Functional neuroanatomy of deductive inference: a language-independent distributed network

Studies of brain areas supporting deductive reasoning show inconsistent results, possibly because of the variety of tasks and baselines used. In two event-related functional magnetic imaging studies we employed a cognitive load paradigm to isolate the neural correlates of deductive reasoning and address the role (if any) of language in deduction. Healthy participants evaluated the logical status of arguments varying in deductive complexity but matched in linguistic complexity. Arguments also varied in lexical content, involving blocks and pseudo-words in Experiment I and faces and houses in Experiment II. For each experiment, subtraction of simple from complex arguments (collapsing across contents) revealed a network of activations disjoint from regions traditionally associated with linguistic processing and also disjoint from regions recruited by mere reading. We speculate that this network is divided into "core" and "support" regions. The latter include left frontal (BA 6, 47) and parietal (BA 7, 40) cortices, which maintain the formal structure of arguments. Core regions, in the left rostral (BA 10p) and bilateral medial (BA 8) prefrontal cortex, perform deductive operations. Finally, restricting the complex-simple subtraction to each lexical content uncovered additional activations which may reflect the binding of logical variables to lexical items.