A direct comparison of theta estimates to AN and SW is shown in Figure 4. Theta power did not differ between the AN and SW conditions in LT area, since they both relied on lexical-semantic access subserved by the temporal cortex (Halgren et al., 1994; Dronkers et al., 2004; Ruff et al., 2008). However, the AN condition elicited stronger theta power than SW in both anterior and posterior inferoprefrontal regions (Table 1). This finding indicates that the inferior prefrontal cortex is sensitive to task difficulty since detecting “animals” as a special semantic category imposed demands on the controlled access to the semantic domain that exceeded mere access to the lexical form. This interpretation is consistent with similar findings in BOLD–fMRI studies showing that task difficulty results in increased activity in inferior prefrontal cortex (Gold and Buckner, 2002; Binder et al., 2009). In addition, the ACC also showed greater theta power to AN than SW. Greater engagement of the ACC during a semantically more demanding task as compared to the lexical decision was similarly reported by Ruff et al. (2008). Indeed,
