Auditory hallucinations and the P3a: Attention-switching to speech in schizophrenia

P300 in schizophrenia: Then and now

The 1965 discovery of the P300 component of the electroencephalography (EEG)-based event-related potential (ERP), along with the subsequent identification of its alteration in people with schizophrenia, initiated over 50 years of P300 research in schizophrenia. Here, we review what we now know about P300 in schizophrenia after nearly six decades of research. We describe recent efforts to expand our understanding of P300 beyond its sensitivity to schizophrenia itself to its potential role as a biomarker of risk for psychosis or a heritable endophenotype that bridges genetic risk and psychosis phenomenology. We also highlight efforts to move beyond a syndrome-based approach to understand P300 within the context of the clinical, cognitive, and presumed pathophysiological heterogeneity among people diagnosed with schizophrenia. Finally, we describe several recent approaches that extend beyond measuring the traditional P300 ERP component in people with schizophrenia, including time-frequency analyses and pharmacological challenge studies, that may help to clarify specific cognitive mechanisms that are disrupted in schizophrenia. Moreover, we discuss several promising areas for future research, including studies of animal models that can be used for treatment development.

Reduced duration mismatch negativity elicited by the multi-feature 'optimal' paradigm in early-phase psychosis

BACKGROUND

MMN and P3a are EEG-derived event related potentials that are thought to be prospective biomarkers for schizophrenia and, potentially, early-phase psychosis (EPP).

METHODS

EPP (n = 12) and healthy control (n = 35) participants listened to a multi-feature optimal paradigm with five deviant types (gap, duration, location, intensity, and frequency).

RESULTS

There was a significant amplitude difference between the EPP and HC group with duration MMN (p =.02). No significant amplitude differences between groups were found for the P3a waveform. There were several correlations for the EPP group with the BNSS, SOFAS, and PANSS-general questionnaires. Length of illness was not associated with MMN or P3a.

CONCLUSIONS

The optimal paradigm is suitable for eliciting multiple deviant types within a short amount of time in both clinical and healthy populations. This study confirms duration MMN deficits within an EPP group and that MMN is related to functional outcomes and positive and negative symptomology.

Visual P300 as a neurophysiological correlate of symptomatic improvement by a virtual reality-based computer AT system in patients with auditory verbal hallucinations: A Pilot study

Previous comparative trials showed that virtual reality (VR) therapies achieved larger effects than gold-standard cognitive-behavioral therapy (CBT) on overall auditory verbal hallucinations (AVHs). However, no trial has examined the corresponding underlying electrophysiological mechanisms. We performed a pilot randomized comparative trial evaluating the efficacy of a virtual reality-based computer AT system (CATS) over CBT for schizophrenia (SCZ) patients with treatment-resistant AVHs and explored these potential electrophysiological changes via the visual P300 component. Patients (CATS, n = 32; CBT, n = 33) completed the clinical assessments pre- and post-interventions and at 12-week follow-up. The visual P300 were measured before and after both therapies. The analysis of changes in psychiatric symptoms used linear mixed-effects models, and the P300 response in temporal and time-frequency domains was analyzed with repeated-measures analysis of variance. There was no interaction effect between change in clinical symptoms and treatment group. However, several statistically significant within-group improvements were found for CATS and CBT over time. AVH improved significantly after both treatments, as measured with the Psychotic Symptom Rating Scales-Auditory Hallucinations (PSYRATS-AH) sub-scores. Especially for the CATS group, omnipotence beliefs, anxiety symptoms, self-esteem, and quality of life also remained improved at the 12-week follow-up. Moreover, P300 amplitude had a significant interaction effect and correlation with AVH response. Overall, our analysis did not demonstrate general clinical superiority of CATS over CBT, but CATS improved refractory AVH in SCZ patients, likely by increasing P300 amplitude. These findings support the continued development of CATS for persistent AVH and suggest further trials to clarify the neurological effects of CATS.

Sensory gating in tobacco-naïve cannabis users is unaffected by acute nicotine administration

OBJECTIVES

Long-term cannabis use has been associated with the appearance of psychotic symptoms and schizophrenia-like cognitive impairments; however these studies may be confounded by concomitant use of tobacco by cannabis users. We aimed to determine if previously observed cannabis-associated deficits in sensory gating would be seen in cannabis users with no history of tobacco use, as evidenced by changes in the P50, N100, and P200 event-related potentials. A secondary objective of this study was to examine the effects of acute nicotine administration on cannabis users with no tobacco use history.

