Standing sentinel during human sleep: Continued evaluation of environmental stimuli in the absence of consciousness.
Neuroimage September 1, 2018 Christine Blume, Renata Del Giudice, Malgorzata Wislowska et al.
The human brain continues to evaluate voice familiarity during all NREM sleep stages and REM sleep, suggesting a 'sentinel processing mode' even without wake-like consciousness. Using 256-channel EEG in 17 healthy sleepers, the study found that unfamiliar voices elicit larger brain responses in a 1–15 Hz range, indicating they remain salient. Sleep spindles and the negative slope of slow oscillations attenuate information processing, but this inhibition is scaled to stimulus salience rather than being uniform. The work also examined processing of subjects' own names versus unfamiliar names, but the primary finding concerns voice familiarity processing across sleep stages.