This relationship allows us to constrain, voxel by voxel, the integral of the power of the EEG/MEG source estimates in accordance with the BOLD effect size. Specifically, we can scale the source time course estimated from the ERP/ERF, so that the time integral of the power of the scaled source estimates equals the BOLD effect size [24] as illustrated in Fig. 5. Namely, this process is referred to as the fMRI-EEG/MEG co-registration.
