Vidushi Sinha of voanews.com writes:

A new study finds that an hour-long cell phone call causes a spike in biochemical activity in the user's brain. The researchers can't say whether that's a good thing or a bad thing, but the finding has renewed the debate over cell phone safety and raised calls for more health studies.

Cell phones are everywhere. Decades of research into whether cell phone radiation might cause brain tumors or impotence have been inconclusive. The wireless companies insist the phones are safe. The new study from the National Institutes of Health doesn't settle the debate, but offers some new food for thought.

In the study, 47 healthy people were tested over a one-year period. Participants had cell phones placed on their left and right ears. One cell phone was activated but muted for 50 minutes, the other was off. After that, the subjects were tested with both cell phones turned off.

With the phones at their ears, the subjects' brains were scanned using a sophisticated imaging technique. Dr Nora Volkow, who conducted the study along with colleagues at the National Institute on Drug Abuse, says the brain scans showed heightened metabolic activity in brain cells closest to the activated devices.

"This right area of the brain that was very close to the antenna shows the largest increase in metabolism as compared when the telephones were off," says Volkow. "Even though the radio frequencies that are emitted from current cell phone technologies are very weak, they are able to activate the human brain to have an effect.''

The effect was a seven percent increase in the rate at which brain cells closest to an active cell phone antenna metabolized sugar into energy - an essential and normal activity. Dr Giuseppe Esposito, an expert on nuclear medicine, says the study demonstrates clearly that mobile phone signals can excite brain cells. But it doesn't answer that nagging question.

"The study does not bring any evidence to the fact that cell phones cause damage to the brain," says Esposito. "It just tells us that cell phones cause stimulation to the brain."

Many studies have explored potential links between cell phone use and brain cancer. Skeptics wonder if such harmful effects might only turn up after five, 10 or even 15 years.

Esposito believes the best scientific studies have yet to be done. "We need what are called epidemiological studies where you will follow a population using cell phones - high users or light users - and then see what happens over the years."

Experts hope the NIH study renews interest in the question of cellphone safety.

"This is a study that is interesting and will almost certainly provoke additional studies," says Dr Andrew Sloan of the Case Medical Center.

While we're waiting for those additional studies, experts say we can reduce potential health risks by using hands-free devices to operate our cell phones, not carrying them close to our bodies, and limiting the length of our calls.