Functional frontalisation with age: mapping neurodevelopmental trajectories with fMRI.

The aim of this study was to investigate whether previously observed hypofrontality in adolescents with attention deficit-hyperactivity disorder (ADHD) during executive functioning [Rubia K, Overmeyer S, Taylor E, Brammer M, Williams S, Simmons A, Andrew C, Bullmore ET. Hypofrontality in attention deficit hyperactivity disorder during higher order motor control: a study using fMRI. Am J Psychiatry 1999;156(6):891-896] could be attributed to delayed maturation of frontal cortex. Brain activation of 17 healthy subjects, 9 adolescents and 8 young adults, during performance of a motor response inhibition task and a motor timing task was measured using functional magnetic resonance imaging (fMRI). The effect of age on brain activation was estimated, using the analysis of variance and regression, at both voxel and regional levels. In the delay task, superior performance in adults was paralleled by a significantly increased power of response in a network comprising prefrontal and parietal cortical regions and putamen. In the stop task, alternative neuronal routes--left hemispheric prefrontal regions in adults and right hemispheric opercular frontal cortex and caudate in adolescents--seem to have been recruited by the two groups for achieving comparable performances. A significant age effect was found for the prefrontal activation in both task, confirming the hypothesis of a dysmaturational pathogenesis for the hypofrontality in ADHD.