Fall 2003 Volume 16, Number 2	A Better Brain Map on the Way
	Surgeons removing tissue that edges "eloquent" areas of the brain-those tied to the basic ability to communicate-are well aware of the risks. The prospect of stopping seizures while making a patient forever mute is the stuff of nightmares. So when cortical mapping (electrical cortical stimulation or ECS) came to Hopkins more than a decade ago, it mercifully revealed a patient's individual speech, motor and other danger zones before surgery. In place at a handful of medical centers worldwide, ECS has opened the door to previously "un-doable" brain surgery for tumors, vascular flaws or epilepsy.
"But things aren't perfect," says neurologist Nathan Crone, M.D., who's testing a new way to halt side effects and make mapping faster, more precise and ultimately, noninvasive. In present mapping, a grid of electrodes is surgically implanted atop the brain. A weak current passes through a chosen electrode pair while the patient reads aloud or names a picture. If the current disrupts the task-the patient suddenly draws a blank-then nearby tissue is indeed language-linked. "But testing electrodes a pair at a time takes hours," says Crone. Also, he says, diagnostic brain-stimulation can itself trip seizures -- mostly small ones called afterdischarges. "Of course you don't want any seizures, no matter how small. More important here, the seizures get in the way of our mapping. Sometimes there are areas we just can't figure out." But Crone's new method, called ESA, for event-related spectral analysis, can test the entire brain at once, without stimulation. Again, a patient performs a verbal task, but this time the implanted electrodes record electrical signals the brain generates when it's at work. From a cacophony of whole-brain output, Crone tunes in higher frequency gamma waves-like a mother picking out its chick in the henhouse-that signal language processing is going on. Crone's been refining his gold standard technique -- as one journal called it -- for 10 years with NIH support, eyeing broader clinical use. "We're nearly ready to leave experimental status," he says. "And then we hope to perform ESA noninvasively. "Meanwhile, our surgeons and epileptologists are always asking, What'd you find on this patient? That's because our ESA, for now, provides a useful preliminary map they can confirm with their more traditional version. But one day, ours may replace it." For more information, call 410- 955-6772.