Functionally distinct language and Theory of Mind networks work together, especially during language comprehension

Communication requires the ability to generate and interpret linguistic signals, as well as the ability to infer the beliefs, desires, and goals of others (“Theory of Mind”, ToM). These two abilities have been shown to dissociate: on the one hand, individuals with severe aphasia retain the ability to think about others’ mental states; on the other hand, individuals with autism spectrum disorders are impaired in their social reasoning, but their basic language processing is often intact. In line with this evidence from developmental and acquired disorders, fMRI studies have shown that linguistic and ToM abilities are implemented in distinct sets of brain regions. And yet, language is fundamentally a social tool that allows us to share thoughts with one another. Thus, the language and ToM networks should work closely together in spite of being implemented in distinct neural circuits. Here, we investigated potential interactions between these networks during naturalistic cognition using the functional correlation approach in fMRI. Although inter-region correlations within each network were higher than between-network correlations across experiments, we also observed reliably above-baseline synchronization of BOLD signal fluctuations between the two networks during rest and, to an even greater extent, during story comprehension. This synchronization was functionally specific: neither network synchronized with the executive control network. Thus, coordination between the language and ToM networks appears to be an inherent characteristic of their functional architecture, and is increased during naturalistic language processing.