Disrupted white matter integrity in primary insomnia and major depressive disorder: relationships to sleep quality and depression severity.

This study examined the integrity of white matter tracts in 25 participants with primary insomnia (PI), 50 participants with major depressive disorder (MDD), and 25 healthy controls. Seven white matter tracts, selected based on prior research, were quantified by fractional anisotropy (FA) as well as by related measures of diffusivity using diffusion tensor imaging (DTI) on a 3-T scanner. All 100 participants were free of significant medical, psychiatric (excluding the MDD group) and sleep disorders (excluding the PI group), were free of central nervous system medications, and completed an extensive clinical assessment. Subjective and objective sleep measures revealed significant sleep disruption in both the PI and MDD groups. Relative to the controls, both the PI and MDD groups demonstrated impaired integrity in three of the seven white matter tracts: the genu of the corpus callosum (GenuCC), the superior longitudinal fasciculus (SLF), and the inferior longitudinal fasciculus (ILF). We demonstrated reduced FA in the GenuCC, reduced FA and reduced axial diffusivity (AD) in the SLF, as well as reduced AD and radial diffusivity in the ILF. Finally, in an exploratory analysis of the combined cohorts, FA in the GenuCC and FA in the SLF were negatively correlated with depression severity and positively correlated with total sleep time. Abnormalities documented in the GenuCC, SLF and ILF, and present in both the PI and MDD groups may suggest some shared neurobiology.