Functional magnetic resonance imaging (fMRI) studies have demonstrated a critical role for a cortical region in the right temporo-parietal junction (RTPJ) in "theory of mind" (ToM), or mental state reasoning. In other research, the RTPJ has been implicated in the deployment of attention to an unexpected stimulus. One hypothesis ("attention hypothesis") is that patterns of RTPJ activation in ToM tasks can be fully explained by appeal to attention: stimuli that apparently manipulate aspects of ToM are in fact manipulating aspects of attention. On an alternative hypothesis ("ToM hypothesis"), functional regions identified by ToM tasks are selective for ToM, and not just for any unexpected stimulus. Here, we used fMRI to test these competing hypotheses: are brain regions implicated in ToM, including the RTPJ, LTPJ, and precuneus, recruited specifically for mental states, or for any unexpected stimulus? We first identified brain regions implicated in ToM, using a standard paradigm: participants read stories about false beliefs and false physical representations (e.g., outdated photographs). Participants also read a new set of stories describing mental or physical states, which were unexpected or expected. Regions of interest analyses revealed a higher response in the RTPJ, LTPJ, and precuneus, for mental versus physical stories, but no difference for unexpected and expected stories. Whole-brain random effects analyses also revealed higher activation in these regions for mental versus physical stories. This pattern provides evidence for the ToM hypothesis: the response in these functional regions is selective for mental state content, whether that content is unexpected or expected.
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