Science News - July 2, 2011

group has found ways to space the electrodes on a grid to optimize the signals from the neurons for more precise movement. Together with Justin Williams at the University of Wisconsin–Madison, Moran built a small electrode array to fit over the brain’s sensorimotor cortex, a region concerned both with movement and the perception of outside stimuli. Jasper, one of three monkeys in Moran’s lab, is now using the new array to play video games and reach for and grasp virtual objects on a computer screen, all without moving a muscle.

This summer, the researchers will get their first look at how the device performs in human patients who need it. A thin, flexible grid will be implanted under the skull of a paralyzed patient at the University of Pittsburgh. Researchers will train the patient to use mind control to carry out movements on a computer screen. Over the next three years, as improvements are made to the device, future patients may be able to perform more complicated tasks and control a simple robotic arm. Moran says his goal is to develop an implantable device that will last years — up to 10 — making the choice to have the surgery practical.

“What we need is a type of implant that will be 95 to 99 percent effective and that is going to last for a decade,” he says.

s.m. Chase ET AL/JOURNAL OF NEUROSCIENCE 2010

While some scientists doubt that ECoG signals can provide enough information for fine movements, such as turning a key in a lock, others are working to attain more detailed information from the signals. Last year, biomedical engineer Soumyadipta Acharya of Johns Hopkins University in Baltimore and his team decoded signals for predicting the movement of individual fingers as they flexed and extended. The findings, published in the August 2010 Journal of Neural Engineering, show that ECoG, with some refinements, can probably provide the dexterity needed to operate a switch or turn a doorknob, Acharya says.

A feel for the future

As paralyzed patients learn to use robotic arms to reach for their morning

Cursor control Patients moving a cursor with their minds can’t always keep it directly on target. The colored lines above show actual cursor paths taken to an intended target (corresponding color). scientists are finding ways to account for the differences between intent and actual movement.

coffee, the question becomes, how exactly do they hold onto the cup? While a Styrofoam cup will crumble under a clenching grip, a cup of any kind will slip from a loose one.

“For prosthetics, the better we get at moving arms out to things, the more we need to work on the sensors to allow us to feel those things,” Shenoy says.

Feeling requires the ability to turn the system around and put signals back into the brain. Some investigators have tried putting small amounts of electric current into the system. Shenoy says the problem with that approach is that sending electricity into the brain activates many cells at once, rather than a target cell.

“Putting electric current into the brain is like going into a classroom where each student in the classroom is a different neuron, and shouting loudly when you wanted to speak to only one student,” he says.

Working with Karl Deisseroth of Stan-
ford, Shenoy is using an approach called
optogenetics to put light-sensitive pro-
teins into target neurons in monkeys
(SN: 1/30/10, p. 18). When sensors at the
end of a prosthetic hand make contact
with a coffee mug, a signal would cause
light sources to shine on those neurons.
Though the light bathes many neurons,
only the neurons that have been tagged
would respond.