The difference between your brain and a monkey's brain is microscopic.
Ground-breaking work by researchers at Medical College of Georgia and the Augusta Department of Veterans Affairs Medical Centers has located a long-sought structural difference between the brains of humans and those of primates. And it helps explain the difference in communication and complex thought that distinguishes man from even a chimpanzee, which shares most of the same genetic material as man, said physical anthropologist Daniel Buxhoeveden, the lead author of a recent paper in the American Journal of Physical Anthropology.
It was long assumed the difference was found in the size of man's brain, which for the most part is 3.5 times bigger than a chimpanzee. But the relative size of the brain was not out of proportion, previous studies showed. And from the outside, the language areas of both brains appeared too similar to explain the distinction, Dr. Buxhoeveden said.
Looking at Wernicke's area, a spot in the temporal region of the brain known to be involved in language, the Augusta researchers compared minicolumns, microscopic columns of 80 to 100 cells that make up the basic functioning units of the brain. The Augusta team found not only that man's cell groupings were more complex and larger, but also that there were more of them in a particular region. The also found distinct differences in the minicolumns and their numbers between the left side of the brain, the language side for most people, and the right side. That difference did not show up in the primates.
For Manuel Casanova, a psychiatrist and neurologist, it is physical proof of a long-held theory that it is not the size of the brain but what's inside that counts.
"This debate started in the early 1970s," Dr. Casanova said. "That question has just been answered by our study."
And it came about only because the researcher chose not to focus on individual cells such as neurons but on the organization of the cells into functional units, Dr. Casanova said.
"Intelligence is not in the neuron but in the circuitry," Dr. Casanova said. "What we're doing is at the microscopic level and we're teasing out circuitry with all the different chemicals, with all of the different cells. (This) would have been missed if we had focused on the single cell."
The size difference, in fact, probably resulted from adding minicolumns and complexity within the brain, Dr. Buxhoeveden said.
"It's not by adding more cells per se in a random fashion but by adding more columns," he said. In fact, the columns and their organization appear highly adaptable and may be influenced by the environment in infancy, Dr. Buxhoeveden said.
With funding from the Stanley Foundation, the Augusta researchers hope to build on their findings by applying them to different disorders, such as schizophrenia and autism.
Finding a physical clue to language lends itself to understanding the evolutionary nature of language, Dr. Casanova said.
"We are different because of language," he said. "We advance as a species because of language."
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