Like a fingerprint, the precise structure of the brain differs from person to person. The exact locations for speech, reading, and walking, for example, are unique to each individual. There is no single "road map" that fits all. For neurosurgeons who must decide how much of a patient's brain tumor to remove, that variability has created a dilemma. Not taking out enough of a tumor increases the possibility of a fatal regrowth; but removing too much runs the risk of damaging vital areas of the brain, perhaps even causing permanent disability.
UW neurosurgeon George Ojemann and colleagues have created a way to map the vital areas of each patient's brain in order to protect vital functions during surgery. Originally developed for use during epilepsy surgery, the technique was adopted in about 1986 for brain tumor surgery as well. UW researchers have completed the largest study ever of the effectiveness of brain mapping for brain tumor patients. The brain mapping technique not only has become a successful part of treatment, allowing surgeons to remove larger amounts of the tumor than previously believed possible and avoiding the damage sometimes encountered in major brain operations; it also is providing a window on how the brain actually functions.
The method involves stimulating parts of the brain and recording brain activity while the patient remains awake but sedated. Areas of the brain governing motor activities can be spotted when stimulation causes the hand or leg to move, for example. Areas responsible for language are identified by stimulating the brain while the patient reads aloud or names objects flashed on slides. When the language centers are touched, the patient will hesitate while reading or naming objects.
Ojemann has been using the technique to study the neurobiology of language and verbal memory.
Until recently, scientists believed that language processing functions were confined to two main areas: Broca's area, for speech production, and Wernicke's area, for speech comprehension. Ojemann and colleagues have discovered that there are separate areas in the brain for different linguistic functions, such as for naming, reading, recent verbal memory, syntax, and word comprehension. A specific language function such as naming, for instance, is associated with many essential and widely dispersed nerve cells, which are all activated in parallel when that function is carried out. Each language function has its own such "system." Moreover, there are different systems for a linguistic function in different languages: a system for verbs in French would be distinct from the system for verbs in English, for example.
The results of Ojemann's work furnish a key piece to the puzzle of how the brain processes language. The picture that is emerging from efforts at the UW and institutions elsewhere is that language processing is far more complex than previously thought.