Detection of spreading depression features from the scalp of epileptic patients.

Spreading depression (SD), a pathological cortical negative DC potential, is caused by an elevation of potassium ions in the extracellular space. This leads to a transient relocation of ions within neurons and a slow spread through brain tissue. Our previous research established a correlation between scalp SD and seizures in patients with intractable epilepsy using our novel electroencephalography (EEG). In this study, we enhanced our EEG system by incorporating a Near-infrared spectroscopy (NIRS) module for multi-modal EEG-NIRS measurements. The aim is to provide an investigation into the defining characteristics and methods for detecting SD.Clinical Relevance-: The detection of SD serves as a novel biomarker for epilepsy, capable of forewarning seizures within a time range from 10 secs to 30 min. This detection plays a crucial role in predicting and preventing seizures and providing diagnostic information for drug-resistant epilepsy patients.

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. DATA AVAILABILITY STATEMENT: The data presented in this study are available on request.

The Effects of Silicone Enclosure Colour on the Function of Optical Sensors.

The colour of the silicone enclosure of an implantable reflectance-based optical probe plays a critical role in sensor performance. Red-coloured probes that are highly reflective to near-infrared light have been found to increase photodetector power by a factor of 6 for wavelengths between 660 and 950 nm and triple the magnitude of measured cardiac pulsations compared to traditional black probes. The increase in photodetector power and cardiac pulsation magnitude is presumably due to increased spatial range resulting from a higher magnitude of superficial tissue scattering. Conversely, probes with highly absorbent colours such as black and blue result in more stable signals and are expected to have higher spatial resolution and depth of penetration.

Studying the Accuracy and Function of Different Thermometry Techniques for Measuring Body Temperature.

The purpose of this study was to determine which thermometry technique is the most accurate for regular measurement of body temperature. We compared seven different commercially available thermometers with a gold standard medical-grade thermometer (Welch-Allyn): four digital infrared thermometers (Wellworks, Braun, Withings, MOBI), one digital sublingual thermometer (Braun), one zero heat flux thermometer (3M), and one infrared thermal imaging camera (FLIR One). Thirty young healthy adults participated in an experiment that altered core body temperature. After baseline measurements, participants placed their feet in a cold-water bath while consuming cold water for 30 min. Subsequently, feet were removed and covered with a blanket for 30 min. Throughout the session, temperature was recorded every 10 min with all devices. The Braun tympanic thermometer (left ear) had the best agreement with the gold standard (mean error: 0.044 °C). The FLIR One thermal imaging camera was the least accurate device (mean error: -0.522 °C). A sign test demonstrated that all thermometry devices were significantly different than the gold standard except for the Braun tympanic thermometer (left ear). Our study showed that not all temperature monitoring techniques are equal, and suggested that tympanic thermometers are the most accurate commercially available system for the regular measurement of body temperature.

Association of cortical spreading depression and seizures in patients with medically intractable epilepsy.

OBJECTIVE: Monitoring of the ultra-low frequency potentials, particularly cortical spreading depression (CSD), is excluded in epilepsy monitoring due to technical barriers imposed by the scalp ultra-low frequency electroencephalogram (EEG). As a result, clinical studies of CSD have been limited to invasive EEG. Therefore, the occurrence of CSD and its interaction with epileptiform field potentials (EFP) require investigation in epilepsy monitoring. METHODS: Using a novel AC/DC-EEG approach, the occurrence of DC potentials in patients with intractable epilepsy presenting different symptoms of aura was investigated during long-term video-EEG monitoring. RESULTS: Various forms of slow potentials, including simultaneous negative direct current (DC) potentials and prolonged EFP, propagated negative DC potentials, and non-propagated single negative DC potentials were recorded from the scalp of the epileptic patients. The propagated and single negative DC potentials preceded the prolonged EFP with a time lag and seizure appeared at the final shoulder of some instances of the propagated negative DC potentials. The slow potential deflections had a high amplitude and prolonged duration and propagated slowly through the brain. The high-frequency EEG was suppressed in the vicinity of the negative DC potential propagations. CONCLUSIONS: The study is the first to report the recording of the propagated and single negative DC potentials with EFP at the scalp of patients with intractable epilepsy. The negative DC potentials preceded the prolonged EFP and may trigger seizures. The propagated and single negative DC potentials may be considered as CSD. SIGNIFICANCE: Recordings of CSD may serve as diagnostic and prognostic monitoring tools in epilepsy.

Non-invasive monitoring of spreading depression.

Spreading depression (SD), a slow propagating depolarization wave, plays an important role in pathophysiology of different neurological disorders. Yet, research into SD-related disorders has been hampered by the lack of non-invasive recording techniques of SD. Here we compared the manifestations of SD in continuous non-invasive electroencephalogram (EEG) recordings to invasive electrocorticographic (ECoG) recordings in order to obtain further insights into generator structures and electrogenic mechanisms of surface recording of SD. SD was induced by KCl application and simultaneous SD recordings were performed by scalp EEG as well as ECoG electrodes of somatosensory neocortex of rats using a novel homemade EEG amplifier, AgCl recording electrodes, and high chloride conductive gel. Different methods were used to analyze the data; including the spectrogram, bi-spectrogram, pattern distribution, relative spectrum power, and multivariable Gaussian fit analysis. The negative direct current (DC) shifts recorded by scalp electrodes exhibited a high homogeneity to those recorded by ECoG electrodes. Furthermore, this novel method of recording and analysis was able to separate SD recorded by scalp electrodes from non-neuronal DC shifts induced by other potential generators, such as the skin, muscles, arteries, dura, etc. These data suggest a novel application for continuous non-invasive monitoring of DC potential changes, such as SD. Non-invasive monitoring of SD would allow early intervention and improve outcome in SD-related neurological disorders.