Brains of adult mammals retain remarkable ability to undergo plastic reorganization. Deafferentations due to peripheral nerve or spinal cord injuries, result in parts of the somatosensory cortex which loose their peripheral inputs, acquiring novel inputs originating in the intact parts of the system. For example, after injuries to the dorsal columns of the spinal cord at cervical levels, intact inputs from the face expand to reactivate neurons in the deafferented hand cortex. The reorganization results in changes in the topographic organization of the brain, which takes place at multiple levels of the system - the cortex, the thalamic nuclei and the brain stem nuclei. The ability of the brain to reorganize has the potential to be utilized for facilitating functional recoveries by potentiation of remaining neuronal circuits after injuries. Brain reorganization can also have undesirable perceptual consequences such as phantom sensations. Experiments from many laboratories have lead to our current understanding of the nature of reorganization, and have given tantalizing clues about the possible mechanisms of adult brain plasticity. © 2012 by Nova Science Publishers, Inc. All rights reserved.