An event-related potential study in schizophrenia using Japanese sentences

N400 event-related brain potential index of semantic processing and two-year clinical outcomes in persons at high risk for psychosis: A longitudinal study

The N400 event-related brain potential (ERP) semantic priming effect reflects greater activation of contextually related versus unrelated concepts in long-term semantic memory. Deficits in this measure have been found in persons with schizophrenia and those at clinical high risk (CHR) for this disorder. In CHR patients, we previously found that these deficits predict poorer social functional outcomes after 1 year. In the present study, we tested whether these deficits predicted greater psychosis-spectrum symptom severity and functional impairment over 2 years. We measured N400 semantic priming effects at baseline in CHR patients (n = 47) who viewed prime words each followed by a related/unrelated target word at stimulus-onset asynchronies (SOAs) of 300 or 750 ms. We measured psychosis-spectrum symptoms using the Structured Interview for Prodromal Symptoms and role and social functioning with the Global Functioning: Role and Social scales, at baseline, 1 (n = 29) and 2 years (n = 25). There was a significant interaction between the N400 semantic priming effect at the 300-ms SOA and time on GF:Role scores, indicating that, contrary to expectations, smaller baseline N400 semantic priming effects were associated with more improvement in role functioning from baseline to Year 1, but baseline N400 priming effects did not predict role functioning at Year 2. N400 priming effects were not significantly associated with different trajectories in psychosis-spectrum symptoms or social functioning. Thus, CHR patients' N400 semantic priming effects did not predict clinical outcomes over 2 years, suggesting that this ERP measure may have greater value as a state or short-term prognostic neurophysiological biomarker.

Semantic priming and neurobiology in schizophrenia: A theoretical review

In this theoretical review we bridge the cognitive and neurobiological sciences to shed light on the neurocognitive foundations of the semantic priming effect in schizophrenia. We review and theoretically evaluate the neurotransmitter systems (dopaminergic, GABAergic and glutamatergic) and neurobiological underpinnings of behavioural and electrophysiological (N400) semantic priming in the pathology, and the main hypotheses on their geneses: a disinhibition of the semantic spread of activation, a disorganised semantic storage or noisy lexical-semantic associations, a psychomotor artefact, an artefact of relatedness proportions, or an inability to mobilise contextual information. We further assess the literature on the endophenotype of Formal Thought Disorder from multiple standpoints, ranging from neurophysiology to cognition: considerations are weaved on neuronal (PV basket cell, SST, VIP) and receptor deficits (DRD1, NMDA), neurotransmitter imbalances (dopamine), cortical and dopaminergic lateralisation, inter alia. In conclusion, we put forth novel postulates on the underlying causes of controlled hypopriming, automatic hyperpriming, N400 reversals (larger amplitudes for close associations), indirect versus direct hyperpriming, and the endophenotype of lexical-semantic disturbances in schizophrenia.

Evaluation of N-400 Evoked Response Potential in schizophrenia: An endophenotype or a disease marker?

N400 evoked response potentials (ERP) reliably map key semantic deficits in schizophrenia. Assessing them as endophenotypes might help in better understanding of schizophrenia risk and their use as biomarkers. We aimed to study N400 as an endophenotype marker by comparing schizophrenia (SCZ), unaffected first-degree relatives (FDR) and healthy controls (HC) and, by assessing its ability to discriminate these groups. Drug naïve or free SCZ probands (n=30), their unaffected FDRs (n=30) and HC (n=30), underwent a 40-channel ERP recording while performing a custom-made, Hindi- sentence context paradigm task, containing congruent and incongruent conditions. Fifteen centro-parietal (CP) leads, further classified into three regions-midline (CPM), right (CPR) and left (CPL) were selected as electrodes-of-interest for assessing N400. During the incongruent condition, compared to both FDRs and HC, SCZ showed significantly longer N400 latency, at CPM, CPR and CPL, and significantly lesser (more negative) amplitude, at CPM; no significant difference was noted between FDR and HC groups. On discriminant functional analysis, significant N400 predictors could accurately classify 73.3% SCZ from HC and 75% of SCZ from FDR. We conclude that N400 deficits, elicited by the incongruent condition of the sentence task, could be potential biomarkers to define disease state in schizophrenia; they may not be endophenotype markers.

N400 event-related brain potential as an index of real-world and neurocognitive function in patients at clinical high risk for schizophrenia

AIM

The N400 event-related potential is a neurophysiological index of cognitive processing of real-world knowledge. In healthy populations, N400 amplitude is smaller in response to stimuli that are more related to preceding context. This 'N400 semantic priming effect' is thought to reflect activation of contextually related information in semantic memory (SM). N400 semantic priming deficits have been found in schizophrenia, and in patients at clinical high risk (CHR) for this disorder. Because this abnormality in processing relationships between meaningful stimuli could affect ability to navigate everyday situations, we hypothesized it would be associated with real-world functional impairment in CHR patients. Second, we hypothesized it would correlate with global neurocognitive impairment in this group.

METHODS

We measured N400 semantic priming in 35 CHR patients who viewed prime words each followed by a related or unrelated target word, at stimulus-onset asynchrony (SOA) of 300 or 750 ms. We measured academic/occupational and social function with the global function (GF): Role and Social scales, and cognitive function with the MATRICS Consensus Cognitive Battery (MCCB).

RESULTS

Decreased N400 semantic priming at the 300-ms SOA correlated with lower GF:Role scores. Decreased N400 semantic priming at the 750-ms SOA correlated with lower MCCB composite scores.

CONCLUSIONS

Deficits in activating contextually related concepts in SM over short time intervals may contribute to functional impairment in CHR patients. Furthermore, N400 priming deficits over longer intervals may be a biomarker of global cognitive dysfunction in this population. Longitudinal studies are needed to determine whether these deficits are associated with schizophrenia risk within this population.

