Spurious signal detection and delusions of reference in first-episode schizophrenia

Background: Delusions of reference (DOR) are a group of highly prevalent psychotic symptoms. In DOR, patients experience attentional capture by certain otherwise neutral aspects in the environment, which were regarded as self-referential. Theoretically, aberrant salience as a result of excessive dopamine firing may lead to spurious signal detection in patients with DOR. We test the hypothesis that patients presenting with and DOR have increased false alarms in a visual and an auditory signal detection task, compared with patients not experiencing the symptom and with healthy controls. Methods: A total of 32 patients with first-episode schizophrenia (mean age 24.3±6.9 years, 19 men) and 17 healthy controls (mean age 24.7±7.7 years, 9 men) were recruited. Controls and patients were matched in age, sex and education. Patients were further divided into a DOR group (n=15) and a non-DOR group (n=17). DOR was assessed using the Ideas of Reference Interview Scale (IRIS). Spurious signal detection was tested using the randomized and sequential Contour Integration Test (Field, Hayes, and Hess 1993) for visual processing and the Babble Task (Hoffman et al, 2007) for auditory processing. Performance was compared between groups using ANOVA and post-Hoc analysis. Signal detection analyses were carried out to differentiate between genuine spurious signal detection and response bias. Relationship between IRIS scores and false alarm rates was explored. Results: Spurious signal detection was observed in both DOR groups and healthy controls in low signal-to-noise trials. In the Contour Integration Test, patients with DOR were more likely to detect spurious signals particularly when the stimuli were presented at a moderate signaltonoise ratio compared with the other two groups (p<0.01), with an effect size of 1.11 (Cohen’s d). False alarms are correlated with DOR severity (r=0.39, p<0.01). All three groups demonstrated good sensitivity and conservative response in signal detection. A similar trend was seen in the Babble Task. Discussion: Spurious signal detection is a common phenomenon under noisy conditions, which can be elicited also in healthy subjects. In DOR, there appears to be increased spurious signal detection, at a moderate signal-to-noise ratio. This observation cannot be accounted for by a general decline in task performance or a more liberal response bias, suggesting genuine false detection of signals in patients with DOR. This study provided initial findings for further investigation into the neurocognitive substrates of DOR

Delusions of reference, excessive top-down processing, and default mode network in first-episode schizophrenia

Poster 170BACKGROUND: Delusions of reference (DOR) refer to the detection of spurious self-information in otherwise neutral or ambiguous environmental stimuli. Empirical studies of DOR using an information processing framework are lacking. We hypothesize, at the neurocognitive level, that DOR may be related to an excessive use of an internally generated, top-down processing strategy; whereas at the neurophysiological level, this may be related to the hyperactivity and hyperconnectivity in the default mode network (DMN) of the brain. The DMN has been implicated in self-focused attention and ‘stimulus-independent thoughts’, as well as baseline monitoring and automatic attention to salient environmental stimuli, and a link to psychotic symptoms has been observed. The first part of this study explore whether a relationship exists between DOR and excessive top-down processing; the second part of this study test the hypothesis that patients with DOR as chief compliant specifically present with aberrant DMN function and increased top-down processing. METHODS: In Study 1, a total of 30 schizophrenic patients are assessed for DOR using the Ideas of Reference Interview Schedule (IRIS), and are tested using a visual processing (“contour integration”) and a verbal processing (“babbling”) task. Excessive top-down processing is measured by the score of spurious information perceived in the two tasks. In Study 2, to test the hypothesis that DOR is specifically related to DMN and increased top-down processing, 45 first-episode schizophrenic patients are recruited into one of three groups according to their symptomatology: (A) patient with I/DOR as chief presentation (n = 15); (B) patients with positive symptoms other than I/DOR as chief presentation (n = 15); and (C) patients without clinically significant positive symptoms (n = 15). A group of normal controls (n = 15) is also included. Participants are matched by age, sex and education level. Functional MRI scanning is performed under a resting condition and a block-design 0- and 2-back working memory task condition. ANOVA F test is used for the analysis of between group differences in DMN activity. For functional connectivity analysis, Pearson's correlation is performed in seed regions of interest according to previously defined components of the DMN. RESULTS: In the exploratory study, interim data analysis (n = 9; 5 men, mean age 23.8 years) showed a positive correlation between severity of DOR and spurious information detected in the contour integration test (Spearman's rho = 0.45) and the babble task (Spearman's rho = 0.42), although the results did not reach statistical significance because of the sample size. Spurious information processing in the auditory and visual tasks also showed strong correlation (Spearman's rho = 0.65, p = 0.056). Data collection for both parts of the study is expected to be completed by March 2010. DISCUSSION: This study tests the hypothesis that excessive top-down processing and aberrant DMN function seen in schizophrenia is specifically related to DOR, a group of important symptom central to psychotic disorders. DOR are found in up to 67% of schizophrenic patients, and their roles as prodromal and relapse signal and schizotypal trait highlight their potential as a state and trait marker for schizophrenia. Identification of the neurocognitive and neurophysiological mechanisms of DOR will provide important insight into understanding psychosis. Copyright © 2010 Published by Elsevier B.V