Milena Kostova

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.

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.

ERP evidence of a meaningfulness impact on visual global/local processing: When meaning captures attention

Event-related potentials (ERPs) were recorded to investigate whether the meaningfulness of experimental stimuli impacted performances during global/local visual tasks. Participants were presented with compound stimuli, based on either meaningful letters, meaningful objects, or meaningless non-objects. The ERP recordings displayed typical early components, P1 and N1, evoked by task-related processes that affected global and local processes differently according to the meaningfulness of the stimuli. The effect of meaningfulness of the stimuli during global processing showed that P1 amplitudes were larger in response to objects and non-objects compared to letters, while letters and objects elicited larger N1 amplitudes than non-objects. Second, during local processing, the mean amplitudes of the ERPs recorded for object and letter stimuli were systematically smaller than the amplitudes recorded for non-object stimuli for both P1 and N1 components. In addition, object and letter stimuli elicited comparable mean ERP responses during local processing. These results are discussed in terms of the influences of both attentional and top-down identification processes. Taken together, these findings suggested that looking for meaning is crucial in the perception of visual scenes and that the meaningfulness nature of the stimuli should be taken into account in future studies.

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 and P300 modulation as functions of processing level in schizophrenia patients exhibiting formal thought disorder.

In a semantic priming paradigm, the effects of different levels of processing on N400 were assessed by changing task demands in 10 schizophrenics and 10 matched controls. In the lexical decision task subjects had to discriminate between words and nonwords, and in the physical task subjects had to discriminate between cyan and blue ink letters. A lexicality test of reaction times demonstrated that the physical task was performed non-lexically in both groups. Moreover, a semantic priming reaction time effect was obtained only in the lexical decision task for the control group. The level of processing clearly affected event-related potentials. An N400 priming effect was only observed for the control group in the lexical decision task. By contrast, in the physical task a P300 effect was observed for either related or unrelated targets in both groups. Taken together, these results indicate that FTD schizophrenics are impaired specifically when task performance induces the semantic aspects of words as indexed by reduction of the N400 priming effect.

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.

An event‐related potential study of predictive and integrative semantic context processing in subjects with schizotypal traits

Context processing abnormalities may explain thought disorder in schizophrenia/schizotypy. This study aimed to assess predictive and integrative context processing in subjects with high or low scores on the Schizotypal Personality Questionnaire (SPQ). The N400 amplitude was recorded during semantic judgment of sentence pairs ending with a lateralized expected or unexpected word from the same or a different category (related and unrelated violation). In both groups, the N400 amplitude was less negative for expected words versus unrelated violations, regardless of which hemisphere received the stimulus, and for related versus unrelated violations, but only for left-hemisphere stimuli. The N400 amplitude for unrelated violations was less negative in subjects with high SPQ scores for both hemispheres. These results indicate that subjects with schizotypal traits use context to predict or integrate congruent words, but fail to inhibit incongruent words.

Effect of semantic coherence on episodic memory processes in schizophrenia

Schizophrenia is associated with severe episodic retrieval impairment. The aim of this study was to investigate the possibility that schizophrenia patients could improve their familiarity and/or recollection processes by manipulating the semantic coherence of to-be-learned stimuli and using deep encoding. Twelve schizophrenia patients and 12 healthy controls of comparable age, gender, and educational level undertook an associative recognition memory task. The stimuli consisted of pairs of words that were either related or unrelated to a given semantic category. The process dissociation procedure was used to calculate the estimates of familiarity and recollection processes. Both groups showed enhanced memory performances for semantically related words. However, in healthy controls, semantic relatedness led to enhanced recollection, while in schizophrenia patients, it induced enhanced familiarity. The familiarity estimates for related words were comparable in both groups, indicating that familiarity could be used as a compensatory mechanism in schizophrenia patients.

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.

An Event Related Potentials Study of Semantic Coherence Effect during Episodic Encoding in Schizophrenia Patients

The objective of this electrophysiological study was to investigate the processing of semantic coherence during encoding in relation to episodic memory processes promoted at test, in schizophrenia patients, by using the N400 paradigm. Eighteen schizophrenia patients and 15 healthy participants undertook a recognition memory task. The stimuli consisted of pairs of words either semantically related or unrelated to a given category name (context). During encoding, both groups exhibited an N400 external semantic coherence effect. Healthy controls also showed an N400 internal semantic coherence effect, but this effect was not present in patients. At test, related stimuli were accompanied by an FN400 old/new effect in both groups and by a parietal old/new effect in the control group alone. In the patient group, external semantic coherence effect was associated with FN400, while, in the control group, it was correlated to the parietal old/new effect. Our results indicate that schizophrenia patients can process the contextual information at encoding to enhance familiarity process for related stimuli at test. Therefore, cognitive rehabilitation therapies targeting the implementation of semantic encoding strategies can mobilize familiarity which in turn can overcome the recollection deficit, promoting successful episodic memory performance in schizophrenia patients.