Researchers have used a neural implant to recapture a lost decision-making process in monkeys—demonstrating that a neural prosthetic can recover cognitive function in a primate brain. The results suggest that neural implants could one day be used to recover specific brain functions in patients with brain injuries or localized brain disease.
While the results of today’s study may take many years to translate into humans, they suggest that even cognitive processes, such as deciding whether or not to grab a cup of coffee or remembering where you left your keys, could one day be augmented by brain chips.
Paralyzed patients have previously used brain implants and brain-machine interfaces to control robotic arms (see “Brain Chip Helps Quadriplegics Move Robotic Arms with Their Thoughts”). And more than 80,000 Parkinson’s patients around the world have a deep-brain stimulation implant, which functions like a pacemaker to reduce their tremors and other movement problems (see “Brain Pacemakers”). In the new study, however, the implants could actually interpret neuronal inputs from one part of the brain and effectively communicate those outputs to another brain region.
The researchers used an array of electrodes to record the electrical activity of neurons in the prefrontal cortex of monkeys while they performed a memory task. The prefrontal cortex is involved in decision making and directs many types of cognitive responses associated with memory or other types of information processing.
The five monkeys in the study were trained to play a matching game in which they were shown an image on a screen and then had to use hand movements to steer a cursor to that same image out of two to seven others that they were shown anywhere from one to 90 seconds later.
This kind of movement decision is different than a simple reflexive movement. “The monkeys have to find out where the image is and then select the kind of movement to move the cursor there,” says Sam Deadwyler, a brain scientist at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina, and a senior author on the study.
From their recordings in the prefrontal cortex, the research team extrapolated a mathematical model of the electrical activity of neurons involved in the movement decision. The study authors had previously shown that this kind of mathematical model, called MIMO—short for multi-input/multi-output—could interpret and replace memories in rats with the neural implant (see “A First Step Toward a Prosthesis for Memory”).
In the new study, the model took multiple signals produced by the brain layer that integrates sensory information related to the task. It then extracted the relevant information to choose a particular movement. The implant can stimulate neurons in order to influence the decision to move the hand to select the correct image.
To test the implant’s ability to improve or recover the decision process, the researchers gave the monkeys cocaine intravenously, since cocaine disrupts decision making. Without the activity of the implant, cocaine-affected monkeys frequently could not choose the correct image. But with the device, their decision making was on par, if not slightly better, than normal, even under the influence of cocaine.
Deadwyler suspects that a generalized pattern for particular tasks could be generated even in humans (as has been demonstrated in rats), so that an injured patient could receive an implant encoded with a cognitive mathematical model that was previously derived from healthy brains. “As long as you can extract the information that is coming and generate the normal output pattern for that input, you could bypass the damaged connection.”