THE SEATS OF REASON - AN IMAGING STUDY OF DEDUCTIVE AND INDUCTIVE REASONING

WE carried out a neuroimaging study to test the neurophysiological pre dictions made by different cognitive models of reasoning. Ten normal v olunteers performed deductive and inductive reasoning tasks while thei r regional cerebral blood flow pattern was recorded using [O-15]H2O PE T imaging. In the control condition subjects semantically comprehended sets of three sentences. In the deductive reasoning condition subject s determined whether the third sentence was entailed by the first two sentences. In the inductive reasoning condition subjects reported whet her the third sentence was plausible given the first two sentences. Th e deduction condition resulted in activation of the left inferior fron tal gyrus (Brodmann areas 45, 47). The induction condition resulted in activation of a large area comprised of the left medial frontal gyrus , the left cingulate gyrus, and the left superior frontal gyrus (Brodm ann areas 8, 9, 24, 32). Induction was distinguished from deduction by the involvement of the medial aspect of the left superior frontal gyr us (Brodmann areas 8, 9). These results are consistent with cognitive models of reasoning that postulate different mechanisms for inductive and deductive reasoning and view deduction as a formal rule-based proc ess.