This article argues that rapid eye movement (REM) dreaming is elaborative encoding for episodic memories. Elaborative encoding in REM can, at least partially, be understood through ancient art of memory (AAOM) principles: visualization, bizarre association, organization, narration, embodiment, and location. These principles render recent memories more distinctive through novel and meaningful association with emotionally salient, remote memories. The AAOM optimizes memory performance, suggesting that its principles may predict aspects of how episodic memory is configured in the brain. Integration and segregation are fundamental organizing principles in the cerebral cortex. Episodic memory networks interconnect profusely within the cortex, creating omnidirectional “landmark” junctions. Memories may be integrated at junctions but segregated along connecting network paths that meet at junctions. Episodic junctions may be instantiated during non–rapid eye movement (NREM) sleep after hippocampal associational function during REM dreams. Hippocampal association involves relating, binding, and integrating episodic memories into a mnemonic compositional whole. This often bizarre, composite image has not been present to the senses; it is not “real” because it hyperassociates several memories. During REM sleep, on the phenomenological level, this composite image is experienced as a dream scene. A dream scene may be instantiated as omnidirectional neocortical junction and retained by the hippocampus as an index. On episodic memory retrieval, an external stimulus (or an internal representation) is matched by the hippocampus against its indices. One or more indices then reference the relevant neocortical junctions from which episodic memories can be retrieved. Episodic junctions reach a processing (rather than conscious) level during normal wake to enable retrieval. If this hypothesis is correct, the stuff of dreams is the stuff of memory.

Although the analogy between dreams and ancient mnemotechniques is tempting because they share several phenomenological characteristics, this analogy is superficial at a closer look. Unlike mneomotechnically encoded material, rapid eye movement (REM) dreams are inherently difficult to remember, do not usually allow conscious subsequent retrieval of all interconnected elements, and have been found to support subsequent episodic memory in only rare cases.

The target article addresses historical and present-day mnemotechnics as a practice. It also deserves scrutiny as culture writ small. For would-be Hermetic adepts of the Renaissance and Baroque, the ancient art of memory (AAOM) provided both an iconography and a projective-test vision of possibilities. In contemporary fiction, Memory Palaces become a metaphor for the workings of mind, of culture, and of information technology.

Llewellyn's claim that rapid eye movement (REM) dream imagery may be related to the processes involved in memory consolidation during sleep is plausible. However, whereas there is voluntary and deliberate intention behind the construction of images in the ancient art of memory (AAOM) method, there is a lack of intentionality in producing dream images. The memory for dreams is also fragile, and dependent on encoding once awake.

We propose that rapid eye movement (REM) and slow-wave sleep contribute differently to the formation of episodic memories. REM sleep is important for building up invariant object representations that eventually recur to gamma-band oscillations in the neocortex. In contrast, slow-wave sleep is more directly involved in the consolidation of episodic memories through replay of sequential neural activity in hippocampal place cells.

The question that we deal with in this commentary is the need to clarify the synergistic role of different non–rapid eye movement (NREM) sleep stages (stages 2 and 3–4) with REM and while awake in elaborative encoding of episodic memory. If the assumption is that there is isomorphism between neuronal and cognitive networks, then more detailed analysis of NREM sleep and dreams is absolutely necessary.

In her target article, Sue Llewellyn concludes that an unconstrained form of consciousness is necessary for the elaboration of meaningful associations. Unlike the author's view that dedifferentiation of memory encoding processes across wakefulness and sleep determines schizophrenia, our proposal suggests this mechanism could reflect a common neurobiological substrate for psychosis across several different diagnostic domains.

Llewellyn suggests that episodic memories undergo “elaborative encoding” during rapid eye movement (REM) dreams, generating novel associations between recent and remote memories that are then instantiated during non-REM (NREM) sleep. This hypothesis conflicts with our knowledge of the physiology of NREM and then REM sleep stages and their ordered succession. Moreover, associations during sleep might also involve the extraction of hidden patterns rather than de novo associations.

