Cortical plasticity and the development of behavior after early frontal cortical injury.

It has been known for over 100 years that frontal lobe injury in children is often associated with considerably more functional recovery than after similar injury in adulthood. Systematic study of frontal cortical injury in laboratory animals has shown that this recovery is tightly tied to developmental age: There is a brief window of time during cortical development during which the brain is able to compensate. Simply being young is not sufficient because injury prior to this critical period leads to miserable behavioral outcomes. For humans, the least favorable time for cortical injury is likely at the end of the gestational period, perhaps including the 1st month or so of life whereas the most favorable time is around 1 to 2 years of age. In addition to age, the extent of behavioral recovery is influenced by age at assessment, the nature of the behavioral assessment, sex, and lesion size. Anatomical studies have shown that functional recovery following early cortical injury is correlated with a reorganization of remaining cortical circuitry, including increased dendritic arborization and increased spine density. Recovery, and the compensatory anatomical changes, can also be potentiated by application of different treatments including behavioral therapy, trophic factors, and neuromodulators. Finally, there is preliminary evidence in laboratory animals to suggest that it may be possible to induce neural regeneration in the injured brain and that the regenerated brain functions to support functional recovery.