A role for right ventrolateral prefrontal cortex in reasoning about indeterminate relations.

While the role of left prefrontal cortex in reasoning tasks has long been recognized, the role of right prefrontal cortex remains unclear. One patient study [Goel, V., Tierney, M., Sheesley, L., Bartolo, A., Vartanian, O., & Grafman, J. (2007). Hemispheric specialization in human prefrontal cortex for resolving certain and uncertain inferences. Cerebral Cortex, 17(10), 2245-2250] has suggested that right prefrontal cortex plays an essential role in resolving indeterminate relations. To test this hypothesis, and to identify the involvement of specific regions within right prefrontal cortex we scanned 17 normal volunteers with fMRI while they engaged in a transitive inference task involving determinate and indeterminate relations. The results show a nice crossover interaction such that, right ventrolateral prefrontal cortex (BA 47) is selectively activated by the processing of indeterminate trials with no belief-bias cues, while left lateral prefrontal cortex (BA 45) is selectively activated by the processing of indeterminate trials containing belief-bias cues. These results are not only consistent with, but also amplify, the lesion data by identifying specific regions within right and left prefrontal cortex.