Processing of auditory stimuli during visual attention in patients with schizophrenia

Arcuate fasciculus architecture is associated with individual differences in pre-attentive detection of unpredicted music changes

The mismatch negativity (MMN) is an event related brain potential (ERP) elicited by unpredicted sounds presented in a sequence of repeated auditory stimuli. The neural sources of the MMN have been previously attributed to a fronto-temporo-parietal network which crucially overlaps with the so-called auditory dorsal stream, involving inferior and middle frontal, inferior parietal, and superior and middle temporal regions. These cortical areas are structurally connected by the arcuate fasciculus (AF), a three-branch pathway supporting the feedback-feedforward loop involved in auditory-motor integration, auditory working memory, storage of acoustic templates, as well as comparison and update of those templates. Here, we characterized the individual differences in the white-matter macrostructural properties of the AF and explored their link to the electrophysiological marker of passive change detection gathered in a melodic multifeature MMN-EEG paradigm in 26 healthy young adults without musical training. Our results show that left fronto-temporal white-matter connectivity plays an important role in the pre-attentive detection of rhythm modulations within a melody. Previous studies have shown that this AF segment is also critical for language processing and learning. This strong coupling between structure and function in auditory change detection might be related to life-time linguistic (and possibly musical) exposure and experiences, as well as to timing processing specialization of the left auditory cortex. To the best of our knowledge, this is the first time in which the relationship between neurophysiological (EEG) and brain white-matter connectivity indexes using DTI-tractography are studied together. Thus, the present results, although still exploratory, add to the existing evidence on the importance of studying the constraints imposed on cognitive functions by the underlying structural connectivity.

Reductions in Complex Mismatch Negativity to Extra Tone Gestalt Pattern Deviance in First-Episode Schizophrenia

Although "simple" mismatch negativity (sMMN) to stimulus parameter changes is robustly reduced in long-term schizophrenia (Sz), it is much less reduced in individuals at their first psychotic episode in the schizophrenia-spectrum (FESz). "Complex" MMN (cMMN) reflecting pre-attentive acoustic pattern analysis is also markedly reduced in Sz, but is little studied in FESz. The computational complexity of pattern analysis reflected in cMMN may more greatly stress auditory processing, providing a more sensitive measure of auditory processing deficits at first break. If so, cMMN would provide information about the underlying pathophysiology early in disease course, and may serve as a biomarker for pathology in the Sz prodrome. Twenty-two FESz individuals were compared to 22 volunteer healthy controls (HC) on sMMN and cMMN tasks. For sMMN, pitch- and duration-deviants were presented among standard repetitive tones. For cMMN, repeated groups of 3 identical tones were presented with occasional (14%) groups including an extra identical 4th tone deviant. FESz did not show reductions of pitch-deviant (Cohen's d = 0.08) or duration-deviant MMNs (d =-0.02), but showed large reduction in extra-tone cMMN (d = 0.83). Reduced cMMN was associated with poor social functioning. Reduction in cMMN but not in sMMNs in FESz suggests impairments in late perceptual pattern processing. cMMN is sensitive to subtle pathology and functioning early in disease course which may, in turn, impact social functioning. Future studies in clinical high risk individuals are needed to determine whether this putative biomarker of disease presence is sensitive to the prodromal stage of schizophrenia.

Neural correlates of auditory sensory memory dynamics in the aging brain

The auditory system allows us to monitor background environmental sound patterns and recognize deviations that may indicate opportunities or threats. The mismatch negativity and P3a potentials have generators in the auditory and inferior frontal cortex and index expected sound patterns (standards) and any aberrations (deviants). The mismatch negativity and P3a waveforms show increased positivity for consecutive standards and deviants preceded by more standards. We hypothesized attenuated repetition effects in older participants, potentially because of differences in prefrontal functions. Young (23 ± 5 years) and older (75 ± 5 years) adults were tested in 2 oddball paradigms with pitch or location deviants. Significant repetition effects were observed in the young standard and deviant waveforms at multiple time windows. Except the earliest time window (30-100 ms), repetition effects were absent in the older group. Repetition effects were significant at frontal but not temporal lobe sites and did not differ among pitch and location deviants. However, P3a repetition was evident in both ages. Findings suggest age differences in the dynamic updating of sensory memory for background sound patterns.

Complex mismatch negativity to tone pair deviants in long-term schizophrenia and in the first-episode schizophrenia spectrum

Mismatch negativity (MMN) is an event-related potential to stimulus change. MMN to infrequent deviant tones that differs in a simple physical parameter from repetitive standard tones is reduced in patients with long-term schizophrenia (Sz; d=~1). However, this simple MMN is not uniformly reduced at the first-episode of schizophrenia-spectrum psychosis (FESz; d<0.1 for pitch; <0.4 for duration). Deviant stimuli that violate pattern rules also evoke MMN. This complex MMN is evoked by deviations in the relation of sounds to each other. The simplest pattern involves tone pairs. Although the pitch of first tone in the pair varies, the second tone's pitch always follows a rule (e.g., always 3 semitones higher). We measured complex MMN to deviant tone pairs that descended in pitch among standard tone pairs that ascended in pitch, never before examined in Sz or in FESz. Experiment 1 showed significant reductions in complex MMN in 20 Sz compared to 22 matched controls. Experiment 2 replicated smaller complex MMN in a shorter protocol in 24 Sz compared to 21 matched controls, but showed no significant complex MMN reduction in 21 FESz compared to 21 matched controls. Although reduced in Sz, indicating deficits in generation of a simple acoustic pattern rule, the tone pair complex MMN was within normal limits in FESz. This suggests that more complex perceptual pattern analysis processes are, at least partially, still intact at the first break. Future work will determine at what point of pattern complexity subtle auditory perception pathophysiology will be revealed in FESz.

Meta-analysis of mismatch negativity to simple versus complex deviants in schizophrenia

Mismatch negativity (MMN) deficits in schizophrenia (SCZ) have been studied extensively since the early 1990s, with the vast majority of studies using simple auditory oddball task deviants that vary in a single acoustic dimension such as pitch or duration. There has been a growing interest in using more complex deviants that violate more abstract rules to probe higher order cognitive deficits. It is still unclear how sensory processing deficits compare to and contribute to higher order cognitive dysfunction, which can be investigated with later attention-dependent auditory event-related potential (ERP) components such as a subcomponent of P300, P3b. In this meta-analysis, we compared MMN deficits in SCZ using simple deviants to more complex deviants. We also pooled studies that measured MMN and P3b in the same study sample and examined the relationship between MMN and P3b deficits within study samples. Our analysis reveals that, to date, studies using simple deviants demonstrate larger deficits than those using complex deviants, with effect sizes in the range of moderate to large. The difference in effect sizes between deviant types was reduced significantly when accounting for magnitude of MMN measured in healthy controls. P3b deficits, while large, were only modestly greater than MMN deficits (d=0.21). Taken together, our findings suggest that MMN to simple deviants may still be optimal as a biomarker for SCZ and that sensory processing dysfunction contributes significantly to MMN deficit and disease pathophysiology.

