Event-Related Potentials and Fast Optical Imaging of Cortical Activity During an Auditory Oddball Task

Event-related potentials (ERP) have been repeatedly used to study the spatiotemporal dynamics of the attentional response in the well-known oddball paradigm. We combined electroencephalography (EEG) with frequency-domain near-infrared spectroscopy (fNIRS) of the frontal cortex to measure neuronal activity with a high spatial and temporal resolution. The aim of this study was to determine the precise chronology of event-related optical signals (EROS) and their consistency with ERPs. In agreement with previous studies, the oddball condition produced larger waveforms for rare (1500 Hz pure tone) with respect to frequent stimuli (1000 Hz), with N1, P2, N2, P3a, and P3b components. At a latency corresponding to the mismatch negativity/N2 wave component, EROS showed the organization of a complex activity in a functional network of frontal areas, with rare tones activating the left premotor dorsal cortex and the left inferior frontal cortex and decreasing the activity of the right superior frontal gyrus. Rare tones elicited also a strong N500 (N400-like) wave component that EROS contributed to localize at the level of the right medial frontal gyrus by EROS. The simultaneous recording of fNIRS and EEG measurements with high temporal accuracy over the human prefrontal cortex supports the potential for this approach to unravel the functional cortical network involved in cognitive processing.