METHODS

Three components (P50, N100, P200) of the mid-latency auditory-evoked response (MLAER) were elicited by a paired-stimulus paradigm in 43 healthy, non-tobacco smoking male volunteers between the ages of 18-30. Cannabis users (CU, n = 20) were administered nicotine (6 mg) and placebo gum within a randomized, double-blind design. Non-cannabis users (NU, n = 23) did not receive nicotine.

RESULTS

Between-group sensory gating effects were only observed for the N100, with CUs exhibiting a smaller N100 to S1 of the paired stimulus paradigm, in addition to reduced dN100 (indicating poorer gating). Results revealed no significant sensory gating differences with acute administration of nicotine compared to placebo cannabis conditions.

CONCLUSIONS

These findings suggest a relationship between gating impairment and cannabis use; however, acute nicotine administration nicotine does not appear to impact sensory gating function.

Champ versus Chump: Viewing an Opponent’s Face Engages Attention but Not Reward Systems

When we play competitive games, the opponents that we face act as predictors of the outcome of the game. For instance, if you are an average chess player and you face a Grandmaster, you anticipate a loss. Framed in a reinforcement learning perspective, our opponents can be thought of as predictors of rewards and punishments. The present study investigates whether facing an opponent would be processed as a reward or punishment depending on the level of difficulty the opponent poses. Participants played Rock, Paper, Scissors against three computer opponents while electroencephalographic (EEG) data was recorded. In a key manipulation, one opponent (HARD) was programmed to win most often, another (EASY) was made to lose most often, and the third (AVERAGE) had equiprobable outcomes of wins, losses, and ties. Through practice, participants learned to anticipate the relative challenge of a game based on the opponent they were facing that round. An analysis of our EEG data revealed that winning outcomes elicited a reward positivity relative to losing outcomes. Interestingly, our analysis of the predictive cues (i.e., the opponents’ faces) demonstrated that attentional engagement (P3a) was contextually sensitive to anticipated game difficulty. As such, our results for the predictive cue are contrary to what one might expect for a reinforcement model associated with predicted reward, but rather demonstrate that the neural response to the predictive cue was encoding the level of engagement with the opponent as opposed to value relative to the anticipated outcome.

Auditory Hallucinations: An Audiological Horizon?

BACKGROUND

 Interesting data and theories have emerged regarding auditory hallucinations (AHs) in patients with schizophrenia. The possibility that these patients may have changes in the anatomy of the auditory cortex and/or subcortical structures of the central auditory nervous system and present with deficits on audiological tests is important information to the audiology community. However, it seems clear that, in general, audiologists are not sufficiently aware of these findings.

PURPOSE

 There are two main purposes of this article: (1) to educate audiologists about AHs related to schizophrenia and related issues, and (2) to encourage audiologists and hearing scientists to become involved in the evaluation and research of AHs. This fascinating disorder is one in which audiologists/hearing scientists are well suited to make a significant contribution.

RESEARCH DESIGN

 A review and synthesis of the literature was conducted. Relevant literature was identified through PubMed, Google Scholar, as well as independent book chapters and article searches. Keywords driving the searches were AHs, auditory illusions, verbal and musical hallucinations, schizophrenia, and central auditory disorders. Given the currency of the topic, the information collected was primarily between 1990 and 2020.

STUDY SAMPLE

 The review is organized around categorization, prevalence, models, mechanisms, anatomy, pathophysiology, and audiological correlates related to AHs.

DATA COLLECTION AND ANALYSIS

 Searches were conducted using well-known search engines and manual searches by each author. This information on AHs was then analyzed collectively by the authors for useful background and relevance, as well as important for the field of audiology.

RESULTS

 Several anatomical, physiological, and functional imaging studies have shown compromise of the auditory cortex in those with schizophrenia and AHs. Potentially related to this, are studies that demonstrated sub-par performance on behavioral audiologic measures for this unique clinical population. These findings align well with the kind of hearing disorder for which audiologists are well-trained to make significant contributions.

CONCLUSION

 Neurobiological and audiological evidence is accumulating on patients with schizophrenia and AH potentially rendering it as both an auditory and psychiatric disorder. Audiologists should consider expanding their horizon and playing a role in the clinical investigation of this disorder.

Inhibitory Top-Down Control Deficits in Schizophrenia With Auditory Verbal Hallucinations: A Go/NoGo Task

Objective: Auditory verbal hallucinations (AVH), with unclear mechanisms, cause extreme distresses to schizophrenia patients. Deficits of inhibitory top-down control may be linked to AVH. Therefore, in this study, we focused on inhibitory top-down control in schizophrenia patients with AVH. Method: The present study recruited 40 schizophrenia patients, including 20 AVH patients and 20 non-AVH patients, and 23 healthy controls. We employed event-related potentials to investigate the N2 and P3 amplitude and latency differences among these participants during a Go/NoGo task. Results: Relative to healthy controls, the two patient groups observed longer reaction time (RT) and reduced accuracy. The two patient groups had smaller NoGo P3 amplitude than the healthy controls, and the AVH patients showed smaller NoGo P3 amplitude than the non-AVH patients. In all the groups, the parietal area showed smaller NoGo P3 than frontal and central areas. However, no significant difference was found in N2 and Go P3 amplitude between the three groups. Conclusions: AVH patients might have worse inhibitory top-down control, which might be involved in the occurrence of AVH. Hopefully, our results could enhance understanding of the pathology of AVH.