Impact of Reward and Loss Anticipation on Cognitive Control: An Event-Related Potential Study in Subjects With Schizophrenia and Healthy Controls

INTRODUCTION

Deficits of cognitive functions and motivation are core aspects of schizophrenia. The interaction of these deficits might contribute to impair the ability to flexibly adjust behavior in accordance with one's intentions and goals. Many studies have focused on the anterior N2 as a correlate of cognitive control based on motivational value.

AIMS

Given the key role of motivation impairment in schizophrenia as a predictor of functional outcome, we aimed to study the impact of reward- and avoidance-based motivation on cognitive control using N2.

METHOD

Event-related potentials were recorded during the execution of the "Monetary Incentive Delay (MID)" task in 34 patients with schizophrenia (SCZ) stabilized on second-generation antipsychotics and 22 healthy controls (HC). Cognitive domains were assessed using the MATRICS Consensus Cognitive Battery. Negative symptom domains (Avolition/apathy and Expressive deficit), as well as positive and disorganization dimensions were also assessed in SCZ.

RESULTS

We did not observe any group difference in N2 amplitude or latency. In HC, N2 amplitude was significantly larger for anticipation of large loss with regard to all reward conditions and for all incentive versus neutral conditions. In SCZ, N2 amplitude did not discriminate between large loss and reward or between incentive and neutral conditions. N2 amplitude was not correlated with psychopathological dimensions or MCCB-assessed cognitive deficits in SCZ.

CONCLUSION

Our data in HC are in line with the hypothesis that N2 amplitude reflects the impact of motivational salience on cognitive control. Our results in SCZ indicate a deficit in the discrimination of motivational salience to the service of cognitive control, independently of psychopathology and other cognitive deficits.

Mismatch negativity to pitch pattern deviants in schizophrenia

Simple mismatch negativity (MMN) to infrequent pitch deviants is impaired in individuals with long-term schizophrenia (Sz). The complex MMN elicited by pattern deviance often manifes is cut from here]->ts later after deviant onset than simple MMN and can ascertain deficits in abstracting relationships between stimuli. Sz exhibit reduced complex MMN, but so far this has only been measured when deviance detection relies on a grouping rule. We measured MMN to deviants in pitch-based rules to see whether MMN is also abnormal in Sz under these conditions. Three experiments were conducted. Twenty-seven Sz and 28 healthy matched controls (HC) participated in Experiments 1 and 2, and 24 Sz and 26 HC participated in Experiment 3. Experiment 1 was a standard pitch MMN task, and Sz showed the expected MMN reduction (~ 115 ms) in the simple pitch deviant compared to HC. Experiment 2 comprised standard groups of six tones that ascended in pitch, and deviant groups where the last tone descended in pitch. Complex MMN was late (~ 510 ms) and significantly blunted in Sz. Experiment 3 comprised standard groups of 12 tones (six tones ascending in pitch followed by six tones descending in pitch, like a scale), and deviant groups containing two repetitions of six ascending tones (the scale restarted midstream). Complex MMN was also late (~ 460 ms) and significantly blunted in Sz. These results identify a late pitch pattern deviance-related MMN that is deficient in schizophrenia. This suggests specific deficits in later more complex deviance detection in schizophrenia for abstract patterns.

Neurophysiological Characterization of Attentional Performance Dysfunction in Schizophrenia Patients in a Reverse-Translated Task

Attentional dysfunction in schizophrenia (SZ) contributes to the functional deficits ubiquitous to the disorder. Identifying the neural substrates of translational measures of attentional dysfunction would prove invaluable for developing therapeutics. Attentional performance is typically assessed via continuous performance tasks (CPTs), though many place additional cognitive demands with little cross-species test-relevance. Herein, event-related potentials (ERPs) were used to investigate the neurophysiological correlates of attention and response inhibition of SZ and healthy participants, whereas they performed the cross-species-translated five-choice CPT (5C-CPT). Chronically ill, medicated SZ patients and matched controls (n=25 SZ and 26 controls) were tested in the 5C-CPT, in conjunction with ERP and source localization assessments. The ERPs generated in response to correctly identified target and non-target trials revealed three peaks for analysis, corresponding to sensory registration (P₁), response selection (N₂), and response action (P₃). Behavioral responses revealed that SZ patients exhibited impaired attention driven by impaired and slower target detection, and poorer cognitive control. ERPs revealed decreased N₂ amplitudes reflecting poorer response selection for both target and non-target trials, plus reduced non-target P₃s in SZ patients, the latter accounting for 37% of variance in negative symptoms. Source analyses revealed that the brain regions of significant differences localized to the left dorsolateral prefrontal cortex during response selection and the posterior cingulate cortex for cognitive processes. SZ patients exhibited impaired attention and cognitive control, characterized by less robust frontal and parietal ERP distributions across the response selection and cognitive response time windows, providing neurophysiological characterization of attentional dysfunction in SZ using the reverse-translated 5C-CPT.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

DISCUSSION

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

Abnormal Complex Auditory Pattern Analysis in Schizophrenia Reflected in an Absent Missing Stimulus Mismatch Negativity

The simple mismatch negativity (MMN) to tones deviating physically (in pitch, loudness, duration, etc.) from repeated standard tones is robustly reduced in schizophrenia. Although generally interpreted to reflect memory or cognitive processes, simple MMN likely contains some activity from non-adapted sensory cells, clouding what process is affected in schizophrenia. Research in healthy participants has demonstrated that MMN can be elicited by deviations from abstract auditory patterns and complex rules that do not cause sensory adaptation. Whether persons with schizophrenia show abnormalities in the complex MMN is unknown. Fourteen schizophrenia participants and 16 matched healthy underwent EEG recording while listening to 400 groups of 6 tones 330 ms apart, separated by 800 ms. Occasional deviant groups were missing the 4th or 6th tone (50 groups each). Healthy participants generated a robust response to a missing but expected tone. The schizophrenia group was significantly impaired in activating the missing stimulus MMN, generating no significant activity at all. Schizophrenia affects the ability of "primitive sensory intelligence" and pre-attentive perceptual mechanisms to form implicit groups in the auditory environment. Importantly, this deficit must relate to abnormalities in abstract complex pattern analysis rather than sensory problems in the disorder. The results indicate a deficit in parsing of the complex auditory scene which likely impacts negatively on successful social navigation in schizophrenia. Knowledge of the location and circuit architecture underlying the true novelty-related MMN and its pathophysiology in schizophrenia will help target future interventions.

