Replication of a P50 auditory gating deficit in Australian patients with schizophrenia

Transitioning illicit drug preferences and emerging user identities in Ohio: The proliferation of methamphetamine use among African Americans

Understanding the social dynamics of local methamphetamine markets is critical to improving community health and reducing social costs associated with illicit drug use. We examine a local drug market in Summit County, Ohio, wherein methamphetamine users ascribe themselves different ethnic identities from those long associated with the drug elsewhere in the United States. Qualitative interviews with 52 study participants demonstrate that very poor and homeless White males and females are now using methamphetamine; however, even more surprising is that 31 of the participants identified themselves as poor or homeless, male or female African, Native, biracial, or multiracial Americans. The drug use trajectory of these 31 participants in particular involved a transition from a historical preference for crack to a present one for methamphetamine and, in some cases, a preference for concurrent use of methamphetamine and heroin. Many of these methamphetamine users also emphasized their ethnic identity to distinguish themselves as nonproducers of methamphetamine in comparison to Whites, who are commonly associated with methamphetamine production. Findings appear to suggest an emergent means of identity management resulting from the ethnic diversity of users in this methamphetamine market. These findings may have relevance in other communities with similar demographics and drug markets and may hold important implications for drug treatment, policy-making, and law enforcement professionals' work associated with methamphetamine users, producers, and distributors.

Sensory gating deficits in the attenuated psychosis syndrome

BACKGROUND

Individuals with an "Attenuated Psychosis Syndrome" (APS) have a 20-40% chance of developing a psychotic disorder within two years; however it is difficult to predict which of them will become ill on the basis of their clinical symptoms alone. We examined whether P50 gating deficits could help to discriminate individuals with APS and also those who are particularly likely to make a transition to psychosis.

METHOD

36 cases meeting PACE (Personal Assessment and Crisis Evaluation) criteria for the APS, all free of antipsychotics, and 60 controls performed an auditory conditioning-testing experiment while their electroencephalogram was recorded. The P50 ratio and its C-T difference were compared between groups. Subjects received follow-up for up to 2 years to determine their clinical outcome.

RESULTS

The P50 ratio was significantly higher and C-T difference lower in the APS group compared to controls. Of the individuals with APS who completed the follow-up (n=36), nine (25%) developed psychosis. P50 ratio and the C-T difference did not significantly differ between those individuals who developed psychosis and those who did not within the APS group.

CONCLUSION

P50 deficits appear to be associated with the pre-clinical phase of psychosis. However, due to the limitations of the study and its sample size, replication in an independent cohort is necessary, to clarify the role of P50 deficits in illness progression and whether this inexpensive and non-invasive EEG marker could be of clinical value in the prediction of psychosis outcomes amongst populations at risk.

Multi-components of evoked-brain potentials in deficit and nondeficit schizophrenia

INTRODUCTION

The present study aims to detect the specific and common impairment index relative to evoked brain potentials (EBPS ) in deficit schizophrenia (DS) and nondeficit schizophrenia (NDS), and investigates the relationship between EBPs and clinical variables.

METHODS

The study used EBPs in 21 patients with DS, 38 patients with NDS, and 50 healthy controls (HCs) to investigate P300 waves, mismatch negative (MMN), sensory gating (SG) P50 and contingent negative variation (CNV). A comparison of three groups and the relationship between EBPs and clinical variables were performed using general linear model analyses and partial correlation, respectively.

RESULTS

Compared with HCs, both groups of patients showed delayed N1 , N2 , and P3a latency, and reduced N1 and N2 amplitude. The MMN showed delayed latency. The P50 ratios and the inhibited ratios were impaired, whereas SG loss ratios increased. CNV amplitude was reduced. Compared with HCs, NDS showed delayed latency of S2'-C in CNV, whereas DS showed shortened latency. Only NDS, when compared with HCs, showed delayed latency of P3b , Also, only DS, when compared with HCs, showed delayed latency of point A in CNV. Latency of point A in CNV of DS, correlated with a poorer Global Assessment of Functioning Scale (6 weeks) and was independent of clinical characteristics.

DISCUSSION

Schizophrenia represents a clinical syndrome with shared impairments in brain function, whereas DS is a relatively homogeneous subgroup of schizophrenia with unique pathophysiological changes.

The effect of acute exogenous melatonin on P50 suppression in healthy male volunteers stratified for low and high gating levels

Sensory gating is frequently found to be disturbed in patients with schizophrenia. In addition, a disruption of the circadian rhythm together with a low nocturnal melatonin output is regularly found in these patients. Since there is some evidence that a brief period of sleep normalizes sensory gating in schizophrenia patients, it is conceivable that their disrupted melatonin level may contribute to the deficits in P50 suppression. In this initial study, the effects of acutely administered melatonin on sensory gating in healthy subjects were investigated. In a double-blind placebo-controlled crossover design, 21 healthy male volunteers were administered melatonin (4 mg) or placebo, after which they were tested in a P50 suppression paradigm. In the group as a whole, melatonin did not affect P50 suppression. However, melatonin increased the P50 ratio in the individuals with high baseline suppression. In contrast to what was expected, melatonin reduced P50 suppression, albeit only in those individuals with high baseline suppression. The current study does not support a beneficial effect of acute exposure to exogenous melatonin on sensory gating. Future research should focus on melatonin's ability to restore basic sleep rhythms and its subsequent effects on sensory gating, in both healthy volunteers and patients with schizophrenia.

Association between the 2-bp deletion polymorphism in the duplicated version of the alpha7 nicotinic receptor gene and P50 sensory gating

There is considerable evidence implicating the 15q13.3 region in neuropsychiatric disorders, with the α7 nicotinic receptor gene CHRNA7 the most plausible candidate. This region has multiple duplications and many copy number variants (CNVs). A common CNV involves a partial duplication of CHRNA7 (CHRFAM7A), which occurs in either orientation. We examined the distribution of these alternative genomic arrangements in a large cohort of psychiatric patients, their relatives and controls using the 2-bp deletion polymorphism as a marker for the orientation of CHRFAM7A. We investigated three common alleles for association with psychosis and with the P50 sensory gating deficit, which is strongly associated with psychosis and strongly linked to 15q13.3. We found significant within-family association with P50 (empirical P=0.004), which is robust to population stratification. Most of the effect came from the 2-bp deletion allele, which tags the variant of CHRFAM7A in the same orientation as CHRNA7. This allele is associated with the presence of the P50 sensory gating deficit (empirical P=0.0006). Tests comparing within-family and between-family components of association suggest considerable population stratification in the sample. We found no evidence for association with psychosis, but this may reflect lower power using this phenotype. Four out of six previous association studies found association of different psychiatric phenotypes with the same 2-bp deletion allele.

