Background: Functional neuroimaging studies have implicated the insular cortex in emotional processing, including the evaluation of one's own emotion, as well as in the neurobiology of major depressive disorder (MDD). Nevertheless, it remains largely unknown whether MDD patients exhibit morphologic changes of the insular cortex, and whether such changes reflect state or trait markers of the disorder.
Methods: We delineated the anterior and posterior insular cortices using magnetic resonance imaging in 29 currently depressed patients (mean age=32.5 years, 7 males), 27 remitted depressed patients (mean age=35.1 years, 9 males), and 33 age- and gender-matched healthy control subjects (mean age=34.0 years, 12 males).
Results: Both current and remitted MDD patients showed significant volume reduction of the left anterior insular cortex as compared with healthy controls, but there was no group difference in the posterior insular cortex volume. Insular volumes did not correlate with the severity of depressive symptoms. Furthermore, the presence of melancholia and co-morbidity with anxiety disorders did not affect insular cortex volumes.
Limitations: Although there was no difference in the insular cortex volume between medicated and unmedicated patients, a comprehensive investigation of medication effects was not possible, as complete data (e.g., dose, duration) were not available.
Conclusions: These findings suggest that the morphologic abnormality of the anterior insular cortex, which plays a major role in introspection and emotional control, may be a trait-related marker of vulnerability to major depression, supporting the notion that MDD involves pathological alterations of limbic and related cortical structures.
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