Stanford Scientists Improve Algorithm for Brain-Implantable Prosthetics

by Dan Holden | November 22, 2012

ReFIT Stanford 112212

Researchers at Stanford University have improved an algorithm that could enable brain-implantable prosthetics, called neuroprosthetics, to improve the speed, accuracy and control of prosthetic limbs.

The algorithm taps into that part of the brain that creates the potential for motor control, which still exists even when a limb is no longer there or active. The Stanford-developed ReFIT (for Recalibrated Feedback Intention-Trained Kalman filter) algorithm harnesses this potential via a chip that is implanted in the brain to record action potentials and send them to a computer. The frequency of nerve impulses indicates the direction and speed of the user’s desired movements.

“Able-bodied rhesus monkeys were tasked with using the ReFIT algorithm to mentally direct a mouse cursor to an onscreen dot, and then hold it for half a second,” said a Stanford statement. “Testing showed that ReFIT performed far better than previous algorithms, and allowed the monkeys to reach their target twice as quickly as before – offering an impressive 75 to 85 percent of the speed of real arms.”

The above image shows the improvement of the ReFIT algorithm (middle), when compared to a previous-generation algorithm (right)

“This paper reports very exciting innovations in closed-loop decoding for brain-machine interfaces. These innovations should lead to a significant boost in the control of neuroprosthetic devices and increase the clinical viability of this technology,” said Jose Carmena, associate professor of electrical engineering and neuroscience at the University of California Berkeley.

The Stanford team approached the challenge of neuroprosthetics from a new angle compared to previous efforts, with the ReFIT algorithm designed to focus on reading small groups of neurons, rather than the usual method of interpreting individual neurons. This led to an increase in longevity for ReFIT, up from the usual limit of around a year for previous similar systems, to over four years of successful operation.

The FDA has approved clinical human trials of ReFIT, and the Stanford team is currently focusing on improving cursor movement yet further. The creation of mind controlled robotic limbs has also not been ruled out for the future – an intriguing prospect indeed.

The results of the study were published November 18 in the journal Nature Neuroscience.

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