Concurrent recordings of slow DC-potentials and epileptiform discharges: Novel EEG amplifier and signal processing techniques

Ionic currents within the brain generate voltage oscillations. These bioelectrical activities include ultra-low frequency electroencephalograms (DC-EEG, frequency less than 0.1 Hz) and conventional clinical electroencephalograms (AC-EEG, 0.5–70 Hz). Although AC-EEG is commonly used for diagnosing epilepsy, recent studies indicate that DC-EEG is an essential frequency component of EEG and can provide valuable information for analyzing epileptiform discharges. During conventional EEG recordings, DC-EEG is censored by applying high-pass filtering to i) obliterate slow-wave artifacts, ii) eliminate the bioelectrodes' half-cell potential asymmetrical changes in ultralow-low frequency, and iii) prevent instrument saturation. Spreading depression (SD), which is the most prolonged fluctuation in DC-EEG, may be associated with epileptiform discharges. However, recording of SD signals from the scalp's surface can be challenging due to the filtering effect and non-neuronal slow shift potentials. In this study, we describe a novel technique to extend the frequency bandwidth of surface EEG to record SD signals. The method includes novel instrumentation, appropriate bioelectrodes, and efficient signal-processing techniques. To evaluate the accuracy of our approach, we performed a simultaneous surface recording of DC- and AC-EEG from epileptic patients during long-term video EEG monitoring, which provide a promising tool for diagnosis of epilepsy. The data presented in this study are available on request. •Recording DC-EEG signals from the scalp can be challenging without a high-pass filter.•A novel device has been designed for simultaneous recording of AC and DC potentials.•This includes a unique amplifier, bioelectrodes, and signal processing techniques.•The device has the potential to be a valuable tool for diagnosing epilepsy.