New evidence in animals suggests that theories about how the brain processes sight, sound and touch may need updating. Researchers from Wake Forest University Baptist Medical Center and colleagues report their findings in the current issue of the Proceedings of the National Academy of Sciences.
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. “