At the University of Washington scientists have successfully rerouted nerve signals leading to monkeys’ wrists, using a lab-built device that made a direct artificial connection between brain and muscles. Reporting in the latest Nature, Chet T. Moritz, et. al. believe their experiment is “the first demonstration that direct artificial connections between cortical cells and muscles can compensate for interrupted physiological pathways and restore volitional control of movement to paralysed limbs.”
From University of Washington press release:
What was exciting about this direct stimulation, said Dr. Eberhard Fetz, University of Washington professor of physiology & biophysics and a researcher at the Washington National Primate Research Center at the UW, is that it avoids the complex process of decoding neural signals to control a computer or robotic device. Direct stimulation of muscles may allow individuals to have more natural control of movement through their own volition. The experiments were performed with laboratory instrumentation, but the researchers also built a portable electronics device from off-the-shelf components to convert signals from the motor cortex neuron cells into stimuli. The device would fit in a matchbox and runs on AA batteries and would allow long-term practice with the artificial connection.
The research was conducted at the Washington National Primate Center and supported by the National Institutes of Health (NIH) Neurology Institute. Monkeys learned to use direct, artificial stimulation from arbitrarily chosen motor cortex cells, delivered to multiple muscles, to flex and extend their wrist to play a video game. Their wrist nerves had been temporarily numbed with a local anesthetic like lidocaine, which paralyzed the muscles. Despite the nerve block, the monkeys were able to control the contraction strength of their wrist muscles to match a set of targets on a computer screen. Controlling the degree of muscle contraction is what allows us to pick up an egg without breaking the shell or to grab tightly to a handrail to avoid a fall.
The monkeys got better at the video game with practice as they learned to control the neurons that triggered muscle stimulation. This method of learning to control a computer cursor is comparable to biofeedback training to moderate hand temperature or heart rate.
The scientists also found that neurons unrelated to wrist movement could provide signals to move wrist muscles. Moreover, muscles that flex and extend the wrist could be activated separately from different neurons.
“Nearly every motor cortex neuron we tested in the brain could be used to control the stimulation of the wrist muscles,” said Dr. Chet Moritz, UW senior fellow in physiology and biophysics and lead author on the study, which also included UW researcher Steve Perlmutter. In particular, even brain cells initially unrelated to movement could be controlled and used to stimulate muscles.
“With biofeedback the brain can rapidly learn to control new cells to generate movement,” Fetz noted. Because of this, perhaps someday researchers may help stroke patients by using stimulation from undamaged brain areas to restore function lost from damage in other areas of the brain.
Abstract: Direct control of paralysed muscles by cortical neurons doi:10.1038/nature07418
Press release: Brain nerve cells can directly control stimulation of paralyzed muscles through an artificial connection
(hat tip: MIT Technology Review)