In an article published online in The Journal of Physiology on September 23, researchers from Neuroscience Research Australia (NeuRA), Randwick, New South Wales, and the University of New South Wales, Sydney, Australia, used proprioceptive illusion to demonstrate that a person’s brain can be made to believe that an artificial finger is his or her own. This is the first time an illusion of body representation was created using sensory inputs from the muscle alone; prior theories used additional sensory inputs through touch and vision. The discovery provides new insight into conditions where body representation in the brain is disrupteddue to changes in the central or peripheral nervous systems, for example phantom limb syndrome, stroke, and schizophrenia.
Nineteen participants, with a mean age of 36, held an artificial finger with their left hand that was located 12cm above their right index finger. Anesthesia numbed the skin and removed feelings of joint movement, and participants could not see their hands. The experimenter held the participant’s other index finger and thumb on the artificial finger and passively moved them congruently or incongruently for three minutes. When the artificial finger and the right index finger were moved congruently, subjects reported they were holding their own index finger, demonstrating to the researchers that the brain incorporated the artificial finger into its proprioception. Subjects more strongly agreed that they were holding their own finger after congruent movement.
The researchers also found a new type of sensory grasp effect in which perceived distances between index fingers decreases when subjects hold an artificial finger, and from this suggest that the brain generates possible scenarios and tests them against available sensory information.
“It may seem silly to ask yourself whether your index finger is part of your body. However, our current findings demonstrate that this question has led to important insights into key brain functions,” said Simon Gandevia, MD PhD DSc FAA FRACP, deputy director of NeuRA.”These findings could lead to new clinical interventions where the addition or the removal of specific sensory stimuli is used to change someone’s body image.”