A Brain Chip to Control Paralyzed Limbs

Research is under way to make a brain chip capable of triggering muscle movement.

Scientists are now building a device that records brain signals and transmits them to paralyzed muscles, potentially returning muscle control to severely paralyzed patients. In the prosthetic system, which is still in early development, a brain chip records neural signals from the part of the brain that controls movement. The chip then processes those signals, sending precise messages to wires implanted in different muscles of the patient's arm or hand, triggering the paralyzed limb to grab a glass or scratch the nose. "Our ultimate goal is for a person to think and effortlessly move the arm ," says Robert Kirsch , associate director of the Functional Electrical Stimulation Center , at Louis Stokes Veterans Affairs Medical Center, in Cleveland, OH.

An implanted device that triggers specific muscles helps paralyzed patients move their limbs. A central stimulator is connected to wires that will be implanted in muscle. Credit: The Cleveland FES Center

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In spinal-cord injuries and some types of stroke and neurodegenerative disease, neural circuits between the brain and the body are damaged, leaving patients with profound movement problems. Scientists have already made remarkable progress in overcoming this neural blockade by developing new ways to stimulate muscles. In functional electrical stimulation (FES), electrical current is applied to specific nerves or muscles to trigger muscle contractions. When the wearer makes a predesignated motion with his or her head or shoulders, he or she triggers stimulation of certain muscles, enabling the limb to move in a specific way. Devices that can restore hand function and bladder control to some paralysis patients have already been approved by the FDA.

In a system Kirsch and his colleagues are testing for people with spinal-cord injuries severe enough to render them paralyzed from the neck down, a pacemaker-like stimulator is surgically implanted in the patient's chest or abdomen, with connecting wires implanted in up to 12 different muscles. Another set of wires records activity in muscles that are under the patient's voluntary control. These signals are then used to trigger activity in the paralyzed muscles.

But for some patients, especially severely paralyzed individuals with control over few muscles, using signals recorded directly from the brain to control the paralyzed limbs could provide an easier and more intuitive way to move. So the Cleveland researchers are working with John Donoghue , a neuroscientist at Brown University, who has developed implantable brain chips that record and process electrical activity directly from neurons. The device, made by Cyberkinetics Neurotechnology Systems , in Foxborough, MA, consists of a tiny chip containing 100 electrodes that record signals from hundreds of neurons in the motor cortex, the part of the brain that modulates movement. A computer algorithm then translates this complex pattern of activity into a signal used to control a computer or prosthetic limb. So far, the chip has been tested in three patients--the first people ever to receive this type of implant. (See " Implanting Hope ," March 2005; " Brain Chips Give Paralyzed Patients New Powers "; and " Piloting a Wheelchair with the Power of the Mind .")