During dreaming, as well as during wakefulness, elaborative encoding, indexing and ancient art of memory (AAOM) techniques, such as the method of loci, may coincide with emotion regulation. These techniques shed light on the link between dreaming and emotional catharsis, post-traumatic stress disorder, supermemorization during sleep as opposed to wakefulness, and the developmental role of rapid eye movement (REM) sleep in children.

Individuals high in the personality trait Openness to Experience appear to engage spontaneously (during wake) in processes of elaborative encoding similar to those Llewellyn identifies in both dreaming and the ancient art of memory (AAOM). Links between Openness and dreaming support the hypothesis that dreaming is part of a larger process of cognitive exploration that facilitates adaptation to new experiences.

A method is proposed where static patterns or snapshots of cortical activity that could be stored as hyperassociative indices in hippocampus can subsequently be retrieved and reinjected into the neocortex in order to enable neocortex to then proceed to unfold the corresponding sequence, thus implementing an index-based sequence memory storage and retrieval capability.

We studied the world's most distinguished experts in the use of mnemonic techniques: the top participants of the World Memory Championships. They neither feel the use of mnemonics to be dreamlike, nor does their REM sleep differ from mnemonic-naive control subjects. Besides these empirical data, also theoretical considerations contradict an isomorphism between features of REM sleep dreaming and mnemonic principles.

Classic traditions have linked dreams to memory (e.g., “dreaming is another kind of remembering” [Freud 1918/1955]) and modern notions like implicit memory subsume dreaming by definition. Llewellyn develops the more specific thesis that rapid eye movement (REM) dreams, because of their similarities to mnemonic techniques, have the function of elaboratively encoding episodic memories. This proposal is premature, requiring exigent testing. Other analogs of dreams, for example, jokes, do not invoke function but do contribute to dream science.

Llewellyn's proposal that rapid eye movement (REM) dreaming reflects elaborative encoding mediated by the hippocampus (“seahorse”) offers an interesting perspective for understanding hallucinations accompanying sleep paralysis (SP; “night-mare”). SP arises from anomalous intrusion of REM processes into waking consciousness, including threat-detection systems mediated by the amygdala (“almond”). Unique aspects of SP hallucinations offer additional prospects for investigation of Llewellyn's theory of elaborative encoding.

Sometimes while sleeping we find ourselves thrown amidst an authentic, albeit bizarre, world. The process of integration by means of which memory elements might be fabricated into a seamless world indistinguishable from the world of waking life is not explained by Llewellyn, who focuses instead on the elaborative encoding of memories. Ontological implications of the sometimes indiscernibility of wake and dream worlds are considered.

Whereas the target article stresses the neurobiology and psychology of dreams, this commentary emphasizes that the role of dreams in emotional integration and adaptation contributes to a fuller understanding of dreaming and memory. The dream presented in the target article is used, within the constraints of space, as a possible example of a broader approach to dream material.

Revision of Freud's theory requires a new way of seeking dream meaning. With the idea of elaborative encoding, Sue Llewellyn has provided a method of dream interpretation that takes into account both modern sleep science and the ancient art of memory. Her synthesis is elegant and compelling. But is her hypothesis testable?

Brain activation patterns and mental, electrophysiological, and neurobiological features of rapid eye movement (REM) sleep suggest more functions than only elaborative encoding. Hence, the periodic occurrence of REM sleep episodes and dreaming may be regarded as a recurrent adaptive interference, which incorporates recent memories into a broader vital context comprising emotions, basic needs and individual genetic traits.

It is argued that Llewellyn's hypothesis about the lack of rapid eye movement (REM)-sleep dreaming leading to loss of personal identity and deficits in episodic memory, affectivity, and prospection is insufficiently grounded because it does not integrate data from neurodevelopmental studies and makes reference to an outdated definition of episodic memory.

By integrating the classic psychological principles of ancient art of memory (AAOM) with the most recent paradigms in cognitive neuroscience (i.e., the concepts of hodotopic organization and nonlinear dynamics of brain neural networks), Llewellyn provides an up-to-date model of the complex psychological relationships between memory, imagination, and dreams in accordance with current state-of-the-art principles in neuroscience.