Developmental changes in human cerebral functional organization for word generation.

A fundamental issue in cognitive neuroscience is the nature of developmental changes in human cerebral functional organization for higher cognitive functions. Event-related functional magnetic resonance imaging was used to measure developmental changes in the functional neuroanatomy subserving controlled lexical association. First, brain regions showing significant differences in activity between school-age children and young adults, despite equivalent task performance, were identified. Then, activity in these regions was more fully characterized in individuals spanning the ages of 7-32 years old. Cross-sectional and regression analyses showed systematic increases and decreases in levels of activity over age, by region. Age-related increases in activity were primarily newly recruited, later-stage processing regions, such as in left frontal and left parietal cortex. Decreases, on the other hand, were all positive activations that attenuated with age and were found across a wider neuroanatomical range, including earlier processing regions such as bilateral extrastriate cortex. The hemodynamic magnitude, neuroanatomical location and maturational timecourse of these progressive and regressive changes have implications for models of the developing specialization in human cerebral functional organization.