Change in the Neural Response to Auditory Deviance Following Cognitive Therapy for Hallucinations in Patients With Schizophrenia

Adjunctive psychotherapeutic approaches recommended for patients with schizophrenia (SZ) who are fully or partially resistant to pharmacotherapy have rarely utilized biomarkers to enhance the understanding of treatment-effective mechanisms. As SZ patients with persistent auditory verbal hallucinations (AVH) frequently evidence reduced neural responsiveness to external auditory stimulation, which may impact cognitive and functional outcomes, this study examined the effects of cognitive behavioral therapy for voices (CBTv) on clinical and AVH symptoms and the sensory processing of auditory deviants as measured with the electroencephalographically derived mismatch negativity (MMN) response. Twenty-four patients with SZ and AVH were randomly assigned to group CBTv treatment or a treatment as usual (TAU) condition. Patients in the group CBTv condition received treatment for 5 months while the matched control patients received TAU for the same period, followed by 5 months of group CBTv. Assessments were conducted at baseline and at the end of treatment. Although not showing consistent changes in the frequency of AVHs, CBTv (vs. TAU) improved patients' appraisal (p = 0.001) of and behavioral/emotional responses to AVHs, and increased both MMN generation (p = 0.001) and auditory cortex current density (p = 0.002) in response to tone pitch deviants. Improvements in AVH symptoms were correlated with change in pitch deviant MMN and current density in left primary auditory cortex. These findings of improved auditory information processing and symptom-response attributable to CBTv suggest potential clinical and functional benefits of psychotherapeutical approaches for patients with persistent AVHs.

Interaction of Background Noise and Auditory Hallucinations on Phonemic Mismatch Negativity (MMN) and P3a Processing in Schizophrenia

Auditory hallucinations (AHs) are among the cardinal symptoms of schizophrenia (SZ). During the presence of AHs aberrant activity of auditory cortices have been observed, including hyperactivation during AHs alone and hypoactivation when AHs are accompanied by a concurrent external auditory competitor. Mismatch negativity (MMN) and P3a are common ERPs of interest within the study of SZ as they are robustly reduced in the chronic phase of the illness. The present study aimed to explore whether background noise altered the auditory MMN and P3a in those with SZ and treatment-resistant AHs.

METHODS

MMN and P3a were assessed in 12 hallucinating patients (HPs), 11 non-hallucinating patients (NPs) and 9 healthy controls (HCs) within an auditory oddball paradigm. Standard (P = 0.85) and deviant (P = 0.15) stimuli were presented during three noise conditions: silence (SL), traffic noise (TN), and wide-band white noise (WN).

RESULTS

HPs showed significantly greater deficits in MMN amplitude relative to NPs in all background noise conditions, though predominantly at central electrodes. Conversely, both NPs and HPs exhibited significant deficits in P3a amplitude relative to HCs under the SL condition only.

SIGNIFICANCE

These findings suggest that the presence of AHs may specifically impair the MMN, while the P3a appears to be more generally impaired in SZ. That MMN amplitudes are specifically reduced for HPs during background noise conditions suggests HPs may have a harder time detecting changes in phonemic sounds during situations with external traffic or "real-world" noise compared to NPs.

Hyper-Activated Brain Resting-State Network and Mismatch Negativity Deficit in Schizophrenia With Auditory Verbal Hallucination Revealed by an Event-Related Potential Evidence

Schizophrenia is a holergasia with unclear mechanism and high heterogeneity. Auditory verbal hallucination (AVH) study might help in understanding schizophrenia from the perspective of individual symptoms. This study aimed to investigate the activities of the resting-state networks (RSN) in the electroencephalogram (EEG) and mismatch negativity (MMN) in task-related state of schizophrenia patients with AVH. We recruited 30 schizophrenia patients without any medication for more than 4 weeks (15 AVH patients and 15 Non-AVH patients) and 15 healthy controls. We recorded the EEG data of the participants in the resting-state for 7 min and the event-related potential (ERP) data under an auditory oddball paradigm. In the resting-state EEG network, AVH patients exhibited a higher clustering coefficient than Non-AVH patients and healthy controls on delta and beta bands and a shorter characteristic path length than Non-AVH patients and healthy controls on all frequency bands. For ERP data, AVH patients showed a lower MMN amplitude than healthy controls (p = 0.017) and Non-AVH patients (p = 0.033). What's more, MMN amplitude was positively correlated with clustering coefficient, and negatively correlated with characteristic path length on delta, theta, beta and gamma band in AVH patients. Our results indicate that AVH patients showed a hyper-activity in resting-state and may have impaired higher-order auditory expectations in the task-related state than healthy controls and Non-AVH patients. And it seems reasonable to conclude that the formation of AVH may occupy certain brain resources and compete for brain resources with external auditory stimuli.

