Recently, I was lucky enough to assist in (who am I kidding…obstruct) a sleep and anaesthesia study aimed at monitoring participants by Electroencephalogram (EEG) in various states of consciousness. The study, run by Dr Katie Warnaby of The Anaesthesia Neuroimaging Research Group at The Nuffield Department of Clinical Neuroscience, makes use of both EEG and functional Magnetic Resonance Imaging (fMRI). The research aim is to learn about the effects anaesthesia has on the brain and and in so doing help us both understand ourselves and understand how to most effectively monitor patients undergoing surgery.
The study’s goal of improving the understanding of brain activity under anaesthesia has two research outcomes. The first is broadening our knowledge of how best to maintain anaesthesia with minimal patient risk. The second is an improved understanding of the change in state from consciousness to “diminished consciousness” under anaesthesia, a mental shift that could be used to measure the so called “neural correlates of consciousness”.
While sleep can have many of the same characteristics as anaesthesia, subjective accounts differ in that subjects report an altered perception including a “shift” in experiential time, not seen in normal sleep. It has been suggested, most intriguingly, in the study of bees that this may in part be due to a shift in the body’s own circadian rhythm under anaesthesia. More direct evidence for the profound loss of consciousness under anaesthesia include numerous EEG studies that show a frequency shift in brain activity in humans under increasing levels of anaesthetisation (e.g. a change of power in the alpha wave band and increased slow wave activity), along with a decrease in attention, and impairments in forming explicit memories (memories that can be recounted later). Even so, questions remain as to whether failures in memory consolidation are precipitated by a loss in consciousness, the stress and pain of surgery or dysfunction at some intermediary step in the memory formation pathway.
The Brain Imaging of Anaesthesia study is currently looking for participants! If you might be interested in advancing our understanding of both consciousness and medicine please click here! Dr Warnaby’s lab is also involved in the study of post-operative pain and its manifestation in the brain. So click here if you’re into pain.
Cheeseman et. al (2012). General anesthesia alters time perception by phase shifting the circadian clock. Proceedings of the National Academy of Sciences, 109(18), 7061-7066.
Hagihira, S. (2015). Changes in the electroencephalogram during anaesthesia and their physiological basis. British journal of anaesthesia, 115(suppl_1), i27-i31.
Voss, L., & Sleigh, J. (2007). Monitoring consciousness: the current status of EEG-based depth of anaesthesia monitors. Best practice & research Clinical anaesthesiology, 21(3), 313-325.
Mhuircheartaigh et. al (2013). Slow-wave activity saturation and thalamocortical isolation during propofol anesthesia in humans. Science Translational Medicine, 5(208), 208ra148-208ra148.
Warnaby et. al (2017). Investigation of slow-wave activity saturation during surgical anesthesia reveals a signature of neural inertia in humans. Anesthesiology: The Journal of the American Society of Anesthesiologists, 127(4), 645-657.
