Combined MEG and EEG suggest a limbic source network of the P3 including retrosplenial cortex and hippocampus

The P3 is evoked by most target and salient distractor stimuli, but its neural generators have remained controversial. Here we reevaluate the role of retro-splenial cortex and hippocampus as potential generators of the P3. Combined magneto- and electroencephalography signals were recorded during a visual oddball paradigm. Observers were instructed to respond to rare targets of a deviant shape and ignore rare non-targets of a deviant color. Source analysis was based on noise-normalized minimum norm estimates in an individual, MRI-based cortical source space. Critically, the source space was extended with the hippocampus. Source analysis showed strong sources in retrosplenial cortex and hippocampus at the P3 peak. Subsequent activity was observed in insula and anterior mid-cingulate cortex. The source configuration was similar for rare target and non-target stimuli. Simulations and further analyses show that the source in retrosplenial cortex is strongly attenuated in magnetoencephalography, whereas the source in hippocampus contributes to both recording modalities. These data support that retrosplenial cortex is a main generator of the P3 in EEG and that the hippocampal P3 source can be recorded with extracranial EEG and MEG. The source configuration presented here suggests that the P3 is confined to limbic circuits.