There are differences in the sounds of two voices or two musical instruments even if they hit the same note, and somehow the brain knows that. A new study shows that the auditory cortex, an area of the brain that interprets sound, is important for frequency processing and pitch perception. The research findings, published in the January 2001 issue of the Journal of Neurophysiology, provides insight into how a physical feature such as sound can be transformed into a mental phenomenon. The study’s lead is author Mark Jude Tramo, a neurologist at Massachusetts General Hospital, an assistant professor at Harvard Medical School, and a musician. In this study, Tramo and his colleagues looked at how people perceive these differences in pitch. “Something in the auditory cortex allows us to decipher all of this so easily,” says Tramo, who also is on staff at Massachusetts Eye and Ear Infirmary.