High-density mapping in an N400 paradigm: evidence for bilateral temporal lobe generators

Objective: The aim of this study was to obtain a more detailed description of N400 scalp topography than has previously been reported. Methods: High-density (128 channel) visual event-related potentials were measured in an N400 paradigm using semantically incongruous sentence endings. Results: The stimuli elicited an N400 with a centroparietal scalp distribution. In addition, P400s with similar timing and functional characteristics were observed at non-standard recording locations inferior to the temporal lobes. Conclusions: The data are consistent with intracranial evidence for bilateral activation of anterior medial temporal lobe structures. These structures are oriented such that the positive regions of their scalp fields lie largely outside of the area sampled by standard electrode montages. P400s at other non-standard scalp locations, including infraorbital and infraoccipital sites, may reflect volume conduction from the same generators, or activation of non-temporal lobe generators.