Differential alteration of automatic semantic processing in treated patients affected by bipolar mania and schizophrenia: an N400 study

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.

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.

Neural Correlates of Semantic Inhibition in Relation to Hypomanic Traits: An fMRI Study

OBJECTIVES

Language modifications are a core feature of mania, but little is known about the semantic mechanisms behind these disturbances. The aim of the present study was thus to identify deficits in semantic inhibition and their respective neural activation patterns in a sample of individuals assessed for hypomanic personality traits.

METHODS

Thirty-six young adults with no neurological or psychiatric diagnoses were assessed for hypomanic personality traits with the Hypomanic Personality Scale (HPS) and underwent an fMRI task of semantic ambiguity resolution.

RESULTS

Regression analyses revealed a positive association between the HPS score and activity in the left superior frontal gyrus, left inferior parietal lobule, and anterior cingulate gyrus during semantic ambiguity resolution.

CONCLUSION

We found a link between HPS scores and brain areas that are part of the cognitive control loop and semantic memory network during language processing in a nonclinical sample of individuals. The hyperactivation of these regions may reflect a compensatory neural response in a population with greater vulnerability to BD.

Abnormal neural hierarchy in processing of verbal information in patients with schizophrenia

Previous research indicates abnormal comprehension of verbal information in patients with schizophrenia. Yet the neural mechanism underlying the breakdown of verbal information processing in schizophrenia is poorly understood. Imaging studies in healthy populations have shown a network of brain areas involved in hierarchical processing of verbal information over time. Here, we identified critical aspects of this hierarchy, examining patients with schizophrenia. Using functional magnetic resonance imaging, we examined various levels of information comprehension elicited by naturally presented verbal stimuli; from a set of randomly shuffled words to an intact story. Specifically, patients with first episode schizophrenia (N = 15), their non-manifesting siblings (N = 14) and healthy controls (N = 15) listened to a narrated story and randomly scrambled versions of it. To quantify the degree of dissimilarity between the groups, we adopted an inter-subject correlation (inter-SC) approach, which estimates differences in synchronization of neural responses within and between groups. The temporal topography found in healthy and siblings groups were consistent with our previous findings - high synchronization in responses from early sensory toward high order perceptual and cognitive areas. In patients with schizophrenia, stimuli with short and intermediate temporal scales evoked a typical pattern of reliable responses, whereas story condition (long temporal scale) revealed robust and widespread disruption of the inter-SCs. In addition, the more similar the neural activity of patients with schizophrenia was to the average response in the healthy group, the less severe the positive symptoms of the patients. Our findings suggest that system-level neural indication of abnormal verbal information processing in schizophrenia reflects disease manifestations.

Modulation of the N400 component in relation to hypomanic personality traits in a word meaning ambiguity resolution task

AIM

High levels of hypomanic personality traits have been associated with an increased risk of developing bipolar disorder (BD). Changes in semantic content, impaired verbal associations, abnormal prosody, and abnormal speed of language are core features of BD, and are thought to be related to semantic processing abnormalities. In the present study, we used event-related potentials to investigate the relation between semantic processing (N400 component) and hypomanic personality traits.

METHODS

We assessed 65 healthy young adults on the Hypomanic Personality Scale (HPS). Event-related potentials were recorded during a semantic ambiguity resolution task exploring semantic ambiguity (polysemous word ending a sentence) and congruency (target word semantically related to the sentence).

RESULTS

As expected, semantic ambiguity and congruency both elicited an N400 effect across our sample. Correlation analyses showed a significant positive relationship between the Social Vitality subscore of the HPS and N400 modulation in the frontal region of interest in the incongruent unambiguous condition, and in the frontocentral region of interest in the incongruent ambiguous condition.

CONCLUSION

We found differences in semantic processing (i.e., detection of incongruence and semantic inhibition) in individuals with higher Social Vitality subscores. In the light of the literature, we discuss the notion that a semantic processing impairment could be a potential marker of vulnerability to BD, and one that needs to be explored further in this clinical population.

P600 alteration of syntactic language processing in patients with bipolar mania: Comparison to schizophrenic patients and healthy subjects

BACKGROUND

Disturbances in thought, speech, and linguistic processing are frequently observed in bipolar manic patients, but the underlying neurophysiological mechanisms are not well understood. P600 is a distinct, positive event-related potential component elicited by syntactic violations. Using the P600 ERP, we examined neural processing of syntactic language comprehension in patients with bipolar mania compared to patients with schizophrenia and healthy people.

