Linear changes appear to be the best models of developmental change in several studies between late childhood and adulthood [27–32, 35, 42, 52]. However, there is also substantial evidence for non-linear changes in studies including lower age ranges. For example, inverted U-shaped activations between childhood and adulthood with peaks in adolescence have been observed [33, 34, 70, 74] which need to be further investigated in future studies of larger sample sizes. The majority of functional developmental imaging studies have controlled for performance differences in order to establish true age effects. However, very few studies have controlled for other factors that are likely to influence brain development, such as differences in pubertal status or sex hormones. Also, so far, only three studies have examined age by sex effects, which are fundamental to understand the developmental underpinnings of sex-dimorphic differences. Lastly, functional MRI studies have been largely cross-sectional. Longitudinal imaging studies are necessary to avoid confounds of cohort effects inherent to cross-sectional studies.
