Black swans: challenging the relationship of anaesthetic-induced unconsciousness and electroencephalographic oscillations in the frontal cortex

The study of general anaesthesia and electroencephalographic oscillations in the frontal cortex spans at least four decades, with several notable findings:

• In 1977, Tinker and colleagues¹ proposed, based on studies of the nonhuman primate, that anteriorization—the shift of electroencephalographic power from posterior cortex to frontal cortex—correlated with unresponsiveness during general anaesthesia.
• In the early 1990s, Steriade contributed to our understanding of the neurophysiology of sleep and general anaesthesia in animals, including descriptions of three distinct oscillations involving corticothalamic networks: a slow rhythm at < 1 Hz, a delta rhythm at 1-4 Hz, and a faster theta/alpha rhythm at 7-14 Hz.²³
• In the mid-1990s, the shift of alpha oscillations to more anterior structures was identified during both propofol sedation⁴ and isoflurane/nitrous oxide anaesthesia.⁵
• In 2001, anteriorized alpha and slow-wave activity was posited by John and colleagues⁶ to be an agent-invariant marker of anaesthetic-induced unconsciousness, based on a study of 176 surgical patients.
• In 2004, the disappearance of occipital alpha oscillations and shift to high-power frontal alpha oscillations was found to be associated with propofol-induced unconsciousness in healthy human participants.⁷
• In 2013, Purdon and colleagues⁸ found, using high-density electroencephalography in human volunteers, that anteriorization of alpha and phase-amplitude coupling patterns correlated with propofol-induced unconsciousness.
• In 2014, both propofol and sevoflurane anaesthesia were found to be associated with anterior alpha and slow oscillations in surgical patients.⁹

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