METHOD

P600s were recorded from 21 manic patients with bipolar disorder, 26 patients with schizophrenia, and 29 healthy subjects during the presentation of 120 auditory sentences with syntactic violations or non-violations. Subjects were asked to judge whether each sentence was correct or incorrect.

RESULTS

Patients with mania and schizophrenia had significantly smaller P600 amplitudes associated with syntactic violations compared with healthy subjects. There was no difference in P600 amplitude between patient groups. For behavioral performance, patients with schizophrenia had significantly less accurate rates and longer reaction times compared with healthy subjects, whereas manic patients exhibited no significant differences in accuracy and only showed increased reaction times in comparison with healthy subjects.

LIMITATIONS

Psychotropic drug usage and small sample size.

CONCLUSION

Patients with bipolar mania have reduced P600 amplitude, comparable to patients with schizophrenia. Our findings may represent the first neurophysiological evidence of abnormal syntactic linguistic processing in bipolar mania.

The bimodal P300 oddball component is decreased in patients with an adjustment disorder: An event-related potentials study

OBJECTIVE

We found previously that use of a bimodal oddball design with synchronized pairs of audio-visual stimuli increased the sensitivity of the P300 wave to detect subclinical anxiety-depression in otherwise healthy subjects. Here, we wished to determine whether these P300 modulations would also be encountered when a clinical population comprised of patients with an adjustment disorder (AJD) was compared to healthy controls.

METHOD

Two groups, each comprised of twenty-five participants (AJD patients, and controls; N=50) had to detect deviant stimuli among frequent stimuli in an oddball task by clicking on a button. Separate blocks involving audio (A), visual (V) or bimodal congruent (AV) stimuli were used and compared.

RESULTS

P300 amplitudes of the control group were higher than those displayed by AJD patients, but only in the bimodal AV oddball task, while unimodal (visual or auditory) oddball tasks did not reveal any significant differences.

CONCLUSIONS

The increased sensitivity of the bimodal P300 that we observed previously in subclinical anxiety-depression was also observed in AJD patients.

SIGNIFICANCE

The impaired "bimodal congruence effect" in AJD suggests that these patients have altered integrative processes, which has potential implications for cognitive therapy.

Follow-up of N400 in the Rehabilitation of First-episode Schizophrenia

BACKGROUND

The N400 component of event-related potentials (ERP) has recently drawn widespread attention at home and abroad. This study was to explore the relationship between N400 changes and risperidone treatment and rehabilitation infirst-episode schizophrenia (FES).

METHODS

ERP component N400 was recorded by Guangzhou Runjie WJ-1 ERP instruments, in 58 FES before and 6 months, 15 months after risperidone treatment, and in 62 normal controls. The patients' syndromes were assessed by Positive and Negative Syndrome Scale (PANSS). And the stimuli are Chinese sentences with matching (congruent) or mismatching (incongruent) ending words.

RESULTS

N400 latencies were prolonged, and amplitudes were decreased in Cz, Pz, Fz, C3, C4, in FES compared with in NC, before treatment. The prolonged N400 latencies and decreased amplitudes were negatively correlated with the patients' positive scale and total scale of PANSS. There are significant differences of N400 amplitudes and latencies in 6 months and 15 months follow-up after treatment. Before treatment, 6 months and 15 months after treatment, N400 latencies are 446 ± 35 ms, 440 ± 37 ms, 414 ± 31 ms (F = 9.72, P < 0.01) in incongruent situation; N400 amplitudes are 5.2 ± 4.6 μV, 5.7 ± 4.8 μV, 7.3 ± 5.0 μV (F = 2.06, P > 0.05) in congruent situation, and 8.5 ± 5.9 μV, 10.1 ± 5.0 μV, 11.9 ± 7.0 μV (F = 3.697, P < 0.05) in incongruent situation.

CONCLUSIONS

N400 could be used to predict the effects of treatment of schizophrenia to some degree. The linguistic and cognitive impairment in schizophrenia can be improved by antipsychotic drugs.

Emotional Meaning in Context in Relation to Hypomanic Personality Traits: An ERP Study

The ability to integrate contextual information is important for the comprehension of emotional and social situations. While some studies have shown that emotional processes and social cognition are impaired in people with hypomanic personality trait, no results have been reported concerning the neurophysiological processes mediating the processing of emotional information during the integration of contextual social information in this population. We therefore chose to conduct an ERP study dealing with the integration of emotional information in a population with hypomanic personality trait. Healthy participants were evaluated using the Hypomanic Personality Scale (HPS), and ERPs were recorded during a linguistic task in which participants silently read sentence pairs describing short social situations. The first sentence implicitly conveyed the positive or negative emotional state of a character. The second sentence was emotionally congruent or incongruent with the first sentence. We analyzed the difference in the modulation of two components (N400 and LPC) in response to the emotional word present at the end of the “target” sentences as a function of the HPS score and the emotional valence of the context. Our results showed a possible modulation of the N400 component in response to both positive and negative context among the participants who scored high on the Mood Volatility subscale of the Hypomanic Personality Scale. These results seem to indicate that the participants with hypomanic personality traits exhibited specificities in the integration of emotions at the level of the early-mobilized neurocognitive processes (N400). Participants with hypomanic personality traits found it difficult to integrate negative emotional contexts, while simultaneously exhibiting an enhanced integration of positive emotional contexts.