Auditory mismatch detection, distraction, and attentional reorientation (MMN-P3a-RON) in neurological and psychiatric disorders: A review

Involuntary attention allows for the detection and processing of novel and potentially relevant stimuli that lie outside of cognitive focus. These processes comprise change detection in sensory contexts, automatic orientation toward this change, and the selection of adaptive responses, including reorientation to the original goal in cases when the detected change is not relevant for task demands. These processes have been studied using the Event-Related Potential (ERP) technique and have been associated to the Mismatch Negativity (MMN), the P3a, and the Reorienting Negativity (RON) electrophysiological components, respectively. This has allowed for the objective evaluation of the impact of different neuropsychiatric pathologies on involuntary attention. Additionally, these ERP have been proposed as alternative measures for the early detection of disease and the tracking of its progression. The objective of this review was to integrate the results reported to date about MMN, P3a, and RON in different neurological and psychiatric disorders. We included experimental studies with clinical populations that reported at least two of these three components in the same experimental paradigm. Overall, involuntary attention seems to reflect the state of cognitive integrity in different pathologies in adults. However, if the main goal for these ERP is to consider them as biomarkers, more research about their pathophysiological specificity in each disorder is needed, as well as improvement in the general experimental conditions under which these components are elicited. Nevertheless, these ERP represent a valuable neurophysiological tool for early detection and follow-up of diverse clinical populations.

Normal categorical perception to syllable-like stimuli in long term and in first episode schizophrenia

Schizophrenia is associated with deficits in language processing that are evident even at first-episode. However, there is debate as to how early in the processing stream the linguistic deficits appear. We measured categorical processing of artificial syllables that varied in voice-onset time (VOT), and how sensory biasing impacts categorical perception. VOT varied in 5 ms increments from 0 ms (strong /ba/) to 40 ms (strong /pa/). Participants chose whether a syllable sounded more like /ba/ or /pa/. Twenty-two individuals with long-term schizophrenia (Sz) were compared to 21 controls (HCSz), and 17 individuals at their first-episode of schizophrenia (FE) were compared to 19 controls (HCFE). There were three conditions: equiprobable - each syllable had an equal probability of being presented; /ba/-biased - 0 ms VOT (strong /ba/) presented 70% of the time; /pa/-biased - 40 ms VOT (strong /pa/) presented 70% of the time. All groups showed categorical perception and category shifts during biased conditions. Sz and FE were statistically indistinguishable from controls in the point of categorical shift, slope of their response function, and the VOT needed to reliably perceive /pa/. Together, this suggests intact ability to map acoustic stimuli to phonetic categories when based on timing differences in voiced information, both early and late in the disease.

Neurophysiologic measures of target engagement predict response to auditory-based cognitive training in treatment refractory schizophrenia

Cognitive impairment is a core feature of schizophrenia and a strong predictor of psychosocial disability. Auditory-based targeted cognitive training (TCT) aims to enhance verbal learning and other domains of cognitive functioning through "bottom-up" tuning of the neural systems underlying early auditory information processing (EAIP). Although TCT has demonstrated efficacy at the group level, individual response to TCT varies considerably, with nearly half of patients showing little-to-no benefit. EEG measures of EAIP, mismatch negativity (MMN) and P3a, are sensitive to the neural systems engaged by TCT exercises and might therefore predict clinical outcomes after a full course of treatment. This study aimed to determine whether initial malleability of MMN and P3a to 1-h of auditory-based TCT predicts improvements in verbal learning and clinical symptom reduction following a full (30-h) course of TCT. Treatment refractory patients diagnosed with schizophrenia were randomly assigned to receive treatment-as-usual (TAU; n = 22) or TAU augmented with TCT (n = 23). Results indicated that malleability (i.e., change from baseline after the initial 1-h dose of TCT) of MMN and P3a predicted improvements in verbal learning as well as decreases in the severity of positive symptoms. Examination of MMN and P3a malleability in patients after their first dose of TCT can be used to predict clinical response to a full course of treatment and shows promise for future biomarker-informed treatment assignment.

