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 on 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 per cent of the easier matches correct and 40 per cent 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 neighbouring 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 USC, led by Theodore Berger, analysed 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 per cent.
The researchers then impaired the monkeys' performance deliberately, by dosing them with cocaine. Their scores promptly fell by 20 per cent.
"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; Berger, Vasilis Marmarelis and Dong Song of USC; and Greg A Gerhardt of the University of Kentucky.
The technology used in the study could easily be contained on an implantable chip, 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.