The Ageing Brain: Age-dependent changes in the electroencephalogram during propofol and sevoflurane general anaesthesia  P.L. Purdon, K.J. Pavone, O. Akeju, A.C. Smith, A.L. Sampson, J. Lee, D.W. Zhou, K. Solt, E.N. Brown  British Journal of Anaesthesia  Volume 115, Pages i46-i57 (July 2015) DOI: 10.1093/bja/aev213 Copyright © 2015 The Author(s) Terms and Conditions

Fig 1 Trends in the spectrum and coherence from 18 to 90 yr old during propofol anaesthesia. (a) The frontal EEG spectrum as a function of age. Slow (0.1–1 Hz) oscillations are present in all patients during general anaesthesia maintained solely with propofol. Alpha (8–12 Hz) oscillations appear to diminish with age. (b) The trend in alpha power appears to decrease with age. The green line represents a linear regression model describing the relationship between age and alpha power. (c) The frontal EEG coherence as a function of age. The alpha band coherence is robust in young patients and decreases with age, starting at about 65 yr. (d) The trend in alpha coherence decreases with age. The green line represents a linear regression model describing the relationship between age and alpha coherence. British Journal of Anaesthesia 2015 115, i46-i57DOI: (10.1093/bja/aev213) Copyright © 2015 The Author(s) Terms and Conditions

Fig 2 Trends in the spectrum and coherence from 18 to 90 yr old during sevoflurane anaesthesia. (a) The frontal EEG spectrum as a function of age. Slow (0.1–1 Hz) oscillations are present in all patients during general anaesthesia maintained solely with sevoflurane. Alpha (8–12 Hz) oscillations are evident during young adulthood and appear to diminish with age. (b) The trend in alpha power appears to decrease with age. The green line represents a linear regression model describing the relationship between age and alpha power. (c) The frontal EEG coherence as a function of age. The alpha band coherence is robust in young patients and decreases with age, starting at about 65 yr. (d) The trend in alpha coherence decreases with age. The green line represents a linear regression model describing the relationship between age and alpha coherence. British Journal of Anaesthesia 2015 115, i46-i57DOI: (10.1093/bja/aev213) Copyright © 2015 The Author(s) Terms and Conditions

Fig 3 Median spectra, coherence, spectrograms, and cohereogram of young and elderly age groups for propofol. (a) Power spectrum for both young patients (18–38 yr old), represented by blue line, and elderly patients (70–90 yr old), represented by green line. The power spectra show peaks in the slow (0.1–1 Hz) and alpha (8–12 Hz) frequency bands. The elderly patients show a marked decrease in power across all frequency bands. The power in the alpha band appears to decrease more than other bands, quantified in terms of alpha-to-slow ratio. (b) The group spectrogram for young patients shows prominent power in the slow and alpha frequency bands. (c) The group spectrogram for elderly patients shows a visible absence of power in the alpha frequency band. (d) Coherence for both young patients (18–38 yr old), represented by blue line, and elderly patients (70–90 yr old), represented by green line. The coherence is significantly lower in elderly patients, particularly in the alpha band. The peak coherent frequency is also lower in elderly patients. (e) The group cohereogram for young patients shows prominent coherence in the slow and alpha frequency bands. (f) The group cohereogram for elderly patients shows a visible absence of coherence in the alpha frequency band. British Journal of Anaesthesia 2015 115, i46-i57DOI: (10.1093/bja/aev213) Copyright © 2015 The Author(s) Terms and Conditions

Fig 4 Median spectra, coherence, spectrograms, and cohereogram of young and elderly age groups for sevoflurane. (a) Power spectrum for both young patients (18–38 yr old), represented by blue line, and elderly patients (70–90 yr old), represented by green line. The power spectra show peaks in the slow (0.1–1 Hz) and alpha (8–12 Hz) frequency bands. The elderly patients show a marked decrease in power across all frequency bands. The power in the alpha band appears to decrease more than other bands, quantified in terms of alpha-to-slow ratio. (b) The group spectrogram for young patients shows prominent power in the slow and alpha frequency bands. (c) The group spectrogram for elderly patients shows a visible absence of power in the alpha frequency band. (d) Coherence for both young patients (18–38 yr old), represented by blue line, and elderly patients (70–90 yr old), represented by green line. The coherence is significantly lower in elderly patients, particularly in the alpha band. The peak coherent frequency is also lower in elderly patients. (e) The group cohereogram for young patients shows prominent coherence in the alpha frequency band. (f) The group cohereogram for elderly patients shows a visible absence of coherence in the alpha frequency band. British Journal of Anaesthesia 2015 115, i46-i57DOI: (10.1093/bja/aev213) Copyright © 2015 The Author(s) Terms and Conditions

Fig 5 Analysis of episodes of burst suppression under propofol or sevoflurane. (a) Representation of the probability (Pr) that patients experience an episode of burst suppression during anaesthetic maintenance with propofol. (b) Representation of the probability that patients experience an episode of burst suppression during anaesthetic maintenance with sevoflurane. (c) The proportion of elderly patients who experience burst suppression is greater than that for young patients under propofol. (d) The proportion of elderly patients who experience burst suppression is greater than that for young patients under sevoflurane. British Journal of Anaesthesia 2015 115, i46-i57DOI: (10.1093/bja/aev213) Copyright © 2015 The Author(s) Terms and Conditions