Structural abnormality in schizophrenia versus bipolar disorder: A whole brain cortical thickness, surface area, volume and gyrification analyses

Abstract

Objectives: The profiles of cortical abnormalities in schizophrenia and bipolar disorder, and how far they resemble each other, have only been studied to a limited extent. The aim of this study was to identify and compare the changes in cortical morphology associated with these pathologies.

Methods: A total of 384 subjects, including 128 patients with schizophrenia, 128 patients with bipolar disorder and 127 sex-age-matched healthy subjects, were examined using cortical surface-based morphology. Four cortical structural measures were studied: cortical volume (CV), cortical thickness (CT), surface area (SA) and gyrification index (GI). Group comparisons for each separate cortical measure were conducted.

Results: At a threshold of P = 0.05 corrected, both patient groups showed significant widespread CV and CT reductions in similar areas compared to healthy subjects. However, the changes in schizophrenia were more pronounced. While CV decrease in bipolar disorder was exclusively explained by cortical thinning, in schizophrenia it was driven by changes in CT and partially by SA. Reduced GI was only found in schizophrenia. The direct comparison between both disorders showed significant reductions in all measures in patients with schizophrenia.

Conclusions: Cortical volume and cortical thickness deficits are shared between patients with schizophrenia and bipolar disorder, suggesting that both pathologies may be affected by similar environmental and neurodegenerative factors. However, the exclusive alteration in schizophrenia of metrics related to the geometry and curvature of the brain cortical surface (SA, GI) suggests that this group is influenced by additional neurodevelopmental and genetic factors.

Keywords: Bipolar disorder; Cortical thickness; Gyrification index; Neuroimaging; Schizophrenia; Surface area; Surface-based morphometry.

Fig. 1

Brain regions showing significant statistical differences between patients with schizophrenia and healthy subjects at p = 0.05, corrected for multiple comparisons across space. Panels depict cortical volume (a), cortical thickness (b), cortical surface area (c), and gyrification index (d), respectively. The right side of the image represents the left side of the brain. The statistical maps show uncorrected values (i.e., sig = −log10(p)) masked by the significant clusters. The statistical results were only significant in the direction of reduced values in patients.

Fig. 2

Brain regions showing significant statistical differences between patients with bipolar disorder and healthy subjects at p = 0.05, corrected for multiple comparisons across space. Left and right panels depict cortical volume (a) and cortical thickness (b), respectively. The right side of the image represents the left side of the brain. The statistical maps show uncorrected values (i.e., sig = −log10(p)) masked by the significant clusters. The statistical results were only significant in the direction of reduced values in patients.

Fig. 3

Brain regions showing significant statistical differences between patients with schizophrenia and patients with bipolar disorder at p = 0.05, corrected for multiple comparisons across space. Panels depict cortical volume (a), cortical thickness (b), cortical surface area (c), and gyrification index (d), respectively. The right side of the image represents the left side of the brain. The statistical maps show uncorrected values (i.e., sig = −log10(p)) masked by the significant clusters. The statistical results were only significant in the direction of reduced values in patients with schizophrenia.