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Rewriting Life

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.

The findings also have implications for the development of neural prosthetics. For example, the device could be connected directly to the spinal cord or muscle rather than to another part of the brain. “If a person had a spinal-cord injury and the link from brain to muscle is impaired, this connection could bypass that injury and reconnect brain cells to the muscle,” says Fetz. His group is currently working on this application.

Such a device might one day be used to boost the effects of rehabilitation therapy. Rehab exercises are designed to boost the brain’s innate plasticity–in essence, they try to make the damaged brain develop a new neural pathway to control movement of specific muscles. Devices such as Fetz’s chip may be able to speed along this process by strengthening connections between two different brain areas. “This study gives a preliminary indication that there are methods that can be used to almost engineer this rerouting,” says Andrew Schwartz, a neuroscientist at the University of Pittsburgh who studies neural prosthetics.

While the findings are exciting, there is still a long way to go before the technology can be applied to human beings. In terms of stroke rehabilitation, scientists would first need to figure out precisely which two parts of the brain should be reconnected. “In order to restore function, you can’t just make more connections–you have to make the right connections,” says John Donoghue, a neuroscientist at Brown University who is developing a different type of implantable prosthetic.

Donoghue’s chip, which is already being tested in human trials, uses many recording electrodes, but it currently doesn’t have the ability to stimulate other parts of the brain or body. (With his device, neural signals are sent to a computer, which decodes the information and uses it to move a cursor on a computer screen. See “Implanting Hope,” March 2005, and “Brain Chips Give Paralyzed Patients New Powers.”) However, Donoghue says he is currently working on stimulating capabilities as well.

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