Local haemodynamic changes preceding interictal spikes: a simultaneous electrocorticography (ECoG) and near-infrared...

The mechanisms that drive neurons to synchronize in epileptic spikes are still subject to debate. In the present study, we used a combination of electrocorticography and near-infrared spectroscopy (ECoG/NIRS) to evaluate haemodynamic changes before, during and after epileptic spikes induced by administration of bicuculline methiodide (BM) onto the sensorimotor cortex in 8 adult Sprague-Dawley rats. Simultaneous ECoG/NIRS signals were recorded during an initial reference period (to measure spontaneous bioelectrical/metabolic activities) and then again 60 min after BM administration. Spikes in the ECoG were detected by an in-house program based on MatLab 7.0. The appearance times of the P1 peaks were used to determine corresponding time periods in the NIRS for further analysis. We observed a pronounced pre-spike modification in the haemodynamics, which became visible latest 5 s before the spike, achieving after some oscillations its minimum at round about the P1 appearance time. The post-spike period was characterized by an initial increase in oxyhaemoglobin (HbO) and total haemoglobin (HbT) to a maximum at about 2 s after the spike followed by a phase of declining oscillations disappearing after 10 to 15 s after the spike. We discuss the mechanisms underlying the haemodynamic and electrical changes that occur before, during and after epileptiform spikes. The haemodynamic changes observed with NIRS and occurring before the spikes constitute a haemodynamic predictor of electrical synchronization of spikes.