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Abstract
Traumatic experiences are associated with increased emotional arousal. Overnight consolidation strengthens the episodic content of emotional memories, but it is still unclear how sleep influences the associated arousal response. To investigate this question, we compared the effects of sleep and wake on psychophysiological and subjective reactivity during emotional memory retrieval. Participants provided affective ratings for negative and neutral images while heart rate deceleration (HRD) and skin conductance responses (SCRs) were monitored. Following a 12-hour delay of sleep or wakefulness, participants completed an image recognition task where HRD, SCRs and affective ratings were recorded again. HRD responses to previously-encoded (“old”) negative images were preserved after sleep but diminished after wakefulness. No between-group difference in HRD was observed for novel negative images at recognition, indicating that the effects of sleep for old images were not driven by a generalised overnight increase in visceral activity, or circadian factors. No significant effects of sleep were observed for SCRs or subjective ratings. Our data suggest that cardiac arousal experienced at the time of encoding is sensitive to plasticity-promoting processes during sleep in a similar manner to episodic aspects of emotional memory.
Highlights
Distressing emotional experiences are associated with amplified levels of arousal, which constitutes the affective tone of resultant emotional memories[1]
A main effect of Emotion indicated that heart rate deceleration (HRD) reactivity was generally stronger for negative images than neutral images (F(1,46) = 34.50, p < 0.001, ƞp2 = 0.43)
There was no main effect of Session (F(1,46) = 1.75, p = 0.19, ƞp2 = 0.04) indicating that, across both valences and groups, HRD did not differ between encoding and recognition
Summary
Distressing emotional experiences are associated with amplified levels of arousal, which constitutes the affective tone of resultant emotional memories[1]. The alternative view proposes that the affective tone of emotional experiences becomes unbound from the episodic representation during overnight consolidation, weakening the associated arousal response when reflecting on negative past experiences[14,15]. To address these frameworks, several studies have compared changes in affective ratings for emotional images after post-encoding intervals of sleep and wakefulness. While some report a decrease in emotional reactivity across sleep (vs wake)[16,17], others report a sleep-related preservation[13,18,19] or intensification[20] of mnemonic arousal These mixed results likely arise from a complex interplay between sleep and the dynamic inputs to subjective emotional appraisals, including physiological signals and behavioural goals[21]. Overnight weakening of SCRs and HRD responses to object images, these effects were observed for both negative and neutral stimuli, suggesting a generalised sleep-associated depotentiation of visceral activity[29]
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