Scientists have designed a brain implant that sharpened decision making
and restored lost mental capacity in monkeys, providing the first
demonstration in primates of the sort of brain prosthesis that could
eventually help people with damage from dementia, strokes or other brain injuries.
The device, though years away from commercial development, gives
researchers a model for how to support and enhance fairly advanced
mental skills in the frontal cortex of the brain, the seat of thinking
and planning.
The new report appeared Thursday in The Journal of Neural Engineering.
In just the past decade, scientists have developed brain implants that
improve vision or allow disabled people to use their thoughts to control
prosthetic limbs or move computer cursors. The new paper, led by
researchers at Wake Forest Baptist Medical Center and the University of
Southern California, describes a device that improves brain function
internally, by fine-tuning communication among neurons.
Previous studies have shown that a neural implant can do this for memory
in rodents, but the new report extends that work significantly, experts
said — into brains that are much closer to those of humans.
In the study, researchers at Wake Forest trained five rhesus monkeys to
play a picture-matching game. The monkeys saw an image on a large screen
— of a toy, a person, a mountain range — and tried to select the same
image from a larger group of images that appeared on the same screen a
little while later. The monkeys got a treat for every correct answer.
After two years of practice, the animals developed some mastery, getting
about 75 percent of the easier matches correct and 40 percent of the
harder ones, markedly better than chance guessing.
The monkeys were implanted with a tiny probe with two sensors; it was
threaded through the forehead and into two neighboring layers of the
cerebral cortex, the thin outer covering of the brain.
The two layers, called L-2/3 and L-5, are known to communicate with each
other during decision making of the sort that the monkeys were doing
when playing the matching game.
The device recorded the crackle of firing neurons during the animals’
choices and transmitted it to a computer. Researchers at U.S.C., led by
Theodore Berger, analyzed this neural signal, and determined its pattern
when the monkeys made correct choices.
To test the device, the team relayed this “correct” signal into the
monkeys’ brains when they were in the middle of choosing a possible
picture match, and it improved their performance by about 10 percent.
The researchers then impaired the monkeys’ performance deliberately, by
dosing them with cocaine. Their scores promptly fell by 20 percent.
“But when you turn on the stimulator, they don’t make those errors; in
fact, they do a little better than normal,” said Robert E. Hampson of
Wake Forest, a study author.
His co-authors were Sam A. Deadwyler, Ioan Opris and Lucas Santos, all
of Wake Forest; Dr. Berger, Vasilis Marmarelis and Dong Song of U.S.C.;
and Greg A. Gerhardt of the University of Kentucky.
The technology used in the study could easily be contained on an
implantable chip, Dr. Deadwyler said, and it is possible to envision a
system that could help people with brain damage.
“The whole idea is that the device would generate an output pattern that
bypasses the damaged area, providing an alternative connection” in the
brain, he said.
Many hurdles remain. Decision making, like memory, is a multifaceted
process that involves many neural circuits, depending on the decision
being made.
A device focused on just one circuit is likely to be very limited. But
not long ago, even a simple neural prosthesis would have seemed like
science fiction.
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