Researchers theorize that HIV infection itself and/or the treatments used to fight it might explain their finding that HIV patients had brain function similar to those of persons 15-20 years older.

Dr. Beau Ances, of Washington University School of Medicine in St. Louis, and colleagues used functional magnetic resonance imaging (fMRI) and "arterial spin labeling" to examine 26 HIV-positive patients and 25-negative patients, with both groups comparable in mean age and education.

HIV serostatus and age independently affected fMRI measures, though they did not interact, the authors wrote. The brains of those HIV-infected needed to work harder to complete particular assignments. Reduced brain blood flow was observed even among young, recently infected patients.

"Brain blood flow levels decline naturally as we age, but HIV, the medications we use to control it or some combination of the two appear to be accelerating this process independently of aging," Ances said.

In the future, fMRI might be used as a noninvasive biomarker for HIV infection in the brain, the team suggested.

The full report, "HIV Infection and Aging Independently Affect Brain Function as Measured by Functional Magnetic Resonance Imaging," was published in the Journal of Infectious Diseases (2010;201:336-340).