Early haemodynamic changes observed in patients with epilepsy, in a visual experiment and in simulations

Objective: The objective of this study was to investigate whether previously reported early blood oxygen level dependent (BOLD) changes in epilepsy could occur as a result of the modelling techniques rather than physiological changes. Methods: EEG-fMRI data were analysed from seven patients with focal epilepsy, six control subjects undergoing a visual experiment, in addition to simulations. In six separate analyses the event timing was shifted by either -9,-6,-3,+3,+6 or +9. s relative to the onset of the interictal epileptiform discharge (IED) or stimulus. Results: The visual dataset and simulations demonstrated an overlap between modelled haemodynamic response function (HRF) at event onset and at ±3. s relative to onset, which diminished at ±6. s. Pre-spike analysis at -6. s improved concordance with the assumed IED generating lobe relative to the standard HRF in 43% of patients. Conclusion: The visual and simulated dataset findings indicate a form of "temporal bleeding", an overlap between the modelled HRF at time 0 and at ±3. s which attenuated at ±6. s. Pre-spike analysis at -6. s may improve concordance. Significance: This form of analysis should be performed at 6. s prior to onset of IED to minimise temporal bleeding effect. The results support the presence of relevant BOLD responses occurring prior to IEDs.