Brainwave viscosity in propofol anaesthesia

Human EEG during propofol anaesthesia shows large-scale changes including traveling slow waves( 1 ). Slow-wave saturation is a potentially individualised marker of loss of perception( 2 ). However, much remains unclear about the dynamics of slow waves. Iterated empirical mode decomposition (itEMD( 3 )) is a novel data-driven method for segregating data into physiologically relevant oscillatory modes. We used itEMD to identify spectral modes and their sources / sinks in propofol EEG. Viscosity is a physical quantity expressing the magnitude of resistance to flow. Considering traveling electric potentials in the brain as a flow, we extended the notion of viscosity to traveling brainwaves. Using this, we explored how brainwave viscosity changes in volunteer propofol anaesthesia.