High-resolution spatio-temporal neuronal activation in the visual oddball task: a simultaneous EEG/fMRI study

The combined use of EEG and fMRI allows for the fusion of electrophysiological and hemodynamic information in the study of human cognitive functions. In order to investigate cerebral activity during a visual oddball task, simultaneous EEG/fMRI recording from 10 healthy subjects was performed. A devoted data-analysis method based on trial-by-trial coupling of concurrent EEG and fMRI for the high-resolution spatio-temporal analysis of P300 neuronal activation was developed. Our results obtained from fMRI data showed the involvement of inferior and medial frontal gyrus, cingulated motor area, middle temporal gyrus, and inferior parietal lobule in the oddball task; furthermore, activations were generally right lateralized, in accordance with previous findings. Using the high temporal resolution of EEG, we could separate neuronal activations specifically related to P300 activity, and therefore study the activation timing. We found that the detection of rare targets, that is able to elicit the P300 component, stimulates a limbic-parietofrontal circuit, with latencies ranging between 300 and 400 ms. Our findings suggest that the proposed approach might be extended to other event-related experimental paradigms, and might represent an valuable tool for a clearer understanding of the cerebral mechanisms underlying a wide range of cognitive functions.