Brain damage and neuroplasticity: mechanisms of recovery or development?

Brain damage may be followed by a number of dynamic events including reactive synaptogenesis, rerouting of axons to unusual locations and altered axon retraction processes. In the present theoretical review, the relationship between these morphological changes and behavioral recovery of function is examined from two perspectives. First, an examination of the research literature reveals that the association between these reorganizational events and recovery of function is inconsistent, and it is proposed that in most cases a causal relationship between neural reorganization and behavioral recovery remains speculative at best. It is further noted that aberrant neural circuitry has been associated with neurological dysfunction in many studies. Second, evolutionary considerations suggest that there is little reason to believe that neural reorganizational events emerged to 'heal' damaged brains. Both experimental and evolutionary orientations support the idea that neuronal circuitry changes in response to injury can be better understood as developmental growth processes that are triggered or potentiated in response to cell loss, rather than as recovery or healing processes. The contribution of 'growth' to behavioral recovery of function may be inconsistent because these growth processes are occurring against the backdrop of a damaged brain and may make connections different from those ordinarily seen. Further, they must be considered in conjunction with phenomena such as diaschisis and compensation which may also influence behavioral changes following neural injury.