Insomnia is linked with abnormalities in the brain's white matter -- the tissues that form connections and carry information between different parts of the brain, a small Chinese study suggests.
The researchers said these disruptions occur in areas of the brain involved in the regulation of sleep and wakefulness as well as cognitive function.
The researchers explained that white matter tracts are bundles made up of long fibers of nerve cells that connect one part of the brain to another. "If white matter tracts are impaired, communication between brain regions is disrupted," said researcher Shumei Li. She's from the department of Medical Imaging at Guangdong No. 2 Provincial People's Hospital, Guangzhou, China.
Although the study found an association between white tract matter abnormalities and insomnia, it wasn't designed to prove cause-and-effect.
People with primary insomnia have ongoing trouble falling asleep or staying asleep. This nightly tossing and turning isn't related to another medical condition or known cause, according to the researchers.
It can lead to daytime sleepiness and cognitive impairment. Some people with primary insomnia also suffer from depression and anxiety disorders, the researchers said.
Up to 5 percent of adults have this sleep disorder, but it's unclear exactly why they can't sleep and how the condition affects their brain, the researchers noted.
"Insomnia is a remarkably prevalent disorder," said Li. "However, its causes and consequences remain elusive."
For the study, the researchers recruited 23 patients with primary insomnia and 30 healthy volunteers. All of the participants completed surveys that enabled study authors to evaluate their mental status and sleep patterns.
Using an advanced MRI technique called diffusion tensor imaging (DTI), the researchers also looked at the pattern of water movement in white matter to identify any irregularities.
They found that participants with insomnia had significantly reduced white matter "integrity" in several regions of the brain. One area was the thalamus, which regulates consciousness, sleep and alertness. Another was the corpus callosum, the area that bridges the two halves of the brain, the study authors said.
"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," said Li.
Previous studies have shown that sleep deprivation can affect a variety of brain functions, Li pointed out.
She noted her team's findings suggest that long-term insomnia could accompany other mental health issues, such as depression and anxiety.
"Our results can potentially provide the evidence about how the lack of sleep may lead to the impairment of white matter related to emotional or cognitive disorders," Li said.
Those who had more severe cases of insomnia or suffered from the disorder for longer periods of time had greater white matter abnormalities. The researchers suggested this could be due to the loss of myelin -- the protective coating around the nerve fibers in white matter.
The study findings were published online on April 5 in the journalRadiology.
The brain is constantly creating new connections while unused synapses degenerate, according to Dr. Douglas Moul, a senior sleep psychiatrist at the Cleveland Clinic.
"The brain sets up new connections, reformats, and breaks down connections on a daily basis -- breaking down and tearing up connections are daily brain processes," he said.
It's still unclear, however, if treating insomnia would restore lost connections, Li said. "This is a very interesting and open question," she said. "We are also very interested in knowing whether this damage is irreversible or not if the insomnia gets cleared up. But our current study is still not enough to answer this question."
The Cleveland Clinic's Moul said this study falls short of helping scientists gain a better understanding of why sleep is so important. "Sleep is a time for brain maintenance and repair," he said. "Studies have demonstrated that brain maintenance and repair time is more prominent during sleep."
However, he pointed out that the study doesn't provide clues about why people need sleep.