Cognitive function mediates the relationship between age and anaesthesia-induced oscillatory-specific alpha power

Abstract

Cognitive decline is common among older individuals, and although the underlying brain mechanisms are not entirely understood, researchers have suggested using EEG frontal alpha activity during general anaesthesia as a potential biomarker for cognitive decline. This is because frontal alpha activity associated with GABAergic general anaesthetics has been linked to cognitive function. However, oscillatory-specific alpha power has also been linked with chronological age. We hypothesize that cognitive function mediates the association between chronological age and (oscillatory-specific) alpha power. We analysed data from 380 participants (aged over 60) with baseline screening assessments and intraoperative EEG. We utilized the telephonic Montreal Cognitive Assessment to assess cognitive function. We computed total band power, oscillatory-specific alpha power, and aperiodics to measure anaesthesia-induced alpha activity. To test our mediation hypotheses, we employed structural equation modelling. Pairwise correlations between age, cognitive function and alpha activity were significant. Cognitive function mediated the association between age and classical alpha power [age → cognitive function → classical alpha; β = -0.0168 (95% confidence interval: -0.0313 to -0.00521); P = 0.0016] as well as the association between age and oscillatory-specific alpha power [age → cognitive function → oscillatory-specific alpha power; β = -0.00711 (95% confidence interval: -0.0154 to -0.000842); P = 0.028]. However, cognitive function did not mediate the association between age and aperiodic activity (1/f slope, P = 0.43; offset, P = 0.0996). This study is expected to provide valuable insights for anaesthesiologists, enabling them to make informed inferences about a patient's age and cognitive function from an analysis of anaesthetic-induced EEG signals in the operating room. To ensure generalizability, further studies across different populations are needed.

Keywords: aging; alpha oscillations; anaesthesia; aperiodic activity; cognitive decline.

Graphical Abstract

Figure 1

Consort diagram. It illustrates the steps taken for cohort selection and the number of patients.

Figure 2

Pairwise correlations between age, cognitive function and clAlpha power. (A) Illustration showing all paired combinations between the variables of interest. (B) Scatter plot depicting the significant pairwise correlation between clAlpha and cognitive function. (C) Scatter plot depicting the significant pairwise correlation between age and cognitive function measured by MoCA (telephone version of the MoCA test). (D) Scatter plot depicting the significant pairwise correlation between age and clAlpha power. Thick lines show the best linear regression, and the shade depicts the 95% CI of the regression for illustrative purposes. Statistical assessments of the correlations were done using Spearman correlation.

Figure 3

Pairwise correlations between age, cognitive function and the two components of clAlpha activity, osAlpha power and aperiodic activity. (A) Illustration showing that clAlpha power can be decomposed into osAlpha power and an aperiodic component. (B) Graphical depiction of how the ‘specparam’ algorithm carries out this separation. It shows a representative PSD with a fitted aperiodic power-law decay and an oscillatory-specific component modelled as a Gaussian function. (C–F) Scatterplots showing the significant correlations between (C) age and osAlpha power, (D) age and offset, (E) osAlpha power and cognitive function measured using the telephone version of the MoCA and (F) offset and cognitive function. Thick lines show the best linear regression, and the shade indicates the 95% CI for the regression for illustrative purposes. Statistical assessments of the correlations were done using Spearman correlation.

Figure 4

Path diagrams of mediation analyses. A shows the path diagrams of a mediation model in which clAlpha power is explained by direct (only by age) and indirect (age influences cognitive function, which in turn affects clAlpha power) paths. B and C correspond to analogous models in which age and cognitive function explain osAlpha power and aperiodic offset instead of clAlpha power. Numbers beside each arrow correspond to the regression coefficients (beta values). Red symbolizes indirect effects, and blue symbolizes the direct effects of the mediation analyses. *P < 0.05 and ***P < 0.001. ns, non-significant effects.