Hierarchical systems in the default mode network when reasoning about self and other mental states

Humans spend time contemplating the minds of others. But this ability is not limited to external agents - we also turn the lens for reading minds inward, reflecting on our own thoughts, emotions, and sense of self. Some processes involved in reasoning about minds may rely on shared mechanisms, while others may be specific to the agent under consideration. We developed a paradigm where participants performed either a mental state inference task or a control task targeting either another person presented onscreen or their own mind. Using fMRI and multi-voxel pattern analysis, we replicate a well-established self-other axis along the medial wall of prefrontal cortex: ventral regions selectively decoded mental state inference patterns for self, but not other, whereas more dorsal regions decoded mental state inference for both self and other, compared to control conditions. Posterior cingulate cortex, on the other hand, differentiated the target of mental state inference. Using a cross-classification analysis, we also found patterns in the dorsomedial prefrontal cortex, ventromedial prefrontal cortex, and right temporoparietal junction were sensitive to mental state reasoning in general, regardless of the target agent. These findings highlight one process reflecting reasoning specific to the agent and another reflecting the reasoning process itself.