Catecholaminergic Modulation of Semantic Processing in Sentence Comprehension

Catecholamine (CA) function has been widely implicated in cognitive functions that are tied to the prefrontal cortex and striatal areas. The present study investigated the effects of methylphenidate, which is a CA agonist, on the electroencephalogram (EEG) response related to semantic processing using a double-blind, placebo-controlled, randomized, crossover, within-subject design. Forty-eight healthy participants read semantically congruent or incongruent sentences after receiving 20-mg methylphenidate or a placebo while their brain activity was monitored with EEG. To probe whether the catecholaminergic modulation is task-dependent, in one condition participants had to focus on comprehending the sentences, while in the other condition, they only had to attend to the font size of the sentence. The results demonstrate that methylphenidate has a task-dependent effect on semantic processing. Compared to placebo, when semantic processing was task-irrelevant, methylphenidate enhanced the detection of semantic incongruence as indexed by a larger N400 amplitude in the incongruent sentences; when semantic processing was task-relevant, methylphenidate induced a larger N400 amplitude in the semantically congruent condition, which was followed by a larger late positive complex effect. These results suggest that CA-related neurotransmitters influence language processing, possibly through the projections between the prefrontal cortex and the striatum, which contain many CA receptors.

Language-Related Neurophysiological Deficits in Schizophrenia

Schizophrenia is a severe psychiatric disorder that affects all aspects of one's life with several cognitive and social dysfunctions. However, there is still no objective and universal index for diagnosis and treatment of this disease. Many researchers have studied language processing in schizophrenia since most of the patients show symptoms related to language processing, such as thought disorder, auditory verbal hallucinations, or delusions. Electroencephalography (EEG) and magnetoencephalography (MEG) with millisecond order high temporal resolution, have been applied to reveal the abnormalities in language processing in schizophrenia. The aims of this review are (a) to provide an overview of recent findings in language processing in schizophrenia with EEG and MEG using neurophysiological indices, providing insights into underlying language related pathophysiological deficits in this disease and (b) to emphasize the advantage of EEG and MEG in research on language processing in schizophrenia.

Test-retest reliability of N400 event-related brain potential measures in a word-pair semantic priming paradigm in patients with schizophrenia

The N400 event-related brain potential (ERP), a negative voltage deflection occurring approximately 400ms after onset of any meaningful stimulus, is reduced in amplitude when the stimulus is preceded by related context. Previous work has found this N400 semantic priming effect to be decreased in schizophrenia, suggesting impairment in using meaningful context to activate related concepts in semantic memory. Thus, N400 amplitude may be a useful biomarker of abnormal semantic processing and its response to treatment in schizophrenia. To help assess the validity of N400 amplitude as a longitudinal measure in schizophrenia, we evaluated its test-retest reliability. ERPs were recorded in sixteen schizophrenia patients who viewed prime words, each followed at 300- or 750-ms stimulus-onset asynchrony (SOA) by a target that was either a related or unrelated word, or nonword. Participants' task was to indicate whether or not the target was a real word. They were retested on the same procedure one week later. Test-retest reliability was assessed by calculating Pearson's r and intraclass correlation coefficients (ICCs) across timepoints for N400 amplitudes for related and unrelated targets, at each SOA. Consistent with previous results, there were no significant differences between patients' N400 amplitudes for related and unrelated targets, at any SOA/timepoint combination. Pearson's r and ICCs for N400 amplitudes at Fz across timepoints were significant for both target types at each SOA (ranges: r 0.52-0.64, ICC 0.52-0.63; all p<.04). The results suggest potential utility of N400 amplitude as a longitudinal neurophysiological biomarker of semantic processing abnormalities in schizophrenia.

Behavioral and brain measures (N400) of semantic priming in patients with schizophrenia: test-retest effect in a longitudinal study

AIM

The purpose of this study was to investigate whether deficits in the behavioral and/or N400 semantic priming (SP) effect observed in patients with schizophrenia constitute a stable cognitive feature of the disorder or whether they may be influenced by the severity of each individual's symptomatology.

METHODS

A 1-year test-retest study was conducted on 15 patients with schizophrenia and 10 healthy participants who performed an SP task. Both behavioral measures and event-related potentials measures of SP were recorded twice (test and retest sessions).

RESULTS

At test, patients exhibited a deficit in SP as was revealed by both the behavioral and the event-related potentials measures of the amplitude of the N400 component. At retest, behavioral SP remained impaired, whereas N400 SP was significantly improved.

CONCLUSION

These results provide evidence that SP impairments in schizophrenia as measured by N400 should not be considered as stable cognitive markers of the disorder. The behavioral and the N400 measures of SP indicated different levels of sensitivity to subtle cognitive and brain processes, which are subject to change over the clinical course of schizophrenic disorder.

Natural speech comprehension in bipolar disorders: an event-related brain potential study among manic patients

BACKGROUND

Thought and language disturbances are crucial clinical features in Bipolar Disorders (BD), and constitute a fundamental basis for social cognition. In BD, clinical manifestations such as disorganization and formal thought disorders may play a role in communication disturbances. However, only few studies have explored language disturbances in BD at a neurophysiological level. Two main Event-Related brain Potentials (ERPs) have been used in language comprehension research: the N400 component, elicited by incongruous word with the preceding semantic context, and the Late Positive Component (LPC), associated with non-specifically semantic and more general cognitive processes. Previous studies provided contradictory results regarding N400 in mood disorders, showing either preserved N400 in depression or dysthymia, or altered N400 in BD during semantic priming paradigm. The aim of our study was to explore N400 and LPC among patients with BD in natural speech conditions.

