In early 2007, a 64-year-old Swiss woman was admitted to the emergency room of a local hospital after having suffered a moderate right hemispheric stroke. Several days following her hospitalization, the woman began to experience what she described to her physicians as a “pale,” “transparent” arm that began at her elbow, which she could move and utilize to complete actions. The phenomenon the Swiss woman experienced was a Supernumerary Phantom Limb (SPL), which is characterized by the sensation of possessing an extra limb that did not exist previously. Though uncommon, conditions such as SPL and phantom limb (the sensation that a missing limb is still attached to the body) typically arise due to some form of insult to the somatosensory region of the brain or from the removal or lack of body parts.
In the healthy brain, multisensory circuits organize visual, tactile, and proprioceptive inputs to the brain in order to compose a somatotopic map of which body parts are inherently our own. However, even the normal brain can be manipulated into believing in the existence of an extra limb. More