Abstract

Background: Several lines of evidence have shown that auditory networks are dysfunctional in schizophrenia and bipolar disorders. Auditory cortices show abnormalities in hallucinations or during remission. It was aimed to assess resting state connectivity of auditory cortices in schizophrenia and bipolar disorder in this study.
Method: Patients with bipolar I disorder (BD-I, n=28), bipolar II disorder (BD-II, n=21), schizophrenia (n=30) and healthy controls (HCs, n=30) were enrolled in to the study. T1-weighted anatomical and gradient-echo based EPI sequences were acquired to assess volumetric and functional analyses. Auditory related cortices localized with our volumetric analysis, and then those regions used as a seed in our functional data to guide us within network and global connectivity alterations. Since our seed regions are chosen in high resolution T1 image, we also investigated voxel-based morphometrical changes.
Results: Left angular gyrus appeared to be most significant brain area which has a decreased volume in schizophrenia and BD-II. Our with-in auditory network connectivity analysis showed that supramarginal gyrus and primary auditory areas have significant connectivity changes. Global connectivity alterations of those regions resulted as follows; supramarginal gyrus had hyperconnectivity with medial prefrontal cortices and decreased connectivity with medial superior temporal gyrus (STG) in BD-I and BD-II groups. The left superior temporal sulcus (STS) had increased connectivity with bilateral posterior cingulate cortex in BD-I and BD-II, increased connectivity with dorsal prefrontal cortices in the schizophrenia group. The STS had increased connectivity with medial STG in the BD-I and schizophrenia groups, whereas decreased connectivity in the BD-II group.
Conclusion: These findings may indicate auditory network dysfunction which may predispose to deficient auditory information processing and association in bipolar disorder and schizophrenia. We discussed possible pathways of auditory alterations and we conclude that further task based studies in larger cohorts are needed in order to determine the relationship between symptoms and auditory network dysfunction.

Key words: Schizophrenia, bipolar disorder, auditory cortex, functional connectivity, seed based analysis