Recently there's been increasing hope for people who have lost the use of their arms, as various research institutes have started developing prosthetic arms that can be controlled by thought alone. So far, all of the systems have just allowed users to control a single arm – for many of the tasks that we perform on a daily basis, that's simply not enough. Now, however, scientists at North Carolina's Duke University have succeeded in getting two rhesus monkeys to control both arms of animated digital avatars, using nothing but their mind.

A team led by neurobiologist Dr. Miguel Nicolelis started by observing the activity of almost 500 neurons in both cerebral hemispheres of the animals' brains. One of the monkeys then learned to use its own hands on physical joysticks, to move the arms of an avatar monkey on a computer screen. Whenever that avatar successfully performed a specific bimanual motor task (putting its hands on targets that would pop up), the real monkey would receive a fruit juice reward.

That monkey was subsequently trained to control the avatar arms simply by moving its own arms, with no joysticks present. When its arms were then "gently restrained," it learned to work the avatar arms just by thinking of moving its own. A computer decoded its neural activity, and moved the avatar arms accordingly.

The second monkey repeatedly watched the task being performed by the avatar arms, and was then taken straight to using nothing but brain control to get those arms to perform the same task on command. This is particularly important for human applications, as most users of the technology wouldn't have the ability to start by training with real-world arm movements.

Once both monkeys got the hang of things, it was noticed that the plasticity in the cortical areas of their brains increased. According to the scientists, this suggests that the animals had incorporated the on-screen arms into their own internal body image – in other words, they thought of them as if they were their real arms.

Additionally, it was discovered that when the monkeys performed the bimanual tasks, the associated neural activity was more than just the sum of the activity that accompanies left- and right-hand-only movements. There's something else at work when both arms are used at once, a fact which could guide the development of mind-controlled prostheses.

A paper on the research was published yesterday in the journal Science Translational Medicine. All of the findings will be incorporated into the Walk Again Project, a collaborative effort that is tasked with developing a brain-controlled exoskeleton.