An incongruent reality: the N400 in relation to psychosis and recovery

BACKGROUND

Cognitive impairments and delusions are hallmarks of schizophrenia, and are thought to be due in part to abnormalities in semantic priming. The N400, a neural measure of semantic processing, is found to be reduced in schizophrenia. However, it is unclear if individuals with other psychoses (e.g., mood disorders or substance abuse with psychotic features) also show this impairment, and whether N400 reduction relates to real-world functioning and recovery.

METHODS

Eighty-nine individuals from the Suffolk County Mental Health Project, a longitudinal study of first-admission psychosis, and 35 healthy adults were assessed using matched, related, and unrelated picture-word pairs to elicit the N400. Patients' real-world functioning, symptomatology, and recovery were tracked since first hospitalization; EEG assessment was completed during year 15 of the study.

RESULTS

Participants with schizophrenia had slower reaction times and reduced N400 to semantically incongruent stimuli relative to healthy participants. Schizophrenia and other psychoses did not differ on N400, suggesting that N400 abnormalities characterize psychosis broadly. When grouped by recovery status, patients who remained ill had a significantly blunted N400, while those who recovered did not differ from healthy adults. Few patients with schizophrenia achieved recovery; therefore recovery results are limited to the other psychosis group. Furthermore, reduced N400 and increased reaction times correlated with greater psychotic symptoms, worse global assessment of functioning scores, unemployment, and impaired social functioning.

CONCLUSIONS

Abnormalities in the N400 are not specific to schizophrenia; in addition, the N400 may be a useful neural correlate of recovery and real-world functioning across psychotic disorders.

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.

Event-related brain potential study of expectancy and semantic matching in schizotypy

Priming studies have revealed semantic processing abnormalities in subjects that display high schizotypal traits. The objective of the present study was to further elucidate the contribution of predictive (expectancy) and integrative (semantic matching) context processing to the semantic deficit described in schizotypy. Thirty-six participants were assigned into high or low schizotypy groups according to their score on the Schizotypal Personality Questionnaire (SPQ), and event-related brain potentials were recorded while these individuals performed semantic judgments based on asymmetrically associated word pairs. Viewed in one direction (forward), the target was highly predictable from the prime, whereas in the backward direction, the prime-to-target association was weak. It was assumed that the forward condition would be dependent on expectancy generation, while the backward condition would rely on semantic matching. In the low-SPQ group, forward and backward related words evoked a reduced (less negative) N400 amplitude compared to unrelated words, resulting in a significant forward and backward N400 priming effect, respectively. By contrast, only forward related words were facilitated in the high-SPQ group, resulting in significant forward priming and a lack of backward priming. Furthermore, the N400 amplitude for forward related words was less negative within the high-SPQ group in comparison to the low-SPQ group, which indicated easier semantic access to predictable words for high-SPQ individuals. Therefore, schizotypy may be associated with an imbalance in the use of predictive and integrative context processing strategies, namely preserved, if not over allocated, expectancy generation along with altered integration of unpredictable words due to semantic matching deficit.

EEG biomarkers in major depressive disorder: discriminative power and prediction of treatment response

Major depressive disorder (MDD) has high population prevalence and is associated with substantial impact on quality of life, not least due to an unsatisfactory time span of sometimes several weeks from initiation of treatment to clinical response. Therefore extensive research focused on the identification of cost-effective and widely available electroencephalogram (EEG)-based biomarkers that not only allow distinguishing between patients and healthy controls but also have predictive value for treatment response for a variety of treatments. In this comprehensive overview on EEG research on MDD, biomarkers that are either assessed at baseline or during the early course of treatment and are helpful in discriminating patients from healthy controls and assist in predicting treatment outcome are reviewed, covering recent decades up to now. Reviewed markers include quantitative EEG (QEEG) measures, connectivity measures, EEG vigilance-based measures, sleep-EEG-related measures and event-related potentials (ERPs). Further, the value and limitations of these different markers are discussed. Finally, the need for integrated models of brain function and the necessity for standardized procedures in EEG biomarker research are highlighted to enhance future research in this field.

