Comprehension of implicit meanings in social situations involving irony: a functional MRI study

To understand implicit social meanings, the interaction of literal meanings and relevant information in a situational context is important. However, previous studies have not investigated such contextual interactions. Using functional magnetic resonance imaging (fMRI), we investigated cortical mechanisms underlying the processing of implicit meanings, particularly irony, in realistic social situations, focusing on contextual interactions. Healthy subjects were shown pictures depicting daily communicative situations during judgment tasks involving situational appropriateness and literal correctness. The left medial prefrontal cortex showed significantly greater activation during tasks involving situational judgments than during literal judgments. The right temporal pole was activated task-independently during irony-specific processing. The medial orbitofrontal cortex was activated task-dependently during irony processing in situational judgment tasks. These regions have been reported to be involved in theory of mind, and have not been implicated in previous studies on the linguistic processing of implicit meanings. This suggests that the intentional assessment of situational appropriateness for task execution is carried out in the left medial prefrontal cortex, whereas irony is processed in the right temporal pole by assessing situational context automatically, and is judged based on the situational context in the medial orbitofrontal cortex. Our results show that the processing of implicit meanings and irony in contextually rich situations depends on brain mechanisms involved in the "theory of mind," based on processing relevant information in a situational context, and suggest different functions in each region.