Deep-Brain Stimulation: Why Does It Help Some and Harm Others?

deep-brain stimulation
Researchers at Washington Univ. may have the answer

A recent study from researchers at Washington University School of Medicine in St. Louis may help explain why effects of deep-brain stimulation can vary so much – and perhaps more importantly, point the way toward improving the treatment.

Individuals suffering from numerous neurological conditions have turned to deep-brain stimulation, which places electronic stimulators within the brain, for partial or sustained relief of their symptoms. But the side effects, including memory loss or lessened coordination, can cause problems as great as those they alleviate.

The stimulators typically are implanted in structures known as the thalamus and the basal ganglia that are near the center of the brain. These structures, the researchers found, serve as hubs where the neurological networks that control movement, vision and other brain functions cross paths and exchange information. The findings were published in a December issue of Neuron.

“The sites we target for deep-brain stimulation were discovered serendipitously,” said co-author Scott Norris, MD, assistant professor of neurology and of radiology at Washington University School of Medicine. “Someone had a stroke or an injury in a specific part of the brain, and suddenly their tremor, for example, got better, and so neurologists concluded that targeting that area might treat tremor. We’ve never really had a way to personalize treatment or to figure out if there are better sites that would be effective for more people and have fewer side effects.”

The creation of individual maps of the functional networks in the basal ganglia and thalamus helped offer clues to the wide range of symptoms. Researchers analyzed 10 hours of MRI brain scan data on each of 10 individuals. From this, they created 3D maps color-coded by functional network for each individual. One of the functional networks is devoted to vision, two relate to movement, two involve paying attention, three relate to goal-directed behaviors, and the last network is the default network, which is active when the brain is at rest.

The researchers discovered that each functional network followed its own path through the deep structures of the brain, intermingling with other networks at defined meeting spots. Some of these spots – such as the motor integration zone, where a movement and a goal-directed network come together – were located in much the same place in all 10 people. The locations of other networks and their points of intersection varied more from person to person.

“I showed a neurosurgeon where we’d found the motor integration zone, and he said, ‘Oh, that’s where we put the electrodes for essential tremor, and it always works,’” said Nico Dosenbach, an assistant professor of occupational therapy, pediatrics and radiology.

“A lot of what I do is basic science – understanding how the brain works,” Dosenbach continued. “But now we can make a map and give it to neurosurgeons and potentially improve treatment for these devastating conditions. We still have to prove the hypothesis that deep-brain stimulation outcomes are linked to functional networks, and translation will take time, but this really could make a difference in people’s lives.”

SOURCE: Washington University School of Medicine

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