The Brain Remembers “Phantom” Hands!

New research has shown that a brain can remember the representation of an amputated hand—even decades later. A team of scientists from the University of Oxford Brain Lab have opened up a pathway to the possibility of controlling prosthetic limbs via the brain.

Team leader, Dr. Tamar Makin said in the August 30. 2016 news release, “It has been thought that the hand ‘picture’ in the brain, located in the primary somatosensory cortex, could only be maintained by regular sensory input from the hand. In fact, textbooks teach that the ‘picture’ will be ‘overwritten’ if its primary input stops. If that was the case, people who have undergone hand amputation would show extremely low or no activity related to its original focus in that brain area—in our case, the hand. However, we also know that people experience phantom sensations from amputated body parts, to the extent that someone asked to move a finger can ‘feel’ that movement.”

Study leader Sanne Kikkert told OTW, “One of the most mysterious questions about the brain’s ability to adaptively change to new circumstances is: what happens to the brain once a key input is lost (e.g. through amputation)? It has been thought that the hand representation in the brain, located in the primary somatosensory cortex, is maintained by regular sensory input from the hand. Indeed, textbooks teach that any sensory representation in the brain will be ‘overwritten’ if its primary input stops. Following this explanation, people who have undergone hand amputation would show extremely low or no activity related to its original focus in the brain area of the missing hand.

“However, we know that amputees often experience phantom sensations from their missing hand, such that when they are asked to move a phantom finger they can ‘feel’ that movement. In fact, some amputees experience exceptionally vivid phantom sensations, allowing them to move the individual fingers of their phantom hand. In this study, we were interested in finding how the representation of a missing hand is stored in the brain.

“Our results showed that the representation of the missing hand persisted even decades after amputation. In fact, the fine-grained finger information still matched well to that of two-handed controls, also tested in the study. Therefore, our results indicate that the brain ‘remembers’ the representation of an amputated hand, long after the sensory input is lost. It does not erase the original function of a brain area, as previously thought.

“The brain ‘remembers’ a missing hand, even decades after arm amputation. This representation of the missing hand is detailed and similar to that of two-handed controls. This representation could be used in the future for the more intuitive fine-grained control of neuroprosthetic arms.

“Our findings remove a barrier to the development neuroprosthetics (prosthetic limbs controlled directly by the brain): the assumption that a person would lose the brain representation that could control the prosthetic intuitively. If the brain retains a representation of the individual fingers, this could be exploited to provide the fine-grained control needed.”