Movement by the power of thought
US researchers have developed a system which translates brain activity into movements of a prosthetic arm, a discovery which could help patients paralysed by strokes, injuries and other diseases to regain their independence.
Writing in this week's Nature, University of Pittsburgh researcher Andrew Schwartz and his colleagues have successfully trained monkeys to use their thoughts to feed themselves with a robot. The monkeys were each fitted with a small implantable electrode which was inserted into the main motor area on one side of the brain.The electrodes were able to pick up the electrical chatter of nerve cells signaling to each other about the next movement the animal was going to make. This activity was relayed to a computer which decoded the nerve signals and turned them into movements of a robot arm sitting beside the animal. With time and training, just by thinking along the right lines, the monkeys were able to use the robot arm to reach out to a variety of locations and to pick up a food item and return it to their mouths with high accuracy.
The trick that the team have used is to develop a way to accurately interpret the neurological signals that encode the direction and speed of planned movements. Scientists have discovered that individual motor nerve cells become most active when a movement takes place in a certain direction preferred by that cell. Movements in other directions tend to excite the cell less. This means that by eavesdropping on the activity of a large number of cells simultaneously it's possible to work out the direction of the planned movement, and this is the information then sent to the robot.
The work marks a major step forward in the field, which previously offered paralysed patients little more than the ability to move a cursor around a screen. A system like this could, theoretically, be linked back up to a paralysed person's own muscles, or used to allow an amputee to precisely and naturally control a prosthesis.