Neural prosthesis restores decision-making ability in monkeys
By Ben Coxworth
September 17, 2012
We may sometimes joke that we lack the ability to make decisions, but the fact is that for people with certain types of brain damage, proper decision-making is indeed impossible. This isn’t so much about things like choosing between vanilla and chocolate, however. Instead, these individuals simply can’t decide on how to respond to everyday situations, so they either don’t respond, or they respond inappropriately. Help may be on the way, though, in the form of a brain-stimulating device that has been shown to work on monkeys.
The prosthetic device was developed by researchers from Wake Forest Baptist Medical Center, the University of Kentucky and the University of Southern California. It incorporates an array of electrodes, which is capable of both measuring the electrical impulses made by individual neurons, and of stimulating those neurons.
The research project began with five Rhesus monkeys, who were trained on a match-to-sample exercise – an image was flashed on a computer screen followed by a pause, after which the monkeys had to select that same image from a selection of up to eight images that appeared on the screen. After training for two years, the animals reached a success rate of about 70 to 75 percent.
For the experiment, the prosthesis was attached to the monkeys’ prefrontal cortex. More specifically, it was wired into two cortical layers known as L2/3 and L5. During the decision-making process, these areas communicate with one another – L2/3 provides input to L5 in the way of electrical signals, and L5 outputs those signals as a call to action.
The wired-up monkeys then performed the match-to-sample exercise, with the scientists recording how the neurons in both areas fired during successful matches. They subsequently gave the monkeys a dopamine-modifying drug, namely cocaine. This disrupted communication between L2/3 and L5, causing the monkeys’ performance to drop by 13 percent.
Next, however, the prosthesis was used to stimulate the L5 neurons, causing them to fire in the same pattern that they would when receiving accurate input from L2/3. This caused the monkeys’ performance to improve to the point that it was actually 10 percent better than it was even before they were put on cocaine.
In a nutshell, because the two decision-making parts of the brain couldn’t communicate, the prosthesis stepped in and “played back” prerecorded instructions to bridge the gap. It is hoped that down the road, descendants of the device could be used in humans.
“In the case of brain injury or disease where larger areas are affected, the system would record the inputs to that area from other areas and, when they occur, program the delivery of the appropriate output patterns to brain regions that normally receive signals from the injured area, thereby restoring lost brain function” said Wake Forest’s Prof. Sam Deadwyler, lead author of a paper on the research.