Imaging of early brain injury and cortical plasticity.

The human brain undergoes complex organizational changes during development in and ex utero. Pathogenic events affecting the developing brain cause abnormalities or lesions, the patterns of which depend on the stage of brain development. During the first and second trimester, cortical neurogenesis predominantly takes place, characterized by proliferation, migration, and organization of neuronal cells. Brain pathology is characterized by maldevelopments. During the third trimester, growth and differentiation events are predominant, which persist into postnatal life. Disturbances of brain development during this period mainly cause lesions. During the early third trimester, periventricular white matter is especially affected, whereas toward the end of the third trimester, gray matter, either cortical or deep gray matter, appears to be more vulnerable. These patterns of brain maldevelopments or lesions offer excellent models to study mechanisms of organization and reorganization in the developing brain. Evidence for superior brain plasticity is well established for language function after early left-sided lesions. Some evidence exists for higher compensatory potential within in the motor system; maintenance of ipsilateral tracts seems to play a certain, but only incomplete functional role after unilateral lesions in early and mid gestation. The visual system seems to have limited compensatory potential.