Researchers have found that deep brain stimulation by sending in electric shocks to a part of the brain that plays a key role in memory improved people's ability to learn. This could raise hope for patients of Alzheimer’s.
The study, conducted at UCLA and published in Thursday's edition of the New England Journal of Medicine, was small and highly preliminary, involving just seven patients with epilepsy. But deep brain stimulation helped all seven subjects — including some who suffered memory impairment— navigate faster and more accurately through a virtual town.
This study was based on animal studies that found deep brain stimulation not only boosted activity in the brain's memory centers, but spurred the growth of new brain cells when those regions were damaged. The fact that the same technique improved memory performance in humans makes some researchers optimistic that it might be a way to block or reverse the destruction of brain cells in patients with Alzheimer's.
Deep brain stimulation involves the insertion of guide wires through the skull and into the brain, where they deliver electrical current to clusters of neurons that no longer function properly. It is widely used in the treatment of Parkinson's disease, in which damage to regions of the brain's motor cortex cause tremors, rigidity and unsteady gait. About 90,000 Americans have had the battery-powered, stopwatch-sized devices implanted in their brains, and they often show marked improvement. But the neurostimulator has not been found to slow or block the progression of that disease.
The technique is also being used for patients with epilepsy, to disrupt the storm of electrical current in the brain that causes seizures. The patients who took part in the memory trial were candidates for this treatment, and in preparation for surgery they had electrical probes inserted in their brains — giving researchers the opportunity to conduct their experiment.
The goal was to explore whether stimulation to two key memory regions of the brain would deliver improvement in cognition. The researchers, led by Nanthia Suthana, PhD, also at the University of California, Los Angeles, monitored the electrodes to record neuron activity as memories were being formed. The 7 epilepsy patients played the video game on a laptop at their beds. Using a joystick, they took the role of taxi drivers in a small town consisting of four blocks by four blocks. They searched for passengers and dropped them off at any of six stores they were asked to find. The electrical stimulation was turned on while they learned the locations of some stores, but not others.
While navigating the new landscape, the subjects sometimes got deep brain stimulation to one of two areas — the hippocampus or an adjacent structure called the entorhinal cortex — and other times got no neurostimulation at all.
The researchers found that when subjects' entorhinal region was stimulated while they navigated through the maze for the first time, they were speedier and more accurate in learning the way to certain destinations than when they explored a similar maze without stimulation. When electrodes delivered stimulation directly to the hippocampus, some subjects improved their performance while others got worse.
Itzhak Fried, a UCLA neurosurgeon who worked on the study, called the hippocampus “the master organ of memory.” But he said the greater improvements seen in the memories of patients who got stimulation to the adjacent entorhinal region suggested a new target for treating memory loss. “The entorhinal cortex is a gateway into the hippocampus,” Fried said. “If you are to consciously recollect incoming information, it needs to be processed here.”
In an editorial accompanying the study, University of Toronto neurologist Sandra E. Black called the potential application of deep brain stimulation in the treatment of memory disorders “enticing.”
And Dr. Maria Carrillo, scientific director of the Alzheimer's Assn., agreed that electrically stimulating the brain's memory centers may hold greater promise. But she cautioned that the complexity and breadth of destruction in Alzheimer's make it resistant to simple fixes. “It's a little early to talk about deep brain stimulation as a treatment for Alzheimer's disease,” she said. “But certainly it's tantalizing.”
“Losing our ability to remember recent events and form new memories is one of the most dreaded afflictions of the human condition,” Fried said. “Our preliminary results provide evidence supporting a possible mechanism for enhancing memory, particularly as people age or suffer from early dementia. At the same time, we studied a small sample of patients, so our results should be interpreted with caution.”
Andres M. Lozano, a neurosurgeon at the University of Toronto who has conducted similar experiments in mice, said this line of research already had piqued the interest of people with normal memory function who seek a little intellectual edge. “These are major ethical issues society will have to grapple with when the time comes…This opens up a Pandora's box,” Lozano said.
Alzheimer's disease - a form of dementia that affects memory, thinking and behavior - affects six million Americans and 30 million people worldwide. It's the sixth leading cause of death in the U.S., and the fifth leading cause of death for those ages 65 and older. This study was funded by the National Institutes of Health and the Dana Foundation.
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