Seeing things in psychosis: Reduced theta power in early neural responses to ambiguous visual stimuli predicts perceptual distortions

Objective: In this study we aimed to identify possible neural origins of perceptual disturbances in psychotic disorders. Methods: Individuals with schizophrenia and bipolar disorder with psychosis (n = 40), their biological siblings (n = 17), and healthy controls (n = 27) viewed ambiguous object stimuli equivalent in primary visual cortical processing demands, allowing for identification of neural abnormalities occurring beyond basic sensory processing. Magnetoencephalography was collected and neural oscillations were quantified using time–frequency analysis. Results: Individuals with schizophrenia showed reduced early theta responses over occipital cortex and diminished late desynchronization of alpha/beta in select conditions over parietal cortex. Reduced theta was associated with more schizotypal traits and self-reported perceptual anomalies. Less alpha/beta desynchronization was marginally associated with greater negative symptoms. Conclusions: Visual cortical anomalies in schizophrenia beyond primary visual cortex are reflected in reduced early occipital theta oscillations. This impaired bottom-up sensory processing is related to everyday perceptual abnormalities. Diminished later alpha/beta desynchronization in schizophrenia may reflect difficulty disengaging from default mode to access top-down mechanisms that facilitate perception. Significance: Early sensory signals, communicated through theta-band oscillations, and later semantic processing, engaged through the desynchronization of alpha/beta oscillations, contribute to ambiguous object detection as well as perceptual disturbances in schizophrenia.