Consistent altered internal capsule white matter microstructure in insomnia disorder.

Area of Science:

• Neuroimaging
• Sleep Medicine
• White Matter Integrity

Background:

• Replicable neural correlates for insomnia disorder remain elusive.
• Altered white matter microstructure in the anterior internal capsule is a potential, yet understudied, target.
• Investigating white matter fractional anisotropy (FA) offers a path to understanding insomnia mechanisms.

Purpose of the Study:

• To examine white matter fractional anisotropy (FA) in the internal capsule across three independent samples of individuals with and without insomnia disorder.
• To identify replicable neural targets associated with insomnia.
• To explore the relationship between insomnia severity and internal capsule FA.

Main Methods:

• Combined diffusion tensor imaging data from three independent samples (n=137; 73 with insomnia disorder, 64 controls).
• Assessed white matter microstructure using fractional anisotropy (FA) via tract-based spatial statistics.
• Conducted region-of-interest analysis on the internal capsule and correlated FA with Insomnia Severity Index (ISI) scores.

Main Results:

• Lower FA was observed in the right anterior internal capsule of individuals with insomnia disorder compared to controls.
• A significant negative association was found between higher insomnia severity (ISI score) and lower FA in the right internal capsule.
• Whole-brain analyses did not reveal significant group differences or associations after multiple comparison correction.

Conclusions:

• The anterior internal capsule shows consistent, albeit small, alterations related to insomnia disorder.
• These findings support a circuit-based understanding of insomnia, as the internal capsule connects brain regions implicated in the disorder.
• The internal capsule represents a promising target for future research into the neural underpinnings of insomnia.