events, in the time window [ti−150 ms; ti+150 ms], and the P300 response intensity ai was estimated by means of a least-squares fit of ai·p with respect to ki. After calculating the P300 response time-courses for each of the 6 selected electrodes, a global P300 response time-course was calculated by averaging them. In order to obtain a P300 reference time-course for EEG–fMRI correlation analysis, the global P300 response time-course was convolved with a canonical hemodynamic response function (HRF), generated using a gamma function (delay time, 2 s; rise time, 4 s; fall time, 6 s; undershoot, 0.2; restore time, 2 s). Finally, the P300 reference time-course was normalized by subtracting the minimum value and dividing by the difference of maximum and minimum values.