Abnormal auditory pattern perception in schizophrenia

Mismatch negativity (MMN) in response to deviation from physical sound parameters (e.g., pitch, duration) is reduced in individuals with long-term schizophrenia (Sz), suggesting deficits in deviance detection. However, MMN can appear at several time intervals as part of deviance detection. Understanding which part of the processing stream is abnormal in Sz is crucial for understanding MMN pathophysiology. We measured MMN to complex pattern deviants, which have been shown to produce multiple MMNs in healthy controls (HC). Both simple and complex MMNs were recorded from 27 Sz and 27 matched HC. For simple MMN, pitch- and duration-deviants were presented among frequent standard tones. For complex MMN, patterns of five single tones were repeatedly presented, with the occasional deviant group of tones containing an extra sixth tone. Sz showed smaller pitch MMN (p=0.009, ~110ms) and duration MMN (p=0.030, ~170ms) than healthy controls. For complex MMN, there were two deviance-related negativities. The first (~150ms) was not significantly different between HC and SZ. The second was significantly reduced in Sz (p=0.011, ~400ms). The topography of the late complex MMN was consistent with generators in anterior temporal cortex. Worse late MMN in Sz was associated with increased emotional withdrawal, poor attention, lack of spontaneity/conversation, and increased preoccupation. Late MMN blunting in schizophrenia suggests a deficit in later stages of deviance processing. Correlations with negative symptoms measures are preliminary, but suggest that abnormal complex auditory perceptual processes may compound higher-order cognitive and social deficits in the disorder.

Increased distractibility in schizotypy: Independent of individual differences in working memory capacity?

Individuals with schizophrenia typically show increased levels of distractibility. This has been attributed to impaired working memory capacity (WMC), since lower WMC is typically associated with higher distractibility, and schizophrenia is typically associated with impoverished WMC. Here, participants performed verbal and spatial serial recall tasks that were accompanied by to-be-ignored speech tokens. For the few trials wherein one speech token was replaced with a different token, impairment was produced to task scores (a deviation effect). Participants subsequently completed a schizotypy questionnaire and a WMC measure. Higher schizotypy scores were associated with lower WMC (as measured with operation span, OSPAN), but WMC and schizotypy scores explained unique variance in relation to the mean magnitude of the deviation effect. These results suggest that schizotypy is associated with heightened domain-general distractibility, but that this is independent of its relationship with WMC.

The effect of deviance predictability on mismatch negativity in schizophrenia patients

Mismatch negativity (MMN) is an electrophysiological index of prediction error processing and recently has been considered an endophenotype marker in schizophrenia. While the prediction error is a core concept in the MMN generation, predictability of deviance occurrence has rarely been assessed in MMN research and in schizophrenia patients. We investigated the MMN to 12% temporally predictable or unpredictable duration decrement deviant stimuli in two runs in 29 healthy controls and 31 schizophrenia patients. We analyzed MMN amplitudes and latencies and its associations with clinical symptoms at electrode Fz. With a stimulus onset asynchronicity of 500 ms in the regular predictable condition, a deviant occurred every 4s while it varied randomly in the unpredictable condition. In the random condition we found diminished MMN amplitudes in patients which normalized in the regular deviance condition, resulting in an analysis of variance main effect of predictability and a predictability x group interaction. Deviance predictability did not affect the MMN of control subjects and we found no relevant results with regard to MMN latencies. Our results indicate that MMN amplitudes in patients normalize to the level of the control subjects in the case of a temporally fixed regular deviant. In schizophrenia patients the detection of deviance is basically intact. However, the temporal uncertainty of deviance occurrence may be of substantial relevance to the highly replicated MMN deficit in schizophrenia patients.

A predictive coding account of MMN reduction in schizophrenia

The mismatch negativity (MMN) is thought to be an index of the automatic activation of a specialized network for active prediction and deviance detection in the auditory cortex. It is consistently reduced in schizophrenic patients and has received a lot of interest as a clinical and translational tool. The main neuronal hypothesis regarding the mechanisms leading to a reduced MMN in schizophrenic patients is a dysfunction of NMDA receptors (NMDA-R). However, this hypothesis has never been implemented in a neuronal model. In this paper, we examine the consequences of NMDA-R dysfunction in a neuronal model of MMN based on predictive coding principle. I also investigate how predictive processes may interact with synaptic adaptation in MMN generations and examine the consequences of this interaction for the use of MMN paradigms in schizophrenia research.

Paying attention to MMN in schizophrenia

The aim of this review is to explore the phenomenon of reduced mismatch negativity (MMN) in persons with schizophrenia and the possible relationship it has with attention impairments. In doing so we discuss (i) the prediction error account of MMN, (ii) reduced MMN as a faulty predictive processing system in persons with schizophrenia, (iii) the role of these systems in relevance filtering and attentional resource protection, (iv) attentional impairments in persons with schizophrenia, and (v) research that has explored MMN and attention in schizophrenia groups. Our review of the literature suggests that no study has appropriately examined the functional impact of smaller MMN in schizophrenia on the performance of a concurrent attention task. We conclude that future research should explore this notion further in the hope that it might embed MMN findings within outcomes of functional significance to individuals with the illness and those providing treatment. This article is part of a Special Issue entitled SI: Prediction and Attention.

Mismatch negativity (MMN) deficiency: a break-through biomarker in predicting psychosis onset

Currently, the mismatch negativity (MMN) deficit is one of the most robust and replicable findings in schizophrenia, reflecting cognitive and functional decline, psychosocial and socio-occupational impairment, and executive dysfunction in these patients. An important break-through has very recently taken place here in the prediction of conversion to psychosis when the MMN in particular to change in tone duration was recorded in clinically at risk-mental state (ARMS) individuals. Attenuations in the MMN in these patients may be very useful in helping clinicians determine who are most likely to develop a psychotic disorder, as we will review in the present article.

The Active Therapeutic Processes of Acceptance and Commitment Therapy for Persistent Symptoms of Psychosis: Clients’ Perspectives

Background: There is limited research on the applicability and effectiveness of Acceptance and Commitment Therapy (ACT) for people experiencing psychotic disorders. Clinical trials suggest ACT may be efficacious in reducing distress and rehospitalization rates in psychosis. Mindfulness and reduced literal believability of thought content have been associated with reduced distress for this population. Aims: To better understand ACT for psychosis, this study investigated clients’ perspectives of the hypothesized active therapeutic processes of ACT. Method: Semi‑structured interviews, conducted with nine adults diagnosed with schizophrenia or schizoaffective disorder and persistent positive symptoms, were analysed thematically. Results: Four themes emerged: Usefulness of therapy; Changes attributed to ACT; Understanding of therapy; and Non-specific therapy factors. All participants found therapy useful and recommended ACT. Mindfulness, defusion, acceptance and values work were described as the most useful therapy components and contributing to positive changes. Self-rated frequency of symptoms did not change; however a reduction in the intensity and distress associated with symptoms was reported. Non-specific therapy factors were deemed useful by participants but not directly related to outcome. Conclusions: These findings are consistent with the theoretically defined underlying active processes of ACT and are relevant for this population. The findings also indicate important clinical implications for ACT for this client group: greater attention to the client connecting metaphors and concepts to the intended meaning may be valuable; caution should be used with some mindfulness and defusion techniques for intense experiences; and values work may be particularly useful for this population.

