Theory of Mind brain regions are sensitive to the content, not the structural complexity, of belief attributions

A distinct group of brain regions, the ‘Theory of Mind (ToM) network’, is implicated in representing other people’s mental states, yet we currently know little about which aspects of mental state attribution are represented or processed in these regions. Using fMRI, we investigated whether ToM regions, compared to language-processing regions, are sensitive to two dimensions along which mental state attributions vary: (1) structural complexity and (2) social content of the attributed thought. In short vignettes describing a character's belief, the belief structure was either first-order or higher-order, and the content was mundane or socially-relevant. All ToM regions showed sensitivity to distinctions in content; no ToM region showed sensitivity to structural manipulation. By contrast, language regions were sensitive to both manipulations. We conclude that while increased structural complexity of belief attributions modulates language processing, this type of complexity is not part of the representational space of the ToM-network.