Auditory Mismatch Negativity and P300a Elicited by the "Optimal" Multi-feature Paradigm in Early Schizophrenia

The mismatch negativity (MMN) is an EEG-derived event-related potential (ERP) elicited by any violation of a predicted auditory "rule," regardless of whether one is attending to the stimuli and is thought to reflect updating of the stimulus context. Redirection of attention toward a rare, distracting stimulus event, however, can be measured by the subsequent P3a component of the P300. Chronic schizophrenia patients exhibit robust MMN deficits, as well as reductions in P3a amplitude. While, the substantial literature on the MMN in first-episode and early phase schizophrenia in this population reports reduced amplitudes, there also exist several contradictory studies. Conversely, P3a reduction in this population is relatively consistent, although the literature investigating this is small. The primary goal of this study was to contribute to our understanding of whether auditory change detection mechanisms are altered in early phase schizophrenia and, if so, under what conditions. Event-related potentials elicited by duration, frequency, gap, intensity, and location deviants (as elicited by the "optimal" multi-feature paradigm) were recorded in 14 early phase schizophrenia (EP) patients and 17 healthy controls (HCs). Electrical activity was recorded from 15 scalp electrodes. MMN/P3a amplitudes and latencies for each deviant were compared between groups and were correlated with clinical measures in EPs. There were no significant group differences for MMN amplitudes or latencies, though EPs did exhibit reduced P3a amplitudes to gap and duration deviants. Furthermore, PANSS (Positive and Negative Syndrome Scale) positive symptom scores were correlated with intensity MMN latencies and duration P3a amplitudes in EPs. These findings suggest that MMNs may not be as robustly reduced in early phase schizophrenia (relative to chronic illness), but that alterations may be more likely in patients with increased positive symptomatology. Furthermore, these findings offer further support to previous work suggesting that the understudied P3a may have good complementary utility as a marker of early cortical dysfunction in psychosis.

An Update on Promising Biomarkers in Schizophrenia

Given the heterogeneity of symptoms in patients with schizophrenia and current treatment limitations, biomarkers may play an important role in diagnosis, subtype stratification, and the assessment of treatment response. Though many potential biomarkers have been studied, we have chosen to focus on some of the most promising and potentially clinically relevant biomarkers to review herein. These include markers of inflammation, neuroimaging biomarkers, brain-derived neurotrophic factor, genetic/epigenetic markers, and speech analysis. This will provide a broad overview of putative biomarkers that could become clinically relevant in the future, though none currently appear ready to assist the clinician in identifying cases of schizophrenia, subtypes of the disorder, treatment choice, or response. Nonetheless, some biomarkers, such as C-reactive protein (CRP), may be useful at identifying individuals who may be more highly inflamed, which could drive treatment choice. Though checking CRP is not a standard of practice, this is one example of how biomarkers may drive treatment decisions in the future, supporting precision medicine. Similarly, technological advances may one day allow clinicians to detect changes in speech patterns, which could represent a noninvasive, clinically useful tool in the future. We conclude the review by highlighting two important potential clinical uses for biomarkers in schizophrenia: the identification of individuals who may convert from clinical high risk and the stratification of patients via different biomarkers that may supersede clinical diagnosis. Given the enormous burden of illness of schizophrenia, the search for clinically relevant biomarkers is of great importance to improve the lives of patients with the disorder.

Understanding auditory verbal hallucinations: a systematic review of current evidence

OBJECTIVE

Auditory verbal hallucinations (AVHs) are core features of psychotic illness and remain significant in predicting poor outcome and risk. There has been a wide range of approaches to understanding these experiences.

METHOD

A systematic literature review summarizing different methods of investigation and their results; phenomenology, descriptive psychopathology, psychological, cognitive neurobiology, and neuroimaging.

RESULTS

A number of 764 papers and texts were screened and 113 reviewed. Phenomenological studies are comparably few in number, and psychopathology remains based on concepts defined in the early 20th century. Psychological models focus on voice content and emotional reaction, and suggest a continuum of AVHs from normal experience. Neuropsychological models include AVHs as misattribution of inner speech, whilst functional neuroimaging studies focus on the spontaneous activity and connectivity of auditory networks.

CONCLUSION

There has been a large growth in research on AVHs in recent decades dominated by neurobiological and neuroimaging studies. Future research should include focus on phenomenological aspects and AVHs change over the course of developing illness. Integration between branches of enquiry is needed, and the risk is that without this, models are proposed and investigated that bear scant relevance to the symptom itself.