Neural correlates of local contextual processing deficits in schizophrenic patients

Deficits in processing contextual information are one of the main features of cognitive dysfunction in schizophrenia, but the neurophysiologic substrate underlying this dysfunction is poorly understood. We used ERPs to investigate local contextual processing in schizophrenic patients. Local context was defined as the occurrence of a short predictive series of stimuli occurring before delivery of a target event. Response times of predicted targets were faster in controls compared to patients. Schizophrenia patients failed to generate the P3b latency shift between predicted and random targets that was observed in controls and demonstrated a prominent reduction of the peak of an early latency context dependent positivity. The current study provides evidence of contextual processing deficits in schizophrenia patients by demonstrating alteration in the behavioral and neural correlates of local contextual processing.

MMN responsivity to manipulations of frequency and duration deviants in chronic, clozapine-treated schizophrenia patients

Event-related potential (ERP) probing of abnormal sensory processes in schizophrenia with the mismatch negativity (MMN) has shown impairments in auditory change detection, but knowledge of the acoustic features leading to this deficit is incomplete. Changes in the duration and frequency properties of sound stimuli result in diminished MMNs in schizophrenia but it is unclear as to whether this reduced responsiveness is seen with more subtle changes in sound frequency. In a sample of 19 healthy controls and 21 patients with chronic schizophrenia treated with clozapine, MMN was assessed in response to tone frequency changes of 5%, 10% and 20%, and to tone duration changes. Patients exhibited reduced amplitudes and shorter latencies than controls to all frequency changes, and attenuated amplitudes to tone duration increments and decrements. Clozapine dose was related to MMN, with increasing dose being positively associated with frequency-MMN amplitudes (10% ∆f, 20% ∆f) and negatively associated with the amplitude and latency of duration-MMNs. These data support the well-established findings of auditory sensory abnormality in schizophrenia and underscore the sensitivity of MMN to relatively small auditory change detection deficits that may appear to characterize chronic schizophrenia.

Somatosensory system deficits in schizophrenia revealed by MEG during a median-nerve oddball task

Although impairments related to somatosensory perception are common in schizophrenia, they have rarely been examined in functional imaging studies. In the present study, magnetoencephalography (MEG) was used to identify neural networks that support attention to somatosensory stimuli in healthy adults and abnormalities in these networks in patient with schizophrenia. A median-nerve oddball task was used to probe attention to somatosensory stimuli, and an advanced, high-resolution MEG source-imaging method was applied to assess activity throughout the brain. In nineteen healthy subjects, attention-related activation was seen in a sensorimotor network involving primary somatosensory (S1), secondary somatosensory (S2), primary motor (M1), pre-motor (PMA), and paracentral lobule (PCL) areas. A frontal-parietal-temporal "attention network", containing dorsal- and ventral-lateral prefrontal cortex (DLPFC and VLPFC), orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), superior parietal lobule (SPL), inferior parietal lobule (IPL)/supramarginal gyrus (SMG), and temporal lobe areas, was also activated. Seventeen individuals with schizophrenia showed early attention-related hyperactivations in S1 and M1 but hypo-activation in S1, S2, M1, and PMA at later latency in the sensorimotor network. Within this attention network, hypoactivation was found in SPL, DLPFC, orbitofrontal cortex, and the dorsal aspect of ACC. Hyperactivation was seen in SMG/IPL, frontal pole, and the ventral aspect of ACC in patients. These findings link attention-related somatosensory deficits to dysfunction in both sensorimotor and frontal-parietal-temporal networks in schizophrenia.

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

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

Diminished parietal cortex activity associated with poor motion direction discrimination performance in schizophrenia

The results of multiple investigations indicate visual motion-processing abnormalities in schizophrenia. There is little information, however, about the time course and neural correlates of motion-processing abnormalities among these subjects. For the present study, 13 schizophrenia and 13 healthy subjects performed a simple motion direction discrimination task with peripherally presented moving grating stimuli (5 or 10 deg/s). Dense-array electroencephalography data were collected simultaneously. The goal was to discern whether neural deviations associated with motion-processing abnormalities among schizophrenia patients occur early or late in the visual-processing stream. Schizophrenia patients were worse at judging the direction of motion gratings, had enhanced early neural activity (about 90 ms after stimulus onset), and deficient target detection-related late neural activity over parietal cortex (about 400 ms after stimulus onset). In addition, there was a strong association (accounting for 36% of performance variance) between poor behavioral performance and lower target detection-related brain activity among schizophrenia patients. These findings suggest that abnormalities in later stages of motion-processing mechanisms, perhaps beyond extrastriate cortex, may account for behavioral deviations among schizophrenia subjects.

Multimodal effects of local context on target detection: evidence from P3b

We used the P300 component to investigate how changes in local context influenced the ability to detect target stimuli. Local context was defined as the occurrence of a short predictive series of stimuli before delivery of a target event. EEG was recorded in 12 subjects during auditory and visual sessions. Stimuli were presented in the center of the auditory and visual field and consisted of 15% targets (1000 Hz tone or downward facing triangle) and 85% of equal amounts of three types of standards (1500, 2000, and 2500 Hz tones or triangles facing left, upward, and right). Recording blocks consisted of targets preceded by either randomized sequences of standards or by sequences including a three-standard predictive sequence signaling the occurrence of a subsequent target event. Subjects pressed a button in response to targets. Peak target P300 (P3b) amplitude and latency were evaluated for targets after predictive and nonpredictive sequences using conventional averaging and a novel single-trial analysis procedure. Reaction times were shorter for predictable targets than for nonpredicted targets. P3b latency was shorter for predicted targets than for nonpredictive targets, and there were no significant P3b amplitude differences between predicted and random targets, as determined by both conventional averaging and single-trial analysis. Comparable effects on amplitude and latency were observed in both the auditory and visual modalities. The results indicate that local context has differential effects on P3b amplitude and latency, and exerts modality-independent effects on cognitive processing.

Prefrontal cortex is critical for contextual processing: evidence from brain lesions

We investigated the role of prefrontal cortex (PFC) in local contextual processing using a combined event-related potentials and lesion approach. Local context was defined as the occurrence of a short predictive series of visual stimuli occurring before delivery of a target event. Targets were preceded by either randomized sequences of standards or by sequences including a three-stimulus predictive sequence signalling the occurrence of a subsequent target event. PFC lesioned patients were impaired in their ability to use local contextual information. The response time for controls revealed a larger benefit for predictable targets than for random targets relative to PFC patients. PFC patients had reduced amplitude of a context-dependent positivity and failed to generate the expected P3b latency shift between predictive and non-predictive targets. These findings show that PFC patients are unable to utilize predictive local context to guide behaviour, providing evidence for a critical role of PFC in local contextual processing.