Lateral asymmetry and reduced forward masking effect in early brainstem auditory evoked responses in schizophrenia

Individuals diagnosed with schizophrenia show deficiencies of basic neurophysiological sorting mechanisms. This study further investigated this issue, focusing on the two phenomena, laterality of coding and auditory forward masking. A specific audiometric method for use in psychiatry was the measuring set up to register brain stem audiograms (ABRs). A sample of 49 schizophrenic patients was compared with three control groups consisting of healthy reference subjects (n=49), attention deficit hyperactivity disorder (ADHD) patients (n=29), Asperger syndrome (AS) patients (n=13) and drug-induced psychotic patients (n=14). Schizophrenic patients showed significant abnormal laterality of brainstem activity in wave II of the auditory brainstem response (ABR) in comparison with all other study groups. Forward masking effects in the superior olive complex were coded significantly differently by schizophrenic patients compared to control groups except for the AS group. The results suggest deficits in the coding of auditory stimuli in the lower parts of the auditory pathway in schizophrenia and indicate that increased peripheral lateral asymmetry and forward masking aberrances could be neurophysiological markers for the disorder.

Nicotinic mechanisms in the treatment of psychotic disorders: a focus on the α7 nicotinic receptor

Nicotine is heavily abused by persons with schizophrenia. Nicotine better enables people with schizophrenia to filter out extraneous auditory stimuli. Nicotine also improves prepulse inhibition when compared to placebo. Nicotine similarly increases the amplitude of patients' duration mismatch negativity. The 15q13-14 region of the genome coding for the α7 nicotinic receptor is linked to schizophrenia. Multiple single nucleotide polymorphisms have been identified in this 15q13-14 gene promoter region that are more frequently present in people with schizophrenia than in normal controls. Abnormalities in expression and regulation of central nicotinic cholinoceptors with decreased α7 binding in multiple brain regions are also present. Nicotine enhances cognition in schizophrenia. Alternative agents that activate the nicotinic receptor have been tested including 3-[2,4-dimethoxybenzylidene]anabaseine (DMXB-A). This compound improved attention, working memory, and negative symptoms in an add-on study in nonsmoking patients with schizophrenia. There are multiple other nicotinic agents, including positive allosteric modulators, in the preclinical stages of development. Finally, the effects of varenicline and clozapine and their relation to smoking cessation are discussed.

Differential sensory gating functions between smokers and non-smokers among drug-naive first episode schizophrenic patients

Although an acute effect of cigarette smoking and nicotine on sensory gating of schizophrenias has been investigated in published papers, the chronic effect of cigarette smoking on this phenomenon has not yet been reported. We report the effects of chronic cigarette smoking, without new acute exposure before testing, on sensory gating using the P50 auditory evoked potential in a group of drug-naive first episode schizophrenic smokers and healthy smokers. Sensory gating was evaluated using auditory P50 suppression elicited using the conditioning (S1)-testing (S2) paradigm. Fifty six male drug-naive first episode schizophrenic patients were compared to 41 healthy male controls. Patients were classified into subgroups of current smokers (n=18) and non-smokers (n=38) to explore the effects of smoking on sensory gating. All subjects did not smoke a cigarette for at least 1h prior to testing. Schizophrenic patients showed an increased S2 amplitude and a poorer sensory gating as measured by both S2/S1 ratio and S1-S2 difference of P50 amplitude, as compared to healthy controls. However, smokers showed an increased S1 amplitude and better sensory gating than did non-smokers both in schizophrenia patients and healthy controls. Our findings support a sensory gating deficit among first episode schizophrenic patients. However, it was less pronounced among schizophrenic patients who were current cigarette smokers, suggesting a positive effect of chronic cigarette smoking on ameliorating this sensory gating deficit in schizophrenia. Our findings of the present study present new evidence supporting the self-medication hypothesis of self-medication by cigarette smoking in schizophrenia to possibly ameliorate pre-existing functional deficits.

Do COMT, BDNF and NRG1 polymorphisms influence P50 sensory gating in psychosis?

BACKGROUND

Auditory P50 sensory gating deficits correlate with genetic risk for schizophrenia and constitute a plausible endophenotype for the disease. The well-supported role of catechol-O-methyltransferase (COMT), brain-derived neurotrophic factor (BDNF) and neuregulin 1 (NRG1) genes in neurodevelopment and cognition make a strong theoretical case for their influence on the P50 endophenotype.

METHOD

The possible role of NRG1, COMT Val158Met and BDNF Val66Met gene polymorphisms on the P50 endophenotype was examined in a large sample consisting of psychotic patients, their unaffected relatives and unrelated healthy controls using linear regression analyses.

RESULTS

Although P50 deficits were present in patients and their unaffected relatives, there was no evidence for an association between NRG1, COMT Val158Met or BDNF Val66Met genotypes and the P50 endophenotype.

CONCLUSIONS

The evidence from our large study suggests that any such association between P50 indices and NRG1, COMT Val158Met or BDNF Val66Met genotypes, if present, must be very subtle.

P50 gating in deficit and nondeficit schizophrenia

Dysfunctional auditory sensory processing has generally been found in schizophrenia and it has been suggested that these deficits might be related to clinical and psychosocial variables. The present study included P50 recordings using a simple-paired click auditory evoked potential paradigm in sixty patients with deficit schizophrenia (DS), sixty patients with nondeficit schizophrenia (NDS), and sixty comparison subjects. The Schedule for the Deficit Syndrome was used to categorize patients as DS or NDS. The two patient groups did not differ in clinical variables, except for higher negative dimension and lower community outcome scores in DS than in NDS patients. There were no differences in P50 ratios between deficit and nondeficit subgroups; compared with normal subjects both groups of schizophrenia patients showed impaired P50 ratios (p<0.0001). This ratio appears to be independent of positive and negative symptoms. However, impairment in P50 gating correlated with poorer community outcome. The data document the existence of early auditory sensory processing abnormalities in DS and NDS, and might suggest that common neuronal network abnormalities underlie both forms of schizophrenia. Deficient P50 gating may be associated with impaired functional outcome in schizophrenia.

