Mon Jun 26, 11:25 AM ET WASHINGTON (Reuters) - Cell phone emissions excite the part of the brain cortex nearest to the phone, but it is not clear if these effects are harmful, Italian researchers reported on Monday. ADVERTISEMENT Their study, published in the Annals of Neurology, adds to a growing body of research about mobile phones, their possible effects on the brain, and whether there is any link to cancer. About 730 million cell phones are expected to be sold this year, according to industry estimates, and nearly 2 billion people around the world already use them. Of these, more than 500 million use a type that emits electromagnetic fields known as Global System for Mobile communications or GSM radio phones. Their possible effects on the brain are controversial and not well understood. Dr. Paolo Rossini of Fatebenefratelli hospital in Milan and colleagues used Transcranial Magnetic Stimulation or TMS to check brain function while people used these phones. They had 15 young male volunteers use a GSM 900 cell phone for 45 minutes. In 12 of the 15, the cells in the motor cortex adjacent to the cell phone showed excitability during phone use but returned to normal within an hour. The cortex is the outside layer of the brain and the motor cortex is known as the "excitable area" because magnetic stimulation has been shown to cause a muscle twitch. The researchers stressed that they had not shown that using a cell phone is bad for the brain in any way, but people with conditions such as epilepsy, linked with brain cell excitability, could potentially be affected. "It should be argued that long-lasting and repeated exposure to EMFs (electromagnetic frequencies) linked with intense use of cellular phones in daily life might be harmful or beneficial in brain-diseased subjects," they wrote. "Further studies are needed to better circumstantiate these conditions and to provide safe rules for the use of this increasingly more widespread device." Medical studies on cell phone use have provided mixed results. Swedish researchers found last year that using cell phones over time can raise the risk of brain tumors. But a study by Japan's four mobile telephone operators found no evidence that radio waves from the phones harmed cells or DNA. The Dutch Health Council analyzed several studies and found no evidence that radiation from mobile phones was harmful.