Under ordinary circumstances, the genetically determined circuitry in the brain remains largely stable throughout life. It was thought, until about 30 years ago, that no new neural circuits could be formed in the adult mammalian brain. Recently, functional MRI studies in amputees have shown that almost all patients have experienced motor cortical remapping. The majority of motor reorganization has occurred as a downward shift of the hand area of the cortex onto the area of face representation, especially the lips. Sometimes there is a side shift of the hand motor cortex to the ipsilateral cortex. In patients with phantom limb pain, the reorganization was great enough to cause a change in cortical lip representation into the hand areas only during lip movements. It has also been found that there is a high correlation between the magnitude of phantom limb pain and the extent to which the shift of the cortical representation of the mouth into the hand area in motor and somatosensory cortical reorganization has occurred. Additionally, as phantom pains in upper extremity amputees increased, there was a higher degree of medial shift of the facial motor representation. There are multiple theories that try to explain how cortical remapping occurs in amputees, but none have been supported to a great extent.