O-03 Source modelling of endogenous potentials (ERPS), elicited by omitted targets, based on simultaneous EEG-FMRI recordings

Background ERPs occurring independently of any specific sensory event are purely endogenous (emitted potentials) and their neural generators univocally linked with cognitive components. Aim of the study was to localize and compare the sources of the scalp-recorded ERPs from two visual tasks: a standard two-stimulus oddball and an omitted-target oddball task, combining the high temporal resolution of electrophysiology with the fine spatial information provided by fMRI. Material and methods Thirteen healthy right-handed volunteers (5 females; mean age 26 years, range 22–29), were enrolled. The source modelling (dipole analysis) of ERPs was seeded to the clusters of fMRI activations. The simultaneous EEG-fMRI recording guaranteed the same cognitive states during the experimental session. Results Data depicted an antero-to-posterior neural circuitry for the rare, task–relevant events. P300 (P3b) was generated in frontal, temporo-parietal and parietal areas (these latter only in the standard oddball), namely the temporo-parietal junction (TPj), the premotor and motor area (M1) and the anterior intraparietal sulcus (aIPs). Anterior Insula contributed to the pP2, a recently described prefrontal component (different from the P3a) associated with the stimulus–response mapping. The anticipatory prefrontal negativity (pN) and Bereitschaftspotential (BP) were produced by anterior areas, namely the inferior and middle frontal gyrus over the lateral brain surface and the SMA-CMA areas over the medial cortex. Conclusions Recording emitted ERPs from omission of target stimuli in a simultaneous EEG-fMRI event-related paradigm allows a detailed spatio-temporal modeling of the neural generators of purely endogenous late potentials and provide useful insight to the interpretation of emitted/endogenous ERPs.