Human beings are uniquely equipped with the capacity to reason in sophisticated ways about others’ thoughts and feelings, an ability often referred to as a ‘theory of mind’ (Premack & Woodruff, 1978; Gopnik & Wellman, 1994; Leslie et al., 2004). Recent literature on theory of mind has expanded considerably, and contemporary theoretical work has sought to differentiate ways in which different component psychological processes may contribute to mental state reasoning (Schaafsma et al., 2015; Van Overwalle & Vandekerckhove, 2013). Several prominent accounts have sought to explain an empirical dissociation between mentalizing-related activity in the dorsal medial prefrontal cortex (DMPFC) and the ventral medial prefrontal cortex (VMPFC): the former region is characteristically implicated in reasoning about unknown others while the latter is consistently evoked with participants reason about the self and close others (see meta-analysis by Van Overwalle & Baetens, 2009). A ‘similarity’ account sees the activity of ventral MPFC as related to its role in simulating the minds of others by reference to our own thoughts and feelings (Mitchell, Banaji, & Macrae, 2005; Mitchell, Macrae, & Banaji, 2006). According to this viewpoint, we can employ the same neuro-cognitive resources and mechanisms when thinking about others as when introspecting about our own mental states, provided that others are seen to be sufficiently similar to the self. A second theoretical view contends that VMPFC is responsible for encoding and reasoning about the minds of close others, who are members of our family, tribe, or another meaningful social group (Krienen, Tu, & Buckner, 2010).

In the present dissertation work a third alternative is proposed, according to which person-specific knowledge of others’ unique personal characteristics allows for nuanced and individuated inferences about their transient mental states and enduring dispositional traits. We theorize that rich experiential knowledge of particular individuals can be leveraged into person-specific theories of mind, instantiated in the MPFC, which facilitate mental state reasoning that is tailored to the minds of those persons we know especially well. In Study 1, we provide neuroimaging (fMRI) results in favor of this ‘person-specific theory-of-mind hypothesis’, showing that ventral VMPFC is more responsive to well-known targets than to poorly-known targets, regardless of perceived similarity and affective closeness. Moreover, activity in medial prefrontal cortex is associated with trial-by-trial variation in the availability of person-specific knowledge, and with participants’ willingness to attribute idiosyncratic traits to social targets. In a second fMRI study (Study 2), we explore the formation of person-specific theories of mind regarding initially unfamiliar targets, revealing a comparable pattern of hemodynamic activity.