METHODS

ERPs from 19 bipolar type I patients with manic or hypomanic symptomatology and 19 healthy controls were recorded. Participants were asked to listen to congruous and incongruous complete sentences and to judge the match between the final word and the sentence context. Behavioral results and ERPs data were analyzed.

RESULTS

At the behavioral level, patients with BD show worst performances than healthy participants. At the electrophysiological level, our results show preserved N400 component in BD. LPC elicited under natural speech conditions shows preserved amplitude but delayed latency in difference waves.

LIMITATIONS

Small size of samples, absence of schizophrenic group and medication status.

CONCLUSIONS

In contrast with the only previous N400 study in BD that uses written semantic priming, our results show a preserved N400 component in ecological and natural speech conditions among patients with BD. Possible implications in terms of clinical specificity are discussed.

Evaluation of trait adjectives and ego pathology in schizophrenia: an N400 study

The N400, an event-related brain potential (ERP), can be triggered by semantic or arithmetic violations in visual or auditory stimulus material. Schizophrenia patients exhibit an altered N400 presumably resulting from impaired semantic memory associative networks. The present study investigates, whether an altered N400 can also be found in semantic violations of the own self-concept. We use simple descriptive sentences to combine semantics with the self-concept in order to explore differences and possible deficits in schizophrenia patients. Schizophrenia patients and controls were shown trait adjectives in reference to themselves. Participants had to decide if the presented trait adjective was congruent or incongruent with their own self-concept. Only in controls, the N400 was significantly more negative in the incongruent compared to the congruent condition. Controls seemed to profit from a stable self-concept as they were faster in judging if a given trait was descriptive for the self than for someone else, which might result from processes related to the self-reference effect. Interestingly, in schizophrenia patients, the higher the scores for ego pathology were, the smaller the N400 effect turned out to be. The diminished N400 effect is probably associated with a disturbed self-concept in schizophrenia.

Event-related brain potential study of semantic priming in unaffected first-degree relatives of schizophrenia patients

Schizophrenia is associated with abnormalities in using meaningful stimuli to activate or prime related concepts in semantic long-term memory. A neurophysiological index of this activation is the N400, an event-related brain potential (ERP) waveform elicited by meaningful stimuli, which is normally reduced (made less negative) by relatedness between the eliciting stimulus and preceding ones (N400 semantic priming). Schizophrenia patients exhibit N400 semantic priming deficits, suggesting impairment in using meaningful context to activate related concepts. To address whether this abnormality is a trait-like marker of liability to schizophrenia or, alternatively, a biomarker of the illness itself, we tested for its presence in schizophrenia patients' unaffected biological relatives. We recorded ERPs from 12 unaffected first-degree relatives of schizophrenia patients, 12 schizophrenia patients, and 12 normal control participants (NCPs) who viewed prime words each followed at 300- or 750-ms stimulus-onset asynchrony (SOA) by an unrelated or related target word, or a nonword, in a lexical-decision task. As expected, across SOAs, NCPs exhibited smaller (less negative) N400 amplitudes for related versus unrelated targets. The same pattern held in relatives, whose N400 amplitudes for related and unrelated targets did not differ from NCPs'. In contrast, consistent with previous results, schizophrenia patients exhibited larger N400 amplitudes than NCPs (and relatives) for related targets, such that patients' N400 amplitudes for related and unrelated targets did not differ. N400 amplitudes for unrelated targets did not differ between the three groups. Thus, N400 semantic priming deficits in a visual word-pair paradigm may be an illness biomarker for schizophrenia.

Association of abnormal semantic processing with delusion-like ideation in frequent cannabis users: an electrophysiological study

RATIONALE

Frequent cannabis use is a risk marker for schizophrenia and delusions, but the neurocognitive mechanisms of this relationship remain unclear.

OBJECTIVES

We sought evidence that cannabis users have deficits in processing relationships between meaningful stimuli, similar to abnormalities reported in schizophrenia, and that these deficits are associated with delusion-like ideation. We used the N400 event-related brain potential (ERP) waveform as a neurophysiological probe of activation of concepts in semantic memory. We hypothesized that cannabis users would exhibit larger (more negative) than normal N400 amplitudes in response to stimuli meaningfully related to a preceding prime-reflecting deficient activation of concepts related to the prime. We further hypothesized that the magnitude of this abnormality would correlate with severity of delusion-like ideation.

METHODS

We recorded ERPs in 24 frequent cannabis users and 24 non-using comparison participants who viewed prime words followed by targets which were either words related or unrelated to the prime or pronounceable nonwords. The participants' task was to indicate whether the target was a word. Delusion-like ideation was measured via the Schizotypal Personality Questionnaire.

RESULTS

Contrary to our hypothesis, cannabis users exhibited smaller than normal N400s to both related and unrelated targets. These abnormalities correlated with delusion-like ideation in cannabis users only.

CONCLUSIONS

The results are consistent with a generalized abnormality of activation within semantic memory neural networks in cannabis users. Further research is needed to investigate whether such an abnormality plays a role in the development of delusion-like ideation in cannabis users.

