Neurobiological Commonalities and Distinctions Among Three Major Psychiatric Diagnostic Categories: A Structural MRI Study

Abstract

Background: Schizophrenia (SZ), bipolar disorder (BD), and major depressive disorder (MDD) are distinct diagnostic categories in current psychiatric nosology, yet there is increasing evidence for shared clinical and biological features in these disorders. No previous studies have examined brain structural features concurrently in these 3 disorders. The aim of this study was to identify the extent of shared and distinct brain alterations in SZ, BD, and MDD. We examined gray matter (GM) volume and white matter (WM) integrity in a total of 485 individuals (135 with SZ, 86 with BD, 108 with MDD, and 156 healthy controls [HC]) who underwent high-resolution structural magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) at a single site.

Results: Significant 4-group (SZ, BD, MDD, and HC groups) differences (P < .05, corrected) in GM volumes were found primarily in the paralimbic and heteromodal corticies. Post hoc analyses showed that the SZ, BD, and MDD groups shared GM volume decreases in 87.9% of the total regional volume with significant 4-group differences. Significant 4-group differences in WM integrity (P < .05 corrected) were found in callosal, limbic-paralimbic-hetermodal, cortico-cortical, thalamocortical and cerebellar WM. Post hoc analyses revealed that the SZ and BD groups shared WM alterations in all regions, while WM alterations were not observed with MDD.

Conclusions: Our findings of common alterations in SZ, BD, and MDD support the presence of core neurobiological disruptions in these disorders and suggest that neural structural distinctions between these disorders may be less prominent than initially postulated, particularly between SZ and BD.

Keywords: bipolar disorder; gray matter volume; major depressive disorder; schizophrenia; white matter integrity.

Fig. 1.

(A) Significant differences in gray matter volumes among schizophrenia, bipolar disorder, major depressive disorder and healthy controls. Significant at P < .05 corrected by AlphaSim correction. (B) Gray matter volumes in regions showing significant differences among the participants with schizophrenia, bipolar disorder major depression disorder and healthy controls. (C) Shared alterations in gray matter volume in schizophrenia, bipolar disorder and major depression disorder compared with healthy controls. Significant at P < .05 corrected by AlphaSim correction. *Permutation t test for each disorder vs healthy controls (P < .05 corrected, Benjamin Hochberg correction). R, right; L, left; Bil, bilateral; OFC, orbital frontal cortex; ACG, anterior cingulate gyrus; PCG, posterior cingulate gyrus; TPO, temporal pole; PHG, parahippocampus gyrus; INS, insula; IOG, inferior occipital gyrus; DLPFC, dorsal lateral prefrontal cortex; CUN, cuneus; ANG, angular gyrus; IPL, inferior parietal lobe; SMA, supplementary motor area; PreCG, precentral gyrus.

Fig. 2.

(A) Significant differences in fractional anisotropy values among schizophrenia, bipolar disorder, major depressive disorder and healthy controls. Significant at P < .05 corrected by AlphaSim correction. (B) Fractional anisotropy values in white matter fibers showing significant differences among the participants with schizophrenia, bipolar disorder major depression disorder and healthy controls. *Permutation t test for each disorder vs healthy controls (P < .05 corrected; Benjamin Hochberg correction). CC, corpus callosum; PTCR, posterior thalamic radiations; EC-R, right external capsule; SLF-L, left superior longitudinal fasciculus.