Increased aperiodic neural activity during sleep in major depressive disorder

Abstract

Background. In major depressive disorder (MDD), patients often express subjective sleep complaints while polysomnographic studies report only subtle alterations in neural oscillations. We hypothesize that the study of aperiodic electroencephalographic (EEG) dynamics, a marker of excitation-to-inhibition balance, may bring new insights into our understanding of sleep abnormalities in MDD. Specifically, we investigate aperiodic neural activity during sleep and its relationships with the time of sleep, depression severity, and responsivity to antidepressant treatment. Methods. Polysomnography was recorded in 38 MDD patients (in unmedicated and 7d medicated states) and 38 age-matched healthy controls (N1=76). Aperiodic EEG activity was evaluated using the Irregularly Resampled Auto-Spectral Analysis with slopes' means and intra-individual variability as outcome measures. Depression severity was assessed with the Hamilton Depression Rating Scale. We replicated the analysis using two independently collected datasets of medicated patients and controls (N2=60, N3=80). Results. Unmedicated patients showed flatter aperiodic slopes compared to controls during N2 (p-value=0.002) and steeper slopes compared to their later medicated state (p-values<0.02) during all sleep stages. Within unmedicated patients, slopes were flatter during late compared to early N2 sleep (p-value=0.006). Late N2 slopes further correlated with depression severity after 7d of antidepressant treatment (r=-0.34, p-value=0.04). Variability of slopes was increased in both unmedicated (p-values<0.03) and medicated states (p-values <0.006) of patients' N2, N3, and REM sleep compared to controls. Conclusion. Flatter slopes of aperiodic EEG power with increased variability may reflect unstable, noisy neural activity due to increased excitation-to-inhibition balance, representing a new disease-relevant feature of sleep in MDD.

Prior context and individual alpha frequency (IAF) influence predictive processing during language comprehension

“…Additionally, whilst IAF influenced N400 amplitudes, we did not detect any effects relating to the 1/f aperiodic slope. Although we investigated 1/f as a between-subjects (trait-like) measure, in line with prior research (e.g., Demuru & Fraschini, 2020;Dziego et al, 2023;McSweeney et al, 2021;, the 1/f slope also shows state-like changes and has been linked with norepinephrine activity and phasic changes in neural gain (Pertermann et al, 2019;Rosenblum, 2023). Consequently, future research may benefit from examining 1/f on a trial-by-trial basis to determine whether changes relating to prediction may be more transient.…”