A role for the right prefrontal and bilateral parietal cortex in four-term transitive reasoning: an fMRI study with abstract linear syllogism tasks.

Previous imaging studies have identified many brain regions activated during reasoning, but there are differences among the findings concerning specific regions engaged in reasoning and the contribution of language areas. Also, little is known about the relation between task complexity and neural activation during reasoning. The present fMRI study investigated brain activity during complex four-term transitive reasoning with abstract material (determinate or partially indeterminate) and compared the resulting images to those obtained during a memorization task. The memory condition required subjects to memorize unrelated elements whereas the reasoning conditions required them to integrate information from premises and to infer relations between elements. After contrasting the two kinds of reasoning conditions with the memory condition we found that right prefrontal and bilateral parietal regions are specifically activated during reasoning. We also demonstrated that different reasoning requirements--the possibility of constructing one (determined reasoning) versus several (undetermined reasoning) models of a situation during task solving--lead to different patterns of brain activity, with higher prefrontal (PFC) activity accompanying undetermined reasoning. We interpret the PFC activity as a reflection of simultaneous maintenance and manipulation of information in reasoning. These findings provide new evidence that specific forms of reasoning (abstract and undetermined) demand recruitment of right PFC and hemispheric coordination and lend new support to the mental model theory of relational reasoning.