Language localized in the brain
August 31, 2011
MIT researchers have found that there are parts of our brain dedicated only to language, a finding that marks a major advance in the search for brain regions specialized for sophisticated mental functions.
Functional specificity refers to the idea that discrete parts of the brain handle distinct tasks. Scientists have long known that functional specificity exists in certain domains: in the motor system, for example, there is one patch of neurons that controls the fingers of your left hand, and another that controls your tongue.
But what about more complex functions such as recognizing faces, using language or doing math? Are there special brain regions for those activities, or do they use general-purpose areas that serve whatever task is at hand?
To determine this, the researchers analyzed each subject individually using fMRI, making sure that patterns of activity in one brain would only ever be compared to patterns of activity from that same brain. The researchers spent the first 10 to 15 minutes of each fMRI scan having their subject do a fairly sophisticated language task while tracking brain activity. This way, they established where the language areas lie in that individual subject, so that later, when the subject performed other cognitive tasks, they could compare those activation patterns to the ones elicited by language.
After having their subjects perform the initial language task (a “functional localizer”), the researchers had each one do a subset of seven other experiments: one on exact arithmetic, two on working memory, three on cognitive control and one on music, since these are the functions most commonly argued “to share neural machinery with language.”
Out of the nine regions they analyzed — four in the left frontal lobe, including the region known as Broca’s area, and five further back in the left hemisphere — eight uniquely supported language, showing no significant activation for any of the seven other tasks. These findings indicate a “striking degree of functional specificity for language,” the researchers said.
The researchers said the results don’t imply that every cognitive function has its own dedicated piece of cortex. However, they said the results give hope to researchers looking to draw some distinctions within the human cortex.
Ref.: Evelina Fedorenko, et al., (in press) PNAS, 2011; [link]