The debate over whether cellphones affect the brain rumbles on. The latest study shows a measurable effect on brain activity - but one which may or may not be harmful, say the team.
US researchers say they've discovered that 50 minutes of cellphone use was associated with increased brain glucose metabolism - a marker of brain activity - in the region closest to the phone antenna.
Previous studies have been inconclusive. The latest major study, late last year, pulled together the best data from previous research to conclude that cellphones really do increase the risk of brain tumors. However, many other studies have found no effect at all.
Nora Volkow, of the National Institutes of Health, tested 47 participants with cellphones on their left and right ears. Their brains were imaged with positron emission tomography (PET), and a fluorodeoxyglucose injection was used to measure brain glucose metabolism.
Volkow's team found that while whole-brain metabolism didn't change when the phone was turned on, there were significant regional effects. Metabolism in the brain region closest to the antenna - the orbitofrontal cortex and temporal pole - was around seven percent higher when the phone was turned on.
"The increases were significantly correlated with the estimated electromagnetic field amplitudes both for absolute metabolism and normalized metabolism," the authors write. "This indicates that the regions expected to have the greater absorption of RF-EMFs from the cell phone exposure were the ones that showed the larger increases in glucose metabolism."
It's evidence, they say, that the brain is sensitive to the effects of RF-EMFs from acute cell phone exposures - although they add that they still don't know how cellphone radiation could affect brain glucose metabolism.
"Although the biological significance, if any, of increased glucose metabolism from acute cell phone exposure is unknown, the results warrant further investigation," say Henry Lai, of the University of Washington, and Lennart Hardell of University Hospital, Orebro, Sweden.
"An important question is whether glucose metabolism in the brain would be chronically increased from regular use of a wireless phone with higher radiofrequency energy than those used in the current study. Potential acute and chronic health effects need to be clarified. Much has to be done to further investigate and understand these effects."