Central auditory dysfunction in schizophrenia as revealed by the mismatch negativity (MMN) and its magnetic equivalent MMNm: a review

Since the early 1990s, the auditory change-detection response, mismatch negativity (MMN) and its magnetoencephalographic (MEG) equivalent MMNm have been applied in a large number of studies on schizophrenia. These studies have enhanced our understanding of the central auditory dysfunction underlying schizophrenia. The attenuation of the MMN amplitude is a systematic and robust neurophysiological finding in these patients. The gradual attenuation of the MMN amplitude resulting from frequency change reflects the progress of the disease, particularly the impairment occurring as a function of illness duration, whereas the MMN deficiency for duration change may be more closely linked to the genetic aspect of the illness. Electroencephalographic (EEG) and magnetoencephalographic (MEG) studies, together, suggest that both the temporal and frontal cortices contributing to MMN generation are affected in schizophrenia patients. Furthermore, abnormalities in auditory perception and discrimination revealed by a deficient temporal MMN generator process might be associated with patients' positive symptoms, whereas the dampened frontal attention-switching function, suggested by the attenuated responses of the frontal MMN generator, might contribute to the negative symptoms such as social withdrawal. In addition, gradual MMN amplitude reduction, in particular that for frequency change, reflects cognitive and functional impairment occurring as a function of illness duration. Finally, as MMN can be detected even in animals such as the mouse, it might provide a useful biomarker for assessing the effects of the drugs developed to fight the cognitive and functional impairments in schizophrenia patients.

Wavelet analysis of the frontal auditory evoked potentials obtained in the passive oddball paradigm in healthy subjects and schizophrenics

The goal of the present study was to apply the oscillatory brain dynamics model to the structural and quantitative analysis of neurocognitive functions considered as a potential marker of schizophrenia. This was achieved in tests of the detection of auditory events deviating in the regular auditory stream (oddball paradigm, MMN effect). It was hypothesized that the post-stimulus peaks of the oscillation power localized in post-stimulus time in the definite EEG oscillators represented neuro-electrical 'events' evoked in the specific neuronal nets characterized by this oscillation frequency band. We suggest that the time-frequency destination of these events related to the activation of the functional neuronal nets could be used for the determination of specific neurocognitive functions. Thus it was an attempt to distinguish the different neuro-functional parts of auditory processing and to compare these results between healthy subjects and patients with schizophrenia. The present results demonstrate the significant difference between the frontal averaged EEG oscillatory dynamics in healthy subjects and patients with schizophrenia related to neurocognitive function marked by the MMN and orienting response N200/P300a.

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

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

Visual sensory processing deficits in Schizophrenia and their relationship to disease state

CONTEXT

Visual Evoked Potential (VEP) abnormalities have been a fairly consistent finding in patients with schizophrenia, and it has been suggested that electrophysiological markers of early sensory processing may be useful as trait markers for the illness, and for development as potential diagnostic measures.

OBJECTIVE

Clear amplitude reductions in the occipital P1 component of the VEP (approximately 100 ms), have been repeatedly demonstrated in patients with schizophrenia. Here, we investigated whether the extent of this deficit was related to age, clinical symptoms, medication status and length of illness, in a large cohort of ethnically homogenous patients.

DESIGN, SETTING AND PARTICIPANTS

VEP responses to simple isolated-check stimuli were examined in 52 DSM-IV diagnosed patients with schizophrenia, and compared with responses from 26 healthy age-matched control subjects. Using high-density electrical scalp recordings, we assessed the integrity of the visual P1 component across the two groups. This study was conducted at St.Vincent's Psychiatric Hospital in Fairview, Dublin, Ireland.

RESULTS

Substantially reduced P1 amplitude was demonstrated in the patient group compared to controls. The deficit was not linked to age, length of illness or medication status. A small positive correlation, accounting for about 11% of the variance, was found between P1 amplitude and clinical symptoms scales (BPRS and SANS). In addition, we found that a slightly later (~110 ms) fronto-central component was relatively increased in the patient group, and was inversely correlated with the occipital P1 amplitude in the patients, but not in the healthy control subjects.

CONCLUSIONS

Our findings clearly demonstrate a deficit in early visual processing in patients with schizophrenia (with a large effect size; Cohen's d = 0.7) that is unrelated to chronicity. The results are consistent with recent findings showing that the P1 deficit is endophenotypic of the disorder and related to genetic risk factors rather than the disease process itself.

Disruption of auditory and visual attention in schizophrenia

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

The Frontal Generator of the Mismatch Negativity Revisited

The mismatch negativity (MMN) is an event-related brain potential elicited by the occurrence of a rare event (deviance) in an otherwise regular acoustic environment, and is assumed to reflect a preattentive mechanism for change detection. A widely adopted model holds that MMN has main generators in the superior temporal planes bilaterally, which are responsible for the sensory memory part of change detection, as well as frontal lobe sources responsible for triggering an attention shift upon change detection. Whereas the temporal sources have been documented in numerous studies across species and methodologies, much less is known about the frontal sources. The present review examines the current state of the evidence for their existence, location, and possible function. It confirms that the frontal generator is still a less consistent finding in MMN research than the temporal generator. There is clear evidence from scalp EEG and, especially, current source density studies for the existence of an MMN generator that is functionally distinct from the main supratemporal generator of the MMN. Evidence from fMRI, PET, optical imaging, EEG source imaging, and lesion studies implicates mainly the inferior frontal and possibly also the medial frontal cortex. However, these results should be taken with caution because of the paucity of support from more direct measures like intracranial recordings and MEG, and the negative findings from several fMRI and PET, as well as EEG source imaging studies. Recent studies also raise questions about the exact role of the frontal generator in triggering an attention shift. Delineating the exact cortical locations of frontal MMN generators, the conditions under which they are activated and, consequently, their function, remains an acute challenge.

Measurement of extensive auditory discrimination profiles using the mismatch negativity (MMN) of the auditory event-related potential (ERP)

OBJECTIVE

Mismatch negativity (MMN), a change-specific component of the auditory event-related potential (ERP), is sensitive to deficits in central auditory processing associated with many clinical conditions. The aim of this study was to obtain a comprehensive multi-dimensional profile of central auditory processing by extending the recently developed fast multi-feature MMN paradigm [Näätänen R, Pakarinen S, Rinne T, Takegata R. The mismatch negativity (MMN): towards the optimal paradigm. Clin Neurophysiol 2004;115:140-144].

METHODS

MMN responses to changes in sound duration, frequency, intensity, and perceived sound-source location at six different magnitudes of deviation were recorded from healthy young adults by using the multi-feature MMN paradigm. In addition, behavioural discrimination accuracy and speed were measured to examine the relationship between MMN and behavioural performance.

RESULTS

All the 24 sound changes elicited significant MMNs. MMN amplitude increased and latency decreased with increasing magnitude of sound change. Furthermore, the MMN amplitude and latency predicted the subjects' accuracy and speed in detecting these deviations.

CONCLUSIONS

This new paradigm provides an extensive auditory discrimination profile for several auditory attributes at different deviation magnitudes in a minimal recording time.

SIGNIFICANCE

The auditory discrimination profiles can offer a comprehensive view of the development, plasticity, and deficits of central auditory processing.

