Principal investigator Richard Salvi, director of the University of Buffalo Center for Hearing and Deafness, says tinnitus is caused by continued exposure to loud noise, normal aging and, to a much lesser extent, as a side effect of taking some anti-cancer drugs. Thirty percent of Iraq and Afghanistan combat veterans suffer from the condition, Salvi said.

"For many years it was thought that the buzzing or ringing sounds heard by people with tinnitus originated in the ear," Salvi said in a statement.

By using positron emission tomography -- or PET scans -- to view the brain activity of people with tinnitus, the researchers showed the phantom auditory sensations originated somewhere in the brain, not in the ear.

Salvi and colleagues discovered when the brain's auditory cortex begins receiving diminished neural signals from the cochlea in the ear, due to injury or age, the auditory cortex "turns up the volume," increasing weak neural signals from the cochlea. This increased volume of these weak signals may be the buzzing, ringing, or hissing characteristic of tinnitus, the researchers say.