fMRI item analysis in a theory of mind task.

Conventional analyses of functional magnetic resonance imaging (fMRI) data compare the brain's response to stimulus categories (e.g., pictures of faces, stories about beliefs) across participants. In order to infer that effects observed with the specific items (a particular set of pictures or stories) are generalizable to the entire population (all faces, or all stories about beliefs), it is necessary to perform an "item analysis." Item analyses may also reveal relationships between secondary (non-hypothesized) features of the items and functional activity. Here, we perform an item analysis on a set of stories commonly used for localizing brain regions putatively involved in Theory of Mind (ToM): right and left temporo-parietal junction (RTPJ/LTPJ), precuneus (PC), superior temporal sulcus (STS) and medial prefrontal cortex (MPFC). We address the following questions: Do brain regions that comprise the ToM network respond reliably across items (i.e. different stories about beliefs)? Do these brain regions demonstrate reliable preferences for items within the category? Can we predict any region's response to individual items, by using other features of the stimuli? We find that the ToM network responds reliably to stories about beliefs, generalizing across items as well as subjects. In addition, several regions in the ToM network have reliable preferences for individual items. Linguistic features of the stimuli did not predict these item preferences.