In adults, patterns of language activation are extensively modulated by the complexity of stimulus. For instance, manipulating the psycholinguistic demands of a simple naming task (by changing word frequency or length of the item to be named) leads to changes in activation across frontal and temporal cortices. Everyday listening demands also result in differential engagement of these regions. Manipulating the intelligibility or syntactic complexity of speech results in changes in activity across frontal and temporal cortices, with frontal regions in particular showing elevated activity for degraded relative to clear speech, or for syntactically complex relative to syntactically simple speech.

Do children’s brains react similarly when confronted with increased processing demands or do they solve this problem differently? I will talk about two fMRI studies that address this question, one involving language production and the other language comprehension. The results indicate that manipulating modality and complexity can affect neural activation in different ways across development, particularly over the frontal cortices. Surprisingly, fundamental differences in developmental patterns can occur across different levels of the same task. I will discuss factors that could cause these differences and argue that characterising complexity-dependent effects is crucial in order to fully understand developmental neural trajectories.