Distinct brain loci in deductive versus probabilistic reasoning

Daniel Osherson, Daniela Perani, Stefano Cappa, Tatiana Schnur, Franco Grassi, Ferruccio Fazio

Research output: Contribution to journalArticlepeer-review

114 Scopus citations


Deductive versus probabilistic inferences are distinguished by normative theories, but it is unknown whether these two forms of reasoning engage similar cerebral loci. To clarify the matter, positron emission tomography was applied during deductive versus probabilistic reasoning tasks, using identical stimuli. Compared to a language comprehension task involving the same stimuli, both probabilistic and deductive reasoning increased regional cerebral blood flow (rCBF) bilaterally in the mesial frontal region and in the cerebellum. In the direct comparison, probabilistic reasoning increased rCBF in left dorsolateral frontal regions, whereas deductive reasoning enhanced rCBF in associative occipital and parietal regions, with a right hemispheric prevalence. The results suggest that reasoning about syllogisms engages distinct brain mechanisms, depending on the intention to evaluate them deductively versus probabilistically.

Original languageEnglish (US)
Pages (from-to)369-376
Number of pages8
Issue number4
StatePublished - Apr 1998

All Science Journal Classification (ASJC) codes

  • Experimental and Cognitive Psychology
  • Cognitive Neuroscience
  • Behavioral Neuroscience


  • Deductive
  • Neural correlates
  • Positron emission tomography
  • Probabilistic reasoning


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