Event-related potentials elicited by the Deutsch "high-low" word illusion in the patients with first-episode schizophrenia with auditory hallucinations

BACKGROUND

The exact cerebral structural and functional mechanisms under the auditory verbal hallucinations (AVHs) in schizophrenia are still unclear. The Deutsch "high-low" word illusion might trigger attentional responses mimicking those under AVHs.

METHODS

We therefore have invited 16 patients with first-episode, paranoid schizophrenia, and 16 age- and gender-matched healthy volunteers to undergo the "oddball" event-related potentials elicited by the illusion. The clinical characteristics of patients were measured with the positive and negative symptom scale.

RESULTS

Besides the longer reaction time to the illusion, the standard P2 latency was shortened, the N2 latency was prolonged, and both N1 and P3 amplitudes were reduced in patients. The P3 source analyses showed the activated bilateral temporal lobes, parietal lobe and cingulate cortex in both groups, left inferior temporal gyrus in controls, and left postcentral gyrus in schizophrenia. Moreover, the N1 amplitude was positively correlated with the paranoid score in patients.

CONCLUSIONS

Our results were in line with previous neurophysiological and neuroimaging reports of hallucination or auditory processing in schizophrenia, and illustrated a whole process of cerebral information processing from N1 to P3, indicating this illusion had triggered a dynamic cerebral response similar to that of the AVHs had engaged.

Electrophysiological Correlates of Aberrant Motivated Attention and Salience Processing in Unaffected Relatives of Schizophrenia Patients

Patients with schizophrenia (SCZ) exhibit debilitating deficits in attention and affective processing, which are often resistant to treatment and associated with poor functional outcomes. Impaired orientation to task-relevant target information has been indexed by diminished P3b event-related potentials in patients, as well as their unaffected first-degree relatives, suggesting that P3b may be a vulnerability marker for schizophrenia. Despite intact affective valence processing, patients are unable to employ cognitive change strategies to reduce electrophysiological responses to aversive stimuli. Less is known about the attentional processing of emotionally salient task-irrelevant information in patients and unaffected first-degree relatives. The goal of the present study was to examine the neural correlates of salience processing, as indexed by the late positive potential (LPP), during the processing of emotionally salient distractor stimuli in 31 patients with SCZ, 28 first-degree relatives, and 47 control participants using an oddball paradigm. Results indicated that despite intact novelty detection (P3a), both SCZ and first-degree relatives demonstrated deficiencies in attentional processing, reflected in attenuated target-P3b, and aberrant motivated attention, with reduced early-LPP amplitudes for aversive stimuli relative to controls. First-degree relatives revealed a unique enhancement of the late-LPP response, possibly underlying an exaggerated evaluation of salient information and a compensatory engagement of neural circuitry. Furthermore, reduced early-LPP and target-P3b amplitudes were associated with enhanced symptom severity. These findings suggest that, in addition to P3b, LPP may be useful for monitoring clinical state. Future studies will explore the value of P3 and LPP responses as vulnerability markers for early detection and prediction of psychopathology.

Mismatch negativity in tobacco-naïve cannabis users and its alteration with acute nicotine administration

Chronic cannabis use may interact with factors, such as age of onset of cannabis use, family history, and genetic factors, to elicit schizophrenia (SZ)-like symptoms, including sensory and cognitive deficits. However, evidence of a relationship between cannabis use and cognitive impairment is confounded by concomitant use of tobacco. The objective of this study was to compare tobacco-naïve cannabis users with individuals without a history of tobacco/cannabis use on the auditory mismatch negativity (MMN) event-related potential (ERP), a neural measure of auditory deviance detection which is diminished in SZ. An exploratory arm of the study, conducted within a randomized, double-blind, placebo controlled design, examined the acute effects of nicotine gum (6mg) on MMN in cannabis users. MMN was recorded in response to 5 deviant stimuli within an optimal MMN paradigm in 44 healthy, non-tobacco smoking volunteers aged 18-26. Cannabis users (n=21) started smoking cannabis prior to age 17, at least 1 joint per month. To examine the effects of chronicity, users were grouped into relatively heavy long-term (HLT; n=11) users and light short-term (LST; n=10) users. Impaired deviance detection was shown in cannabis users vs. nonusers as reflected by a smaller MMN to duration deviants. Chronicity of use was also associated with MMN alterations, as HLTs displayed a reduced duration and gap MMN vs. LSTs. Compared with placebo, nicotine treatment enhanced select MMN deviants in cannabis user subgroups. As deficits associated with early and persistent cannabis use are similar to those seen in SZ, these dose-dependant disturbances in early sensory processing with cannabis use may be one cognitive pathway which mediates an increased risk for SZ in vulnerable youth, and be influenced by concurrent cigarette smoking behavior.