Assessment of auditory sensory processing in a neurodevelopmental animal model of schizophrenia--gating of auditory-evoked potentials and prepulse inhibition

The use of translational approaches to validate animal models is needed for the development of treatments that can effectively alleviate cognitive impairments associated with schizophrenia, which are unsuccessfully treated by the current available therapies. Deficits in pre-attentive stages of sensory information processing seen in schizophrenia patients, can be assessed by highly homologues methods in both humans and rodents, evident by the prepulse inhibition (PPI) of the auditory startle response and the P50 (termed P1 here) suppression paradigms. Treatment with the NMDA receptor antagonist PCP on postnatal days 7, 9, and 11 reliably induce cognitive impairments resembling those presented by schizophrenia patients. Here we evaluate the potential of early postnatal PCP (20mg/kg) treatment in Lister Hooded rats to induce post-pubertal deficits in PPI and changes, such as reduced gating, in the P1 suppression paradigm in the EEG. The results indicate that early postnatal PCP treatment to rats leads to a reduction in PPI of the acoustic startle response. Furthermore, treated animals were assessed in the P1 suppression paradigm and produced significant changes in auditory-evoked potentials (AEP), specifically by an increased P1 amplitude and reduced P2 (P200 in humans) gating. However, the treatment neither disrupted normal P1 gating nor reduced N1 (N100 in humans) amplitude, representing two phenomena that are usually found to be disturbed in schizophrenia. In conclusion, the current findings confirm measures of early information processing to show high resemblance between rodents and humans, and indicate that early postnatal PCP-treated rats show deficits in pre-attentional processing, which are distinct from those observed in schizophrenia patients.

Endophenotypes in schizophrenia: a selective review

BACKGROUND

Given the wealth of data in the literature on schizophrenia endophenotypes, it is useful to have one source to reference their frequency data. We reviewed the literature on disease-liability associated variants in structural and functional magnetic resonance images (MRI), sensory processing measures, neuromotor abilities, neuropsychological measures, and physical characteristics in schizophrenia patients (SCZ), their first-degree relatives (REL), and healthy controls (HC). The purpose of this review was to provide a summary of the existing data on the most extensively published endophenotypes for schizophrenia.

METHODS

We searched PubMed and MedLine for all studies on schizophrenia endophenotypes comparing SCZ to HC and/or REL to HC groups. Percent abnormal values, generally defined as >2 SD from the mean (in the direction of abnormality) and/or associated effect sizes (Cohen's d) were calculated for each study.

RESULTS

Combined, the articles reported an average 39.4% (SD=20.7%; range=2.2-100%) of abnormal values in SCZ, 28.1% (SD=16.6%; range=1.6-67.0%) abnormal values in REL, and 10.2% (SD=6.7%; range=0.0-34.6%) in HC groups.

CONCLUSIONS

These findings are reviewed in the context of emerging hypotheses on schizophrenia endophenotypes, as well as a discussion of clustering trends among the various intermediate phenotypes. In addition, programs for future research are discussed, as instantiated in a few recent large-scale studies on multiple endophenotypes across patients, relatives, and healthy controls.

Early auditory sensory processing deficits in mouse mutants with reduced NMDA receptor function

Cognitive deficits in schizophrenia include impairments at automatic, preattentive stages of sensory information processing. These deficits are evident in the prepulse inhibition- (PPI) and habituation of the auditory startle response paradigm, the paired tone paradigm in the EEG, and the peak recovery function of auditory evoked potentials (AEP). Administration of NMDA receptor antagonists reliably disrupts PPI and habituation of the startle, but not gating of AEPs in rodents. In the peak recovery paradigm, patients with schizophrenia and primates treated with NMDA receptor antagonists show reduced maximal response at long interstimulus intervals (ISI), but normal responses at short ISIs. Thus reduced NMDA receptor signalling may underlie alterations in these paradigms observed in schizophrenia. We tested the paradigms mentioned in mouse mutants with reduced expression of the NR1 subunit of the NMDA receptor (N = 15) and their wild-type littermates (N = 16). The NR1 mutant mice showed impaired habituation and PPI of the auditory startle response, as well as impaired gating in the paired tone paradigm. Deficits between the two gating measures did not correlate, corroborating previous evidence that these paradigms measure distinct processes. In the peak recovery paradigm, the NR1 mutants showed increased responses of the AEPs P1 and N1 at short ISIs but no difference between groups were observed at long ISIs. In conclusion, the NR1 hypomorphic mice modelled sensory and sensorimotor gating and startle habituation deficits observed in schizophrenia, but failed to model alterations in the peak recovery function.

Differential effects of acute serotonin and dopamine depletion on prepulse inhibition and p50 suppression measures of sensorimotor and sensory gating in humans

Schizophrenia is associated with impairments of sensorimotor and sensory gating as measured by prepulse inhibition (PPI) of the acoustic startle response and P50 suppression of the auditory event-related potential respectively. While serotonin and dopamine play an important role in the pathophysiology and treatment of schizophrenia, their role in modulating PPI and P50 suppression in humans is yet to be fully clarified. To further explore the role of serotonin and dopamine in PPI and P50 suppression, we examined the effects of acute tryptophan depletion (to decrease serotonin) and acute tyrosine/phenylalanine depletion (to decrease dopamine) on PPI and P50 suppression in healthy human participants. In addition, we also examined for the first time, the effects of simultaneous serotonin and dopamine depletion (ie combined monoamine depletion) on PPI and P50 suppression. The study was a double-blind, placebo-controlled cross-over design in which 16 healthy male participants completed the PPI and P50 paradigms under four acute treatment conditions: (a) balanced/placebo control, (b) acute tryptophan depletion, (c) acute tyrosine/phenylalanine depletion, and (d) acute tyrosine/phenylalanine/tryptophan depletion (combined monoamine depletion). Selective depletion of dopamine had no significant effect on either PPI or P50 suppression, whereas selective serotonin depletion significantly disrupted PPI, but not P50 suppression. Finally, the simultaneous depletion of both serotonin and dopamine resulted in significant reduction of both PPI and P50 suppression. We suggest these results can be explained by theories relating to optimal levels of monoaminergic neurotransmission and synergistic interactions between serotonergic and dopaminergic systems for normal 'gating' function. These findings suggest that a dysfunction in both serotonin and dopamine neurotransmission may, in part, be responsible for the gating deficits observed in schizophrenia, and their normalization following administration of atypical antipsychotic drugs.

