"We addressed a very fundamental question," says Daniel B. Polley, PhD, lead author of the study. "When we notice a sound getting louder, what happens in our brain so that we know it's getting louder?"
Polley is a postdoctoral research fellow in the laboratory of senior author Michael M. Merzenich, PhD, co-director of the Coleman Memorial Laboratory in the UCSF Keck Center for Integrative Neuroscience and UCSF professor of otolaryngology.
The study was published recently in Proceedings of the National Academy of Sciences (November 16, 2004).
"This is a very old idea," Polley notes. "How to relate the bigness of a stimulus to the bigness of its internal representation in the brain." Over the centuries, philosophers and scientists have put together a picture of how our brains model the world through the mechanism of our senses. Physical stimuli such as light, sound, and touch are converted by our sensory organs -- eyes, ears, and skin -- into electrical signals, which are processed by neurons in different areas of the brain. As those neurons fire, we see, hear, and feel. When the light or sound changes in intensity, our neurons fire faster or slower in direct ratio to the change. That ratio varies depending on the sense involved, but is constant for each sense: the louder a sound, the faster the neurons in the auditory cortex fire.
But now that picture has changed. Polley trained two groups of rats to become " experts" at discriminating between very small differences in loudness -- an ability that untrained rats do not have. He then looked at how the expert rats processed ch
Contact: Jennifer O'Brien
University of California - San Francisco