Attenuation of mismatch negativity (MMN) and novelty P300 in schizophrenia patients with auditory hallucinations experiencing acute exacerbation of illness

This study examined measures of early auditory feature analysis, including the mismatch negativity (MMN) and novelty P300 (NP3) in schizophrenia patients (SZ) with persistent auditory hallucinations (AH) during an acute psychotic episode requiring hospitalisation. Neuroelectric activity was recorded in 10 SZ patients and 13 healthy controls (HC) during a passive auditory oddball task including novel environmental sounds. MMN/NP3 amplitudes and latencies were compared between groups and were correlated with trait (PSYRATS) and state measures of AH severity as well as clinical symptom ratings in SZs.SZ patients (vs. HCs) exhibited reduced MMN amplitudes to both rare deviant and novel stimuli, as well as reduced NP3 amplitudes. Additionally, while novelty MMN amplitudes were correlated with measures of hallucinatory trait, NP3 amplitudes were correlated with measures of hallucinatory state. Therefore, in acutely ill SZ patients, individual components of the auditory novelty detection mechanism may be differentially sensitive to varying aspects of AHs.

Physiological correlates of positive symptoms in schizophrenia

Patients with schizophrenia have been hypothesized to have a functional impairment in filtering irrelevant sensory information, which may result in positive symptoms such as hallucinations or delusions. Many evidences suggest that abnormalities in the event-related brain potentials (ERPs), resting state electroencephalography (EEG) and synchronized oscillatory activity of neurons may reflect core pathophysiological mechanisms of schizophrenia. Abnormalities in amplitude and latency of the ERPs reflecting aberrations in gating and difficulties in the detection of changes in auditory stimuli, as well as defects in stimuli evaluation and integration of information are common in patients with schizophrenia. This chapter highlights the findings of electrophysiological studies in schizophrenia dealing with early sensory perception and attention, automatic sensory detection of stimuli changes and cognitive evaluation and integration of information, relevant to the pathophysiological mechanisms underpinning hallucinations and delusions. Results of electrophysiological studies investigating the neural correlates of positive symptoms suggest aberrant intrinsic organization of functional brain networks.

Longitudinal associations between mismatch negativity and disability in early schizophrenia- and affective-spectrum disorders

BACKGROUND

Impaired mismatch negativity (MMN) is a robust finding in schizophrenia and, more recently, similar impairments have been reported in other psychotic- and affective-disorders (including at early stages of illness). Although cross-sectional studies have been numerous, there are few longitudinal studies that have explored the predictive value of this event-related potential in relation to clinical/functional outcomes. This study assessed changes in MMN (and the concomitant P3a) amplitude over time and aimed to determine the longitudinal relationship between MMN/P3a and functional outcomes in patients recruited during the early stage of a schizophrenia- or affective-spectrum disorder.

METHODS

Sixty young patients with schizophrenia- and affective-spectrum disorders and 30 healthy controls underwent clinical, neuropsychological and neurophysiological assessment at baseline. Thirty-one patients returned for clinical and neuropsychological follow-up 12-30months later, with 28 of these patients also repeating neurophysiological assessment. On both occasions, MMN/P3a was elicited using a two-tone passive auditory paradigm with duration deviants.

RESULTS

Compared with controls, patients showed significantly impaired temporal MMN amplitudes and trend-level deficits in central MMN/P3a amplitudes at baseline. There were no significant differences for MMN measures between the diagnostic groups, whilst the schizophrenia-spectrum group showed reduced P3a amplitudes compared to those with affective-spectrum disorders. For those patients who returned for follow-up, reduced temporal MMN amplitude at baseline was significantly associated with greater levels of occupational disability, and showed trend-level associations with general and social disability at follow-up. Paired t-tests revealed that MMN amplitudes recorded at the central-midline site were significantly reduced in patients over time. Interestingly, those patients who did not return for follow-up showed reduced frontal MMN and fronto-central P3a amplitudes compared to their peers who did return for repeat assessment.

CONCLUSIONS

This study provides some evidence of the predictive utility of MMN at the early stages of schizophrenia- and affective-spectrum disorders and demonstrated that MMN impairments in such patients may worsen over time. Specifically, we found that young patients with the most impaired MMN amplitudes at baseline showed the most severe levels of disability at follow-up. Furthermore, in the subset of patients with repeat neurophysiological testing, central MMN was further impaired suggestive of neurodegenerative effects. MMN may serve as a neurophysiological biomarker to more accurately predict functional outcomes and prognosis, particularly at the early stages of illness.

