January 30, 2012 – New clinical insights into patients suffering from brain damage and speech disorders are likely after Georgetown researchers proved that an area in the brain believed to be where human speech is processed is incorrect.
The researchers also discovered the correct area responsible for speech.
The Proceedings of the National Academy of Sciences (PNAS) journal published the Early Edition article today by Georgetown University Medical Center (GUMC) neuroscience professor Josef Rauschecker and Ph.D. candidate Iain DeWitt today.
“Textbooks will now have to be rewritten,” says Rauschecker, the study’s senior author. “…If a patient can’t speak, or understand speech, we now have a good clue as to where damage has occurred.”
In the 1800s, German neurologist Carl Wernicke identified an area toward the back of the brain’s cerebral cortex as the place where speech is processed following studies of brain injuries and strokes.
A Knockout Punch
But the GUMC researchers’ study showed that this area is actually about three centimeters closer to the front of the brain and on the other side of auditory cortex.
This is miles away in terms of brain architecture and function, say the researchers, who analyzed more than 100 imaging studies.
“We gave old theories that have long hung a knockout punch,” says Rauschecker, also a member of the Georgetown Institute for Cognitive and Computational Sciences.
Humans and Primates
DeWitt, who is pursuing his doctorate with Georgetown’s Interdisciplinary Program in Neuroscience, noted that “If you Google ‘language organization in the brain,’ probably every cartoon illustration out there is wrong.”
Rauschecker also notes that the study shows that the real speech processing area matches the one recently found in non-human primates, suggesting the origin of the human language center is older than previously thought.
“Scientists have long argued that speech is unique to humans,” the professor says. “They say monkeys make communication sounds but the fact that they don’t have the same elaborate language that we do is due to different brain processing centers.”
“This finding suggests the architecture and processing between the two species is more similar than many people thought,” he adds.
Rauschecker and DeWitt searched the peer-reviewed, scientific literature for studies that investigated auditory speech perception in humans using different scanning methods — either from functional magnetic resonance imaging (fMRI) or positron emission tomography (PET).
They found 115 brain imaging studies of speech perception, which in total had included over 1,900 participants and generated over 800 brain coordinates for speech processing. They then used a type of analysis that allowed them to measure the degree of agreement among brain coordinates from these studies.
“Other researchers have found what we have, as well, which has caused a lot of controversy in the field as to where Wernicke’s area really is,” Rauschecker says. “This study provides a definitive, irrefutable answer.”