Dream to Predict? REM Dreaming as Prospective Coding

Abstract

The dream as prediction seems inherently improbable. The bizarre occurrences in dreams never characterize everyday life. Dreams do not come true! But assuming that bizarreness negates expectations may rest on a misunderstanding of how the predictive brain works. In evolutionary terms, the ability to rapidly predict what sensory input implies—through expectations derived from discerning patterns in associated past experiences—would have enhanced fitness and survival. For example, food and water are essential for survival, associating past experiences (to identify location patterns) predicts where they can be found. Similarly, prediction may enable predator identification from what would have been only a fleeting and ambiguous stimulus—without prior expectations. To confront the many challenges associated with natural settings, visual perception is vital for humans (and most mammals) and often responses must be rapid. Predictive coding during wake may, therefore, be based on unconscious imagery so that visual perception is maintained and appropriate motor actions triggered quickly. Speed may also dictate the form of the imagery. Bizarreness, during REM dreaming, may result from a prospective code fusing phenomena with the same meaning—within a particular context. For example, if the context is possible predation, from the perspective of the prey two different predators can both mean the same (i.e., immediate danger) and require the same response (e.g., flight). Prospective coding may also prune redundancy from memories, to focus the image on the contextually-relevant elements only, thus, rendering the non-relevant phenomena indeterminate—another aspect of bizarreness. In sum, this paper offers an evolutionary take on REM dreaming as a form of prospective coding which identifies a probabilistic pattern in past events. This pattern is portrayed in an unconscious, associative, sensorimotor image which may support cognition in wake through being mobilized as a predictive code. A particular dream illustrates.

Dreams and Psychedelics: Neurophenomenological Comparison and Therapeutic Implications

“…However, there is accumulating evidence indicating that cognitive bizarreness is just “the other side of the coin” of a more fluid and flexible cognitive processing during REMS compared to non-REMS (NREMS) and waking state [ 49 ]. In this vein, dreaming has been conceptualized as off-line, unconscious thought-in-progress in which associative mechanisms and visual imagery are less tightly constrained by prefrontal cortical control mechanisms, and hence are less strictly confined by logical reasoning but predominantly driven by underlying emotions [ 50 - 53 ]. Compared to waking mentation, therefore, dreaming has the cognitive advantage of facilitating creative insight – the forming of associative elements into new image-based combinations which lead to greater understanding and which are useful to solve a problem [ 54 ].…”

Above and beyond the concrete: The diverse representational substrates of the predictive brain

“…Indeed, during REM a reduced hippocampal input to neocortex is coupled with a massive neural activity (driven by ponto-geniculo-occipital waves) that can randomly activate cortical representations. This highly active state might allow scanning memories to find meaningful regularities between events, and to generate and strengthen new abstractions between both cortical representations activated during the NREM and other, apparently not related, representations (Lewis et al 2018;Llewellyn 2016). Moreover, it has been proposed that during REM the sleeping brain tends to simulate and rehearse fictive scenarios to produce prediction errors and, therefore, refine (i.e., update) the internal models before the next wakefulness (Friston et al 2017b;Hobson et al 2014).…”

Updating Internal Cognitive Models during Sleep

“…The hypothesis that internal model updating mainly (but not exclusively) occurs during REM sleep has been also suggested by theoretical work (Llewellyn, 2015). In this work, Llewellyn (2015) also proposed a distinction between predictive and prospective coding.…”

“…The hypothesis that internal model updating mainly (but not exclusively) occurs during REM sleep has been also suggested by theoretical work (Llewellyn, 2015). In this work, Llewellyn (2015) also proposed a distinction between predictive and prospective coding. Predictive coding refers to the anticipation of upcoming input during wake based on a specific ongoing event, whereas prospective coding creates off-line probabilistic patterns (i.e., schema of plausible sequences of events created during sleep or resting periods) based on past events.…”

“…Predictive coding refers to the anticipation of upcoming input during wake based on a specific ongoing event, whereas prospective coding creates off-line probabilistic patterns (i.e., schema of plausible sequences of events created during sleep or resting periods) based on past events. According to Llewellyn (2015), during REM the sleeping brain scans memories to find meaningful regularities between events and uses these regularities to create associations between the events. These associations generate prospective codes that can be used during wakefulness as a predictive as well as a perceptual/attentional codes to prepare and adapt our behaviors to constantly changing external events.…”