Electrophysiological evidence for primary semantic memory functional organization deficits in schizophrenia

N400, an event-related brain potential (ERP) waveform elicited by meaningful stimuli, is normally reduced by stimulus repetition (N400 repetition priming), and relatedness between the eliciting stimulus and preceding ones (relatedness priming). Schizophrenia patients' N400 relatedness priming deficits suggest impairment in using meaningful prime stimuli to facilitate processing of related concepts in semantic memory. To examine whether this deficiency arises from difficulty activating the prime concept per se, as indexed by reduced N400 repetition priming; or from impaired functional connections among concepts in semantic memory, as reflected by reduced relatedness priming but normal repetition priming; we recorded ERPs from 16 schizophrenia patients and 16 controls who viewed prime words each followed at 300- or 750-ms stimulus-onset asynchrony (SOA) by an unrelated, related or repeated target word, or a nonword, in a lexical-decision task. In both groups, N400s were largest (most negative) for unrelated, intermediate for related, and smallest for repeated targets. Schizophrenia patients exhibited subnormal N400 relatedness priming at the 300-ms SOA, but normal repetition priming at both SOAs, suggesting that their impairment in using prime words to activate related concepts results from abnormal functional connections among concepts within semantic memory, rather than inability to activate the prime concept itself.

Depth-of-processing effects on semantic activation deficits in schizophrenia: an electrophysiological investigation

N400, an event-related brain potential (ERP) waveform elicited by meaningful stimuli, is normally reduced (made less negative) by relatedness between the eliciting stimulus and preceding ones (N400 semantic priming). Schizophrenia patients' N400 semantic priming deficits suggest impairment in using meaningful context to activate related concepts in semantic memory. We aimed to examine the degree to which this impairment can be ameliorated by task instructions that more explicitly require processing of stimulus meaning. We recorded ERPs from 16 schizophrenia patients and 16 controls who viewed prime words each followed at 750-ms stimulus-onset asynchrony by an unrelated or related target word, or a nonword, in a non-semantic task (indicating whether a letter occurred in the target) compared to an explicit semantic task (judging prime-target relatedness). Consistent with previous work, controls exhibited greater N400 semantic priming (larger amplitude reductions for related versus unrelated targets) in the semantic task than in the orthographic task. Schizophrenia patients showed this same pattern, although their N400 semantic priming effects were smaller than controls' across tasks. Nevertheless, patients' priming effects increased as much as did controls' from the orthographic to the semantic task. Thus, connections among related concepts in schizophrenia patients' semantic memory appear grossly intact, such that, given a meaningful stimulus, they can make use of explicit cues to activate related concepts at a neurophysiological level, although their ability to do so remains less than normal. These data provide support for further research on semantic-cueing strategies for cognitive remediation of verbal memory in schizophrenia.

Semantic processing disturbance in patients with schizophrenia: a meta-analysis of the N400 component

BACKGROUND

Theoretically semantic processing can be separated into early automatic semantic activation and late contextualization. Semantic processing deficits have been suggested in patients with schizophrenia, however it is not clear which stage of semantic processing is impaired. We attempted to clarify this issue by conducting a meta-analysis of the N400 component.

METHODS

Twenty-one studies met the inclusion criteria for the meta-analysis procedure. The Comprehensive Meta-Analysis software package was used to compute pooled effect sizes and homogeneity.

RESULTS

Studies favoring early automatic activation produced a significant effect size of -0.41 for the N400 effect. Studies favoring late contextualization generated a significant effect size of -0.36 for the N400 effect, a significant effect size of -0.52 for N400 for congruent/related target words, and a significant effect size of 0.82 for the N400 peak latency.

CONCLUSION

These findings suggest the automatic spreading activation process in patients with schizophrenia is very similar for closely related concepts and weakly or remotely related concepts, while late contextualization may be associated with impairments in processing semantically congruent context accompanied by slow processing speed.

Left but not right hemisphere semantic processing abnormalities in language comprehension in subjects with schizotypy traits

Thought and language disorders in schizophrenia and schizotypy are thought to result from hemispheric dysfunction during semantic processing. Left hemisphere (LH) abnormalities are well established, but little is known about right hemisphere (RH) semantic processes. We explored hemispheric processing in 50 healthy volunteers assigned to high (h-SZT) or low schizotypy (l-SZT) group using the Schizotypal Personality Questionnaire (SPQ). Subjects were asked to make semantic judgments on sentence pair ending with a target that was either expected word (EW) or an unexpected word from the same (related violation, RV) or a different category (unrelated violation, URV). Targets were presented in a dichotic manner to the left or right ear. Analyses of reaction times in the l-SZT group showed semantic compatibility effect (URV-EW) in the LH and semantic memory activation effect (RV-URV) as well as semantic compatibility effect in the RH. The h-SZT group showed semantic memory activation but no semantic compatibility effect in the LH, the RH pattern resembling that of the l-SZT group. The magnitude of the LH semantic compatibility effect was inversely correlated with SPQ total scores and SPQ Cognitive-perceptual factor. Thus, RH semantic processes are effective and there is a deficit in LH focused activation in schizotypy.

Language in schizophrenia Part 2: What can psycholinguistics bring to the study of schizophrenia...and vice versa?

This is the second of two articles that discuss higher-order language and semantic processing in schizophrenia. The companion article (Part 1) gives an introduction to language dysfunction in schizophrenia patients. This article reviews a selection of psycholinguistic studies which suggest that sentence-level abnormalities in schizophrenia may stem from a relative overdependence on semantic associative relationships at the expense of building higher-order meaning. Language disturbances in schizophrenia may be best conceptualized as arising from an imbalance of activity across two streams of processing, one drawing upon semantic relationships within semantic memory and the other involving the use of combinatorial mechanisms to build propositional meaning. I will also discuss some of the ways in which the study of schizophrenia may offer new insights into the cognitive and neural architecture of the normal language system.

What can Event-related Potentials tell us about language, and perhaps even thought, in schizophrenia?

