Emotional Processing in a Nap Paradigm: The Role of Sleep Stages in Memory and Reactivity

It is widely known that sleep has a role in modulating emotional processing. However, while sleep facilitates the consolidation of emotional memories, its influence on emotional reactivity remains unclear. Most prior work has not fully addressed emotional reactivity, often relying solely on subjective or physiological measures, nor has it disentangled the contribution of different sleep stages. Here, using a between-subjects design, we asked participants to complete two picture-based tasks assessing emotional memory and emotional reactivity before and after a manipulation condition (nap, N = 40; wake, N = 40), and again 2 days later. Spontaneous variations in nap duration resulted in participants reaching REM sleep (REM group, N = 20) or not (No-REM group, N = 20). Emotional reactivity, assessed using an emotional picture task consisting of 28 images with different emotional contents (negative and neutral), was measured through subjective ratings and physiological responses (phasic cardiac response and skin conductance response). Sleep preserved memory performance relative to wakefulness, but after 2 days, only negative images maintained a memory advantage in the Nap group; however, no differences emerged as a function of REM sleep occurrence during the nap. For emotional reactivity, subjective arousal decreased after sleep in the REM group, whereas valence ratings declined only after 2 days. Physiologically, heart rate habituation was greater in the No-REM group. Together, these findings indicate that sleep fosters emotional memory consolidation while modulating reactivity in ways that diverge across subjective and physiological domains, with a decrease in subjective arousal ratings and an increase in phasic cardiac response. These findings, which should be interpreted in the context of the observed differences in participants' sleep architecture, highlight the complex role of sleep in emotional processing and underscore the need for standardized experimental paradigms.