arXiv subjects

Chika Koyama

Publications and source records attributed to Chika Koyama.

4 recordsLinked to original sources

arXiv2024

Brain waves are a repetition of a pause and an activity

Brain waves still cannot reliably distinguish between awake and asleep states. Here, I present new original indices, voltage subthreshold wave $τ$ and abovethreshold wave burst, for advanced LFP/EEG readings. Assuming that $τ$ is a microwave that fluctuates every sample such as the equipotential, the total number of $τ$ ($Nτ$) is inferred to be the maximum, and the amplitude of burst (Abst) is inferred to be the minimum. In fact, they invariably had a mean $τ$ duration ($Mτ$) of 2-3 sample intervals in any case. In addition, $τ$ and burst exhibited self-similarity for sample frequency while occupying approximately 30% and 70% of LFP in the natural state, respectively. Its threshold and Abst were correlated with the vigilance state and decreased to 70% by doubling the sample frequency. The dose of sevoflurane, which inhibits and synchronizes neural activity, was linearly correlated with decreases in the threshold and $Nτ$. Thus, $τ$ could reflect the uncertainty of the membrane potential. I propose that $τ$ and burst represent a pause and an activity such as the rhythm of the brain.

q-bio.NC↗

arXiv2021

Microwave amplitude reflecting instability of LFP electrode ground field is useful for consciousness state identification

We recently developed original electroencephalogram indices focusing on microwaves of flattish period (named $τ$), which correlated with volatile anesthesia concentration in dogs. However, this mechanism remains unclear. $τ$ was defined as a subthreshold wave and burst wave was defined as an above-threshold wave. This study shows that these indices well quantified the morphological features of local field potential waveforms in mice, and made it possible to discriminate the specific waveforms of the state of consciousness; awake, shallow sleep, rapid eye movement sleep, and non-rapid eye movement sleep. In addition, examination of $τ$ suggested that microwaves are local fluctuations of the electrode that can be formed for each data sampling, and that its amplitude may increase with the degree of arousal.

q-bio.NC↗

arXiv2020

Power-law distribution in Burst-suppression on electroencephalogram of dogs

Burst-suppression (BS) is a reliable electroencephalogram (EEG) indicator of excessive deep anesthesia common in mammals. Since some intermittent events are known to follow a power-law, we investigated the power-law hypothesis in BS by comparing it with alternative functions focusing on flattish periods and developed a new method for detecting BS as an application of statistical model in dogs. Young-adult 6 beagles and senior 6 beagles were anesthetized with sevoflurane 2.0%-5.0% and three of 64 sec EEG (256 Hz) from Fpz-T4 via scalp electrodes were recorded. Three thresholds for peak-to-peak voltage were set: mean value of peak-to-peak voltage at sevoflurane 2.0% in each dog (AS2%), 3mcrV, and 5mcrV. The subthreshold periods were discriminated as $τ$ events. We fitted the empirical probability distribution of $τ$ by a power-law distribution and an exponential distribution. These two distributions were compared by the normalized log-likelihood ratio test to see which distribution was better fit. At sevoflurane 2.0%-3.0%, by any threshold, the exponential distribution became better fit in all dogs. The power-law distribution became better fit only when BS expressed on EEG. No strict threshold was required for detection of onset of BS. We showed a transition from exponential behavior to power-law behavior on the right tail of $τ$ distributions in response to the appearance of suppression waves with increasing anesthetic. This will be a robust tool for BS detection.

q-bio.NC↗

arXiv2019

New EEG parameters correlated with sevoflurane concentration in dogs: tau and burst

Background: Electroencephalographic (EEG) indicators for anaesthesia depth are being developed. Here, we propose novel EEG parameters created by using two kinds of waveforms discriminated by voltage thresholds from a new perspective. Methods: Six young-adult beagles and 6 senior beagles were anaesthetised with end-tidal sevoflurane (SEV) of 2.0%-4.0% in 0.5% intervals, and 2-channel EEG (256 Hz) was recorded. Two events were discriminated: a consecutive part (τ) with a peak-to-peak potential difference (Vpp) within 1-6, 8, 12, or 20 mcrV, and another part (burst) with Vpp outside the threshold. Number of τ (Nτ), mean τ duration (Mτ), total percentage of τ (SRτ), mean burst duration (Mbst), and amplitude of burst (Abst) were evaluated as anaesthesia depth indicators using Pearsons correlation coefficients (r). Results: When Vpp was near the suppression wave threshold, Nτ had the highest correlation with SEV in both groups. As SEV was increased until onset of burst suppression, Nτ decreased, Mτ remained unchanged, and Mbst and Abst increased. In the young-adult group, mean |r| exceeded 0.95 for Nτ with Vpp of 4-6 mcrV, for Mbst with Vpp of 8-12 mcrV, and for Abst with Vpp of 4-12 mcrV. In the senior group, r exceeded 0.90 for Nτ with Vpp of 4 mcrV and for Abst with Vpp of 5-12 mcrV. Conclusion: We developed new EEG parameters that were almost perfectly correlated with volatile anaesthetic concentrations using traditional bipolar recording. This study suggests that the effect of anaesthetics on EEG can be investigated from two directions: pacemaker (τ) and generator (burst).

q-bio.NC↗