Disturbances of thought and language are fundamental to schizophrenia. Cognitive behavioral and electrophysiological research has implicated problems in two different neurocognitive mechanisms: abnormalities in the structure and function of semantic memory, and abnormalities in combining and integrating words together to build up sentence and discourse context. This review discusses recent electrophysiological evidence suggesting that these two deficits are not completely distinct, but rather that language impairment in schizophrenia results from a dysfunctional interaction between these systems in an effort to build up higher-order meaning. Moreover, although language abnormalities are more pronounced in patients with positive thought disorder, they manifest themselves in all patients when increased demands are placed on the comprehension system. Further investigation of language dysfunction may also provide insights into other aspects of psychotic thought.

Neurocognitive mechanisms of conceptual processing in healthy adults and patients with schizophrenia

This overview outlines findings of cognitive and neurocognitive studies on comprehension of verbal, pictorial, and video stimuli in healthy participants and patients with schizophrenia. We present evidence for a distinction between two complementary neurocognitive streams of conceptual analysis during comprehension. In familiar situations, adequate understanding of events may be achieved by mapping the perceived information on the associative and similarity-based connections between concepts in semantic memory - a process reflected by an N400 waveform of event-related electrophysiological potentials (ERPs). However, in less conventional contexts, a more flexible mechanism may be needed. We suggest that this alternative processing stream, reflected by a P600 ERP waveform, may use discrete, rule-like goal-related requirements of real-world actions to comprehend relationships between perceived people, objects, and actions. This neurocognitive model of comprehension is used as a basis in discussing studies in schizophrenia. These studies suggest an imbalanced engagement of the two conceptual streams in schizophrenia, whereby patients may rely on the associative and similarity-based networks in semantic memory even when it would be more adaptive to recruit mechanisms that draw upon goal-related requirements. Finally, we consider the roles that these conceptual mechanisms may play in real-life behavior, and the consequences that their dysfunction may have for disorganized behavior and inability to plan actions to achieve behavioral goals in schizophrenia.

An event-related brain potential study of schizotypal personality and associative semantic processing

To examine whether schizotypal personality is associated with the degree to which concepts activate each other in semantic memory, event-related brain potentials (ERPs) were recorded during a delayed lexical decision task from healthy volunteers rated for schizotypy. Each target word was directly, indirectly, or not at all related to a prime word preceding it at a 300- or 750-ms stimulus-onset asynchrony (SOA). Overall, N400 amplitudes were largest for unrelated targets, smallest for directly related targets, and intermediate for indirectly related targets. Higher total Schizotypal Personality Questionnaire (SPQ) scores correlated with smaller N400 indirect priming effects (i.e., smaller N400 amplitude differences between unrelated and indirectly related targets) at both SOAs. In addition, schizotypal subscale scores were differentially associated with N400 effects. Higher SPQ Cognitive-Perceptual scores correlated with smaller N400 direct priming effects (smaller N400 amplitude differences between unrelated and directly related targets) at both SOAs, and with smaller N400 indirect priming effects at the shorter SOA. These correlations are consistent with the hypothesis that decreased use of meaningful context to activate related concepts in general, and/or to inhibit unrelated concepts, may play some role in the development of unusual beliefs.

N400 deficits from semantic matching of pictures in probands and first-degree relatives from multiplex schizophrenia families

Endophenotypes is one emerging strategy in schizophrenia research that is being used to identify the functional importance of genetically transmitted, brain-based deficits present in this disease. Currently, event-related potentials (ERPs) are timely used in this search. Several ERPs, including N400, present deficits in relation to schizophrenia. In order to assess the genetic liability of N400 as a possible endophenotype, a picture semantic matching task (congruent and incongruent pairs of pictures) was performed by 21 unaffected first-degree relatives of patients with schizophrenia, 21 DSM-IV diagnosed schizophrenia probands, and 21 control subjects, matched by age, gender and educational level. Probands and relatives were selected form Multiplex schizophrenia families. Significantly reduced N400 amplitude for congruent categories in N400 was found in probands and relatives in relation to controls. The latency onset and the maximum peak latency of N400 were delayed in both, relatives and probands groups compared to control. The voltage maps of incongruous-minus-congruous difference indicate a more reduced right restricted negativity in probands and relatives, when compared to a widely extended bilateral negativity in controls. No general differences were found between patients and relatives. These results demonstrate an electrophysiological deficit in semantic match processing in clinically unaffected first-degree relatives of patients with schizophrenia, suggesting a possible use of this marker as endophenotype.

Neuropsychological correlates of N400 anomalies in patients with schizophrenia: A preliminary report

We investigated N400 anomalies and their relationship with neuropsychological disturbance of schizophrenia. Twelve patients with schizophrenia and 12 normal controls, matched for age, sex, education and handedness underwent both the neuropsychological test and the electrophysiological recordings employing semantic violation sentence paradigm. The patients with schizophrenia showed a reduced N400 amplitude and worse performance in the frontal lobe function test compared to healthy participants. Furthermore, statistically significant positive correlations were found between N400 amplitude and neuropsychological performances on the Stroop Task and Wisconsin Card Sorting Test in patients with schizophrenia. Our results suggest the possibility that N400 anomalies reflect the disturbed integrity of the fronto-temporal network in schizophrenia evidenced by neuropsychological deficits. In addition, we concluded that the N400 amplitude is a candidate for an endophenotype marker of schizophrenia by revealing its relationship to neuropsychological deficits.

