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Common Sleep Problem Linked With Memory Loss

By Tara Parker
June 22, 2008

Brain scans reveal that the mammillary bodies, shown in box and circled, of a sleep apnea patient (right) are smaller than those of a healthy control subject (left).(U.C.L.A./Harper Lab)

The part of the brain that stores memory appears to shrink in people with sleep apnea, adding further evidence that the sleep and breathing disorder is a serious health threat.
The findings, from brain scan studies conducted by researchers at the University of California, Los Angeles, show for the first time that sleep apnea is associated with tissue loss in brain regions that store memory. And while the thinking and focus problems of sleep apnea patients often are attributed to sleep deprivation, the scans show something far more insidious is occurring.

“Our findings demonstrate that impaired breathing during sleep can lead to a serious brain injury that disrupts memory and thinking,” said principal investigator Ronald Harper, professor of neurobiology at the David Geffen School of Medicine at U.C.L.A. The data appear in the June 27 issue of the journal Neuroscience Letters.
Sleep apnea occurs when the muscles in the throat, soft palate and tongue relax during sleep. They sag and narrow the airway and the tongue slides to the back of the mouth, blocking the windpipe and cutting off oxygen to the lungs. The sleeper gasps for air, wakes up briefly and falls back to sleep in a cycle that repeats itself hundreds of times per night. The result is loud snoring and chronic daytime fatigue. The disorder also is linked to a higher risk of stroke, heart disease and diabetes. An estimated 20 million Americans have sleep apnea.

The study focused on structures on the underside of the brain called mammillary bodies, so named because they resemble small breasts. The researchers used magnetic resonance imaging to scan the brains of 43 sleep apnea patients. Compared to images of 66 control subjects, the brains of the sleep apnea patients had mammillary bodies that were nearly 20 percent smaller, particularly on the left side.
The structures also are known to shrink in patients who have other forms of memory loss related to alcoholism or Alzheimer’s disease.

The researchers don’t know why the sleep disorder affects brain tissue but theorize that it’s related to repeated drops in oxygen. During an apnea episode, the brain’s blood vessels constrict, starving its tissue of oxygen and causing cells to die. The inflammatory process, also linked with heart disease and stroke, further damages the tissue.

“The reduced size of the mammillary bodies suggests that they’ve suffered a harmful event resulting in sizable cell loss,” Dr. Harper said. “The fact that patients’ memory problems continue despite treatment for their sleep disorder implies a long-lasting brain injury.”

The data show the importance of early diagnosis and treatment of sleep apnea. Unfortunately, the most effective treatment is a continuous positive airway pressure, or CPAP, machine that many patients find unwieldy and uncomfortable. In a future study, the U.C.L.A. researchers will explore whether vitamin B1 supplements might help restore memory in sleep apnea patients by moving glucose into cells and preventing cell death.

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