EEG-correlated fMRI of P3b component in P300 waves

Electroencephalography-correlated functional magnetic resonance imaging (EEG/fMRI) can be used to identify blood oxygen level-dependent (BOLD) signal changes associated with both physiological and pathological EEG events. Here, we implemented continuous and simulta-neous EEG/fMRI to identify BOLD signal changes related to P3b component of P300, and 64 channels of EEG were re-corded in 11 subjects during Landot Ring task inside a 1.5 T functional magnet resonance (MR) scanner using an MR-compatible EEG recording system. Functional scanning by echoplanar imaging covered almost the entire cerebrum every 2 s, leaving gaps of 2 s without scanning. Off-line MRI artifact subtraction software was applied to obtain continu-ous EEG data. Additionally, a P300 wave matched filter was constructed to inspect P300 wave occurrence following every target stimulus, target stimuli inspected to induce P300 were detected and their MRI scan number were then used as input for an event-related fMRI analysis. Finally MRI statistical parametric maps were constructed and corrected for multi-ple comparisons. By random effect group analysis, activa-tions were detected in the right superior parietal lobule and bilaterally in inferior parietal lobule(p<0.001, uncorrected). The results demonstrated the upper regions were sources of P3b component and involved in target detection in memory comparison task.

fMRI-constrained source analysis of visual P300 in Landolt ring task

An fMRI-constrained source analysis was applied to investigate visual P300 in the Landolt ring task. To study the localization and relative activation timing of P300 generators, we implemented simultaneous EEG/fMRI to identify BOLD signal changes and record 64-channel EEG in 10 subjects during a Landolt ring task inside a 1.5-T fMRI scanner using an MR-compatible EEG recording system. MRI artifact sub-traction software was applied to obtain continuous EEG data. Then, the simultaneous collecting of EEG and fMRI was validated in preserving relevant ERPs. The fMRI-constrained source analysis resulted in an 8-dipole solution. The bilateral middle frontal and the right inferior parietal dipole waveforms showed a short latency peak corresponding to the early P300 activity, while the four parietal and the anterior cingulate dipole waveforms showed a long latency peak corresponding to the late P300 activity. The longest latency peak of the anterior cingulate dipole agrees with its role in initiation of motor re-sponse after successful target recognition. Target detection in the Landolt ring task produces the strongest and most extensive parietal activation (especially superior parietal activation), which might be due to its particular visual attention switching.