The meaning of EEG indicators of loss of consciousness during anaesthesia and coma.

Raw EEG changes correlate well with the effects of anaesthetics on arousal. The purpose of the present paper is to analyse the significance of the EEG spectrograph during unconscious states. The alpha rhythm is a signature of the unconscious and according to the MAB hypothesis (Monoaminergic-Acetylcholinergic Balance) is an index of increased relative inhibitory muscarinic effects on monoaminergic modulated conscious networks. The source of alpha rhythms varies, as does the type of unconscious information: from classical occipital alpha during resting state with eyes closed where no external visual information is processed, to states of unconscious anaesthesia where alpha shifts to fronto-parietal networks. These are spontaneous oscillatory network responses and the effects of GABA agonist anaesthetics increase the amplitude of these intrinsic rhythms. The hypothesis states that the concurrent presence of sustained delta oscillations and alpha spindles signifies suppressed unconscious and conscious responses respectively, and permit neither implicit nor explicit cognition nor recollections. Further, the model will be used to interpret EEG changes associated with more atypical anaesthetics and provide reasons for the related cognitive effects. This will be based on the agents’ pharmacological profiles and how they interact with these dual neuromodulating systems. Evidence will also be drawn from EEG states associated with pathophysiology in coma. The pharmacological interpretation of the EEG makes predictions of awareness in disorders of consciousness. The difficult circumstances of behaviourally inadequate indicators refers to situations of minimally conscious and in particular, vegetative states where decision making is fraught with uncertainty.