St. Louis, May 29, 2001 Scientists have discovered that, unlike many other animals, humans have a reserve of oxygen in the brain. This buffer allows the brain to adapt to arduous situations without demanding a sharp increase in blood flow.

Our finding challenges the previously accepted idea that blood flow increases occur during tasks such as reading to raise oxygen levels in the brain, says study leader Mark A. Mintun, M.D. That idea has been long assumed in brain imaging studies that attempt to understand how the human brain functions.

Mintun is a professor of radiology and professor of psychiatry at Washington University School of Medicine in St. Louis. His groups findings appear in the June 5 issue of Proceedings of the National Academy of Sciences and will appear on the journals website May 29.

Imaging has become a critical tool for exploring the brain at work. By measuring changes in blood flow during different tasks, researchers can see which areas of the brain spring into action when, for example, individuals read or memorize words. Because blood supplies cells with oxygen, they assumed that blood flow increases when a particular area of the brain needs more oxygen. The new evidence suggests otherwise.

I think were still very safe interpreting increased blood flow as a change in brain activity, says Mintun. But why flow increases now is unclear. Understanding that will probably change our view of the human brain and alter the way we design studies.

An extensive network of small blood vessels called capillaries feeds the brain. Because every cell is critical to the organs function, oxygen must diffuse from the capillaries to every nook. Current models suggest that, even if the brain needs only a small amount of extra oxygen, it takes a large increase in blood flow to deliver enough to every cell.

Using positron emission tomography (PET), Mintun and colleagues examined blood flow to the brains of nine healthy volunteers.
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Contact: Gila Z. Reckess
reckessg@msnotes.wustl.edu
314-286-0109
Washington University School of Medicine
28-May-2001