Reduced P50 suppression is associated with the cognitive disorganisation dimension of schizotypy

Individuals with schizophrenia fail to demonstrate a reduction in the P50 event-related potential (ERP) to the second of two identical auditory stimuli presented in close succession. This deficit could lead to sensory overload, cognitive disintegration and perhaps some of the symptoms of schizophrenia. However, evidence linking poor P50 suppression to symptoms in patients with schizophrenia has been equivocal; possibly because of the effects of smoking status and antipsychotic medication on both of these variables. The aim of this study was to remove these potentially confounding factors by testing 74 healthy non-smoking participants and assessing the relationship between P50 suppression and dimensions of schizotypy. Multiple regression analyses revealed that individuals scoring highly on the cognitive disorganisation dimension of schizotypy had reduced P50 suppression and a smaller amplitude of response to the first stimulus. No robust associations were found between any P50 variables and the positive or negative dimensions of schizotypy. N100 suppression was also examined using the dual click paradigm but no relationships were found with any of the schizotypy dimensions. Thus individuals high in the cognitive disorganisation dimension of schizotypy have a deficit in inhibiting repetitive information at an early pre-attentive stage of processing, as measured by the P50 ERP, but this did not extend to a later early attentive stage, as reflected by the N100 wave. This research supports the view that there is a link between poor P50 suppression and certain symptom clusters in schizophrenia.

A meta-analysis of P50 studies in patients with schizophrenia and relatives: differences in methodology between research groups

OBJECTIVE

To determine whether patients with schizophrenia as well as their relatives show deficits in sensory gating reflected by an abnormal P50 ratio and to quantify the differences from controls.

METHODS

A systematic search on articles published between 1982 and 2006 was conducted. 28 patient studies that were suitable for analysis including 891 patients and 686 controls were retrieved. Six studies on P50 of relatives of schizophrenic patients were identified, including 317 relatives and 294 controls.

RESULTS

In the patient studies we found an P50 effect size of 1.28 (SD=0.72). We confirmed high variability in outcomes across studies. Almost half of the studies included where published by one laboratory of the University of Colorado and these results differed significantly from the results found in studies performed in other laboratories. We found correlations between effect size outcome and sound intensity, filter settings and subjects' position which could be explained by differences between the Colorado laboratory and the other groups. In the relative studies we found a mean P50 effect size of 0.85 (+/-0.42).

CONCLUSIONS

The differences in methodology and lack of reported demographics and methodology including raters blinding in some studies makes it hard to compare results across studies and to evaluate the validity and reliability of P50 as a candidate endophenotype for schizophrenia. There are large differences in outcomes from Colorado studies and non-Colorado studies. In contrast to the Colorado studies in the non-Colorado studies P50 suppression would not qualify as an endophenotype for schizophrenia. These differences might be explained by the differences in methodology e.g. lower levels of sound intensity, differences in filter settings and subjects' position. Finally we make some recommendations for future research based on the outcomes of this meta-analysis.

Treating schizophrenia symptoms with an alpha7 nicotinic agonist, from mice to men

Current antipsychotic treatments fail to fully address the range of symptoms of schizophrenia, particularly with respect to social and occupational dysfunctions. Recent work has highlighted the role of nicotinie in both cognitive and attentional deficits as well as deficient processing of repetitive sensory information. The predilection for schizophrenia patients to be extremely heavy cigarette smokers may be related to their attempt to compensate for a reduction in hippocampal alpha7 nicotinic cholinergic receptors by delivering exogenous ligand to the remaining receptors. Studies in rodent models of both learning and memory deficits and deficits in sensory inhibition have confirmed a role for the alpha7 subtype of the nicotinic cholinergic receptor in these processes. Rodent studies also demonstrated the efficacy of a selective partial alpha7 nicotinic agonist, DMXBA, to improve these deficits. Subsequent human clinical trials demonstrated improved sensory inhibition in 12 schizophrenia patients and showed improvement in several subtests of the RBANS learning and memory assessment instrument. These data suggest that therapeutic agents selected for alpha7 nicotinic activity may have utility in treating certain symptoms of schizophrenia.

Schizophrenia and the alpha7 nicotinic acetylcholine receptor

In addition to the devastating symptoms of psychosis, many people with schizophrenia also suffer from cognitive impairment. These cognitive symptoms lead to marked dysfunction and can impact employability, treatment adherence, and social skills. Deficits in P50 auditory gating are associated with attentional impairment and may contribute to cognitive symptoms and perceptual disturbances. This nicotinic cholinergic-mediated inhibitory process represents a potential new target for therapeutic intervention in schizophrenia. This chapter will review evidence implicating the nicotinic cholinergic, and specifically, the alpha7 nicotinic receptor system in the pathology of schizophrenia. Impaired auditory sensory gating has been linked to the alpha7 nicotinic receptor gene on the chromosome 15q14 locus. A majority of persons with schizophrenia are heavy smokers. Although nicotine can acutely reverse diminished auditory sensory gating in people with schizophrenia, this effect is lost on a chronic basis due to receptor desensitization. The alpha7 nicotinic agonist 3-(2,4 dimethoxy)benzylidene-anabaseine (DMXBA) can also enhance auditory sensory gating in animal models. DMXBA is well tolerated in humans and a new study in persons with schizophrenia has found that DMXBA enhances both P50 auditory gating and cognition. alpha7 Nicotinic acetylcholine receptor agonists appear to be viable candidates for the treatment of cognitive disturbances in schizophrenia.

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.

