They found that people with insomnia—defined as trouble sleeping for over a month that’s associated with daytime sleepiness and sleep disturbances—had significantly less white matter connectivity, especially between areas that control sleep and wakefulness, than those without insomnia. Li speculates that this disruption in signals between these regions was triggered by thinning of the myelin surrounding the neurons, which resulted in less chatter among them.

In fact, 83%, or five of the six major nerve tracts that the scientists analyzed, were reduced among people with insomnia. Most were concentrated in the right part of the brain, where emotions and many thinking functions are regulated, as well as where sensory information like sight, smell and touch are processed.