Using electrodes smaller than a human hair, researchers from Wake Forest Baptist and the University of California at San Francisco recorded individual cell activity in the brains of 31 adult rats. Their goal was to test two conflicting ideas about brain organization.
"One theory is that individual senses have separate areas of the brain dedicated to them," said Mark Wallace, Ph.D., the study's lead investigator. "In this view, information is processed initially on a sense-by-sense basis and doesn't come together until much later. However, this view has recently been challenged by studies showing that processing in the visual area of the brain, for example, can be influenced by hearing and touch."
Wallace and colleagues created a map of the rat cerebral cortex, the part of the brain believed responsible for perception. The map was created to show how different areas respond to sight, sound and touch. They found that while large regions are overwhelming devoted to processing information from a single sense, in the borders between them, cells can share information from both senses.
"This represents a new view of how the brain is organized," said Wallace, an associate professor of neurobiology and anatomy at Wake Forest Baptist.
He said these multisensory cells might also help explain how individuals who suffer a loss of one sense early in their life often develop greater acuity in their remaining senses.
"Imaging studies in humans show that when sight is lost at a young age, a portion of the brain that had been dedicated to sight begins to process sound and touch. It is possible that this change begins in these multisensory border regions, where cells that are normally responsive to these different senses are already found."
Wallace said the finding is also important because it suggests that the process of integrating sensory information might happen faster in the cerebral cortex than was previously thought. Wallace said that the ultimate goal of this research is to understand how the integration of multiple senses results in our behaviors and perceptions.
"It should come as no surprise when I say that we live in a multisensory world, being constantly bombarded with information from many senses. What is a bit of a surprise is that although we now know a great deal about how the brain processes information from the individual senses to form our perceptions, we're still in the early stages of understanding how this happens between the different senses. "
Wallace's co-researchers were Barry Stein, Ph.D., professor and chairman of neurobiology and anatomy at Wake Forest Baptist, and Ramnarayan Ramachandran at the University of California.
The project was funded by the National Institutes of Health.
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Proceedings of the National Academy of Sciences