Prepulse inhibition and P50 suppression: commonalities and dissociations

Patients with schizophrenia exhibit reduced levels of both prepulse inhibition of the startle reflex (PPI) and condition-test suppression of the P50 event-related potential. This study investigated the extent to which PPI and P50 suppression, which exhibit similar parametric sensitivities, are intrinsically auditory phenomena or can be induced cross-modally, and reflect common or distinct neural mechanisms of inhibition. PPI, N100, and P50 were assessed in 20 healthy male volunteers, using auditory test probes and both visual and auditory lead stimuli, separated by 100- or 500-ms interstimulus intervals (ISIs). PPI was found in the auditory-lead condition across the complete group, and with visual-lead stimuli in approximately half of the subjects. Intra-modal auditory PPI was significantly higher with the 100-ms ISI than with the 500-ms ISI. P50 suppression was found only with the 500-ms ISI, with no difference between the auditory and visual conditions. Source analyses revealed that suppression was associated with frontal cortical activity. N100 suppression was found only in the auditory condition, with no difference between 100- and 500-ms ISIs. Although both phenomena are considered to provide operational measures of gating, PPI and P50 suppression are differentially sensitive to ISI and therefore reflect partly different neural mechanisms. They are not intrinsically auditory phenomena, and both appear to involve frontal cortical activity. In contrast, N100 suppression is most likely based on refractory mechanisms intrinsic to the auditory system.

P50 sensitivity to physical and psychological state influences

Although P50 is described as a largely preattentive process, increasing evidence suggests that the psychological state of a participant may influence P50 and its suppression. A paired-stimulus paradigm was used to examine the contributions of variability in stimulus parameters and state factors, such as expectancy and vigilance, on P50. Results obtained from 34 healthy subjects indicate that stimulus intensity and background stimulus intensity influenced P50 amplitude whereas stimulus duration had no significant impact. Importantly, P50 suppression varied with fluctuations in P50 amplitude to the first stimulus, and both P50 and its suppression reflected possible declines in attention or vigilance over the course of the session. Findings from this study suggest that P50 is not entirely preattentional and may reflect the psychological state of a participant. Implications of these results for research with schizophrenia patients are discussed.

Event-related potentials elicited by distractors in an auditory oddball paradigm in schizophrenia

Patients with schizophrenia are affected more adversely than healthy controls by distracting conditions, due to their inability to adequately apportion attentional resources to targets or distractors. We attempted to re-evaluate the effects of distractors in 25 patients with chronic schizophrenia and in 12 controls. They performed an auditory target-detection task with 1500 Hz tone distractors and an additional control condition where a 1500-Hz tone was used as the target. The rate of target misses for patients with schizophrenia was 3.79% in non-distractor conditions and 14.79% in distractor conditions. Significantly reduced N100 responses to distractors and distractor condition targets were found. P300 responses to all target stimulus categories were reduced, but P300 responses to distractors were equal to those in the control group. There was a reduction of P300 amplitudes to distractors in both groups; however, only the control group showed significant enlargement of P300 amplitude when the distractors became the target stimuli. There is evidence that patients with schizophrenia tend to be less able to allocate their attentional resources adequately to target vs. distractor stimuli. When the distractors became the target stimuli, their responses remained unchanged, which suggests their inability to appropriately integrate stimulus information with contextual information.

P50 inhibitory gating deficit is correlated with the negative symptomatology of schizophrenia

Abnormal sensory gating in schizophrenia has frequently been reported. The strength of central inhibitory pathways was measured using the P50 component of the auditory evoked potential in a conditioning-testing paradigm. The relationships between a relative decrease in P50 amplitude to repeated auditory stimuli and clinical symptoms remain controversial. Using the Positive and Negative Syndrome Scale, we studied the P50 auditory conditioning-testing paradigm in 81 schizophrenic subjects, categorized into subgroups with and without prominent negative symptoms, in comparison with 88 control subjects. We found increased ratios of testing stimuli to conditioning stimuli in both schizophrenic subgroups relative to findings in the control group. In addition, we found significantly increased mean latencies of the P50 responses to conditioning (C) and testing (T) stimuli and significantly increased T/C ratios in the subgroup with negative symptoms compared with the subgroup with non-negative symptoms.

Auditory recovery cycle dysfunction in schizophrenia: a study using event-related potentials

Previous event-related potential (ERP) studies reported evidence of impaired auditory information processing in patients with schizophrenia. The recovery cycle of the auditory N1 ERP component was measured in 17 patients with schizophrenia and 17 age- and sex-matched healthy volunteers. Subjects performed a visual distraction task while listening to 80-dB SPL, 1000-Hz tone pairs, presented with intra-pair intervals of 1, 3, 5 or 7 s, with inter-pair intervals of 9-13 s. Patients with schizophrenia had significantly reduced N1 amplitudes for S1 stimuli compared with healthy volunteers. For N1 amplitudes elicited by S2 stimuli, there was a significant group effect whilst the main effect of intra-pair interval was not significant. These results provide additional evidence of inhibitory auditory processing deficits in schizophrenia.

Increasing dopaminergic activity: effects of L-dopa and bromocriptine on human sensory gating

Schizophrenic patients show a loss of sensory gating, which is reflected in a reduced P50 suppression. Because most of the symptoms in schizophrenia can be reduced by antagonists of the dopaminergic (D2) system, the loss in sensory gating might be related to an increased dopaminergic activity. Therefore, in the present study, the effects of increased dopaminergic neurotransmisson on sensory gating in healthy volunteers were investigated. In a double-blind, balanced, placebo-controlled design, healthy male volunteers were challenged in two separate studies with either 300 mg L-dopa (precursor of dopamine) or placebo (n=16) and 1.25 mg bromocriptine (D2 agonist) or placebo (n=17). Subsequently, they were tested for their sensory gating (P50 suppression). P50 suppression values in the placebo condition were comparable to those found in literature. Although both L-dopa and bromocriptine reduced P50 amplitude, they did so in an equal ratio for both the response to the conditioning (C) and the testing (T) stimuli, therefore not resulting in a reduction of the P50 suppression ratio (T/C). In the present study, neither L-dopa nor bromocriptine reduced sensory gating in healthy volunteers. This suggests that an increased dopaminergic activity in humans is not responsible for the reduction in sensory gating as seen, for example, in schizophrenia.

