Human social interaction crucially relies on the ability to infer what
other people think. Referred to as Theory of Mind (ToM), this
ability has long been argued to emerge around 4 y of age when
children start passing traditional verbal ToM tasks. This developmental
dogma has recently been questioned by nonverbal ToM
tasks passed by infants younger than 2 y of age. How do young
children solve these tests, and what is their relation to the laterdeveloping
verbal ToM reasoning? Are there two different
systems for nonverbal and verbal ToM, and when is the developmental
onset of mature adult ToM? To address these questions,
we related markers of cortical brain structure (i.e., cortical
thickness and surface area) of 3- and 4-y-old children to their
performance in novel nonverbal and traditional verbal TM tasks.
We showed that verbal ToM reasoning was supported by cortical
surface area and thickness of the precuneus and temporoparietal
junction, classically involved in ToM in adults. Nonverbal ToM
reasoning, in contrast, was supported by the cortical structure of a
distinct and independent neural network including the supramarginal
gyrus also involved in emotional and visual perspective taking,
action observation, and social attention or encoding biases. This
neural dissociation suggests two systems for reasoning about others’
minds—mature verbal ToM that emerges around 4 y of age, whereas
nonverbal ToM tasks rely on different earlier-developing possibly
social-cognitive processes