The boundaries of language and thought: neural basis of inference making

Is human thought fully embedded in language, or do some forms of thought operate independently? To directly address this issue, we focus on inference making, a central feature of human cognition. In a 3T fMRI study we compare logical inferences relying on sentential connectives (e.g., not, or, if..then..) to linguistic inferences based on syntactic transformation of sentences involving ditransitive verbs (e.g., give, say, take). When contrasted with matched grammaticality judgments, logic inference alone recruited “core” regions of deduction (Brodmann Area 10p, 8m), while linguistic inference alone recruited perisylvian regions of linguistic competence, among others (BA 21, 22, 37, 39, 44, 45 and caudate). In addition, the two inferences commonly recruited a set of general “support” areas in fronto-parietal cortex (BA 6, 7, 8, 40, 47). The results indicate that logical inference is not embedded in natural language, while confirming the relative modularity of linguistic processes.