Temporal dynamics of the influence of pre- or anticipated post-sleep stress on dream content

Psychosocial stress induces stress responses at physiological and cognitive levels which disrupt subsequent sleep. A recent study from our group has shown that stress-induced changes are dynamic: stress before sleep led to prolonged sleep latency and changes in the early sleep period, while anticipated post-sleep stress resulted in changes in the late sleep period. A possible explanation is that anticipated stress is spontaneously reactivated during sleep in a dynamic fashion. As reactivations might be linked to dream content, we investigated the influence of anticipated stress vs. pre-sleep stress on dream content in early and late sleep periods. One group of participants performed either a stress or a relaxation task before sleep (pre-sleep group); while another group was informed before sleep that the stress or relaxation task will occur in the morning (post-sleep group). During sleep, they were regularly woken up in the early and late sleep periods and asked about their cognitive activity, while polysomnographic data was recorded. Fifty-five subjects participated and a total of 668 dreams was collected. While there was no difference in the incorporation of threat- and stress-related elements in the dreams, we did find a temporal difference in their emotionality. The threat intensity was influenced in a dynamic manner, with higher impact on early dreams when stress occurred before sleep and higher threat intensity in late dreams when stress was anticipated after sleep. Our results speak for a reactivation of mental activity in temporal proximity to the stressor for some parameters, mainly with impacts on the dream emotionality and length.