Spreading depression and near-infrared spectroscopy during seizures in patients with medically intractable epilepsy

Abstract

Cortical spreading depression (SD), a pathological cortical negative DC potential, is associated with various brain abnormalities. SD is a significant transient and localized relocation of ions within the neurons and spreads slowly like a wave in the brain tissue. SD results from a high extracellular K+ concentration, increasing neuronal excitability and, consequently, brain oxygen consumption. In our previous studies, we developed an electroencephalography (EEG) system capable of recording the SD from the surface scalp of epileptic patients. We demonstrated that SD is associated with seizures in patients with medically intractable epilepsy. In this paper, in addition to EEG measurements, near-infrared spectroscopy (NIRS) was used to measure local brain oxygen consumption during SD and seizures. NIRS is a non-invasive method to measure the hemodynamics of the tissue, such as oxy and deoxyhemoglobin concentrations, representing the gray matter's local neuronal metabolisms. By applying two or more wavelengths in the near-infrared window and measuring the attenuation variations of the relative change in the concentration of deoxyhemoglobin (HHb) and oxyhemoglobin (HbO2), the local oxygen consumption can be estimated. Method: We recorded SD and NIRS simultaneously during epileptiform EEG activities from twelve epileptic patients. Main result: SD occurred in the scalp of epileptic patients and preceded seizures with a varying time lag (0-30 minutes). HHb concentration increased during the SD duration. While HbO2 concentration decreased during the SD duration. Both returned to normal values after the SD event.