Neural adolescent pragmatic development mirrors pragmatic differences in adulthood: an fMRI-study

Pragmatic development is still ongoing during adolescence. However, the developmental trajectory during the adolescent years is understudied and the underlying neural correlates of pragmatic development are unknown. In this study, we used an established fMRI paradigm contrasting indirect and direct speech act processing in a newly acquired adolescent sample (n = 51) and a previously collected adult sample (n = 57). The adolescent sample was split into two groups: Young (ages 13-15) and Mid (ages 16-18); and the adult sample (Old, ages 18-36) into two groups based on pragmatic skill level, established in separate behavioral tests. We observed increased activity with age in the posterior medial prefrontal cortex, and a combination of age-related differences and individual differences in adults in the left posterior intraparietal sulcus (IPS) and the posterior cingulate cortex. These clusters were all located outside of the classical perisylvian language areas ("the language network"). The posterior cingulate cortex cluster overlapped with core nodes of the default mode network. We interpret the IPS finding in terms of its overlap with two relevant networks (one of them is the "multiple demand" network related to cognitive control). The results indicate that young adolescents and adults with low pragmatic skill may be over-interpreting direct speech acts as potentially indirect. The similarity between these two groups across results in turn indicate that a delayed adolescent development may lead to persistent difficulties in adulthood. We have shown that aspects of pragmatic development depend on cognitive abilities other than language and Theory of Mind. By studying adolescence, a presumably uniquely human extended developmental period, we provide a rare empirical angle on the question of which aspects of brain and cultural evolution contributed to the human communicative faculty.