Correlational studies of unconsciousness under anaesthesia: how far can preclinical studies take us?

Determining the electrophysiological correlates of loss of consciousness (LOC) and recovery of consciousness (ROC) under anaesthesia is a holy grail of biomedical science.¹ From a purely practical perspective, a non-invasive metric that tracks sensory awareness and is robust to the combination of anaesthetic drugs and patient factors would be a welcome addition to the anaesthetist's perioperative tool kit.² From a theoretical perspective, such a metric would prove invaluable for endeavours to understand the neural basis of consciousness, and in particular, sensory awareness.² The contribution by Plourde and Arseneau³ in this month's British Journal of Anaesthesia provides evidence towards that end. The authors report that the α₂-agonist dexmedetomidine attenuates high-frequency oscillations in the cortex and thalamus at doses that induce loss of the righting reflex. By comparing these results with their previous work on the thalamocortical effects of isoflurane and propofol,⁴⁵ the authors conclude that changes in thalamic γ-band signals may be electrophysiological correlates of LOC and ROC. It is interesting to note that some of the results presented here differ from previous studies, in which low γ (∼40 Hz) band power increased under anesthesia.⁶ In contrast, the effects on high γ (>80 Hz) signals observed by Plourde and Arseneau³ are likely to represent the suppression of spontaneous spiking activity under anaesthesia, which is well supported in the literature.⁷

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