Cortical map plasticity

It is now well established that the functional organization of the cerebral cortex is plastic, that is, changes in organization occur throughout life in response to normal as well as abnormal experience. The potential for reorganization has been demonstrated in both sensory and motor areas of adult cortex, either as a consequence of trauma, pathological changes, manipulation of sensory experience, or learning. These changes can only be evaluated with reference to an extensive experimental base that has identified a repeatable representation pattern (e.g. somatotopy, tonotopy, or retinotopy), for which change can be detected. While the scope of changes are often at the edge of our technical capabilities to assess, there are striking examples of significant and rapid change (for reviews, see Sanes & Donoghue, 2000; Buonomano & Merzenich, 1998). There is an overwhelming belief that modifications in cortical organization emerge through changes in synaptic efficacy within the cortex and elsewhere in the nervous system. Further, these changes are have been closely linked to the phenomena called long-term potentiation (LTP) and long-term depression (LTD). This review deals mainly with the changes that have been detected in the motor cortex and their link to synaptic modification. Some of the most convincing evidence that learning and practice influences cortical organization and that learning operates through LTP/D-mediated mechanisms has come through work in the motor cortex. This work is also of profound significance to the medical community because it implies that the impaired or damaged motor cortex can be restructured through appropriate physical rehabilitation schemes or through pharmacological means that alter mechanisms accounting for LTP/D.