Rerouting Brain Circuits with Implanted Chips

A new brain chip being tested in monkeys could one day reconnect brain areas damaged by stroke or spinal-cord injury.

A new, implantable and wireless brain chip can create artificial connections between different parts of the brain, paving the way for devices that could reconnect damaged neural circuits. Scientists say the chip sheds light on the brain's innate ability to rewire itself, and it could help explain our capacity to learn and remember new information.

"We have a chance of manipulating and repairing [specific] regions of the brain that might be damaged," says Joseph Pancrazio, director of the neural-engineering program at the National Institute of Neurological Disorders and Stroke in Bethesda, MD. "To be able to repair these kinds of lesions on a neuron-by-neuron basis is extraordinary."

In stroke and spinal-cord injuries, neural circuits may be damaged, leaving patients with profound problems in movement or speech. In recent years, scientists have begun developing brain-cognitive interfaces, which record neural signals and transmit them either to a computer, to another part of the brain, or to another body part in effort to get around the neural blockade.

In the new study, researchers from the University of Washington, in Seattle, showed for the first time in live animals that an implantable device could record signals from one part of the brain and transmit that information to another part, reshaping neural connections in the process. "We essentially set up an artificial-feedback loop between two different parts of the cortex," says Eberhard Fetz, the scientist who led the study.

The device, built entirely of off-the-shelf parts, consists of tiny wire electrodes surgically implanted into a monkey's motor cortex. (Neurons in this area are active when an animal makes a voluntary movement.) The wires record activity from these cells and send the signals to a tiny printed circuit board, which amplifies and processes the signal. That information is then sent to a neighboring circuit board and electrode, which uses the signal to stimulate cells in another part of the motor cortex. The entire apparatus is encased in titanium and attached to the monkey's head, allowing the animal to go about its normal daily activities.

According to research published online in Nature, the device was able to reshape the neural circuits that control muscle movement. At the start of the experiment, neurons at the recording sites triggered movement of the wrist in a different direction than when neurons at the stimulating site were activated. After running the record-stimulate sequence for 24 hours in freely behaving monkeys, researchers found that underlying neural circuits had changed: the wrist movement associated with neurons at the stimulating site more closely resembled the movement associated with neurons at the recording area, indicating that the neural connections between these two areas had strengthened.

The findings support a long-held theory in neuroscience: that activating different brain cells at the same time strengthens connections between those cells. Scientists believe this concept underlies our ability to both learn new information and recover some motor and cognitive function after strokes and other brain injuries. "The findings show that the current conception of long-term strengthening is very much on the right track," says Krishna Shenoy, a neuroscientist at Stanford who is also developing neural implants.