A team of scientists from Case Western Reserve University, Cleveland, OH, and the University of Kansas Medical Center have restored behavior using a neural prosthesis in a rat model of brain injury. Ultimately, the team hopes to develop a device that rapidly and substantially improves function after brain injury in humans.

The prosthesis, called a brain-machine-brain interface, is a closed-loop microelectronic system. It records signals from one part of the brain, processes them in real time, and then bridges the injury by stimulating a second part of the brain that had lost connectivity.

The researchers tested the prosthesis in a rat model of brain injury at the University of Kansas. After mapping the rat’s brain, they developed a model in which anterior and posterior parts of the brain that control the rat’s forelimbs are disconnected. Atop each animal’s head, the brain-machine-brain interface is a microchip on a circuit board smaller than a quarter connected to microelectrodes implanted in the two brain regions.

The device amplifies signals, which are called neural action potentials and produced by the neurons in the anterior of the brain. An algorithm separates these signals, recorded as brain spike activity, from noise and other artifacts. With each spike detected, the microchip sends a pulse of electric current to stimulate neurons in the posterior part of the brain, artificially connecting the two brain regions.

Two weeks after the prosthesis had been implanted and run continuously, the rat models using the full closed-loop system had recovered nearly all function lost due to injury, successfully retrieving a food pellet close to 70% of the time, or as well as normal, uninjured rats. Rat models that received random stimuli from the device retrieved less than half the pellets and those that received no stimuli retrieved about a quarter of them.

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