AUTHOR=Leroy Sophie , Major Sebastian , Bublitz Viktor , Dreier Jens P. , Koch Susanne 

TITLE=Unveiling age-independent spectral markers of propofol-induced loss of consciousness by decomposing the electroencephalographic spectrum into its periodic and aperiodic components

JOURNAL=Frontiers in Aging Neuroscience

VOLUME=Volume 14 - 2022

YEAR=2023

URL=https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2022.1076393

DOI=10.3389/fnagi.2022.1076393

ISSN=1663-4365

ABSTRACT=Background: Induction of general anesthesia with propofol induces radical changes in cortical network organization, leading to unconsciousness. While perioperative frontal electroencephalography (EEG) has been widely implemented in the past decades, validated and age-independent EEG markers for the timepoint of loss of consciousness (LOC) are lacking. Especially the appearance of spatially coherent frontal alpha oscillations (8-12 Hz) marks the transition to unconsciousness (Purdon et al., 2013). 
Here we explored whether decomposing the EEG spectrum into its periodic and aperiodic components unveiled markers of LOC and investigated their age-dependency. We further characterized the LOC-associated alpha oscillations by parametrizing the adjusted power, the center frequency, and the bandwidth of the alpha peak. 

Methods: In this prospective observational trial, EEG were recorded in a young (18-30 years) and an elderly age-cohort (≥70 years) during the transition to propofol-induced unconsciousness. An event marker was set at the timepoint of LOC, defined with the suppression of the lid closure reflex. Spectral analysis was conducted with the multitaper method. Aperiodic and periodic components were parametrized with the FOOOF toolbox. Aperiodic parametrization comprised the exponent and the offset. The periodic parametrization consisted in the characterization of the peak in the alpha range with its adjusted power, center frequency and bandwidth. Three time-segments were defined: preLOC (105s to 75s before LOC), LOC (15s before to 15s after LOC), postLOC (190s to 220s after LOC). Statistical significance was determined with a repeated-measures ANOVA. 

Results: LOC was associated with an increase in the aperiodic exponent (young: p=0.004, elderly: p=0.007) and offset (young: p=0.020, elderly: p=0.004) and an increase in the adjusted power (young: p<0.001, elderly p=0.011) and center frequency (young: p=0.008, elderly: p<0.001) of the periodic alpha peak. We saw age-related differences in the aperiodic exponent and offset after LOC as well as in the power and bandwidth of the periodic alpha peak during LOC.

Conclusion: Decomposing the EEG spectrum over induction of anesthesia into its periodic and aperiodic components unveiled novel age-independent EEG markers of propofol-induced LOC: the aperiodic exponent and offset as well as the center frequency and adjusted power of the power peak in the alpha range.