Fixing Your Brain
When pills fail, electrical implants can mend brains damaged by Parkinson's, stroke, and depression
It is not a class of miracles, however. This is brain surgery, after all, a last resort. And these patients are the most challenging to treat, so the success rates are often lower than those with other groups that are not as sick. Low numbers make it harder to figure out the amount of electric current or site of an implant that leads to the best results. So a lot still depends on the skill of the individual doctor.
The field began to take shape about a decade ago, when researchers traced out brain circuits controlling movement. Previously, doctors treating disorders like Parkinson's--which afflicts about 1.5 million people in the United States--had tried to intervene with a pill. Cells in a part of the brain called the substantia nigra produce dopamine, a chemical essential for movement. When the cells die off, Parkinson's symptoms appear: rigidity, wild trembling, and a wooden, blank face. But the pill, levodopa, can replenish dopamine and restore normality.
At least for a while. "There's a honeymoon period of about five years," says Mahlon Delong, an Emory neurologist and specialist in movement disorders. "But then in some people the freezing symptoms re-emerge. People have 'on'states when the drug works and they can move and 'off' states when they can't. The 'off' periods become more frequent," says Delong. "This is a dreadful problem."
Delong and several colleagues discovered that there are other spots in this circuit where they can intervene, such as the subthalamic nucleus, or STN. "In Parkinson's, there's an abnormal signal. By stimulating STN, we seem to be replacing it with a more tolerable pattern," Delong says. "You can drown out the bad actors."
Back in the OR, Gross is trying to do that for Lawson. Finding the nucleus, a sliver of cells that's at most 8 millimeters thick and hidden in the center of the brain, is not easy. In fact, surgeons missed it in Lawson a year ago--something, Gross says, that happens in perhaps 1 in 100 patients--so this is his second go-round. Brain scans can help with approximate landmarks. Better accuracy comes with the mapping electrode Gross is using. This isn't the stimulating wire--that gets inserted later--but a thinner wire designed for listening. It has now traveled 36.33 millimeters through Lawson's brain, according to a digital display. "Each region has a characteristic firing pattern, and we can see it and hear it," Gross says. "Here we're in the STN. In the next area down, the substantia nigra, there's not as many neuron connections, so the background noise drops off." No sooner are the words out of his mouth than the sound level quiets down. The depth display reads 42.
During the next half-hour, Gross makes two more runs with the electrode, outlining the boundaries of his target. It's not long before he finds the sweet spot. Neurosurgeons replace the mapping electrode with the thicker stimulating one and anchor it to the skull with a plastic cap.
Buzzing. Later this month, after his brain has healed, Lawson will return to the hospital to have a neurologist turn on the pulse generator near his collarbone. It will buzz his brain 24 hours a day. The pulses should make his "on" periods much longer.
advertisement
