Combined MEG and EEG suggest a limbic source network of the P3 in retrosplenial cortex, insula, and hippocampus

Intracranial P3 activity in the hippocampus is a robust phenomenon, but it remains debated if this activity contributes to the extracranial P3. A second limbic P3 source was recently suggested in the retro-splenial cortex based on source analysis and fMRI. The present study tested if these sources could be confirmed by source modeling of a new data set. 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. Source analysis showed a strong P3 source in retrosplenial cortex. Further sources were observed in insular cortex and medial temporal lobe. 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 medial temporal lobe and insula contribute to both recording modalities. These data further support a P3 generator in retrosplenial cortex. Moreover, previously suggested generators in insula and medial temporal lobe, most likely in the hippocampus, are confirmed. In summary, the source configuration presented here suggests that the P3 is confined to limbic circuits.