Such an impact could possibly help if you suffer from migraines or other neurological disorders, the authors of a study published in the August issue of Annals of Neurology suggest.

And it could hurt if you have epilepsy or a brain disease.

Either way, the researchers and other experts caution, much more research needs to be done before any definitive conclusions can be drawn.

The researchers from Fatebenefratelli Hospital in Isola Tiberina, found that the electromagnetic field (EMF) emitted by cell phones can cause some cells in the brain's cortex adjacent to the side of phone use to become excited, while others become inhibited.

They suggest that this could have beneficial effects for people with migraines, stroke or dementia, and possibly detrimental effects for those with epilepsy, the study authors suggested.

"It should be argued that long-lasting and repeated exposure to EMFs linked with intense use of cellular phones in daily life might be harmful or beneficial in brain-diseased subjects. Further studies are needed to better circumstantiate these conditions and to provide safe rules for the use of this increasingly more widespread device," the authors wrote.

E. Roy John, director of New York University Medical Center's Brain Research Laboratories, said, "Using a cell phone is not innocuous. It has an effect on your brain. Whether that's good or bad, we don't yet know, but it's definitely having an effect."

While most cell phone research has focused on whether or not cell phones increase the rate of cancer or benign tumors in the brain, the researchers from Fatebenefratelli Hospital in Isola Tiberina, Italy, turned their attention to what other effects a cell phone might have on the brain.

Fifteen male volunteers, between 20 and 36 years old, were tested using transcranial magnetic stimulation. Each volunteer participated in two sessions. In one session, a signal equivalent to the electromagnetic field emitted from a commonly used type of cell phone was turned on for 45 minutes. In the second test, a sham device was turned on.

Neither the participants nor those administering the test knew whether or not the EMF was on. The tests were administered a week apart. The researchers also tested ear temperatures to see if the EMF raised the temperature.

The researchers found no significant differences in temperature between the EMF group and the sham group.

There was, however, a statistically significant increase in cortical excitability after EMF exposure. And, that excitability lasted around an hour after exposure. Other cells experienced changes in inhibition, but that effect wasn't as strong or as long lasting, the researchers said.

Said John: "This was a very well done study. The effects are clear. The increase in excitability is clear and lasts for about an hour. Is that effect harmful or beneficial? I don't know."

Dr. Jonathan Fellows, a neurologist at Beaumont Hospital in Royal Oak, Mich., said, "This was an interesting study, but the end result is, we don't know what EMFs will do in terms of helping or hurting cortical neurons.

"There's a potential for benefit in terms of hyperexcitability for migraine, stroke or dementia," Fellows said. "Although cell phones have gotten bad press, there could potentially be some good that comes out of cell phone use," he added.

But, Fellows said, for now, all that's known for sure is that the EMF emitted by a cell phone can cause increased excitability in certain brain cells.

Fellows, John and the authors of the study all said more research needs to be done to understand what these changes in brain cell activity actually mean.

Both Fellows and John expressed concern about increasing cell phone use in youngsters. Whatever impact a cell phone might have on the brain will be magnified in children, because their brains are still growing and developing.

"Personally, if I had kids, I would discourage cell phone use," said John.

Both researchers said that a quick phone call to let Mom or Dad know it's time to pick them up probably doesn't pose a problem. It's when kids use the phones to talk for long periods of time -- 15 minutes or longer -- that concerns them more.