Neural processing associated with comprehension of an indirect reply during a scenario reading task.

In daily communication, we often use indirect speech to convey our intention. However, little is known about the brain mechanisms that underlie the comprehension of indirect speech. In this study, we conducted a functional MRI experiment using a scenario reading task to compare the neural activity induced by an indirect reply (a type of indirect speech) and a literal sentence. Participants read a short scenario consisting of three sentences. The first two sentences explained the situation of the protagonists, whereas the third sentence had an indirect, literal, or unconnected meaning. The indirect reply condition primarily activated the bilateral fronto-temporal networks (Brodmann's Areas (BA) 47 and 21) and the dorso-medial prefrontal cortex (dmPFC). In the literal sentence condition, only the left fronto-temporal network (BA 45 and 21) and the dmPFC (posterior region) were activated. In addition, we found greater activation resulting from comprehension of an indirect reply than from literal sentence comprehension in the dmPFC, the left middle frontal area (BA 9), the bilateral inferior frontal area (BA 9/47), and the right middle temporal area (BA 21). Our findings indicate that the right and left fronto-temporal networks play a crucial role in detecting contextual violations, whereas the medial frontal cortex is important for generating inferences to make sense of remarks within a context.