Functional magnetic resonance imaging reveals neuroanatomical dissociations during semantic integration in schizophrenia

BACKGROUND

Schizophrenia symptoms can be conceptualized in terms of a breakdown of a balance between 1) activating, retrieving, and matching stored representations to incoming information (semantic memory-based processing) and 2) fully integrating activated semantic representations with one another and with other types of representations to form a gestalt representation of meaning (semantic integration). Semantic memory-based processes are relatively more dependent on inferior frontal and temporal cortices, whereas particularly demanding integrative processes additionally recruit the dorsolateral prefrontal cortex (DLPFC) and sometimes parietal cortices. We used functional magnetic resonance imaging (fMRI) to determine whether the modulation of temporal/inferior frontal cortices and the DLPFC can be neuroanatomically dissociated in schizophrenia, as semantic integration demands increase. Integration demands were manipulated by varying the nature (concrete vs. abstract) and the congruity (incongruous vs. congruous) of words within sentences.

METHODS

Sixteen right-handed schizophrenia patients and 16 healthy volunteers, matched on age and parental socioeconomic status, underwent event-related fMRI scanning while they read sentences. Blood oxygen level dependent (BOLD) effects were contrasted to words within sentences that were 1) concrete versus abstract and 2) semantically incongruous versus congruous with their preceding contexts.

RESULTS

In both contrasts, large networks mediating the activation and retrieval of verbal and imagistic representations were normally modulated in patients. However, unlike control subjects, patients failed to recruit the DLPFC, medial frontal and parietal cortices to incongruous (relative to congruous) sentences, and failed to recruit the DLPFC to concrete (relative to abstract) sentences.

CONCLUSIONS

As meaning is built from language, schizophrenia patients demonstrate a neuroanatomical dissociation in the modulation of temporal/inferior frontal cortices and the DLPFC.

The time course of building discourse coherence in schizophrenia: an ERP investigation

Impairments in the buildup and use of context may lead to disorders of thought and language in schizophrenia. To test this hypothesis, event-related potentials (ERPs) were measured while patients and healthy controls read sentences that were highly causally related, intermediately related, or unrelated to preceding contexts. Although patients were slower than controls, both groups used the discourse context similarly as evidenced by similar reaction time patterns across conditions. Neurally however, different patterns emerged between patients and controls: within the N400 time window, patients failed to modulate their neural responses across conditions. This failure to differentiate between conditions was specifically correlated with positive thought disorder. Results suggest that schizophrenia patients, particularly those with positive thought disorder, fail to make immediate use of discourse context to build up semantic coherence in the brain.

Electrophysiological insights into conceptual disorganization in schizophrenia

Disorganized speech, or thought disorder, in schizophrenia may reflect abnormal processing of meaningful concepts. To examine whether schizophrenia involves abnormalities in how a meaningful context influences processing of concepts strongly, weakly, or not related to it, we used the N400, an event-related brain potential (ERP) index of semantic relatedness. ERPs were recorded from schizophrenia patients (n=18) and normal controls (n=18) while they viewed category definitions (e.g., a type of fruit), each followed by a target word that was either a high-typicality category exemplar (apple), low-typicality exemplar (cherry), or non-exemplar (clamp). Participants' task was to indicate via button-press whether or not the target belonged to the category. In both patients and controls, N400 amplitude was largest (most negative) for non-exemplars, intermediate for low-typicality exemplars, and smallest (least negative) for high-typicality exemplars. Compared to controls, patients showed a trend toward reduced N400 amplitude differences between non-exemplars and low-typicality exemplars. Most importantly, within patients, reduced N400 amplitude differences between high- and low-typicality exemplars were correlated with psychotic symptoms. This association of an N400 index of semantic processing with psychotic symptoms suggests that psychosis in schizophrenia may be associated with greater similarity in how concepts strongly and weakly meaningfully related to their context are processed.

Delusions and processing of discrepant information: an event-related brain potential study

One possible explanation for why delusions persist despite the awareness of contradictory information is that the new information fails to be integrated. Interestingly, the amplitude of the N400 event-related brain potential (ERP) has been proposed as an index of the integration of information that is discrepant with expectancies whatever the task in which the potential is found. Thus, delusions may persist because of a deficit in integration as indexed by the N400. To test this hypothesis, ERPs were recorded in 35 schizophrenia patients (mean age=30.5+/-5.6 years) and 26 normal controls during a task in which they either had to decide whether or not each target word could be integrated into the category "animal", or had no decision to make, according to the prompt "animal?" or the prompt "inaction". In these conditions, the amplitudes of the N400s to target words that were discrepant with the category were found to be negatively correlated with delusion severity. The patient group was then dichotomized according to a median split of delusion severity, excluding the 5 patients with delusion scores at the median. Mean age, sex ratio, and severity of conceptual disorganization and hallucinations of the two subgroups differed. Controlling for these 4 covariates, the N400s for discrepant targets were found smaller in the 14 More-Delusional patients than in the 16 Less-Delusional patients. These results support the hypothesis that delusions are associated with smaller N400s in patients. Further studies should thus be done to test whether a deficit of N400 processes could have a causal role in the persistence of delusions.

Building up linguistic context in schizophrenia: Evidence from self-paced reading

An impairment in the build-up and use of context has been proposed as a core feature of schizophrenia. The current study tested the hypothesis that schizophrenia patients show impairments in building up context within sentences because of abnormalities in combining semantic with syntactic information. Schizophrenia patients and healthy controls read and made acceptability judgments about sentences containing verbs that were semantically associated with individual preceding words but that violated either the meaning (animacy/semantic constraints) or the syntactic structure (morphosyntactic constraints) of their preceding contexts. To override these semantic associations and determine that such sentences are unacceptable, participants must integrate semantic with syntactic information. These sentences were compared with congruous and pragmatically/semantically violated sentences that imposed fewer semantic-syntactic integration demands. At sentence-final words and decisions, patients showed smaller reaction time differences than controls to animacy/semantically violated or morphosyntactically violated sentences relative to pragmatically/semantically violated or nonviolated sentences. The relative insensitivity to these violations in patients with schizophrenia may arise from impairments in combining semantic and syntactic information to build up sentence context.

