January 11, 2002

There is no "music center" in the brain, but distinct regions are involved in different aspects of music perception. Now there is evidence that the auditory cortex, an area of the brain that interprets sound, plays an important role in frequency processing and pitch perception. A new study, published in the January issue of the Journal of Neurophysiology, provides insight into how a physical feature such as sound can be transformed into a mental phenomenon.

Past research has demonstrated that a particular neuron in the brain will respond to only a few distinct notes or tones. The process of the neurons coordinating together has been something of a mystery. "Now we know that there's no question that you need the neurons in the auditory cortex for fine-tuned pitch discrimination,"says Mark Jude Tramo, MD, PhD, of MGH Neurology and the study's lead author.

There are differences between the sounds of two voices or two musical instruments, even when they hit the same note, and somehow the brain makes this distinction. In their study, Tramo and his colleagues looked at how people perceive such differences in pitch. They studied five patients with neurological abnormalities, ranging from stroke to head trauma, and compared the patients' brain activity and pitch perception to that of normal volunteers. Through their battery of tests, the researchers found that particular subdivisions of the auditory cortex make essential contributions to identifying fine distinctions in pitch.

While the current study examined pure tones — each of which corresponds to one note — Tramo now is studying how the auditory cortex deals with complex tones, such as those involved in speech and musical compositions. "We'd like to figure out how the brain computes the complex information it receives when a musician plays an elaborate song,"he says. "Subtle manipulations go a long way in forming the nuances perceived by the listener." Tramo's co-authors include Gaurav Shah, MD, also of MGH Neurology.