Resting-state and task functional magnetic resonance imaging correlates of early language development in temporal and frontal lobe

Abstract

Language is a critically important cognitive skill that enables both higher-order cognition andinteraction between individuals. Children face a daunting task of acquiring their first language through passive input, a task they do remarkably well in only a few short years. Linguistic processing is known to be lateralized to the left hemisphere in the majority of the population. The exact mechanism by which this lateralization emerges is not fully understood. In this dissertation, I use functional neuroimaging to evaluate the changing laterality of the language network, focused on two nodes. Those two nodes are the inferior frontal gyrus (IFG), which is implicated in syntactic processing, and middle temporal gyrus (MTG), which is implicated in semantic processing, with the goal of understanding how the language network emerges. I use two groups of participants and techniques. I applied resting-state functional neuroimaging to a large accelerated longitudinal imaging study of infants and toddlers aged 8 mo to 30 mo. Secondly, I used both resting-state and task imaging to investigate an n = 4 subset of that study who returned for densely sampled imaging visits between 4.5 y and 6.5 y. These analyses show that laterality related to MTG, but not IFG, increase between 8 mo to 30 mo. These findings are consistent with other work in this domain that suggests IFG does not assume its adult-like role until 9 y or older. Furthermore, task studies in the older population show that IFG remains uninvolved in the language network at those ages, yet IFG participates in the ventral attention network (VAN) (and IFG-related laterality increases between 2.5 y and 4.5 y, despite this). These results suggest that the language network co-opts the VAN to accelerate processing in left hemisphere (LH).