The mesoscopic modelling of burst suppression during anaesthesia

The burst suppression pattern is well recognised as a distinct featureof the mammalian electroencephalogram (EEG) waveform. Consisting ofalternating periods of high amplitude oscillatory and isoelectricactivity It can be induced in health by deep anaesthesia as well asbeing evoked by a range of pathophysiological processes that includecoma and anoxia. While the electroencephalographic phenomenon andclinical implications of burst suppression have been studiedextensively, the physiological mechanisms underlying its emergenceremain unresolved and obscure.Because electroencephalographic bursting phenomenologically resemblesthe bursting observed in single neurons, it would be reasonable toassume that the theoretical insights developed to understand burstingat the cellular (``microscopic'') level would enable insights into thedynamical genesis of bursting at the level of the whole brain(``macroscopic''). In general action potential bursting is the resultof the interplay of two time scales: a fast time scale responsible forspiking, and a slow time scale that modulates such activity. Wetherefore hypothesise that such fast-slow systems dynamically underpinelectroencephalographic bursting. Here we show that a well known mean field dynamical model of theelectroencephalogram, the Liley model, while unable to produce burstsuppression unmodified, is able to give rise to a wide variety ofburst-like activity by the addition of one or more slow systemsmodulating model parameters speculated to be major ``targets'' foranaesthetic action. The development of a physiologically plausibletheoretical framework to account for burst suppression will lead to amore complete physiological understanding of the EEG and themechanisms that serve to modify ongoing brain activity necessary forpurposeful behaviour and consciousness.

Abstract licence: CC BY

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