Brain reactivity to emotion persists in NREM sleep and is associated with individual dream recall.

The brain's ability to detect emotional signals persists during non-rapid eye movement (NREM) sleep. Using electroencephalography, neural responses to emotional voices differed from neutral voices both while awake and during NREM sleep. Emotional voices also triggered more EEG arousals (sleep perturbations) than neutral or control stimuli. The amplitude of sleep event-related potentials and the number of arousals after emotional voices increased linearly with how often participants recalled their dreams. Similar correlations with dream recall frequency appeared for beta and sigma brain oscillations, but not for theta. No such correlations were found for neutral or control stimuli. These findings suggest that emotion-specific neural reactivity during sleep, rather than general alertness, may contribute to encoding or retrieving dreams.

Study at a glance

Abstract

The waking brain efficiently detects emotional signals to promote survival. However, emotion detection during sleep is poorly understood and may be influenced by individual sleep characteristics or neural reactivity. Notably, dream recall frequency has been associated with stimulus reactivity during sleep, with enhanced stimulus-driven responses in high vs. low recallers. Using electroencephalography (EEG), we characterized the neural responses of healthy individuals to emotional, neutral voices, and control stimuli, both during wakefulness and NREM sleep. Then, we tested how these responses varied with individual dream recall frequency. Event-related potentials (ERPs) differed for emotional vs. neutral voices, both in wakefulness and NREM. Likewise, EEG arousals (sleep perturbations) increased selectively after the emotional voices, indicating emotion reactivity. Interestingly, sleep ERP amplitude and arousals after emotional voices increased linearly with participants' dream recall frequency. Similar correlations with dream recall were observed for beta and sigma responses, but not for theta. In contrast, dream recall correlations were absent for neutral or control stimuli. Our results reveal that brain reactivity to affective salience is preserved during NREM and is selectively associated to individual memory for dreams. Our findings also suggest that emotion-specific reactivity during sleep, and not generalized alertness, may contribute to the encoding/retrieval of dreams.