A brain scan of someone older than 40 or so will likely show several small, white areas that indicate islands of abnormal brain tissue. Until now, these spots have been considered harmless signs of aging, something that doctors referred to jokingly as "unidentified bright objects" or UBOs. But UBOs may not be so funny after all. Researchers at the Mayo Clinic in Rochester, Minn., now believe that UBOs represent tiny areas where the brain's wiring has been damaged by lack of oxygen. In other words, this condition, known as leukoaraiosis (pronounced lū kō-ahr-ī-ō′sis), represents a disease rather than the brain equivalent of liver spots on the skin or gray hair.
In a study published in the journal Radiology, the researchers performed functional MRI scans on the brains of elderly participants enrolled in the Mayo Clinic Study of Aging. In 18 participants, the amount of leukoaraiosis added up to a moderate 25 milliliters. In 18 others the same age the volume of the white spots added up to less than 5 milliliters.
While receiving an fMRI (a technique for measuring brain activity by detecting the changes in blood oxygenation and flow), the participants were asked to perform two tests. One involved identifying word pairs, and the other required them to differentiate straight from diagonal lines. Members of both groups performed equally well, but those with more UBOs showed less activation in the language and visual-spatial areas of the brain that were activated by the tests.
"They weren't experiencing symptoms from the leukoaraiosis because the brain has ways of compensating to maintain function," said Dr. Kirk M. Welker, an assistant professor of radiology in the Mayo Clinic's College of Medicine and the lead author of the study. "But in order to compensate, the brain has to recruit adjacent areas to pick up the slack, and the networks in the brain become less strong."
This forces the brain to work harder to achieve the same level of performance, which may increase the need for oxygen, and perhaps lead to chronic oxygen deprivation and the creation of more UBOs.
Attributing symptoms to leukoaraiosis remains difficult because the condition is so common. "The hardest part of our research was finding elderly people without leukoaraiosis," said Welker. "Most have at least a little. That's why we allowed people in the control group to have up to 5 cubic centimeters of leukoaraiosis. It would have been impossible to find enough people with zero."
Tests of brain function, however, show that people with higher levels of leukoaraiosis tend to do less well, and one large study of 600 people conducted over three years found that those with leukoaraiosis were three times more likely to develop cognitive decline, according to Welker.
Leukoaraiosis apparently doesn't increase the risk of Alzheimer's disease, but it appears to accelerate its progression. "People have found a synergistic effect," Welker said. "If you have leukoaraiosis and get Alzheimer's disease, it tends to be worse. People who do research into Alzheimer's disease are starting to view leukoaraiosis as a significant potentiator of the disease."
What can be done to prevent leukoaraiosis? The two chief causes appear to be age and high blood pressure, although people with diabetes appear more susceptible too. Therefore maintaining normal blood pressure and normal levels of blood glucose should be beneficial.
"Hopefully the medical community will become more aware of the importance of leukoaraiosis," said Welker. "By protecting our health as we grow older we can try to prevent its onset."
Tom Valeo writes frequently about health matters. He can be reached at [email protected]