Our results show that real words (SW) are associated with greater event-related theta than pseudowords (PW) in the left temporo-prefrontal areas in contrast to previous time-domain MEG findings of larger or equal N400m to PW compared to SW (Wydell et al., 2003; Vartiainen et al., 2011). Similarly, a stronger activation of the left inferior prefrontal cortex has been observed to PW than to SW with BOLD–fMRI (Binder et al., 2003; Clark and Wagner, 2003; Burton et al., 2005). Some fMRI studies, however, show differential activity in the anterior vs. posterior inferior prefrontal cortex depending on the semantic and phonological task manipulations (Binder et al., 2003; Mechelli et al., 2005; Humphries et al., 2007). Taken together, these findings suggest that PW, which share the structural characteristics with SW, engage the semantic network during the search for semantic representations. Indeed, we acquire new words continually and many of the words that are currently contained in our vocabulary were initially perceived as PW. The words used in the present study had very low frequency (4.3 ± 2.4 occurrences per million), which can explain
