The brain is one of our most delicate organs. It’s not really meant to be prodded and poked, hence the nice protective skull surrounding it. That fragility makes experimental devices that use tiny electrodes poking into the brain to help paralyzed people use computers and potentially let amputees control bionic limbs, a risky proposition. But now a new University of Utah study shows that brain signals controlling arm movements can be detected accurately using new microelectrodes that sit on the brain, but don't penetrate it.

Technology has already been developed to read signals from the brain cells using small arrays of brain penetrating electrodes to help paralyzed people move a computer cursor, operate a robotic arm and communicate. But the new micro electrocorticography (ECoG) technology lets neurosurgeons achieve similar results with a device that is placed under the skull, but over brain areas where it would be risky to place penetrating electrodes, such as areas that control speech, memory and other cognitive functions.

Coauthor of the study, Bradley Greger, says, “this device should allow a high level of control over a prosthetic limb or computer interface. It will enable amputees or people with severe paralysis to interact with their environment using a prosthetic arm or a computer interface that decodes signals from the brain."

ECoG and microECoG represent an intermediate step between electrodes that poke into the brain and electroencephalography (EEG), in which electrodes are placed on the scalp. Because of distortion as brain signals pass through the skull and as patients move, EEG isn't considered adequate for helping disabled people control devices.

The researchers tested microECoGs in two sever epilepsy patients who were already undergoing craniotomies. They tested how well the microelectrodes could detect nerve signals from the brain that control arm movements. The study showed that the microECoG electrodes could be used to distinguish brain signals ordering the arm to reach to the right or left, based on differences such as the power or amplitude of the brain waves.

The study’s lead author, Paul A. House says, "the most optimistic case would be a few years before you would have a dedicated system," noting more work is needed to refine computer software that interprets brain signals so they can be converted into actions, like moving an arm. Once the researchers develop software to decode brain signals detected by microECoG in real-time, it will be tested by asking severe epilepsy patients to control a "virtual reality arm" in a computer using their thoughts.

Although there is no proof yet, Gregor and House believes that the new microECoG array would likely last longer than existing, penetrating electrode arrays.

"If you're going to have your skull opened up, would you like something put in that is going to last three years or 10 years?" Greger asks. Not a hard one to answer.

The study from the University of Utah researchers appears in the journal Neurosurgical Focus.