Los Angeles Times writer Karen Kaplan wrote a good description of an experiment designed to see whether Broca's area really does divide the task of uttering a word with Wernicke's area, as long claimed in neuroanatomy texts. The researchers, at Harvard and UC San Diego, showed subjects a series of 240 distinct words and asked them to "pronounce" the words in their minds. Some of the words required conversion into another tense before being "pronounced." Meanwhile, the researchers watched what happened in Brocas's area, and found that there was activity there associated with 1) selecting a word, 2) deciding on a tense, and 3) mapping out how that word will be pronounced with the mouth. Nothing at all interesting happened in Wernicke's area. Broca's does it all! In less than half a second!
"The finding will make many textbooks obsolete," writes Kaplan.
The result is interesting enough on its own, but more remarkable to me is the methodology employed. See, fMRI doesn't picture the brain at a high enough resolution, or quickly enough, to record this kind of activity. Instead, the researchers needed tiny electrodes implanted deep into the brains of the subjects to measure super fast and subtle reactions at ultra-high resolutions. But no review board was going to--nor should it--approve an experiment that requires brain surgery, no matter how interesting the results might be. Once again, epilepsy steps in to drive neuro-discovery as generous patients, and ingenious, multi-tasking neurosurgeons, offer their services (and/or their brains). The surgeons, in preparation for surgical treatment of epilepsy, are conducting a procedure called intracranial electrophysiology (ICE), in which they implant dozens of electrodes in the area of an epileptic patient's brain to precisely detect where the patient's seizures are starting and where healthy neurons are just doing their thing. The procedure allows neurosurgeons to cut only the pathogenic tissue, leaving behind all the important, good stuff. It takes several days, during which there is a wide open window into the portions of the patient's brain where the electrodes are inserted. If the patient is willing, and if the surgeon is interested, and if the part of the brain being explored is of interest to a neurobiologist who gets word of the surgery, the situation is ripe for research, like the Brooca's area study. Such a scene also led to discovery of the first mirror neurons in human brains (see my news piece in New Scientist) and many other cutting-edge studies. As ICE becomes more common, and as researchers increasingly include it in their repertoire of tools, other textbook chapters will be laid to rest as well.
For centuries, since Hippocrates at least, efforts to understand, describe, and treat epilepsy have been nudging, or hurtling, neuroscience forward. In fact, the reason we know as much as we do about the functional geography of most parts of the human brain--including the general functions of Broca's and Wernicke's areas, is because of earlier explorations inside the brains of epileptics. And there's no sign the trend is turning.
Photo caption: Neurosurgeons implant electrodes deep into the human brain in order to locate the foci of seizures. While the electrodes are in, they can be used for basic research, such as the study described in Karan Kaplan's LA Times, piece. This remarkable X-ray photo is by Ned T. Sahin, the UC San Diego neurobiologist who was the lead author on the Broca's Area study, which appeared in last Friday's issue of Science.