Neurophysiological biomarkers support bipolar-spectrum disorders within psychosis cluster

BACKGROUND

Mismatch negativity (MMN) and P3a are event-related potentials that index deviance detection and the orienting response, respectively. We have previously shown that the MMN/P3a complex is impaired in patients with schizophrenia and affective spectrum psychoses, which suggests that it may index a common pathophysiology and argues against the purported specificity in schizophrenia. Further research is warranted to determine whether patients with bipolar-spectrum disorders show similar impairments in these biomarkers.

METHODS

We assessed patients aged 15-30 years with early schizophrenia-spectrum disorders (schizophrenia, schizoaffective disorder, schizophreniform disorder), early bipolar-spectrum disorders (bipolar I or II, with and without psychotic features) and healthy, matched controls. We acquired MMN/P3a amplitudes during a 2-tone, auditory paradigm with 8% duration deviants. Clinical, psychosocial and neuro psychological assessments were also undertaken.

RESULTS

We included 20 patients with schizophrenia-spectrum disorders, 20 with bipolar-spectrum disorders and 20 controls in our study. Both patient groups showed significantly reduced frontocentral MMN and central P3a amplitudes. The schizophrenia-spectrum group had additional impairments in left temporal MMN and frontal P3a. Both patient groups performed worse than controls across psychosocial and clinical measures; however, only the schizophrenia-spectrum group performed significantly worse than controls for cognitive measures. Correlational analyses between patient groups revealed associations between frontocentral or left temporal MMN and psychiatric symptomatology or quality of life measures.

LIMITATIONS

Limitations to our study include the modest sample size and the lack of control with regards to the effects of other (i.e., nonantipsychotic) psychotropic medications.

CONCLUSION

Compared with patients in early stages of schizophrenia-spectrum disorders, those in the early stages of bipolar-spectrum disorders are similarly impaired in established biomarkers for schizophrenia. These findings support a shared diathesis model for psychotic and bipolar disorders. Furthermore, MMN/P3a may be a biomarker for a broader pathophysiology that overlaps traditional diagnostic clusters.

Neurophysiological studies of auditory verbal hallucinations

We discuss 3 neurophysiological approaches to study auditory verbal hallucinations (AVH). First, we describe "state" (or symptom capture) studies where periods with and without hallucinations are compared "within" a patient. These studies take 2 forms: passive studies, where brain activity during these states is compared, and probe studies, where brain responses to sounds during these states are compared. EEG (electroencephalography) and MEG (magnetoencephalography) data point to frontal and temporal lobe activity, the latter resulting in competition with external sounds for auditory resources. Second, we discuss "trait" studies where EEG and MEG responses to sounds are recorded from patients who hallucinate and those who do not. They suggest a tendency to hallucinate is associated with competition for auditory processing resources. Third, we discuss studies addressing possible mechanisms of AVH, including spontaneous neural activity, abnormal self-monitoring, and dysfunctional interregional communication. While most studies show differences in EEG and MEG responses between patients and controls, far fewer show symptom relationships. We conclude that efforts to understand the pathophysiology of AVH using EEG and MEG have been hindered by poor anatomical resolution of the EEG and MEG measures, poor assessment of symptoms, poor understanding of the phenomenon, poor models of the phenomenon, decoupling of the symptoms from the neurophysiology due to medications and comorbidites, and the possibility that the schizophrenia diagnosis breeds truer than the symptoms it comprises. These problems are common to studies of other psychiatric symptoms and should be considered when attempting to understand the basic neural mechanisms responsible for them.

The visual P3a in schizophrenia and bipolar disorder: effects of target and distractor stimuli on the P300

Amplitude reduction of the P300 event-related potential has long been suggested as a marker for schizophrenia. However, recent research has shown that this reduction in the P300 amplitude is not specific to schizophrenia as it can also be observed in related illnesses such as bipolar disorder. Due to this lack of specificity the P300 elicited using traditional oddball paradigms may be a less valuable endophenotypic marker. The current study employed a cognitively demanding three-stimulus oddball paradigm to elicit the P300 to visual target and distracting stimuli. Patients with schizophrenia showed amplitude reductions of P300 components to targets, distractors and frequent stimuli. The P300 in patients with bipolar disorder was not significantly different from either group. The pattern of results may further the understanding of the nature of the impairment in schizophrenia.

The neurophysiology of auditory hallucinations - a historical and contemporary review

Electroencephalography and magnetoencephalography are two techniques that distinguish themselves from other neuroimaging methodologies through their ability to directly measure brain-related activity and their high temporal resolution. A large body of research has applied these techniques to study auditory hallucinations. Across a variety of approaches, the left superior temporal cortex is consistently reported to be involved in this symptom. Moreover, there is increasing evidence that a failure in corollary discharge, i.e., a neural signal originating in frontal speech areas that indicates to sensory areas that forthcoming thought is self-generated, may underlie the experience of auditory hallucinations.