Neural plasticity. Part 4. Lesion-induced reorganization of the CNS: recovery phenomena

Most patients treated by physical therapists have suffered some neurological trauma resulting from disease or injury. The traditional teaching used to be that damage of central neurons is irreversible. Within the last decade, however, it has been necessary to cast aside this traditional view because of accumulating evidence that the brain is endowed with remarkable plasticity. This paper reviews experimental evidence revealing morphological and functional changes occurring in the CNS in response to neural lesions. Morphological responses to injury include collateral and terminal sprouting, retrieval of vacated synapses, alterations in the ultrastructure of surviving synapses, and denervation supersensitivity. Functional and adaptive changes induced by injury include the unmasking of ineffective synapses, shifts in receptive fields, and reorganization or altered effectiveness of surviving neural networks. These recovery phenomena attest to the brain's dynamic properties. These new insights contradict our conventional view of the absence of growth and reorganizational capabilities in CNS neurons. These newly identified "recovery phenomena" are destined to have a significant impact on physical therapy in the future.