Electrophysiological insights into conceptual disorganization in schizophrenia

Abstract

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 hightypicality 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 nonexemplars, intermediate for low-typicality exemplars, and smallest (least negative) for hightypicality 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. In schizophrenia patients, an N400 index of semantic processing was associated with psychotic symptoms. Psychosis may be associated with greater similarity in how concepts strongly and weakly meaningfully related to their context are processed.

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

“…On balance, however, N400 studies of schizophrenia patients provide evidence of a general reduction in semantic priming, at least at SOAs of approximately 300 ms or greater, during which more controlled or strategic cognitive processing is normally thought to occur. Furthermore, in line with our hypothesis, larger N400s to related targets, and smaller N400 relatedness priming effects, have been found to correlate with severity of delusions (Kiang et al 2007;2008).…”

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

“…These results suggest that persons with schizophrenia are impaired in using meaningful contextual stimuli to activate related concepts. Moreover, several studies have found a correlation between these N400 semantic priming deficits and patients' psychotic symptom severity, raising the possibility that deficits in activating contextually related concepts may underlie the development and maintenance of delusions (Salisbury et al, 2000;Kiang et al, 2007Kiang et al, , 2008.…”

N400 and P300 modulation as functions of processing level in schizophrenia patients exhibiting formal thought disorder

“…GouzoulisMayfrank et al (2003) have also recorded behavioral data arguing in favor of semantic impairments as episodic markers, and as clearly state-dependent, in FTD schizophrenics. Kiang's N400 data (Kiang et al, 2007), showing a trend toward reduced differences in amplitude between non-exemplars and low-typicality exemplars correlated with psychotic symptoms, may be interpreted as state marker of psychotic symptoms.…”