Naturally, there are clear benefits to localizing the neural generators of any scalp ERP activity, although more so when there is clear and independent evidence for the generating area’s function. As already noted, ERP components generally, and the N400 in particular, have been used successfully to answer cognitive questions even as their neural source remained obscure. Still, it is useful to now know that various neuroimaging data all point to a multimodal semantic system, and that MEG activity coincident with the scalp N400 suggests that it does not reflect activity in a single, static source but rather a wave of activity starting (~250 ms) in the posterior half of the left superior temporal gyrus, spreading first forward and ventrally to the left temporal lobe by 365 ms, and thereafter, between 370–500 ms, to the right anterior temporal lobe and to both frontal lobes. With such data in hand, the question becomes not where is the N400 generator localized, or whether there are multiple N400s, but rather what are the functions of the dynamic neural system of which scalp N400s are reflections?
