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.
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 .”)
Experts have high hopes for the new device. “We consider this the only current viable technology on the horizon to provide patients with high levels of cervical injury restoration and control of their limbs,” says Joseph Pancrazio , director of the neural-engineering and neuroprosthesis research program at the National Institutes of Neurological Disorders and Stroke, one of the agencies funding the research.
The project is likely to be complex. Donoghue and colleagues must first make their brain chip wireless and fully implantable. (Currently, patients have some hardware protruding from their skull and are connected to a computer via wires.) An implantable system would minimize the risk of infection, and it might also help patients learn to use the system. Eberhard Fetz , a neuroscientist at the University of Washington, in Seattle, who is developing similar systems in monkeys, says that an implantable device would allow patients to use the system 24 hours a day, which would help them learn to modulate neural signals for precise control.
In the first set of tests, slated to begin next month, patients implanted with the Cyberkinetics chip will try to move a virtual arm, allowing researchers to study what level of control they could hope to achieve and to identify the muscles that need to be stimulated to elicit useful movements. Once researchers have built an implantable chip and have demonstrated that patients can sufficiently control a virtual arm, the team will start integrating the chip and the FES system.
In the long term, researchers will likely have to meld multiple devices. “To fully realize the potential of these systems, we need to think about not just a single FES system for upper limbs,” says Pancrazio. “We need to think about a network of systems. The individual may need systems for ventilation, bladder control, and bowel control.”