Gross anatomical features of the insular cortex in affective disorders

Abstract

Introduction: The number of insular gyri is elevated in patients with schizophrenia. Thus, it has potential as a marker of early neurodevelopmental abnormalities. However, currently it remains unclear whether patients with other neuropsychiatric disorders, such as affective disorders, also have this gross brain anatomical feature.

Materials and methods: The macroscopic features of the insular cortex in 26 patients with bipolar disorder (BD), 56 with major depressive disorder (MDD), and control subjects for each clinical group (24 for BD and 33 for MDD) were assessed using magnetic resonance imaging.

Results: The number of short insular gyri was higher in BD patients than in matched controls bilaterally with well-developed accessory and middle short gyri. Furthermore, the left middle short gyrus was more developed in MDD patients than in matched controls, and was weakly associated with the severity of depressive symptoms.

Discussion: The present results indicate that changes in the gross morphology of the insular cortex in BD and MDD is a potential vulnerability factor associated with their neurodevelopmental pathologies, and may also contribute to the severity of symptoms in MDD.

Keywords: bipolar disorder; insular cortex; magnetic resonance imaging; major depressive disorder; neurodevelopment.

Figure 1

Sample sagittal MR images of different gross insular patterns. The developmental pattern of each gyrus was assessed predominantly using consecutive sagittal slices, with also coronal and axial views simultaneously being referred to. Dotted lines indicate the location of the central insular sulcus that subdivides the insula into the anterior (short) and posterior (long) cortices. The ASG, PSG, and ALG were well-developed in all participants in this study, while the PLS was sometimes deficient panel (A). The AG and MSG in the short insula had a large inter-individual variation, where the gyrus was absent panel (A), underdeveloped [marked with asterisks in panels (B, C)], or well-developed panel (D). AG, accessory gyrus; ALG, anterior long gyrus; ASG, anterior short gyrus; MSG, middle short gyrus, PLS, posterior long gyrus; PSG, posterior short gyrus.

Figure 2

Developmental patterns of the accessory gyrus (AG), middle short gyrus (MSG), and posterior long gyrus (PLG) in the bipolar disorder (BD) group (N = 26), major depressive disorder (MDD) group (N = 56), and marched control groups for each patient group (24 subjects for BD and 33 for MDD). Variations in gyral development were not observed for other insular gyri (i.e., anterior short, posterior short, and anterior long gyri).