Scientists have created a brain implant that not only allows monkeys to control a computer with their thoughts, it also allows them to “feel” the virtual objects. The new, two-way, brain-machine-brain interface represents a major breakthrough in the field of neuroprosthetics. Bolstered by the results, the scientists plan to test the technology on a quadriplegic in just three years.
There have been a number of advances in brain-machine-interface (BMI) research in recent years. Implants have allowed monkeys to control computer cursors and even a robotic arm with impressive precision. In the current study, two macaques were trained to control a virtual arm on the computer screen and use it to “grasp” virtual objects. What separates these macaques from past BMI trainees is that, when their virtual hands contacted the virtual objects they were able to “feel” the objects.
The macaques were shown three identical objects on the computer screen. They were trained to pass the virtual hand over the three objects and to choose the one that evoked a sensation. Controlling the hand was enabled by electrodes implanted into the motor cortex, a major part of the brain for movement control. First, the activity of hundreds of neurons in the region is recorded while the monkeys control the virtual hand with a joystick. In this way the computer learns what “left” and “right,” etc. means in terms of brain activity. Then the joystick is taken away, and the monkeys are trained to control the hand with their thoughts.
The sensation indicating the correct object caused by electric stimulation through a return connection from the computer to the brain. These electrodes were inserted into the somatosensory cortex, the part of the brain that senses touch. As the virtual hand passed over the correct object the somatosensory cortex was stimulated. If the monkeys chose the correct object they received a food reward. They learned the task quickly. One monkey showed improvements after nine trials, the other after only four. After mastering the task the monkeys were picking the right object nine times out of ten. This shows that they can sense and object without any stimulation to the skin.
The following video shows the avatar arm in action.
“We don’t know what the animals perceived,” Miguel Nicolelis, neuroprosthetic aficionado and lead author of the study, told Nature, “but it was a sensation that was created artificially by linking the virtual fingers to the brain directly.” The study was published in Nature October 5th.
Managing the two signals – out from the motor cortex and into the somatosensory cortex – proved tricky for the researchers. The two areas are close enough together in the brain that the electrical stimulation in the somatosensory cortex would actually leak over to the motor cortex and disrupt control of the virtual hand. They got around this by alternating between recording and stimulating every 50 milliseconds. Of course, normal brain activity usually doesn’t take turns, but the fact that the monkeys were still able to learn the task means the constrained methodology still worked.
To give prosthetics sensory feedback would be huge. Some labs are currently trying to develop prosthetics with sensory feedback functions. One example relays feedback signals through the stump ending nerve terminals. Due to variability in the health of the stump tissue and severed neurons, this approach is less than idea. The two-way communication of BMBI, straight to the brain’s pristine movement and sensory centers could make feedback a reality. If BMBI can be used effectively in humans – a big ‘if’ – it would surpass current BMIs that up till now have relied solely on visual feedback for control. “If you want to reach and grasp a glass, visual feedback won’t help you,” Quian Quiroga, a neuroscientist at the University of Leicester, UK said in a commentary in Nature. Quiroga, who was not involved in the study, added, “It’s the sensory feedback that tells you if you have a good grip or if you are about to drop it.”
With the successful BMBI demonstration, Nicolelis and his colleagues are ready to take neuroprostheses to the next level. The Walk Again Project is a collaborative effort involving many scientists from the world’s leading research centers to, through BMI/BMBI technology, do no less than “restore full mobility to patients suffering from a severe degree of paralysis.” Of course, to achieve such a superhuman feat will require superhero suit. In collaboration with Walk Again, Nicolelis’ lab at Duke University are putting together a “wearable robot” or “exoskeleton” designed to support the patient’s body and allow he or she to move at will. As in the study, electrodes will be implanted to give the patient both movement control and the all important feedback. The electrodes will be chronically implanted in at least five different regions on each side of the brain. Whereas a few hundred neurons were sufficient for the macaques to control their virtual arms, the larger human brain requires that a couple thousand brain cells be recorded for proper movement. It’s a major challenge that the researchers will have to overcome before patients can begin donning the exoskeleton. The electrodes will have to be stable for up to a decade, and then there’s always the risk of infection.
The brain chips – if they work – will be a technological triumph by themselves. Custom designed, the brain chips will be low-power and wireless, transmitting their signals to a processing unit worn on the patient’s belt about the size of a cell phone. That brain activity will then be translated to digital motor signals which will control the actuators across the joints of the exoskeleton. Force and stretch sensors throughout the exoskeleton will signal back to the patient’s brain the whereabouts of his or her joints and limbs. They predict that it would only be a matter of weeks before the patient was used to the suit, off on his or her own, experiencing the world like never before.
It’s an ambitious project, to say the least. The scientists are currently working hard to ready the suit for clinical trials over the next three years. You see, they have a deadline: the 2014 World Cup in Brazil. Nicolelis, a native Brazilian, hopes to test the exoskeleton on a grand stage by having a young quadriplegic Brazilian deliver the opening kick.