CONTACT: Dr. Dean Falk(850) 644-7016; [email protected]
By Jill ElishMay 2002
CHANGES IN MUSICAL RIGHT BRAIN MAY HAVE HELPED EARLIEST HUMANS COMMUNICATE
TALLAHASSEE, Fla.-A new computer technology used to trace the evolution of the human brain has revealed surprising changes in the musical right hemisphere, which may have helped our earliest ancestors communicate.
Florida State University anthropology Professor Dean Falk and a team led by Karl Zilles, head of research groups at the Research Center Juelich and at the Vogt Institute for Brain Research in Dusseldorf, Germany, used magnetic resonance imaging (MRI) and a new software to study and compare the brains and skulls of living people, chimpanzees and ancient skulls. They found significant evolutionary changes in the right hemisphere of the brain.
Coverage of the team's findings, which Falk presented at the annual meeting of the American Association of Physical Anthropologists, was published this month in Science magazine.
"There is a surprising amount of change in the right hemisphere. No one expected it because everyone focuses on the left hemisphere where language development is," Falk said. The right hemisphere is the area that processes emotion, music and visual-spatial tasks and controls tone of voice.
"There is something going on in a precise area that I think has to do with prosody - the emotional color that we give our speech," she said.
Although initially a surprise, Falk theorizes that because early humans had limited language skills they may have relied more on tone of voice - something the emotional right hemisphere rules - rather than words to communicate.-
Falk and Zilles used MRI to make highly accurate virtual endocasts - three-dimensional computer images from the right and left sides of human braincases. Using software that Zilles' team developed to compare the two sides, they saw two well-known asymmetries that cause bulges on the frontal lobe behind the right eye and the left occipital lobe at the back of the brain. They also found some new asymmetries, including many areas of the right brain that were larger than the left, such as a semicircle of expansion from just behind the eye socket to the back of the brain.
To determine how these areas changed during human evolution, Falk and Zilles made virtual endocasts of the brains of 10 humans and seven bonobo chimpanzees. They then took the "average" cast of each species and used the software to warp and overlay the chimp endocast on that of the humans so they could directly compare which regions changed most in humans and chimps.
"The assumption is that we and the chimps are descendants from a common ancestor 5 million years ago - the chimps really are our closest cousins," Falk said.
In all, the team found five "hot spots" where the shape of the human brain differed from that of chimps; three were more dramatic on the right side of the brain. They then compared the human and chimp casts with those of 13 hominid skull casts in Falk's collection, ranging from a 2.5 million-year-old early ancestor from Africa, called an australopithecine, to a more recent 60,000-year-old Neanderthal. They found marked changes in parts of the right hemisphere as they moved their analyses of endocasts forward in time.
"There's this link between the asymmetry we see in living people today and the hot spots we see in the fossils," she said. "It blows me away, it's so precise."
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