Abstract
Objectives: The purpose of this study is to investigate the age dependence of bilateral frontal electroencephalogram coupling characteristics, and find potential age-independent depth of anesthesia monitoring indicators for the elderlies.
Approach: We recorded bilateral forehead EEG data from 41 patients (ranged in 19-82 years old), and separated into three age groups: 18-40 years (n = 12); 40-65 years (n = 14), > 65 years (n = 15). All these patients underwent desflurane maintained general anesthesia. We analyzed the age-related EEG spectra, phase amplitude coupling (PAC), coherence and phase lag index (PLI) of EEG data in the states of awake, general anesthesia (GA), and recovery. 
Main results: The frontal alpha power shows age dependence in the state of GA maintained by desflurane. Modulation index (MI) in slow oscillation-alpha and delta-alpha bands showed age dependence and state dependence in varying degrees, the PAC pattern also became less pronounced with increasing age. In the awake state, the coherence in delta, theta and alpha frequency bands were all significantly higher in the > 65 years age group than in the 18-40 years age group (p < 0.05 for three frequency bands). The coherence in alpha-band was significantly enhanced in all age groups in GA (p < 0.01) and then decreased in recovery state. Notably, the PLI in the alpha band was able to significantly distinguish the three states of awake, GA and recovery (p < 0.01) and the results of PLI in delta and theta frequency bands had similar changes to those of coherence. 
Significance: We found the EEG coupling and synchronization between bilateral forehead are age-dependent. The PAC, coherence and PLI portray this age-dependence. The PLI and coherence based on bilateral frontal EEG functional connectivity measures and PAC based on frontal single-channel are closely associated with anesthesia-induced unconsciousness.
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