Restoration of grasp following paralysis through brain-controlled stimulation of muscles

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Abstract
A functional electrical stimulation system in primates that is controlled by recordings made from microelectrodes permanently implanted in the brain can be used to control the intensity of stimulation of muscles that are temporarily paralysed by pharmacological motor nerve blockade, thereby restoring voluntary control of the affected muscles; this is a major advance towards similar restoration of hand function in human patients with spinal cord injury. Functional electrical stimulation (FES) has been used to restore some control over hand movements in people who have suffered paralysis after a spinal-cord injury. It relies on residual movement or muscle activity to control electrical activation of the hand muscles. Current FES systems require pre-programmed information customized for an individual, and only limited grasping movements are possible. This paper reports a potential strategy for overcoming paralysis, involving the rerouting of cortical control signals directly to the muscles through a brain–machine interface. Monkeys whose arms were temporarily paralysed with anaesthetics learned to use the prosthetic to activate multiple muscles in a coordinated manner to grasp and manipulate objects. The system uses data recorded from neurons in the motor cortex to predict the intended activity of the paralysed muscles when carrying out the same task. Voluntary control of the paralysed muscles was induced by stimulating up to five electrodes in the identified muscles, in effect bypassing the monkey's spinal cord. The hope is that in humans, this type of neuroprosthesis might allow much more flexible and dexterous use of the hand than is possible with existing FES systems. Patients with spinal cord injury lack the connections between brain and spinal cord circuits that are essential for voluntary movement. Clinical systems that achieve muscle contraction through functional electrical stimulation (FES) have proven to be effective in allowing patients with tetraplegia to regain control of hand movements and to achieve a greater measure of independence in daily activities1,2. In existing clinical systems, the patient uses residual proximal limb movements to trigger pre-programmed stimulation that causes the paralysed muscles to contract, allowing use of one or two basic grasps. Instead, we have developed an FES system in primates that is controlled by recordings made from microelectrodes permanently implanted in the brain. We simulated some of the effects of the paralysis caused by C5 or C6 spinal cord injury3 by injecting rhesus monkeys with a local anaesthetic to block the median and ulnar nerves at the elbow. Then, using recordings from approximately 100 neurons in the motor cortex, we predicted the intended activity of several of the paralysed muscles, and used these predictions to control the intensity of stimulation of the same muscles. This process essentially bypassed the spinal cord, restoring to the monkeys voluntary control of their paralysed muscles. This achievement is a major advance towards similar restoration of hand function in human patients through brain-controlled FES. We anticipate that in human patients, this neuroprosthesis would allow much more flexible and dexterous use of the hand than is possible with existing FES systems.