fMRI evidence that left posterior temporal cortex contributes to N400 effects of predictability independent of congruity

Previous electrophysiological work argues that predictability and semantic incongruity rapidly impact comprehension, as indicated by modulation of the N400 component between ~300-500ms. An ongoing question is whether effects of predictability in fact reflect pre-activation in long-term memory as opposed to modulating the kind of integration processes triggered by incongruity. We used a functional localizer approach in fMRI to compare the impact of predictability and incongruity in comprehension of adjective-noun phrases. We found that predictability impacted activity in left posterior middle temporal gyrus (pMTG), while incongruity impacted activity in left middle frontal gyrus. Together with parallel data from ERP, these data support the hypothesis that left pMTG activity is a key contributor to N400 effects of predictability and that the mechanism driving this effect is reduced activation of stored lexical representations. We tentatively suggest that the left middle frontal gyrus may play a role in reanalysis when incongruity is encountered.