Detectability of the somatosensory evoked high frequency oscillation (HFO) co-recorded by scalp EEG and ECoG under propofol

Abstract

ObjectiveThe somatosensory evoked potential (SEP) elicited by median nerve stimulation consists of the N20 peak together with the concurrent high frequency oscillation (HFO, > 500 Hz). We describe the conditions for HFO detection in ECoG and scalp EEG in intraoperative recordings.MethodsDuring neurosurgical interventions in six patients under propofol anesthesia, the SEP was recorded from subdural electrode strips (15 recordings) and from scalp electrodes (10/15 recordings). We quantified the spatial attenuation of the Signal-to-Noise Ratio (SNR) of N20 and HFO along the contacts of the electrode strip. We then compared the SNR of ECoG and simultaneous scalp EEG in a biophysical framework.ResultsHFO detection under propofol anesthesia was demonstrated. Visual inspection of strip cortical recordings revealed phase reversal for N20 in 14/15 recordings and for HFO in 10/15 recordings. N20 had higher maximal SNR (median 33.5 dB) than HFO (median 23 dB). The SNR of N20 attenuated with a larger spatial extent (median 7.2 dB/cm) than the SNR of HFO (median 12.3 dB/cm). We found significant correlations between the maximum SNR (rho = 0.58, p = 0.025) and the spatial attenuation (rho = 0.86, p < 0.001) of N20 and HFO. In 3/10 recordings we found HFO in scalp EEG. Based on the spatial attenuation and SNR in the ECoG, we estimated the scalp EEG amplitude ratio N20/HFO and found significant correlation with recorded values (rho = 0.65, p = 0.049).ConclusionsWe proved possible the intraoperative SEP HFO detection under propofol anesthesia. The spatial attenuation along ECoG contacts represents a good estimator of the area contributing to scalp EEG. The SNR and the spatial attenuation in ECoG recordings provide further insights for the prediction of HFO detectability in scalp EEG. The results obtained in this context may not be limited to SEP HFO, but could be generalized to biological signatures lying in the same SNR and frequency range.

High-frequency oscillations in scalp EEG mirror seizure frequency in pediatric focal epilepsy

“…paroxysmal stereotyped artifacts or muscle activity) pose a risk for the detection of “false FR” 32 . Our recordings with evoked HFO point to a low signal-to-noise ratio for scalp FR 33 . Taken together with our unfavorable findings regarding scalp FR, we do not consider scalp FR to have clinical relevance in the data recorded with our setup.…”

“…While LNA technology permits to improve the SNR for specific scalp electrode positions, a significant requirement is optimal spatial sampling 18,31,35–38 . High-density scalp EEG (HD-EEG) is gaining ground in the last decade, as it can be readily implemented in every epilepsy unit, drastically increasing the resolution of scalp recordings and thus facilitating the matching of scalp signals to their cortical correlates 39,40 .…”

“…Scalp HFO are hard to detect, and their analysis in a clinical setting is particularly challenging in terms of time and effort. The feasibility of detection for scalp HFO, corresponding to invasive HFO, has been attested under favorable signal-to-noise ratio (SNR) conditions 17,18 . In this line, we have previously demonstrated that a low-noise amplifier (LNA) significantly enhances the SNR in the HFO spectral range, thus improving HFO detection in the intraoperative electrocorticography (ECoG) compared to a commercial device (CD) 19,20 .…”

High-density ECoG improves the detection of high frequency oscillations that predict seizure outcome

“…FR are generated by a small patch of cortical tissue, i.e. they are spatially highly localized and have a low amplitude (Burnos et al, 2016, Jiruska et al, 2017, von Ellenrieder et al, 2014.…”

Advances in Magnetoresistive Biosensors

“…Furthermore, MEG systems cannot measure brain activities from a focused region of the brain, which MRI scanning techniques or implantable recording electrodes can offer [135,136]. EEG signals suffer from heavy attenuation along the skull and hence the amplitude of the measured signal is compromised [137]. With respect to structural scanning techniques, CT scan has high spatial resolution but shows limited contrast with tissues.…”