Making sense of sentences in schizophrenia: Electrophysiological evidence for abnormal interactions between semantic and syntactic processing

Event-related potentials to critical verbs were measured as patients with schizophrenia and healthy controls read sentences word by word. Relative to their preceding context, critical verbs were (a) congruous, (b) incongruous and semantically unrelated to individual preceding words (pragmatic-semantic violations), (c) incongruous but semantically related to individual preceding words (animacy-semantic violations), or (d) syntactically anomalous. The N400 was modulated normally in patients, suggesting that semantic integration between individual words within sentences was normal in schizophrenia. The amplitude of the P600 to both syntactic and animacy-semantic violations was reduced in patients relative to controls. The authors suggest that, in schizophrenia, an abnormality in combining semantic and syntactic information online to build up propositional meaning leaves sentence processing to be primarily driven by semantic relationships between individual words.

N400 anomalies in schizophrenia are correlated with the severity of formal thought disorder

We explored the link between N400 anomalies and clinical profile in schizophrenia patients. N400 was recorded in 50 schizophrenia patients and 40 healthy controls during a lexical decision task with semantic priming. Comparison between controls and schizophrenia patients showed the classical anomalies reported for N400 in schizophrenia patients: greater amplitude for related words and lack of N400 effect. Analyses of the correlations between N400 effect and various symptoms of schizophrenia (formal thought disorder, positive symptoms, negative symptoms, overall symptoms, mean neuroleptic dose) or socioeducational data (age, vocabulary level, number of years of study) revealed that only the correlation with formal thought disorder was significant: the higher the scores for formal thought disorder, the lower the N400 effect observed.

ERPs of metaphoric, literal, and incongruous semantic processing in schizophrenia

The ability of schizophrenia patients to access metaphorical meaning was studied on the basis of psycholinguistic models of metaphor processing. ERPs were recorded from 20 schizophrenic and 20 control participants who were asked to read metaphorical, literal, and incongruous sentences and to judge their meaningfulness. In all participants, incongruous endings to sentences evoked the most negative N400 amplitude, whereas literal endings evoked more negative N400 amplitude than metaphorical ones, consistent with the direct model of metaphor processing. Although the patients had ERPs patterns that were similar to controls, they exhibited a more negative N400 amplitude for all sentences, LPC amplitude reduction, and latency delay in both components. The results suggest that schizophrenics have no specific anomalies in accessing the meaning of metaphors but are less efficient in integrating the semantic context of all sentences--both figurative and literal.

Association of schizotypy with semantic processing differences: an event-related brain potential study

Disorganized speech in both schizophrenia and schizotypy has been hypothesized to result from abnormalities in how concepts activate one another in semantic memory. To study whether schizotypy is associated with differences in how categories activate their exemplars, we examined the N400 component of the event-related brain potential (ERP) elicited during a category-verification task. ERPs were recorded in young adults from the general population while they viewed category definitions each followed by a target that was either a high-typicality exemplar, low-typicality exemplar, or non-exemplar; participants' task was to indicate whether or not the target belonged to the category. Schizotypy was assessed via the Schizotypal Personality Questionnaire (SPQ). Overall, N400 amplitude was largest for non-exemplars, smallest for high-typicality exemplars, and intermediate for low-typicality exemplars. SPQ score was associated with decreased N400 amplitude to non-exemplars, and increased amplitude to both types of exemplars. SPQ score was negatively correlated with the N400 amplitude difference between non-exemplars and both low- and high-typicality exemplars, but was not correlated with the amplitude difference between low- and high-typicality exemplars. N400 amplitude differences between non-exemplars and both types of exemplars were correlated with the SPQ Interpersonal factor, but not the Disorganized factor. The results are consistent with an association of schizotypy with decreased use of context to activate related items and inhibit unrelated items.

Language disorder in schizophrenia as a developmental learning disorder

Receptive language disorder in schizophrenia is hypothesized to represent a learning disorder that involves a neurodevelopmental etiology. It is argued that a preexisting developmental language disorder may characterize a subset of schizophrenia patients. A primary deficit in the temporal dynamics of brain function is assumed to cause receptive language disorder in schizophrenia. This hypothesized core deficit includes both disturbance in the processing of rapid, sequential information and disruptions to patterns of brain activation and synchronization. These timing deficits may alter the way associative connections are formed and/or accessed in semantic memory. It is suggested that abnormalities in second-messenger pathways of subcortical-cortical circuitry offer an etiological nexus for language dysfunction in schizophrenia and developmental dyslexia.

The relationship between membrane pathology and language disorder in schizophrenia

Receptive language disorder in schizophrenia has been hypothesized to involve a fundamental deficit in the temporal (time-based) dynamics of brain function that includes disruptions to patterns of activation and synchronization. In this paper, candidate mechanisms and pathways that could account for this basic deficit are discussed. Parallels are identified between the patterns of language dysfunction observed for schizophrenia and dyslexia, two separate clinical disorders that may share a common abnormality in cell membrane phospholipids. A heuristic is proposed which details a trajectory involving an interaction of brain fatty acids and second-messenger function that modulates synaptic efficacy, and, in turn, influences language processing in schizophrenia patients. It is additionally hypothesized that a primary deficit of functional excitation originating in the cerebellum, in combination with a compensatory decrease of functional inhibition in the prefrontal cortex, influences receptive language dysfunction in schizophrenia.

