Differential brain structural correlates of insomnia in depression vs. anxiety

Abstract

Introduction Insomnia is common in many psychiatric disorders (1), especially so in affective disorders like major depressive disorder (MDD) (2) and anxiety disorder (2,3). Insomnia is moreover a cardinal risk factor for the development of MDD (4). Nevertheless, the neural correlates of insomnia complaints in psychiatric patients have hardly been investigated, hampering the development of rational treatment and prevention of these disabling symptoms. materials and methods Fifty-nine patients with MDD as well as 61 patients with anxiety disorder filled out the Women’s Health Initiative Insomnia Rating Scale (WHIIRS) (5) and underwent structural magnetic resonance imaging of the brain. The WHIIRS is a brief, five-item scale evaluating insomnia symptoms, which yields a summary score that reflects complaints on sleep quality. Whole-brain voxel-based morphometry was used to investigate the association of the WHIIRS summary score with gray matter density. Results In patients with MDD, the WHIIRS insomnia severity score showed a strong negative correlation with gray matter density in the pulvinar of the thalamus. Gray matter in this area showed no association at all with insomnia severity in patients with anxiety disorder. In contrast, anxiety disorder patients more severe insomnia showed lower frontopolar GM density, an association not found in MDD patients. Conclusion This is the first study to directly compare structural brain correlates of insomnia severity between MDD and anxiety disorder. Unlike previous voxel-based morphometry findings that indicated particularly orbitofrontal involvement in sleep complaints in both well-sleeping (6) and poorly-sleeping (7) people without psychiatric disorder, we here found differential involvement of the pulvinar and frontopolar cortex. These triple dissociations have strong implications for our understanding of insomnia; depending on the psychiatric phenotype, remarkably different cerebral mechanisms can underlie seemingly similar subjective sleep complaints.