S83. IMPAIRED VISUAL CONTRAST PERCEPTION IN PSYCHOSIS

• Published in: Schizophrenia bulletin Vol. 45; no. Supplement_2; p. S339
• Main Authors: Schallmo, Michael-Paul, Grant, Andrea, Marjanska, Malgorzata, Olman, Cheryl, Sponheim, Scott
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 09.04.2019
• Subjects: Poster Session III; Psychosis; Spectrum analysis
• ISSN: 0586-7614; 1745-1701
• DOI: 10.1093/schbul/sbz020.628

Abstract Background Abnormal perceptual experiences are common in people with psychosis and have been linked to greater disease severity and poorer outcomes. While the neural basis of psychosis remains unknown, it has been suggested that an imbalance between excitation and inhibition may lead to neural dysfunction in people with psychotic disorders. It is also unclear to what extent abnormal perceptual functioning occurs across the spectrum of psychotic disorders, or is specific to particular diagnoses (e.g., schizophrenia). Methods To examine the link between neural dysfunction and abnormal perception, we performed a series of experiments to measure: 1) visual contrast discrimination behavior, 2) 7 tesla fMRI responses in visual cortex during contrast discrimination, and 3) neurochemical concentrations in visual cortex using 7 tesla MR spectroscopy. Data were acquired from people with psychosis, their unaffected first-degree biological relatives, and healthy control subjects as part of the ongoing Psychosis Human Connectome Project. In our behavioral task performed outside the scanner, subjects were asked to discriminate between two visual grating stimuli, and report which was higher in contrast. Discrimination thresholds, the minimum difference in contrast that could be perceived with 80% accuracy, were measured using a psychophysical adaptive staircase method. Data from 1 subject with psychosis were excluded for poor catch trial performance (< 80% accuracy). Results Thresholds were significantly higher for subjects with psychosis vs. healthy controls, indicating a reduced sensitivity to visual contrast. Threshold data were fit with a standard model that describes the nonlinear contrast-response function (input vs. output). Preliminary results suggest that the difference in contrast discrimination performance between subjects with psychosis (n = 27) and controls (n = 18) could be described by the model in terms of a multiplicative reduction in visual response magnitude. Preliminary analyses of spectroscopy data revealed no significant differences between subjects with psychosis (n = 22) and controls (n = 25) in the concentrations of glutamate or GABA (scaled to total creatine) in occipital cortex. However, across both groups, higher occipital glutamate concentrations were associated with greater response magnitude values (obtained from modeling the contrast discrimination task data). Discussion Our results may suggest a role for glutamate levels in occipital cortex in determining individual differences in contrast discrimination performance, as well as in impaired contrast perception among individuals with psychosis.