Subcortical visual dysfunction in schizophrenia drives secondary cortical impairments

Visual processing deficits are an integral component of schizophrenia and are sensitive predictors of schizophrenic decompensation in healthy adults. The primate visual system consists of discrete subcortical magnocellular and parvocellular pathways, which project preferentially to dorsal and ventral cortical streams. Subcortical systems show differential stimulus sensitivity, while cortical systems, in turn, can be differentiated using surface potential analysis. The present study examined contributions of subcortical dysfunction to cortical processing deficits using high-density event-related potentials. Event-related potentials were recorded to stimuli biased towards the magnocellular system using low-contrast isolated checks in Experiment 1 and towards the magnocellular or parvocellular system using low versus high spatial frequency (HSF) sinusoidal gratings, respectively, in Experiment 2. The sample consisted of 23 patients with schizophrenia or schizoaffective disorder and 19 non-psychiatric volunteers of similar age. In Experiment 1, a large decrease in the P1 component of the visual event-related potential in response to magnocellular-biased isolated check stimuli was seen in patients compared with controls (F = 13.2, P = 0.001). Patients also showed decreased slope of the contrast response function over the magnocellular-selective contrast range compared with controls (t = 9.2, P = 0.04) indicating decreased signal amplification. In Experiment 2, C1 (F = 8.5, P = 0.007), P1 (F = 33.1, P < 0.001) and N1 (F = 60.8, P < 0.001) were reduced in amplitude to magnocellular-biased low spatial frequency (LSF) stimuli in patients with schizophrenia, but were intact to parvocellular-biased HSF stimuli, regardless of generator location. Source waveforms derived from inverse dipole modelling showed reduced P1 in Experiment 1 and reduced C1, P1 and N1 to LSF stimuli in Experiment 2, consistent with surface waveforms. These results indicate pervasive magnocellular dysfunction at the subcortical level that leads to secondary impairment in activation of cortical visual structures within dorsal and ventral stream visual pathways. Our finding of early visual dysfunction is consistent with and explanatory of classic literature showing subjective complaints of visual distortions and is consistent with early visual processing deficits reported in schizophrenia. Although deficits in visual processing have frequently been construed as resulting from failures of top-down processing, the present findings argue strongly for bottom-up rather than top-down dysfunction at least within the early visual pathway. Deficits in magnocellular processing in this task may reflect more general impairments in neuronal systems functioning, such as deficits in non-linear amplification and may thus represent an organizing principle for predicting neurocognitive dysfunction in schizophrenia.

Electrophysiological indices of automatic and controlled auditory information processing in first-episode, recent-onset and chronic schizophrenia

BACKGROUND

Deficits in amplitudes of auditory event-related potentials (ERP) indexing preattentive, automatic (mismatch negativity, MMN) and controlled, attention-dependent (N2, P3) auditory information processing have been well described in chronic schizophrenia. Normal MMN, but deficient N2 and P3 have been reported in first-episode patients. No study has investigated these ERPs concurrently in first-episode patients; thus, reported differences in MMN, N2 and P3 generation may reflect differences in patient samples rather than genuine differences in abnormal generation of these ERPs.

METHODS

We recorded MMN, N2 and P3 in 26 first-episode patients, 25 recent-onset patients within 1.5 to 5 years after first admission, 25 chronic patients and 39 healthy controls.

RESULTS

Recent-onset and chronic, but not first-episode patients showed reduced MMN. However, among first-episode patients those with low premorbid educational achievement demonstrated significantly reduced MMN. All patient groups showed pronounced N2 deficits and, to a variable extent, abnormalities in P3 generation.

CONCLUSIONS

Abnormalities in N2 and P3 generation appear to reflect premorbid neuropathology, whereas MMN deficits may index both ongoing disease processes associated with illness progression as well as premorbid neurocognitive impairment. ERPs may provide tools to assess static and progressive neuropathology in schizophrenia. These findings need confirmation in longitudinal studies.

Mismatch negativity in schizophrenia: a meta-analysis

BACKGROUND

Mismatch negativity (MMN) is an auditory event-related potential that provides an index of automatic context-dependent information processing and auditory sensory memory. Many studies have reported abnormalities in the generation of MMN in schizophrenia. The objective of this study was to assess the magnitude of this deficit and associated factors.

METHOD

Studies of MMN in schizophrenia were identified and included in a meta-analysis to estimate the mean effect size. Effects of duration of illness, gender ratio, age of patients, type of MMN (duration versus frequency MMN) and characteristics of the test paradigms (deviant probability, magnitude of standard-deviant difference) on effect size were assessed.

RESULTS

Of 62 identified studies 32 met our inclusion criteria. The mean effect size was 0.99 (95% confidence intervals: 0.79, 1.29). Overall, no specific factor was significantly associated with MMN deficits, although MMN to stimuli differing in duration appeared more impaired in schizophrenia than MMN to frequency deviants. In addition, effect sizes of frequency MMN were significantly correlated with duration of illness.

CONCLUSIONS

MMN deficits are a robust feature in chronic schizophrenia and indicate abnormalities in automatic context-dependent auditory information processing and auditory sensory memory in these patients. Reports of normal MMN in first-episode schizophrenia and the association of deficits in frequency MMN with illness duration suggest that MMN may index ongoing neuropathological changes in the auditory cortex in schizophrenia.

Are there common mechanisms in sensation seeking and reality distortion in schizophrenia? A study using memory event-related potentials

A growing literature suggests that the characteristics of sensation seeking and reality distortion expressed in schizophrenia share several mechanisms. In a previous study, the comparison of patients with high vs. low reality distortion using event-related potentials (ERPs) recorded in a recognition memory task for unfamiliar faces identified neural and cognitive anomalies specifically related to the expression of these symptoms. As a follow-up, this study investigated the ERP correlates of sensation seeking in schizophrenia using the same recognition memory protocol. ERPs have been recorded in controls (N=21) and schizophrenia patients separated into high (HSS; N=13) and low (LSS; N=17) scorers according to Zuckerman's Sensation Seeking Scale. The results show a reduced P2a that was found unrelated to reality distortion in the previous study of reality distortion. It identifies interference inhibition impairment as being specifically related to sensation seeking. On the other hand, HSS scorers display enhanced fronto-central and normal P600 effects also found in high reality distortion patients. These results indicate inappropriate context processing and mnemonic binding common to sensation seeking and reality distortion. LSS scorers also display a reduced temporal N300 similar to that found in low reality distortion patients. This anomaly could reflect the lower reactivity to emotionally significant stimuli that underlies anhedonia symptoms. Finally, the N400 effect and a late frontal effect are found in both HSS and LSS. Since they were unrelated to reality distortion, these indices have been related to basic aspects of schizophrenia, e.g., deficient knowledge integration, or other mechanisms, e.g. anxiety or impulsivity. In summary, the present study examines the strategy of investigating variables, such as temperamental characteristics, in addition to symptoms, to show how discrete impairments may contribute to the expression of the illness.

