When you go to catch a Frisbee, you don’t need to stare at your hand until it makes contact. You have an intuitive sense of where your arm is—and where it’s going—based on how your muscles and joints feel. This sense of body position, known as kinesthesia, has proved tricky to build into prosthetic arms. Now, researchers have recreated the feeling of kinesthesia in six arm amputees by sending finely tuned vibrations into the skin of their upper arms and shoulders. The approach improved their ability to feel and control their prosthetic arms when performing actions such as gripping and pinching, the team reports today in Science Translational Medicine.
The amputees in the study had previously undergone surgery to rewire the nerves in their upper bodies to act as messengers for the specific electric signals associated with arm and hand movement. Three also completed tests where they were asked to close their hand as if gripping a cylinder, while not being able to see their prosthetic arm. When the subjects performed the task again while receiving kinesthesia vibrations simulating the feeling of the motion, they more instinctively moved their prosthetics into the grip and were faster in correcting their mistakes, such as when some of their fingers had not closed into the grip. The subjects also indicated in surveys that they felt greater control over their prosthetic arms when receiving the kinesthesia vibrations.
The authors of the study say that more experiments need to be run in order to determine the effectiveness of the vibrations in helping with everyday activities such as picking up objects, and on a test group larger than six people.