Fig. 6.

Steyn-Ross et al. (2004) modelled the abrupt changes in EEG spectral power that have been commonly observed to occur during anaesthetic induction and emergence. (a) the abrupt biphasic response in total modelled EEG spectral power during simulated anaesthetic induction. Anaesthetic action was modelled as a prolongation of the duration of the GABAergic IPSP (λ). (b) Biphasic response in total EEG spectral power during simulated anaesthetic emergence. (c) Actual EEG recordings of anaesthetic induction and emergence with the intravenous anaesthetic agent propofol which illustrate clearly the biphasic variations in total EEG power as anaesthetic concentration is increased and decreased. (d) Steyn-Ross et al. propose that anaesthetic induced variations in EEG spectral power can be explained theoretically by a stochastically driven system switching between two stable states via a saddle node bifurcation caused by anaesthetic induced variations in IPSP duration. Figure adapted from Figs. 3–5 of Steyn-Ross et al. (2004), with permission