Brain plasticity during development: physiological bases and fMRI approach

Brain functional MRI (fMRI) is a new tool for the study of the development of cognitive functions in healthy children (<<natural plasticity>>), as wel l as for the assessment of functional reorganization following brain lesion s. However, methodological difficulties related to the pediatric population (movements, cooperation), along with unsolved issues about the influence o f physiological parameters of the immature brain on fMRI results, explain t he limited number of published studies. Normal brain maturation is characte rized by a transient phase of synaptic redundancy followed by selective syn aptic regression until adulthood, that forms the neurobiological correlates of both learning and individual variability of cortical anatomy and functi onal organization, and of the large potential for post-lesional plasticity in children. fMRI in school-age children demonstrated activation patterns c omparable to adults during motor, language, and working memory tasks. In ne onates and infants, fMRI showed significant differences of visual cortex ac tivation. Post-lesional plasticity is more pronounced in younger children. In motor cortex, activation of ipsilateral hemisphere may be seen in cases of rolandic lesions. Interhemispheric shift of language networks occurs mos tly in cases of destructive or large brain lesions, or in cases of early re fractory epilepsy.