Suppression of P50 evoked potential component, schizotypal beliefs and smoking

Suppression of the P50 component of the evoked potential is an electrophysiological index of sensory gating that is blunted in schizophrenia spectrum disorders. Although P50 suppression is thought to be related to symptomatology, this is yet to be shown. The failure to demonstrate this relation has led some to argue that P50 suppression and symptomatology are not related. However, a possible confound has recently been corroborated [i.e., chronic smoking is related to superior P50 suppression [Crawford et al., Neuroscience Letters 317 (2002) 151]], and a relation has been found in questionnaire-defined individuals with indications of schizotypy [i.e., psychometric schizotypy is related to poor P50 suppression [Croft et al., Biological Psychiatry 50 (2001) 441]]. The present study attempted to replicate and extend both studies by examining P50 suppression, smoking histories, psychometric schizotypy and NEO Five-Factor Inventory (NEO-V) scores in 37 healthy participants. Replicating Crawford et al., P50 suppression was better in the heavier smokers. Providing a partial replication of Croft et al., P50 suppression was inversely related to schizotypy scores in participants who smoked little or not at all; however, P50 suppression was positively related to schizotypy in heavier smokers. Covarying for age and NEO-V scale scores had little effect on these relations. The findings provide evidence of important confounds that would limit our ability to detect P50 suppression/symptom relations in schizophrenia.

Alpha-7 nicotinic receptor agonists: potential new candidates for the treatment of schizophrenia

RATIONALE AND OBJECTIVE

Auditory sensory gating, a biological measurement of the ability to suppress the evoked response to the second of two auditory stimuli, is diminished in people with schizophrenia. Deficits in sensory gating are associated with attentional impairment, and may contribute to cognitive symptoms and perceptual disturbances. This inhibitory process, which involves the alpha(7) nicotinic receptor mediated release of gamma-aminobutyric acid (GABA) by hippocampal interneurons, represents a potential new target for therapeutic intervention in schizophrenia.

METHOD

This paper will review several lines of evidence implicating the nicotinic-cholinergic, and specifically, the alpha(7) nicotinic receptor system in the pathology of schizophrenia and the evidence that alpha(7) nicotinic receptor agonists may ameliorate some of these deficits.

RESULTS

Impaired auditory sensory gating has been linked to the alpha(7) nicotinic receptor gene on the chromosome 15q14 locus. Single nucleotide polymorphisms of the promoter region of this gene are more frequent in people with schizophrenia. Although nicotine can acutely reverse diminished auditory sensory gating in people with schizophrenia, this effect is lost on a chronic basis due to receptor desensitization. Clozapine is able to reverse auditory sensory gating impairment, probably through an alpha(7) nicotinic receptor mechanism, in both humans and animal models with repeated dosing. The alpha(7) nicotinic agonist 3-2,4 dimethoxybenzylidene anabaseine (DMXBA) can also enhance auditory sensory gating in animal models. DMXBA is well tolerated in humans and improves several cognitive measures.

CONCLUSION

Alpha-7 nicotinic receptor agonists appear to be reasonable candidates for the treatment of cognitive and perceptual disturbances in schizophrenia.

Applications of the P50 evoked response to the evaluation of cognitive impairments after traumatic brain injury

This article reviews the applications of the P50 evoked response to paired auditory stimuli (P50 ERP) in the study and evaluation of cognitive impairments after traumatic brain injury (TBI). The cholinergic hypothesis of cognitive impairment after TBI and the relationship of impaired auditory sensory gating to that hypothesis are presented. The neurobiology of impaired sensory gating, the relationship of that neurobiology to the P50 ERP, and the principles of P50 ERP recording are discussed. Studies of the P50 ERP among patients with persistent cognitive complaints after TBI are reviewed. Finally, possible clinical applications and limitations of the P50 ERP in the study, evaluation, and treatment of patients with cognitive impairments after TBI are offered.

Interpreting abnormality: an EEG and MEG study of P50 and the auditory paired-stimulus paradigm

Interpretation of neurophysiological differences between control and patient groups on the basis of scalp-recorded event-related brain potentials (ERPs), although common and promising, is often complicated in the absence of information on the distinct neural generators contributing to the ERP, particularly information regarding individual differences in the generators. For example, while sensory gating differences frequently observed in patients with schizophrenia in the P50 paired-click gating paradigm are typically interpreted as reflecting group differences in generator source strength, differences in the latency and/or orientation of P50 generators may also account for observed group differences. The present study examined how variability in source strength, amplitude, or orientation affects the P50 component of the scalp-recorded ERP. In Experiment 1, simulations examined the effect of changes in source strength, orientation, or latency in superior temporal gyrus (STG) dipoles on P50 recorded at Cz. In Experiment 2, within- and between-subject variability in left and right M50 STG dipole source strength, latency, and orientation was examined in 19 subjects. Given the frequently reported differences in left and right STG anatomy and function, substantial inter-subject and inter-hemispheric variability in these parameters were expected, with important consequences for how P50 at Cz reflects brain activity from relevant generators. In Experiment 1, simulated P50 responses were computed from hypothetical left- and right-hemisphere STG generators, with latency, amplitude, and orientation of the generators varied systematically. In Experiment 2, electroencephalographic (EEG) and magnetoencephalographic (MEG) data were collected from 19 subjects. Generators were modeled from the MEG data to assess and illustrate the generator variability evaluated parametrically in Experiment 1. In Experiment 1, realistic amounts of variability in generator latency, amplitude, and orientation produced ERPs in which P50 scoring was compromised and interpretation complicated. In Experiment 2, significant within and between subject variability was observed in the left and right hemisphere STG M50 sources. Given the variability in M50 source strength, orientation, and amplitude observed here in nonpatient subjects, future studies should examine whether group differences in P50 gating ratios typically observed for patient vs. control groups are specific to a particular hemisphere, as well as whether the group differences are due to differences in dipole source strength, latency, orientation, or a combination of these parameters. Present analyses focused on P50/M50 merely as an example of the broader need to evaluate scalp phenomena in light of underlying generators. The development and widespread use of EEG/MEG source localization methods will greatly enhance the interpretation and value of EEG/MEG data.

