![]() ![]() These results provide fundamental new insights into the neural circuit mechanisms of sevoflurane anesthesia and suggest that anesthetic states may be produced by extracranial perturbations that cause delta-higher frequency phase-amplitude interactions. Taken together, our results suggest that subanesthetic and general anesthetic sevoflurane brain states emerge from impaired information processing instantiated by a delta-higher frequency phase-amplitude coupling syntax. Our results suggest that coherent alpha oscillations are not fundamental for maintaining sevoflurane general anesthesia. Data were analyzed with multitaper spectral, global coherence, cross-frequency coupling, and phase-dependent methods. Therefore, we performed a single-site, randomized, cross-over, high-density electroencephalogram study of sevoflurane and sevoflurane- plus-ketamine general anesthesia in 12 healthy subjects. Coherent frontal alpha oscillations have been postulated as a mechanism of sevoflurane general anesthesia. We conclude that the mechanisms of vasodilation and vasoconstriction, in response to temperature change, are oscillatory in nature and are independent of central sources of variability.Understanding anesthetic mechanisms with the goal of producing anesthetic states with limited systemic side effects is a major objective of neuroscience research in anesthesiology. This can be explained by the reduction in vascular resistance produced by heating, a process where myogenic mechanisms play a key role. Cooling did not affect this phase coherence in any of the frequency intervals, whereas heating enhanced the phase coherence in the respiratory and myogenic intervals. We also show that significant (p < 0.05) phase coherence exists between blood flow and IHR in the respiratory and myogenic frequency intervals. It was not significantly affected by cooling. Weak phase coherence between temperature and blood flow was observed for unperturbed skin, but it increased in all frequency intervals as a result of heating. During heating, there was a significant (p < 0.05) general increase in spectral energy, associated with vasodilation, except in the myogenic interval. That is, during cooling, there was a significant decrease in the average frequency of myogenic blood flow oscillations (p < 0.05) and the myogenic spectral peak became more prominent. We confirm the changes in the energy and frequency of blood flow oscillations during cooling and heating reported earlier. The IHR was derived from simultaneously recorded ECG. In each case a 30 min basal recording was followed by a step change in plate temperature, to either 24 ☌ or 42 ☌. Two 1 h datasets were collected from each of the ten subjects. Beneath the plate, the blood flow was measured by laser Doppler flowmetry and the adjacent skin temperature by a thermistor. A temperature-controlled metal plate (approximately 10 cm2) placed on the volar side of the left arm was used to provide the heating and cooling. ![]() We apply wavelet-based time-localized phase coherence to investigate the relationship between blood flow and skin temperature, and between blood flow and instantaneous heart rate (IHR), during vasoconstriction and vasodilation provoked by local cooling or heating of the skin.
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