Researchers in China have used diffusion MRI to show that the right brain’s white matter tracts are abnormal in patients with primary insomnia.

Led by Shumei Li, MS, of Guangdong No. 2 Provincial People’s Hospital in Guangzhou, China, the study’s authors describe their work comparing the relevant white matter tracts in 23 primary insomnia patients and 30 healthy control participants.

Radiology posted the study online April 5.

The authors define primary insomnia as sleep difficulties that persist for a month or more.

Using diffusion tensor imaging, which draws from the motion of water molecules to generate contrast in MR images, the team found that the primary insomnia patients had significantly lower values for fractional anisotropy (FA).

FA considers the degree to which diffusion tends to occur in one direction versus scattering in many.

In the study, the primary insomnia patients had lower FA values mainly in the right anterior limb of the internal capsule, right posterior limb of the internal capsule, right anterior corona radiata, right superior corona radiata, right superior longitudinal fasciculus, body of the corpus callosum and right thalamus.

In addition, the authors report, multiple regression models showed that abnormal FA values in the thalamus and body corpus callosum, the brain’s largest white-matter region, correlated with the duration of the patients’ insomnia as well as their self-reported scores for depression and their Pittsburgh Sleep Quality Index scores.

“Although the significance of these findings for pathophysiologic models of primary insomnia remains unclear,” the authors conclude, “our study suggests that primary insomnia is characterized by altered structural connectivity related to regulation of sleep and wakefulness, particularly involving limbic cognitive function and sensorimotor regions.”

In a news release from Radiology publisher RSNA, Li emphasizes that the involvement of the thalamus in the pathology of insomnia is “particularly critical, since the thalamus houses important constituents of the body’s biological clock.”

The authors acknowledge the small sample as a limitation and call for a larger study to validate the connection between compromised white matter integrity and sleeplessness.

One question that seems ripe for further inquiry is whether insomnia causes white matter impairment or vice versa.