Abstract

Auditory processing and the complexity of neural activity can both indicate residual conscious-ness levels and differentiate between states of arousal. However, how measures of neural signal diversity, or complexity, manifest in evoked activity, and, more generally, how the electrophys-iological characteristics of auditory responses change in states of reduced consciousness, re-main under-explored. Here, we tested the hypothesis that measures of neural complexity and the spectral slope would discriminate stages of sleep not only in spontaneous EEG, but also in auditory-evoked responses. High-density EEG was recorded in 21 participants to determine the spatial relationship between these measures, and between spontaneous and auditory-evoked signals. Results showed that the complexity and the spectral slope in the 2-20 Hz range dis-criminated between sleep stages and had a high correlation in sleep. In wakefulness, complexity was strongly correlated to the 20-40 Hz spectral slope. Auditory stimulation resulted in reduced complexity in sleep compared to spontaneous activity and modulated the spectral slope in wake-fulness. These findings demonstrate the persistence of electrophysiological markers of arousal during both spontaneous and evoked EEG activity and have direct applications to studies using auditory stimulation to probe neural functions in states of reduced consciousness.