Imaging frontostriatal function in ultra-high-risk, early, and chronic schizophrenia during executive processing

CONTEXT

Individuals experiencing prodromal symptoms of schizophrenia (ultra-high-risk group) demonstrate impaired performance on tasks of executive function, attention, and working memory. The neurobiological underpinnings of such executive deficits in ultra-high-risk individuals remains unclear.

OBJECTIVE

We assessed frontal and striatal functions during a visual oddball continuous performance task, in ultra-high-risk, early, and chronic schizophrenic patients with the use of functional magnetic resonance imaging.

DESIGN

Cross-sectional case-control design.

SETTING

Community; outpatient clinic. Patients Fifty-two individuals (control, n = 16; ultra-high risk, n = 10; early, n = 15; chronic, n = 11) from a referred clinical sample and age- and sex-matched control volunteers underwent scanning.

MAIN OUTCOME MEASURES

Percentage of active voxels and percentage signal change calculated for the anterior cingulate gyrus (ACG), middle frontal gyrus (MFG), inferior frontal gyrus (IFG), basal ganglia, and thalamus. Performance on the visual oddball task was measured with percentage of hits and d' (a measure based on the hit rate and the false-alarm rate).

RESULTS

The ultra-high-risk group showed significantly smaller differential activation between task-relevant and task-irrelevant stimuli in the frontal regions (ACG, IFG, MFG) than the control group. Frontostriatal activation associated with target stimuli in the early and chronic groups was significantly lower than the control group, while the ultra-high-risk group showed a trend toward the early group.

CONCLUSIONS

Our findings suggest that prefrontal function begins to decline before the onset of syndromally defined illness and hence may represent a vulnerability marker in assessing the risk of developing psychotic disorders among ultra-high-risk individuals.

Deviance-related electrophysiological activity in mice: is there mismatch negativity in mice?

OBJECTIVE

Mismatch negativity (MMN) is an auditory event-related potential (ERP) that provides an index of auditory sensory memory and has become an important tool to investigate auditory sensory memory in cognitive neuroscience and disorders such as schizophrenia and dyslexia. The development of a mouse model of human MMN would permit to investigate the molecular biology of normal and dysfunctional MMN generation. However, the presence of MMN-like electrophysiological activity in mice has not been demonstrated.

METHODS

Deviance-related ERPs were recorded in awake mice using 3 frequency deviance paradigms and one duration deviance paradigm. These paradigms were modelled after paradigms used in human studies to characterize MMN.

RESULTS

Significant deviance-related activity was observed in all paradigms. However, in all frequency deviance paradigms this activity manifested as an enhancement of similar activity to the standard due to differences in stimulation rate between deviant and standard stimuli rather than qualitatively different MMN-like activity. In the duration deviance paradigm negative deflections were observed that showed characteristics typical of human MMN.

CONCLUSIONS

MMN-like activity can be observed in mice in duration deviance paradigms. In frequency deviance paradigms effects of different stimulation rates of deviant and standard stimuli seem to be the main determinants of deviance-related activity.

SIGNIFICANCE

Investigations of MMN-like ERPs in mice may permit to investigate the molecular basis for normal and abnormal MMN generation in neuropsychiatric disorders and dyslexia.

[Mismatch negativity in schizophrenia research. An indicator of early processing disorders of acoustic information]

Mismatch negativity (MMN) represents an event-related component of the auditory evoked potentials at about 100-250 ms, evoked by discernible changes in an ongoing uniform acoustic stimulation. The current paper reviews all recently published MMN studies in the field of schizophrenia research. A reduced MMN in schizophrenic patients is found in the majority of the studies. This deficit is likely to be related to the disorder, since antipsychotic medication seems to have little influence on these results. Interestingly, a reduced MMN is also found in first-degree relatives of patients. Clear evidence for a hemispheric lateralization of the MMN reduction in schizophrenic patients is lacking. A hypofunction of the N-methyl-D-aspartate (NMDA) receptor is discussed as a possible explanation of this deficit.

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

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

Altered auditory processing in acutely psychotic never-medicated first-episode patients

Individuals with psychosis fail to differentiate external impulses and suffer from distortions of reality testing. Schizophrenia group illnesses are also associated with deficits in working memory and perception. We examined the manifestations of a very early phase of psychotic illness to automatic auditory deviance detection to clarify the basic mechanisms underlying misinterpretations of perception.

METHODS

Twenty-five never-medicated patients admitted for hospital evaluation of acute psychosis were studied. Fifty-eight EEG channels were recorded during an auditory oddball paradigm. Event-related potentials (ERPs) time-locked to non-attended deviant auditory stimuli were studied in patients and compared with healthy controls. Auditory processing was examined both at the level of the measured biosignals (standard and deviant responses) and with subtraction waveforms. Topographical differences were characterized using global field power (GFP) and minimum norm estimates.

RESULTS

The maximum GFP amplitudes and mean amplitudes of the 58 channels within the time windows corresponding to the previously known 'N2b', 'P3a' and 'P3b' components were clearly reduced in patients when compared to healthy controls. However, the groups did not differ during attention-independent automatic processing corresponding to the 'N1' and 'MMN' components, or with respect to the peak latencies of the GFP maxima.

CONCLUSIONS

Impairment of the processing of a deviance in simple auditory input in acutely ill drug-naive first-episode psychotic patients only appears in attention-dependent processing after about 250 ms. The alterations in auditory processing differed between stimulus types, suggesting at least two mechanisms underlying the auditory discrimination impairments in acute psychosis. After 250 ms there was a linear and gradually increasing difference in magnitude between the groups in their responses to deviant stimuli, probably related to arousal. In addition, however, there was a striking difference between the groups in the processing of standard stimuli. The early processing was similar in patients and controls, but the striking difference appeared in later processing. The sensory memory deficits associated with psychosis may be explained by an abnormality in sensory model formation rather than by impaired deviant detection.

How specific are deficits in mismatch negativity generation to schizophrenia?

BACKGROUND

Mismatch negativity (MMN) is an auditory event-related potential that provides an index of auditory sensory memory. Deficits in MMN generation have been repeatedly demonstrated in chronic schizophrenia. Their specificity to schizophrenia has not been established.

METHODS

Mismatch negativity to both duration and frequency deviants was investigated in gender- and age-matched patients with schizophrenia or schizoaffective disorder (n = 26), bipolar disorder (n = 16), or major depression (n = 22) and healthy control subjects (n = 25).

RESULTS

Only patients with schizophrenia demonstrated significantly smaller mean MMN than did healthy control subjects. Detailed analyses showed significantly smaller MMN to both duration and frequency deviants in patients with schizophrenia than in healthy control subjects; however, the reduction of frequency MMN in patients with schizophrenia was not significant in the comparison across all groups. Mismatch negativity topography did not differ among groups. No consistent correlations with clinical, psychopathologic, or treatment variables were observed.

