Optimization of the BOLD Hemodynamic Response Function for EEG-FMRI Studies in Epilepsy

Simultaneous EEG-fMRI measurements are used to study epileptic patients in order to localize brain regions associated with interictal epileptiform discharges (IEDs). The common approach to this analysis uses the generalized linear model (GLM) with a canonical hemodynamic response function (HRF) to relate EEG activity to predicted BOLD responses. The study aimed to determine whether the canonical HRF is optimal for IED-induced hotspot fMRI analysis and develop optimized HRFs. The optimization of four HRF models was performed on BOLD responses derived from SPM activation clusters from 36 epileptic patients. The results showed that the optimized HRF models improved the sensitivity of the EEG-fMRI analysis of IED events in epilepsy patients compared to standard HRFs. This was evidenced by an increase in the size, number, and maximum t-score values of activated areas.