How can the mouth area of the brain map take over part of the arm and hand area after an amputation?

Following an amputation, the brain undergoes a process known as map expansion (or cortical reorganization), which is a form of neuroplasticity where local brain regions—organized as "maps" in the cerebral cortex—modify their connections and behavior.12

In the case of arm and hand amputees, the area of the brain previously dedicated to processing sensory input from those limbs becomes deprived of its main inputs. Because the brain is highly flexible, the adjacent mouth brain map can shift to occupy this unused cortical territory. This reorganization is specifically associated with the phenomenon of phantom limb syndrome, where individuals experience sensations or pain in a limb that is no longer present. In some patients, these cortical changes have been shown to be reversible through the use of peripheral anesthesia.21