Inhibitory neurophysiological deficit as a phenotype for genetic investigation of schizophrenia

Many investigators have proposed that biological endophenotypes might facilitate the genetic analysis of schizophrenia. A deficit in the inhibition of the P50 evoked response to repeated auditory stimuli has been characterized as a neurobiological deficit in schizophrenia. This deficit is linked to a candidate gene locus, the locus of the alpha7-nicotinic cholinergic receptor subunit gene on chromosome 15q14. Supportive evidence has been found by other investigators, including: 1) linkage of schizophrenia to the same locus; 2) linkage of bipolar disorder to the locus; and 3) replication of the existence of this neurobiological deficit and its relation to broader neuropsychological deficits in schizophrenia. It is certain that there are many genetic factors in schizophrenia and bipolar disorder; what is needed is a complete and precise description of the contribution of each individual factor to the pathophysiology of these illnesses.

Modulating sensory gating in healthy volunteers: the effects of ketamine and haloperidol

BACKGROUND

Antagonists of the N-methyl-D-aspartate (NMDA) receptors induce a broad range of psychophysiologic symptoms in healthy subjects that are similar to those of schizophrenia, such as disturbances in the sensory gating of stimuli. Because antipsychotics reduce symptoms in schizophrenia, they may also reduce the effects of NMDA antagonists.

METHODS

In our study, a group of 18 healthy male volunteers was tested in prepulse inhibition (PPI) and P50 evoked potential paradigms during placebo-placebo, placebo-ketamine (.3 mg/kg; intravenous), and 2-mg haloperidol/.3 mg/kg intravenous ketamine conditions.

RESULTS

Suppression of PPI and P50 in the ketamine condition did not differ from either the placebo-placebo or the haloperidol-ketamine condition; however, a significant reduction in percentage PPI to the lowest prepulse intensity and a reduction of P50 suppression were found in the haloperidol-ketamine condition.

CONCLUSIONS

The combination of haloperidol and ketamine was found to disrupt P50 suppression and PPI in healthy male volunteers, whereas ketamine alone did not affect either measure. This may imply that the disrupted P50 suppression and PPI found in schizophrenia is related to reduced dopaminergic activity, most likely in the prefrontal cortex.

Neurokognitive Grundlagen schizophrener Symptome:

Zusammenfassung. Theoretischer Hintergrund: Kognitive Dysfunktionen und deren neurophysiologische und hirnanatomische Korrelate sind wesentliche Beschreibungselemente der schizophrenen Erkrankung. Vielfach wird sogar vermutet, in den neurokognitiven Defiziten die Kernstörung der Schizophrenie erfassen zu können. Fragestellung und Methode: Es wird ein qualitativer Überblick gegeben zu Modellen und empirischen Befunden bezüglich psychologischer und neuronaler Grundlagen der schizophrenen Syndromdimensionen (Realitätsverzerrung, Desorganisation, Negativsymptomatik) und der wichtigsten Symptome (Halluzinationen, Wahn und Fremdbeeinflussungserleben, Denkstörungen, Affektverflachung). Darüber hinaus werden integrative Erklärungskonzepte referiert, die ein breites Symptomspektrum zu erklären versuchen (Arbeitsgedächtnisdefizit, Filterstörung, Dyskonnektion). Ergebnisse und Schlußfolgerungen: Trotz bestehender Inkonsistenzen in den Befunden und noch zu lösender methodischer Probleme führt die Analyse neurokognitiver Defizite zu einem umfassenderen Krankheitsverständnis der Schizophrenie, das konkrete Ansatzpunkte für psychologische und pharmakologische Interventionen liefert.

Associations of P50 suppression and desensitization with perceptual and cognitive features of "unreality" in schizotypy

BACKGROUND

P50 suppression is an electrophysiologic index of early sensory gating and has consistently been found deficient in schizophrenic patients. This gating deficit is thought to lead to sensory overload and cognitive fragmentation, and correspondingly many symptoms of the disorder. However, the link between P50 suppression deficits and symptomatology is yet to be established, and so this study was designed to determine whether such a relation is present within a nonclinical population.

METHODS

P50 suppression and schizotypy measures were obtained from 36 healthy volunteers, and correlation analyses determined whether measures of schizotypy were related to P50 suppression.

RESULTS

Consistent with the view that P50 gating deficits are related to schizophrenic symptoms, subjects with poorer P50 suppression reported more perceptual anomalies and magical ideation--an unreality syndrome--in contrast to other positive symptoms and to withdrawal. This study also found a trend to P50 suppression desensitization, and that whereas subjects low on "unreality" demonstrated desensitization to the second of the paired clicks, subjects high on "unreality" demonstrated sensitization.

CONCLUSIONS

It is concluded that early sensory gating deficits, in the form of poor P50 suppression, are related to unreality aspects of schizotypy. This supports the view that poor P50 suppression in schizophrenia is related to symptomatology.

Abnormal peripheral auditory asymmetry in schizophrenia

OBJECTIVE

Auditory processing difficulties have been reported in schizophrenia. This study explores peripheral auditory function in patients with schizophrenia in whom certain early disturbances of auditory message filtering have been found and may be associated with certain abnormalities which are particularly localised in the left temporal lobe.

METHODS

Otoacoustic emissions, including click evoked and spontaneous emissions and measurements of functioning of the medial olivocochlear efferent system were obtained from 12 chronic schizophrenic patients and compared with normative data recorded from 12 normal controls.

RESULTS

Otoacoustic emission amplitudes and medial olivocochlear functioning were similar between the normal controls and schizophrenic patients; the schizophrenic patients did, however, differ from the normal controls in otoacoustic emission intensity and in medial olivocochlear asymmetry. A tendency to a higher number of spontaneous peaks, and a significantly higher click evoked otoacoustic emission response amplitude were found in the right ear compared with the left ear of schizophrenic patients. For the medial olivocochlear system, whereas normal controls showed greater attenuation in the right than in the left ear, schizophrenic patients lacked such an asymmetry.

CONCLUSION

In the absence of any attention task, the findings show disturbed peripheral lateralisation in schizophrenia of mechanisms involved in auditory information filtering. Such a lack of right ear advantage in medial olivocochlear functioning may thus be a peripheral reflection of central lateralisation anomalies.

The P50 auditory event-evoked potential in adult attention-deficit disorder: comparison with schizophrenia

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and schizophrenia are both conceptualized as disorders of attention. Failure to inhibit the P50 auditory event-evoked response, extensively studied in schizophrenia, could also occur in ADHD patients, if these two illnesses have common underlying neurobiological substrates.

