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Electric Cartography

“We’re going to attach your head to this bed, okay?” said Rezai, positioning Joan on the operating table.

“Do I have a choice?” she answered with a laugh.

Opting for invasive brain surgery may seem like a dire solution for shaky hands and compulsive thoughts, but patients with serious neurological ailments are often eager to try it. The day before her doctors implanted her pacemaker, Joan described the trauma of daily life with a condition like essential tremor. Wearing a pink blouse, khaki slacks and sandals, the 52-year-old woman from Byron Center, MI, looked like the youthful, good-natured grandmother that she is. But her hands shook uncontrollably. She rattled off a list of quotidian frustrations that helps explain why patients are willing to let doctors drill holes in their heads and stick electrodes into their brains.

Here are some of the things she could not do: Eat soup (she needed two hands). Put on makeup. Brush her teeth. Dial the phone (she often got wrong numbers). Tie her shoes. Hold her grandchildren. “I used to be a nurse,” she explained, her voice itself a little shaky, “but I had to give it up because of the tremor-you know, giving injections, changing dressings, writing in charts. People like to be able to read the chart,” she added with a laugh, “and my handwriting was worse than a doctor’s.” She held an imaginary pen in her right hand, and it carved wild elliptical arcs in the air, as if she were shaking a thermometer.

Like many people with a severe movement disorder, Joan found that drugs were not effective, and the symptoms grew worse over time. On the eve of having her pacemaker implanted, she did not seem unnerved by the prospect of brain surgery-even when Rezai recited possible complications, including a chance of infection and a one to two percent chance of bleeding in the brain. “Going to a dentist,” she said with a tight smile, “is more traumatic for me than this.”

The procedure, needless to say, is a little more complicated than a root canal. Implanting electrodes deep in the brain combines the latest in imaging and stimulation technology with, paradoxically, a slow, painstaking, hands-on mapping of each patient’s neural terrain during surgery. This kind of cartography is essential, Rezai explains, because the geography of each human brain is different. The lay of this precious land must be custom-mapped by the surgical team, so that when the actual electrode is maneuvered into place, it will provide optimal therapeutic results while minimizing possible side effects.

Like all maps, this one begins to take shape with the establishment of coordinates. With a titanium frame attached to her head, Joan underwent a computed tomography scan before being wheeled into the operating room. Rezai then used a software program to merge the results of that scan, a magnetic resonance imaging scan taken the previous day, and a computerized standard brain atlas to create a 3-D image of Joan’s brain. Within that image, Rezai identified the x, y and z coordinates of the target for the electrode he would implant. Having selected a trajectory that avoided blood vessels, fluid-filled structures and other critical neural regions, Rezai’s team began the process of actually exploring a route to the trouble spot, advancing the preliminary probe about six centimeters into the brain. Once they were within about 15 millimeters of the thalamus, they used a hydraulic device to advance the probe in micrometer increments, and the vast portion of the day was spent traversing a distance smaller than the diameter of a dime.

This was done as much by sound as by visualization. The probe, sensitive enough to pick up electrical signals from a single cell, was wired to a laptop computer and amplifier. As one doctor moved it deeper into the brain, the operating room began to fill with the ebb and flow of brain cells firing, talking, reacting; the doctors, meanwhile, stood around with furrowed brows, trying to discern neural nuances in the amplified static. “You can think of the different thalamic nuclei as separate countries,” Rezai explains. “Each country speaks a different language, and we can recognize the language of different cells.”

As the probe neared the thalamus, the surgical team stopped every time it encountered the telltale rat-a-tat of a firing cell. “We’re getting close to one there,” Rezai said, head tilted as if he were listening to a faraway cricket. The crackle grew louder and louder, sounding like heavy rain on a tin roof, or distant gunfire. “We’re in the thalamus now,” he announced.

Every once in a while, the amplifier would spit out a distinctly different sound-a kind of pop or sudden “pfftttt.” “That zip you hear?” Rezai explained. “That’s an injury current,” the sound of a neuron pierced by the probe (it’s unclear if the cells repair themselves, Rezai says, but the damage is considered minimal). The surgeons inserted the probe three times, using slightly different trajectories, to pinpoint the pencil-eraser-sized target of brain tissue.

Five and a half hours into the surgery, satisfied that they had found the right spot in the thalamus, Rezai and his team were ready to insert the permanent electrode. After guiding it into place, the surgeons prepared to test the device. “Okay, Joan,” Rezai said, “I want you to give us your maximum tremor.” She had a hard time doing it, however, because the mere placement of the electrode seemed to dampen her shakiness. “That’s a good sign,” Rezai said.

Why stimulation should even work, actually, is a nagging scientific question. Standing by the electrode’s voltage controller, Erwin Montgomery paid tribute to the fundamental mystery underlying this entire field of surgery. “The $64,000 question is: how the heck does deep-brain stimulation have its effects? Nobody knows the answer.”

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