Functional areas in sensory/motor cortices are usually organized, on a finer scale, in a seamless manner along related functional units that represent, for example, certain visual fields to analyze and certain body parts to control. However, fine-scale functional organization in the prefrontal cortex has rarely been reported. In the present functional magnetic resonance imaging study, we show an example of sub-centimeter scale functional organization in the posterior part of the inferior frontal gyrus (IFG) in the right hemisphere. The spatial relationship was examined in the same subjects with regard to the activations associated with response inhibition and negative feedback processing, which are known to activate similar right IFG regions. We found that these activations were segregated, the activation during response inhibition being more caudal than that during feedback processing, and that the distance between the two activations was only 8.7 mm. Examination of the two-dimensional surface mapping of individual subjects confirmed that the two activations were located in adjacent but different regions. These results provide a specific example of a pair of functionally characterized regions that are located in the close vicinity within the right IFG.
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