Relational reasoning, or the ability to identify and consider relationships between multiple mental representations, is a fundamental component of high-level cognition (Robin & Holyoak, 1995). The capacity to reason with relations enables abstract thought, and may be at the core of what makes human cognition unique (Penn et al., 2008). This capacity improves throughout childhood and adolescence (Ferrer et al., 2009). Here, we sought to better understand the neural mechanisms that support its emergence. We have hypothesized previously, based on fMRI research in adults, that 1) inferior parietal lobe (IPL) plays a central role in representing relationships between mental representations (1st-order relations), and 2) rostrolateral prefrontal cortex (RLPFC) integrates inputs from IPL to build 2nd-order relational structures (i.e., relations between relations).
In the present study, we examined fMRI and cortical thickness data from 85 children and adolescents (ages 6–18). Participants performed a relational matching task in which they viewed arrays of four visual stimuli, and determined whether two stimuli shared a particular feature (a 1st-order relational judgment), or whether two pairs of stimuli matched according to the same feature (a 2nd-order relational judgment). FMRI results provide evidence for increased functional selectivity across ages 6 to 18 in RLPFC and IPL. Specifically, young children engaged RLPFC and IPL indiscriminately for 1st-order and 2nd-order relational judgments, and activation for 1st-order relations diminished with age while activation for 2nd-order relations stayed elevated. Examination of cortical thickness revealed that increased functional selectivity in RLPFC could be partly accounted for by cortical thinning in IPL.