In the early 1990s, Tim Pons, at the National Institutes of Health (NIH), showed that the brain can reorganize if sensory input is cut off (Pons et al. 1991). Hearing about these results,V. S. Ramachandran realized that phantom limb sensations could be due to "crosswiring" in the somatosensory cortex, which is located in the postcentral gyrus (Ramachandran & Blakeslee 1998; Ramachandran & Hirstein 1998), and which receives input from the limbs and body. Input from the left side of the body goes to the right hemisphere and vice versa. The input from extremities comes into the somatosensory cortex in an ordered way, the representation of which is referred to as the somatosensory homonculus. Input from the hand is located next to the input from the arm, input from the foot is located next to input from the hand, and so on. One oddity is input from the face is located next to input from the hand.
Ramachandran reasoned that if someone were to lose their right hand in an accident, they may then have the feelings of a phantom limb because the input that normally would go from their hand to the left somatosensory cortex would be stopped. The areas in the somatosensory cortex that are near to the ones of the hand (the arm and face) will take over (or "remap") this cortical region that no longer has input. Ramachandran and colleagues first demonstrated this remapping by showing that stroking different parts of the face led to perceptions of being touched on different parts of the missing limb (Ramachandran, Rogers-Ramachandran & Stewart 1992). Through magnetoencephalography (MEG), which permits visualization of activity in the human brain (Yang et al. 1994), Ramachandran verified the reorganization in the somatosensory cortex.