Recording Brain Electromagnetic Activity During the Administration of the Gaseous Anesthetic Agents Xenon and Nitrous Oxide in Healthy Volunteers

Andria Pelentritou; Levin Kuhlmann; John Cormack; Will Woods; Jamie Sleigh; David Liley

doi:10.3791/56881

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Method Article

Recording Brain Electromagnetic Activity During the Administration of the Gaseous Anesthetic Agents Xenon and Nitrous Oxide in Healthy Volunteers

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DOI:

10.3791/56881

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January 13th, 2018

Andria Pelentritou¹ , Levin Kuhlmann¹ , John Cormack² , Will Woods³ , Jamie Sleigh⁴ , David Liley¹

¹Centre for Human Psychopharmacology, Swinburne University of Technology, ²Department of Anaesthesia and Pain Management, St. Vincent's Hospital Melbourne, ³Brain and Psychological Science Research Centre, Swinburne University of Technology, ⁴Department of Anaesthesiology, University of Auckland

Summary

Simultaneous magnetoencephalography and electroencephalography provides a useful tool to search for common and distinct macro-scale mechanisms of reductions in consciousness induced by different anesthetics. This paper illustrates the empirical methods underlying the recording of such data from healthy humans during N-Methyl-D-Aspartate-(NMDA)-receptor-antagonist-based anesthesia during inhalation of nitrous oxide and xenon.

Abstract

Anesthesia arguably provides one of the only systematic ways to study the neural correlates of global consciousness/unconsciousness. However to date most neuroimaging or neurophysiological investigations in humans have been confined to the study of γ-Amino-Butyric-Acid-(GABA)-receptor-agonist-based anesthetics, while the effects of dissociative N-Methyl-D-Aspartate-(NMDA)-receptor-antagonist-based anesthetics ketamine, nitrous oxide (N₂O) and xenon (Xe) are largely unknown. This paper describes the methods underlying the simultaneous recording of magnetoencephalography (MEG) and electroencephalography (EEG) from healthy males during inhalation of the gaseous anesthetic agents N₂O and Xe. Combining MEG and EEG data enables the assessment of electromagnetic brain activity during anesthesia at high temporal, and moderate spatial, resolution. Here we describe a detailed protocol, refined over multiple recording sessions, that includes subject recruitment, anesthesia equipment setup in the MEG scanner room, data collection and basic data analysis. In this protocol each participant is exposed to varying levels of Xe and N₂O in a repeated measures cross-over design. Following relevant baseline recordings participants are exposed to step-wise increasing inspired concentrations of Xe and N₂O of 8, 16, 24 and 42%, and 16, 32 and 47% respectively, during which their level of responsiveness is tracked with an auditory continuous performance task (aCPT). Results are presented for a number of recordings to highlight the sensor-level properties of the raw data, the spectral topography, the minimization of head movements, and the unequivocal level dependent effects on the auditory evoked responses. This paradigm describes a general approach to the recording of electromagnetic signals associated with the action of different kinds of gaseous anesthetics, which can be readily adapted to be used with volatile and intravenous anesthetic agents. It is expected that the method outlined can contribute to the understanding of the macro-scale mechanisms of anesthesia by enabling methodological extensions involving source space imaging and functional network analysis.

Introduction

There is good consensus between pre-clinical and clinical neuroscientific evidence suggesting that the phenomenon of human consciousness depends on the integrity of explicit neural circuits. The observation that such circuits are systematically influenced by the descent into unconsciousness has substantiated the need for neuroimaging techniques to be utilized during anesthesia and enable 'navigating' the search for the neural correlates of consciousness. With the possible exception of sleep, anesthesia represents the only method by which one can, in a controlled, reversible and reproducible fashion, perturb, and thus dissect, the mechanisms that sub-serve cons....