involved in the categorization of deviant stimuli. Although N2 amplitude and latency abnormalities have been reported in schizophrenia, their relationship to MRI structural changes, clinical status, and P3 abnormalities has not been defined. We therefore studied the auditory N2 and P3 components elicited by an oddball paradigm in 15 right-handed male subjects with schizophrenia and 14 control subjects who had quantitative MRI measures of temporal lobe gray-matter structures. To provide a methodological comparison, we measured the auditory N2 from both the target ERP (N2t) and the target-minus-frequent ERP difference (N2d) waveforms. Both N2t and N2d amplitude were bilaterally reduced in schizophrenics, with N2d showing a more pronounced reduction. Within the schizophrenic group, N2 amplitude reduction was associated with reduction in gray-matter volume of the left superior temporal gyrus (STG) and of medial temporal lobe structures bilaterally, and clinically, with greater chronicity. P3 amplitude, in contrast, correlated only with left posterior STG volume, and was more prominently associated with delusions and thought disorder. These findings suggest that the N2 and P3 components, though occurring sequentially in the ERP, tap separable anatomic and behavioral abnormalities in schizophrenia.

Event-related potential correlates of impaired selective attention in children at high risk for schizophrenia

Auditory event-related potentials (ERPs) associated with selective attention were recorded in 21 children at high-risk for schizophrenia and in 21 matched controls. The subjects performed a selective listening task. For behavioral evaluation, target counts on the selective listening task and on cognitive performance were assessed. Group-specific differences of ERP components could be demonstrated, as reflected by significant amplitude reductions of the frontally located negative difference wave (Nd) and of the P3 component, following selectively attended stimuli, in the high-risk children. P3 latencies tended to be prolonged in the high-risk group. Reduced Nd was found in 14 and reduced P3 in 16 high-risk children among the 21 matched pairs. Significant correlations between the ERP reductions and psychometric deficit (counting accuracy) were observed. Mismatch negativity (MMN), an ERP component associated with automatic processing of physically deviant stimuli, did not differentiate significantly between groups, but was distinctly reduced in the high-risk group. The Nd and P3 reductions suggest deficits of selective attention in a considerable number of the subjects genetically at risk for schizophrenia. The present findings are discussed with respect to their relevance as indicators of a predisposition to schizophrenia.

P300 in first degree relatives of schizophrenics

It has been reported that the amplitude of P300 is low in schizophrenic patients and high risk children. We recorded P300 components of the event-related potentials in first degree relatives of schizophrenic propositi who were considered to be over the age limit of the risk period for manifestation of schizophrenia and compared them with those of schizophrenic patients and controls. Both the first degree relatives and the schizophrenic patients showed lower P300 amplitude than the controls. There was no significant difference between the first degree relatives and schizophrenic patients in the P300 amplitude. These results would indicate that a low P300 amplitude is a trait marker for schizophrenia.

Endogenous event-related brain potentials and psychometric performance in children at risk for schizophrenia

Two independent groups of high-risk children for schizophrenia and their matched control children were submitted to the following experiments: an auditory oddball paradigm registrating late event-related potentials (ERPs) and a psychometric test battery including the assessment of Wechsler Intelligence Scales, reaction times (after regular and irregular preparatory intervals), and the d2-attention test. The study was intended to clarify whether long-latency ERPs and the selected psychometric tests would contribute to reliably differentiating between these groups. The results showed significantly prolonged latencies of the P3 component of the ERPs to rare, task-relevant target stimuli in both high-risk groups compared with the controls. Similarly, the N2 latencies were delayed in both groups. By contrast, ERP patterns to frequent, nontask-relevant stimuli were very similar, with no significant differences between high-risks and normals; nor did any ERP amplitudes show significant differences. The data are interpreted as a reflection of a subtle deficit in maintaining attention and a subsequent impairment of stimulus discrimination in high-risk children. This is consistent with the psychometric findings of higher error scores in target counts and d2-test, and significantly prolonged reaction times after regular preparatory intervals (PIs) in the high-risks. The findings may hint at a vulnerability for schizophrenia in high-risk children. Given the high prevalence of the attentional dysfunctions in both high-risk groups, however, it is hypothesized their presence does not necessarily imply an unequivocal manifestation of schizophrenia.