A Dorsal versus Ventral Network for Understanding Others in the Developing Brain

Young children strongly depend on others, and learning to understand their mental states (referred to as theory of mind, ToM) is a key challenge of early cognitive development. Traditionally, ToM is thought to emerge around the age of 4 years. Yet, in nonverbal tasks, preverbal infants already seem to consider others' mental states when predicting their actions. These early nonverbal capacities, however, seem fragile and distinct from later-developing verbal ToM. So far, little is known about the nature of these early capacities and the neural networks supporting them. To identify these networks, we investigated the maturation of nerve fiber connections associated with children's correct nonverbal action prediction and compared them with connections supporting verbal ToM reasoning in 3- to 4-year-old children of both sexes, that is, before and after their breakthrough in verbal ToM. This revealed a ventral network for nonverbal action prediction versus a dorsal network for verbal ToM. Nonverbal capacities were associated with maturational indices in ventral fiber tracts connecting regions of the salience network, involved in bottom-up social attention processes. In contrast, verbal ToM performance correlated with maturational indices of the arcuate fascicle and cingulum, which dorsally connect regions of the default network, involved in higher-order social cognitive processes including ToM in adults. As nonverbal tasks were linked to connections of the salience network, young children may make use of salient perceptual social cues to predict others' actions, questioning theories of mature ToM before 4 years.