METHODS

This study examined the inhibition of the P50 auditory event-evoked potential in 16 unmedicated adults with ADHD, 16 schizophrenic outpatients, and 16 normal control subjects. Auditory stimuli were presented in a paired stimulus, conditioning-testing paradigm.

RESULTS

The amplitude of initial or conditioning P50 response did not differ between the three groups; however, significant effects of psychiatric diagnosis on the amplitude of the test response and the ratio of the test to the conditioning response amplitudes were observed. Schizophrenic patients' P50 ratios and test amplitudes were higher than both the ADHD and normal groups.

CONCLUSIONS

Adults with ADHD do not have the inhibitory deficit seen in patients with schizophrenia, suggesting that the mechanism of attentional disturbance in the two illnesses may be fundamentally different.

Amphetamine disrupts P50 suppression in normal subjects

BACKGROUND

P50 suppression is viewed as an operational measure of sensory "gating" that is reduced in patients with schizophrenia and their family members. Previous reports have demonstrated that neural gating is regulated by monoaminergic tone in rodent models of P50 suppression.

METHODS

In this study, 11 healthy subjects participated in P50 event-related potential recordings at baseline and after either oral administration of dextroamphetamine (.3 mg/kg) or placebo, to determine if the administration of a monoaminergic agonist produces P50 suppression deficits similar to those observed in patients with schizophrenia.

RESULTS

As hypothesized, amphetamine disrupted the suppression of the P50 event-related potential. There was a statistically significant decrement in P50 suppression during the amphetamine challenge condition (t10 = 3.15, p < .01, mean difference = -44.1%, d = -2.5) relative to the baseline P50 condition. A comparison of P50 suppression in the placebo and amphetamine conditions (both after a baseline recording session) revealed a significant amphetamine-induced disruption of P50 suppression (t6 = 3.71, p < .01, mean difference = -54.4%, d = -3.14).

CONCLUSIONS

The biochemical alterations associated with an amphetamine-induced disruption of P50 suppression in this study may be related to the pathophysiology of P50 suppression deficits in schizophrenia. The findings are consistent with several careful examinations of suppression deficits in rodent models that have identified the monoaminergic regulation of P50 suppression. These data indicate that amphetamine induces a disruption of P50 suppression in normal subjects.

Human and animal studies of schizophrenia-related gating deficits

Prepulse Inhibition (PPI) of the startle response and the P50 auditory-evoked potential suppression are used to assess impairments in the regulation of the neural substrates and to determine the clinical significance of inhibitory deficits in schizophrenia. The study of gating deficits in schizophrenia and in related animal model studies have already advanced our understanding of the neural substrates of information processing abnormalities in patients with schizophrenia. Individuals with schizotypal personality disorder as well as clinically unaffected family members of patients with schizophrenia show PPI and P50 suppression deficits. These "schizophrenic spectrum" populations are not grossly psychotic, nor are they receiving antipsychotic medications. Therefore, the gating deficits are presumed to reflect core (eg, intermediate phenotypic) schizophrenia-linked information processing abnormalities. Several studies have reported that gating deficits are associated with clinical ratings of psychiatric symptoms, thought disorder, and neuropsychologic deficits in patients with schizophrenia. In addition, recent human pharmacologic studies have indicated that gating deficits can be reversed by rationally-selected compounds. Animal model studies have generally shown convergence with the human studies and may lead to improved identification of efficacious new antipsychotic medications for patients with schizophrenia.

Elementary phenotypes in the neurobiological and genetic study of schizophrenia

This review describes the strategy of using elementary phenotypes for neurobiological and genetic linkage studies of schizophrenia. The review concentrates on practical aspects of selecting the phenotype and then understanding the confounds in its measurement and interpretation. Examples from the authors' studies of deficits in P50 inhibition and smooth pursuit eye movement dysfunction are presented. These two phenotypes share considerable similarity in their neurobiology, including a similar response to nicotine. They also appear to co-segregate with the genetic risk for schizophrenia as autosomal co-dominant phenotypes. Although most schizophrenic patients inherit these abnormalities unilinealy, i.e., from one parent, apparent bilineal inheritance produces a more severe illness, observed clinically as childhood-onset schizophrenia. The initial study showing linkage of the P50 deficit to the chromosome 15q14 locus of the alpha 7-nicotinic acetylcholine receptor is an example of the potential usefulness of these phenotypes for combined genetic and neurobiological study of schizophrenia.

Test-retest reliability of the rat N40 auditory evoked response: preliminary data

The N40 auditory evoked potential (EP) in rats has been used to develop an animal model for the study of sensory gating mechanisms. In an examination of the test-retest reliability of sensory gating indices, derived from the rat N40 EP, six rats were tested four times daily for 5 consecutive days. A paired-click paradigm (S1-S2) was used, and both the S2/S1 amplitude ratio and the S1-S2 amplitude difference measures of sensory gating capacity were calculated. Based on the means of four daily trials, reliability coefficients were as follows; r = 0.69 for S1, and r = 0.66 for S2 amplitudes. A reliability coefficient of 0.59 was found for the S1-S2 difference measure, and one of 0.47 for the S2/S1 ratio measure. These results suggest that the N40 can be used to study sensory gating, but caution has to be exercised in interpreting the data particularly in a repeated measures design.

Multiple site evaluation of P50 suppression among schizophrenia and normal comparison subjects

Normally, when two brief, non-startling auditory stimuli are presented 500 ms apart, with long (e.g., 10 s) interpair intervals, the positive potential occurring approx. 50 ms after the first stimulus (P50) is relatively large, and the P50 to the second stimulus is smaller. In schizophrenia patients, however, the P50 to the second stimulus is larger than normal. In this study, 36 schizophrenia and 36 normal comparison subjects were tested in a two-click paradigm. Data were recorded from six electrode locations (F3, Fz, F4, C3, Cz, C4). The results support the hypothesis that schizophrenia patients have poor P50 suppression that is not an artifact of differential P50 wave morphology or differences in the number of usable trials between groups. In addition, the vertex location alone (Cz) was equal to, if not better than, any combination of sites for differentiating between groups. These results support the use of the Cz site alone in most investigations of P50 suppression deficits among schizophrenia spectrum patients. Further work investigating the neuropathological correlates of poor P50 suppression among schizophrenia patients by recording from multiple electrode locations, however, could be helpful.