Sleep and dreaming in the light of reactive and predictive homeostasis.

Dreaming and the forgetting of dreams are not meaningless byproducts of sleep but are integral to the brain's homeostatic functions, which both restore and anticipate future needs. Mental activity during sleep, especially in the second half of the night, is a self-focused, future-oriented cognitive process. Waking up shifts the brain to a constrained, goal-directed mode of thinking that competes for neural resources with dream production and recall, contributing to dream amnesia. Cortisol is highlighted as a potential factor in predictive homeostasis and forgetting dreams. This theoretical proposal reframes dreaming as part of a reactive and predictive homeostatic system.

Study at a glance

Abstract

Dreams are often viewed as fascinating but irrelevant mental epihenomena of the sleeping mind with questionable functional relevance. Despite long hours of oneiric activity, and high individual differences in dream recall, dreams are lost into oblivion. Here, we conceptualize dreaming and dream amnesia as inherent aspects of the reactive and predictive homeostatic functions of sleep. Mental activity during sleep conforms to the interplay of restorative processes and future anticipation, and particularly during the second half of the night, it unfolds as a special form of non-constrained, self-referent, and future-oriented cognitive process. Awakening facilitates constrained, goal-directed prospection that competes for shared neural resources with dream production and dream recall, and contributes to dream amnesia. We present the neurophysiological aspects of reactive and predictive homeostasis during sleep, highlighting the putative role of cortisol in predictive homeostasis and forgetting dreams. The theoretical and methodological aspects of our proposal are discussed in relation to the study of dreaming, dream recall, and sleep-related cognitive processes.