Activation of the posterior cingulate by semantic priming: a co-registered ERP/fMRI study.

Although the N400 is the best understood semantically sensitive component of the event-related potential (ERP), others have been observed as well. In an earlier lexical decision study, an N300 ERP was found to be enhanced to unprimed targets, although the effect could also be characterized as a prolonged P2 to primed targets as described in other reports. Because its scalp topography suggested its neural source might be of interest, a source localization was conducted that suggested that this component emanated from the dorsal posterior cingulate cortex (dPCC). In order to confirm this word N300 localization, a functional magnetic resonance imaging (fMRI) study was conducted to replicate the ERP study with a separate sample of 17 participants in an event-related design, using a 3-T scanner. A significant activation in the right dPCC was found corresponding to the N300 localization. The activation was greater on the related prime trials, supporting the characterization of the ERP component as being a P2 rather than an N300. A review is provided which suggests that a number of separate lines of ERP research regarding the word N300, the picture N300, the word P2, the phonological mismatch negativity, and the word midline frontal negativity may be most parsimoniously regarded as dealing with the same ERP component and that they all therefore emanate from the dPCC. It is suggested that this region plays a role in stimulus-response mapping in polymodal fashion. It is also suggested that the ERP component be termed a P2-dPCC.