Preferential processing of emotionally and self-relevant stimuli persists in unconscious N2 sleep

- Own names (SONs) and angry voice (AV) stimuli are salient during wakefulness.
- Intriguingly, SONs and AV stimuli remain salient during unconscious N2 sleep.
- Results suggest a 'sentinel processing mode' of the brain during unconscious sleep.
- A K-complex-like response indicates preferential processing of salient stimuli.
- Presumably, delta, theta and sigma ERS reflect the subsequent sleep-protecting mechanism.

Information processing has been suggested to depend on the current state of the brain as well as stimulus characteristics (e.g. salience). We compared processing of salient stimuli (subject's own names [SONs] and angry voice [AV] stimuli) to processing of unfamiliar names (UNs) and neutral voice (NV) stimuli across different vigilance stages (i.e. wakefulness as well as sleep stages N1 and N2) by means of event-related oscillatory responses during wakefulness and a subsequent afternoon nap. Our findings suggest that emotional prosody and self-relevance drew more attentional resources during wakefulness with specifically AV stimuli being processed more strongly. During N1, SONs were more arousing than UNs irrespective of prosody. Moreover, emotional and self-relevant stimuli evoked stronger responses also during N2 sleep suggesting a 'sentinel processing mode' of the brain during this state of naturally occurring unconsciousness. Finally, this initial preferential processing of salient stimuli during N2 sleep seems to be followed by an inhibitory sleep-protecting process, which is reflected by a K-complex-like response.