Direct control of paralysed muscles by cortical neurons

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Abstract
Brain–machine interfaces are a promising approach for treating paralysis due to spinal cord injury, by rerouting control signals from the brain to the muscles. Previous work showed that monkeys can be trained to move robotic arms using signals from electrodes implanted in the brain. Now it is reported that monkeys can learn to move a temporarily paralysed wrist using signals artificially routed from single neurons in the brain that had not previously been associated with that movement. This may have significant implications for future design of brain–machine interfaces, which have traditionally relied on the activity of dedicated populations of neurons. Brain–machine interfaces are a promising approach for treating spinal cord injury-caused paralysis by rerouting control signals from the brain directly to the muscles. This paper demonstrates that monkeys can directly control stimulation of muscles using the activity of neurons in motor cortex, restoring goal-directed movement to a transiently paralysed arm. In addition, monkeys learned to use these artificial connections so that single neurons previously not associated with the movement could be used to control functional stimulation. A potential treatment for paralysis resulting from spinal cord injury is to route control signals from the brain around the injury by artificial connections. Such signals could then control electrical stimulation of muscles, thereby restoring volitional movement to paralysed limbs1,2,3. In previously separate experiments, activity of motor cortex neurons related to actual or imagined movements has been used to control computer cursors and robotic arms4,5,6,7,8,9,10, and paralysed muscles have been activated by functional electrical stimulation11,12,13. Here we show that Macaca nemestrina monkeys can directly control stimulation of muscles using the activity of neurons in the motor cortex, thereby restoring goal-directed movements to a transiently paralysed arm. Moreover, neurons could control functional stimulation equally well regardless of any previous association to movement, a finding that considerably expands the source of control signals for brain-machine interfaces. Monkeys learned to use these artificial connections from cortical cells to muscles to generate bidirectional wrist torques, and controlled multiple neuron–muscle pairs simultaneously. Such direct transforms from cortical activity to muscle stimulation could be implemented by autonomous electronic circuitry, creating a relatively natural neuroprosthesis. These results are 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.