Cortical distribution of N400 potential in response to semantic priming with visual non-linguistic stimuli

We conducted a study on visual semantic priming using related and unrelated image pairs while simultaneously recording electroencephalography (EEG) from 27 scalp electrodes and electrocorticography (ECoG) from a mixture of deep brain and subdural grid/strip electrodes in the left and right hippocampus, the right temporo-basal and temporo-lateral cortices, and the left temporal cortex. The EEG data showed a clear centro-parietal, bi-hemispheric N400 effect in response to unrelated image-pairs compared to related ones. Although with ECoG the N400 effect was more widely spread across both hemispheres, compared to linguistic stimuli, it was relatively localized within each ECoG grid as it was present only in some electrodes and, in some cases, even had its polarity reversed. We advocate this could be due to some grids gauging dipoles at different positions when covering sulci and gyri.