A new study has found that prolonged use of a cell phone increases brain activity but failed to determine whether such use can lead to health problems.

The study, published today in the Journal of the American Medical Association, recruited 47 people in good health to document the effects of cell phone use on the brain. Conducted in 2009 by researchers at the National Institutes of Health in Maryland, the study was created to see whether the electromagnetic fields emitted by cell phones affect the brain's glucose metabolism, considered a marker for brain activity.

Cell phones were placed next to the left and right ears of the volunteers. Scans of the brain were taken with only the right cell phone turned on and with the sound muted for 50 minutes. Brain scans were taken again with both phones turned off.

The results showed that glucose metabolism increased in the area of the brain near the antenna of the phone that was turned on, but not near the one that was turned off. However, the researchers determined that the results were of "unknown clinical significance," meaning they couldn't tell whether the increased brain activity actually entails any health risks.

Concerns have been raised for years over the potential effects of long-term cell phone use on the brain. Despite an array of studies, results have so far proved inconclusive.