Compensatory brain network mechanisms of visual shape completion across the schizo-bipolar spectrum

Visual shape completion is a canonical perceptual process that integrates spatially distributed edge information into unified representations of objects. People with schizophrenia show difficulty in discerning completed shapes but the brain networks and functional connections underlying this perceptual difference remain poorly understood. Equally unclear is whether similar neural differences arise in bipolar disorder or vary across the schizo-bipolar spectrum. To shed light on these topics, we scanned (fMRI) people with schizophrenia (SZ; n=16), bipolar disorder (BP; n=15), or no psychiatric illness (HC; n=20) during rest and during a task in which they discriminated configurations that formed or failed to form completed shapes (illusory and fragmented condition, respectively). Illusory/fragmented task activation differences ("modulations"), resting-state functional connectivity, and multivariate pattern differences were identified on the cortical surface using 360 predefined parcels and 12 functional networks composed of such parcels. Brain activity flow mapping was used to evaluate the likely involvement of resting-state connections for shape completion (Cole et al., 2016). Repeated split-half cross-validation and permutation testing revealed distinct dorsal attention network (DAN) modulations in schizophrenia (SZ vs BP: p=.0006, AUC=.86; SZ vs HC: p=.0004, AUC=.87). Across patients, DAN modulations could predict cognitive disorganization symptom severity via cross-validated linear regression and permutation testing (r=.6, p<.01). Functional connections from the dorsal attention network could model activity in the secondary visual network in each group, except among those with schizophrenia (HC: p=.004, Hedges' g=.76; BP: p=.003, g=1.03; SZ: p=.25, g=.31). Compared to controls, patients' task modulations were more variable from subject to subject and dispersed over a larger number of networks. In summary, dorsal attention network activity may underpin abnormal visual perception in schizophrenia, perhaps as a result of improper feedback into secondary visual areas. Patients with either bipolar disorder or schizophrenia may compensate for abnormal perception by idiosyncratically recruiting regions across multiple non-visual networks.