Progress on brain-machine interface offers hope for long-term amputees

Chicago researchers help monkey amputees control robot arm with their brains

The research advances hope for future robotic prosthetics from which amputees would receive sensory feedback on the limb’s position and what it is touching, according to the neuroscientists and biologists who carried out the study. They found that the brains of the subject generated news connections to control the robotic limb, even if the electrodes that facilitated that control were not implanted until several years after the limb was amputated.

The monkeys were trained to reach for and grasp a ball with a remote robotic arm

Published in Nature Communications, the research involved implanting an array of electrodes into Rhesus monkeys who had previously had arms amputated (in response to injuries at an early age, they stress; not for this research). In two animals, the electrodes were placed in the motor cortex on the opposite side of the brain to the missing limb, but in a third, they were placed on the same side.

The monkeys were then trained (bribed by helpings of fruit juice) to control a robotic arm to grasp a ball, using only their minds. During this activity, the researchers monitored the activity of brain cells around the implants, and used statistical techniques to calculate how the cells were connected to each other.

In the monkeys whose electrodes were opposite to their amputations, they found that initially-sparse neuron connections became more dense in areas used for reaching and grasping. But in the monkeys where the electrodes were on the same side, connections were initially dense but then thinned out and subsequently became more dense in a new pattern.

“That means connections were shedding off as the animal was trying to learn a new task, because there is already a network controlling some other behaviour,” said Dr Karthikeyan Balasubramanian, who led the study. “But after a few days it started rebuilding into a new network that can control both the intact limb and the neuroprosthetic.”

The senior author of the paper, Prof Nicho Hatsopoulos, who specialises in biology and anatomy at the University of Chicago Medical Centre, said that the most significant implication of the research is that long-term amputees can learn to control a robot limb. The study is one of the first to involve amputees; previous research has involved paralysed patients.

In the next phase of the research, the team plans to work with other groups that are developing prostheses equipped with devices for proprioperception — the sense of where a limb is in space — and touch perception. “That’s how we can begin to create truly responsive neuroprosthetic limbs, when people can both move it and get natural sensations through the brain machine interface,” Hatsopoulos said.