Complex social behavior and the relatively large size of the prefrontal cortex are arguably two of the characteristics that distinguish humans from other animals. Grafman presented a framework concerning how the prefrontal cortex (PFC) controls complex behavior using stored structured event complexes (SECs). We report behavioral and imaging data from a modified go/no-go paradigm in which subjects had to classify words (semantic) and phrases (SEC) according to category. In experimental trials, subjects classified items according to social or nonsocial activity; in control trials, they classified items according to font. Subjects were faster to classify social than nonsocial semantic items, with the reverse pattern evident for the social and nonsocial SEC items. In addition, the conditions were associated with different patterns of PFC activation. These results suggest that there are different psychological and neural substrates for social and nonsocial semantic and SEC representations.

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