N400 in schizophrenia patients

PURPOSE OF REVIEW

The purpose of this article is to review major findings in event related potential (ERP) research in schizophrenia patients, specifically focusing on the N400 component.

RECENT FINDINGS

Patients with chronic schizophrenia have difficulty using 'context' (understanding the meaning of the word relative to the sentence) in sentence processing studies and often show differences from control populations in language experiments using word priming. Both of these observations are associated with an abnormal N400 ERP component when compared with nonpsychotic individuals. Many studies of language function rely on priming paradigms that use pairs of words such that the first word in a pair is a 'prime' and a second word in a pair is a 'target', separated from the prime by a period of time known as the Stimulus Onset Asynchrony (SOA). If the SOA is short (i.e., below 400 ms) then it is believed that a priming study examines primarily processes of initial activation within semantic networks; if it is long (i.e., more than 400 ms) then it is believed that a priming study examines primarily processes of context use, generating predictions and matching these predictions against upcoming semantic information. Priming paradigms that use long SOAs are consistently associated with a more negative N400 (hence lack of priming) in schizophrenia, whereas priming paradigms using a short SOA produce either a normal N400 priming response or hyperpriming as shown by a reduced N400 and related to a hypothesized too rapid automatic spread of activation within the semantic memory pathway. Apparent differences among reported study results are likely due to paradigm differences that tap into different aspects of language processing. Although the presence of both hyperactivation within semantic networks and difficulties with the use of context is well known in schizophrenia, it is unclear whether these abnormalities are also present prior to illness onset in people who are at risk for development of schizophrenia or even present at the onset of illness.

SUMMARY

In order to clarify the findings reviewed here, future studies will be needed that focus on examining the N400 response in young people at high risk for developing the illness using multiple paradigms that probe different aspects of language function.

Semantic priming in remitted patients with bipolar disorder

BACKGROUND AND OBJECTIVES

Semantic priming disturbances are increasingly recognized as a feature of schizophrenia, and increased priming has been suggested to constitute a "cognitive correlate" of positive formal thought disorder (FTD). The present study aimed to investigate semantic priming in patients with bipolar disorder (BD).

METHODS

A primed lexical decision task with strongly related (STR), weakly related (WR), or unrelated (UR) prime-target pairs (SOA = 250 ms) was administered to fourteen remitted patients with BD and twelve control subjects matched on key demographic variables. FTD was measured by means of the Scale for Thought, Language and Communication (TLC).

RESULTS

Control subjects showed a robust (59.6 ms) and statistically significant priming effect for STR words, while priming for UR words was non-significant. In patients there was no evidence of priming in either condition. In patients, there were no significant correlations between priming magnitude and TLC scores. However, the only patient with a positive score on the TLC disorganization factor exhibited evidence of hyperpriming.

LIMITATIONS

The present patient sample exhibited very low TLC scores, and no direct comparison to patients with schizophrenia was possible.

CONCLUSIONS

The finding of decreased priming in patients with BD raises the possibility that semantic processing abnormalities in BD are of a different nature than those encountered in schizophrenia. Due to the small size and very low TLC scores of the present patient sample, no definite conclusions can be drawn as to the relationship of formal thought disorder and semantic processing abnormalities in BD.

Test-retest reliability and stability of N400 effects in a word-pair semantic priming paradigm

OBJECTIVE

Elicited by any meaningful stimulus, the N400 event-related potential (ERP) component is reduced when the stimulus is related to a preceding one. This N400 semantic priming effect has been used to probe abnormal semantic relationship processing in clinical disorders, and suggested as a possible biomarker for treatment studies. Validating N400 semantic priming effects as a clinical biomarker requires characterizing their test-retest reliability.

METHODS

We assessed test-retest reliability of N400 semantic priming in 16 healthy adults who viewed the same related and unrelated prime-target word pairs in two sessions one week apart.

RESULTS

As expected, N400 amplitudes were smaller for related versus unrelated targets across sessions. N400 priming effects (amplitude differences between unrelated and related targets) were highly correlated across sessions (r=0.85, P<0.0001), but smaller in the second session due to larger N400s to related targets.

CONCLUSIONS

N400 priming effects have high reliability over a one-week interval. They may decrease with repeat testing, possibly because of motivational changes.

SIGNIFICANCE

Use of N400 priming effects in treatment studies should account for possible magnitude decreases with repeat testing. Further research is needed to delineate N400 priming effects' test-retest reliability and stability in different age and clinical groups, and with different stimulus types.