Semantic and syntactic processes during sentence comprehension in patients with schizophrenia: evidence from event-related potentials

Language and thought disorders are core symptoms in schizophrenia. We therefore studied language comprehension processes in patients with schizophrenia and control subjects during a sentence processing paradigm using event-related potentials (ERPs). In the ERP, assignment of syntactic structure to a string of words is reflected by an early left anterior negativity (ELAN) at about 80 ms after stimulus onset. Integration of syntactic and semantic information into a coherent representation is indexed by a positive potential at 600 ms (P600). Amplitudes of the ELAN and the P600 components are higher for grammatically incorrect sentences. Semantic processes are associated with a negative deflection peaking at 400 ms (N400). N400 amplitude is higher in semantically incongruent sentences. Nineteen patients with DSM IV schizophrenia and 19 healthy controls were presented with correct, semantically incorrect (semantic mismatch) and grammatically incorrect sentences (syntactic mismatch). Syntactic mismatch elicited an ELAN component in both subject groups. However, only controls but not patients with schizophrenia exhibited a P600 syntactic mismatch effect. Semantic mismatch was associated with a larger N400 potential which did not differ between groups. These results suggest that patients with schizophrenia are not impaired in syntactic structure assignment as reflected by the ELAN, but show deficits in semantic-syntactic integration processes underlying the P600.

An electrophysiologic study: can semantic context processes be mobilized in patients with thought-disordered schizophrenia?

OBJECTIVE

The aim of this study was to test the hypothesis that reinforcing the structuring of verbal material may bring about an improvement in contextualization processes in patients with formal thought-disordered schizophrenia.

METHOD

A total of 38 schizophrenia patients with formal thought disorders and 24 matched healthy control subjects performed 2 lexical decision tasks, involving 2 levels of contextual structuring (with 16.7% and 33% of related words, respectively). The event-related potentials, N400 and late positive component (LPC), and behavioural variables (reaction times and error percentages) were analyzed.

RESULTS

A context-structuring effect was observed on LPC, but not on N400. In subjects with schizophrenia, the N400 anomalies (that is, increase in amplitude for the related words and reduction of the N400 effect) persisted in both context-structuring conditions. Similarly, a reduction in LPC amplitude for the unrelated word category, as well as a decrease in the LPC effect, was observed in these patients.

CONCLUSIONS

The schizophrenia patients with formal thought disorders did not benefit from the structuring of the context to implement context integration strategies. This deficit appears to be stable. The results are discussed within the framework of a previously published model of language comprehension.

N400 abnormalities in unmedicated patients with schizophrenia during a lexical decision task

A lexical decision task was used to investigate semantic processing in schizophrenia. Eighteen unmedicated schizophrenics and 18 gender/age-matched controls were tested. Subjects were visually presented with pairs of words. The target word (S2) was either a non-word, semantically related, or unrelated to preceding word (S1). Subjects decided whether the S2 was a word or non-word. Event related potentials (ERPs) elicited by the S2, including N350, and the late positive component (LPC) were measured. The latency of the N350 was prolonged in schizophrenia. The N400 effect, measured by the mean amplitude (300-500 ms) from difference waves (unrelated word-related word, non-word-related word), was smaller in patients. Peak amplitude of the LPC was reduced and latency of the LPC was delayed in the schizophrenics. Behaviorally, control subjects responded much faster to related words compared to unrelated or non-words, while patients showed little difference in processing speed between word categories. A reduced N400 effect suggested inefficient utilization of the context, while prolonged latency of the ERP components suggested a general delay of semantic information processing in schizophrenia.

Functional analysis of the deficit in semantic context processes in schizophrenic patients: an event-related potentials study

AIM

Schizophrenic patients exhibit a deficit in the semantic context processing strategies which might be responsible for the language and communication disorders that are characteristic of this condition. The aim of our study was to identify the nature of the contextualization processes which are lacking in schizophrenic patients, by distinguishing between processes for the generation of expectations and processes of semantic integration.

PATIENTS AND METHOD

Thirteen schizophrenic patients and 12 healthy controls performed two tasks: (a) a lexical decision task (LDT) with a highly structured sentence context and whose experimental characteristics made it possible to call strongly on predictive strategies, and (b) a LDT with classic semantic priming (the context being reduced to a single word). In this latter task, the small number of related words did not prompt the generation of expectations but instead called on the postlexical integration process. The event-related potentials (ERP) were recorded during the administration of the task.

RESULTS AND CONCLUSION

In the sentence task, we observed a modulation in the N400 amplitude due to the presence of expectations both in the schizophrenic and control participants: predictable words evoked a small N400 amplitude compared to the non-predictable words. In contrast, in the simple (priming) task, the semantic link evoked an N400 amplitude modulation in the control group exclusively. Our results indicate that schizophrenics could be able to use context to activate expectations for the most highly predictable item, and that their deficit appears when the processing strategy is based on the integration of the context stored in working memory.

The event-related potentials elicited by content and function words during the reading of sentences by patients with schizophrenia

Thought disorder is one of the main symptoms observed in schizophrenia and has been investigated in terms of language dysfunction. The purpose of the present study was to find whether there were any differences in identifying and processing between content (semantic) and function (syntax) words, and to elucidate whether semantic or syntax is more impaired for the schizophrenics. Event-related potentials were recorded in 13 patients with schizophrenia and 14 healthy controls, while they silently read three sets of passages. Event-related potentials were recorded for content words (noun, verb) and function words (auxiliary verb, particle) separately. For the healthy control group, the mean amplitude of P200 for the content word class was greater than for the function word class with fronto-central dominance. In contrast, no such difference was found for the schizophrenics mainly due to the reduction of P200 amplitude of the content words. Larger P200 for the content than the function word class suggests that greater resources were used to identify the content words. Lack of this difference found in patients with schizophrenia suggested that the disturbances in the semantics may be more attributable to the linguistic impairment than those in the syntax.