CONCLUSIONS

Mismatch negativity deficits, and by extension deficits in early cortical auditory information processing, appear to be specific to schizophrenia. Animal and human studies implicate dysfunctional N-methyl-D-aspartate receptor functioning in MMN deficits. Thus MMN deficits may become a useful endophenotype to investigate the genetic underpinnings of schizophrenia, particularly with regard to the N-methyl-D-aspartate receptor.

Schizophrenia: from phenomenology to neurobiology

Schizophrenia is a common and debilitating illness, characterized by chronic psychotic symptoms and psychosocial impairment that exact considerable human and economic costs. The literature in electronic databases as well as citations and major articles are reviewed with respect to the phenomenology, pathology, treatment, genetics and neurobiology of schizophrenia. Although studied extensively from a clinical, psychological, biological and genetic perspective, our expanding knowledge of schizophrenia provides only an incomplete understanding of this complex disorder. Recent advances in neuroscience have allowed the confirmation or refutation of earlier findings in schizophrenia, and permit useful comparisons between the different levels of organization from which the illness has been studied. Schizophrenia is defined as a clinical syndrome that may include a collection of diseases that share a common presentation. Genetic factors are the most important in the etiology of the disease, with unknown environmental factors potentially modulating the expression of symptoms. Schizophrenia is a complex genetic disorder in which many genes may be implicated, with the possibility of gene-gene interactions and a diversity of genetic causes in different families or populations. A neurodevelopmental rather than degenerative process has received more empirical support as a general explanation of the pathophysiology, although simple dichotomies are not particularly helpful in such a complicated disease. Structural brain changes are present in vivo and post-mortem, with both histopathological and imaging studies in overall agreement that the temporal and frontal lobes of the cerebral cortex are the most affected. Functional imaging, neuropsychological testing and clinical observation are also generally consistent in demonstrating deficits in cognitive ability that correlate with abnormalities in the areas of the brain with structural abnormalities. The dopamine and other neurotransmitter systems are certainly involved in the treatment or modulation of psychotic symptoms. These broad findings represent the distillation of a large body of disparate data, but firm and specific findings are sparse, and much about schizophrenia remains unknown.

Neuromagnetic correlates of impaired automatic categorical perception of speech sounds in schizophrenia

Schizophrenia is associated with dysfunction in language processing. At the earliest stage of language processing, dysfunction of categorical perception of speech sounds in schizophrenia has been demonstrated in a behavioral task. The aim of this study was to assess automatic categorical perception of speech sounds as reflected by event-related changes in magnetic field power in schizophrenia. Using a whole-head magnetoencephalographic recording, the magnetic counterpart of mismatch negativity (MMNm) elicited by a phonetic change was evaluated in 16 right-handed patients with chronic schizophrenia and in 19 age-, sex-, and parental socioeconomic status-matched normal control subjects. Three types of MMNm (MMNm in response to a duration decrement of pure-tone stimuli; a vowel within-category change [duration decrement of Japanese vowel /a/]; vowel across-category change [Japanese vowel /a/ versus /o/]) were recorded. While the schizophrenia group showed an overall reduction in magnetic field power of MMNm, a trend was found toward more distinct abnormalities under the condition of vowel across-category change than under that of duration decrement of a vowel or tone. The patient group did not show abnormal asymmetries of MMNm power under any of the conditions. This study provides physiological evidence for impaired categorical perception of speech sounds in the bilateral auditory cortex in schizophrenia. The language-related dysfunction in schizophrenic patients may be present at the early stage of auditory processing of relatively simple stimuli such as phonemes, and not just at stages involving higher order semantic processes.

Effects of the 5-HT2A agonist psilocybin on mismatch negativity generation and AX-continuous performance task: implications for the neuropharmacology of cognitive deficits in schizophrenia

Previously the NMDA (N-methyl-D-aspartate) receptor (NMDAR) antagonist ketamine was shown to disrupt generation of the auditory event-related potential (ERP) mismatch negativity (MMN) and the performance of an 'AX'-type continuous performance test (AX-CPT)--measures of auditory and visual context-dependent information processing--in a similar manner as observed in schizophrenia. This placebo-controlled study investigated effects of the 5-HT(2A) receptor agonist psilocybin on the same measures in 18 healthy volunteers. Psilocybin administration induced significant performance deficits in the AX-CPT, but failed to reduce MMN generation significantly. These results indirectly support evidence that deficient MMN generation in schizophrenia may be a relatively distinct manifestation of deficient NMDAR functioning. In contrast, secondary pharmacological effects shared by NMDAR antagonists and the 5-HT(2A) agonist (ie disruption of glutamatergic neurotransmission) may be the mechanism underlying impairments in AX-CPT performance observed during both psilocybin and ketamine administration. Comparable deficits in schizophrenia may result from independent dysfunctions of 5-HT(2A) and NMDAR-related neurotransmission.

Duration mismatch negativity in biological relatives of patients with schizophrenia spectrum disorders

BACKGROUND

One of the most consistent findings in schizophrenia research over the past decade is a reduction in the amplitude of an auditory event-related brain potential known as mismatch negativity (MMN), which is generated whenever a deviant sound occurs in a background of repetitive auditory stimulation. The reduced amplitude of MMN in schizophrenia was first observed for deviant sounds that differ in duration relative to background standard sounds, and similar findings have been observed for sounds that are deviant in frequency. The aim of this study was to determine whether first-degree relatives of schizophrenia patients show a similar reduction in MMN amplitude to duration deviants.

METHODS

We measured MMN to duration increments (deviants 100 msec vs. standards 50 msec) in 22 medicated patients with a diagnosis in the schizophrenia spectrum, 17 individuals who were first-degree unaffected relatives of patients, and 21 healthy control subjects.

RESULTS

Mismatch negativity amplitude was reduced in patients and relatives compared with control subjects. There were no significant differences between patients and relatives. In contrast, the subsequent positive component, P3a, was larger in relatives compared with patients.

CONCLUSIONS

These findings suggest that a reduced MMN amplitude may be an endophenotype marker of the predisposition to schizophrenia.

Visual feature conjunction in patients with schizophrenia: an event-related brain potential study

The neural mechanisms supporting performance during single feature and feature conjunction detection were investigated in patients with schizophrenia and age-matched controls using event-related brain potentials. In different blocks of trials, participants responded to visual targets defined by one of two colors, one of two orientations, or both color and orientation. All participants were faster and more accurate in detecting targets defined by a single feature than for targets defined by a conjunction of features. Relative to controls, patients made more errors and were slower in detecting targets defined by a combination of features. Patients also generated a smaller N2 wave to single and conjunctive targets, and showed greater P3b reduction over the right hemisphere for conjunctive targets than for targets defined by color only. In addition, target stimuli generated an increased negativity at the occipital sites that varied in scalp distribution with the attended features in controls but not in patients. Both behavioral and electrophysiological data provide converging evidence for deficits in integrating visual features in schizophrenia and suggest that processing features of visual objects in schizophrenia are partly supported by distinct functional networks.