Semantics vs. world knowledge in prefrontal cortex

Humans have knowledge about the properties of their native language at various levels of representation; sound, structure, and meaning computation constitute the core components of any linguistic theory. Although the brain sciences have engaged with representational theories of sound and syntactic structure, the study of the neural bases of sentence-level semantic computation has so far focused on manipulations that mainly vary knowledge about the world, and not necessarily linguistic knowledge about meaning, as defined by formal semantics. In this MEG study, we vary both semantic and world knowledge in the same experiment, and show that semantic violations, but not world knowledge violations, elicit an effect in the ventromedial prefrontal cortex (vmPFC), while both types of violations engage the left inferior prefrontal cortex. In our previous work, we have shown that the vmPFC is also sensitive to various types of 'coercions', i.e., operations that repair semantic type-mismatch. Together, these results suggest that the vmPFC is involved in the composition of complex meaning, but not in the evaluation of whether an expression fits one's knowledge of the world.