In this study, the researchers used an imaging technique called diffusion-weighted magnetic resonance imaging, which uses the tiny movements of water molecules to create detailed images that show the structures of tissues. They compared the images of the brains of 23 people who had chronic insomnia based on a self-assessment to those from 30 patients who did not. They found that patients with insomnia had less white matter along certain pathways in the right hemisphere, which have been linked to regulating sleep and wakefulness. Pathways to and from the thalamus seemed particularly affected, which was not surprising, since the thalamus is critical to relay signals of sleep. But they also saw less white matter along tracts associated with cognitive, emotional, and sensorimotor function.