Chasing The Dream

The function of REM sleep dreaming is still unknown. We situate our approach to understanding dream phenomenology and dream function within that part of evolutionary theory known as Costly Signaling Theory (CST). We contend that many of the signals produced by the dreaming brain can be and should be construed as 'costly signals'—emotions or mental simulations that produce daytime behavioral dispositions that are costly to the dreamer. For example, often the dreamer will appear in the dream as handicapped in some way (i.e., no clothes, no ID, no money, is under attack, being chased etc.). The dreamer, during waking life, is then influenced by the carry-over effect of the unpleasant dream content. The informational and affective content of the dream creates a mental set in the dreamer that operates during the daytime to facilitate the signaling of a 'handicapped' Self. The subtle signaling effect might be via display of the intense emotions or physical demeanor that had first appeared in the dream. When the dreamer shares his dream with others the dream has a more direct impact on waking life and social interactions. In effect, the dreamer uses his or her dreams to adopt a self-handicapping strategy when dealing with significant others. The increased use of costly signals (the self-handicapping strategy) during the daytime then facilitates some vital communicative goal of the dreamer.

Some forms of sleep mentation depend on REM sleep physiology, it can be said that this mentation is part of that physiology. Not all dreams and not all of the content of REM-related dreams are due to REM physiology alone (see Nielsen, 2000; Solms, 2000). Nevertheless, it is very likely that a significant portion of the content of REM related dreams is related to and even a direct result of various components of REM physiology. For example, when ponto-geniculo-occipital (PGO) spikes occur during a REM episode one is more likely to get dream reports that contain rapid plot shifts and greater amounts of bizarre imagery. In addition, the limbic brain activation patterns that occur during REM very likely accounts for dreams containing emotionally charged social interactions. In short, it is not unreasonable to treat dream reports that occur in temporal relation with REM episodes as part and parcel of REM physiology itself. To construct a theory of dream function it is reasonable to bring in an account of REM physiology.

Some progress has been made in our understanding of REM physiology including REM dream content by adopting evolutionary approaches to dream function. For example, the so-called 'threat simulation theory' of dream function can claim some empirical support given that some studies of dream content are consistent with the theory. In addition, unlike classical Freudian or Jungian theory, threat simulation theory is consistent with a broad range of data from the evolutionary sciences and theory. No elaborate interpretation of dream content is needed to square the dream content data with the (evolutionary) theory. The data or at least some portion of the available data on dream content is nicely predicted by the threat simulation theory. Evolutionary approaches to dream function have the advantage of putting severe constraints on the scope of the theory proposed – namely that the theory be consistent with both the facts concerning dream phenomenology and the rest of the evolutionary sciences. It is not enough to speculate about what dreams might do for the organism – one must propose a function that is consistent with some part of evolutionary theory. If dreams are good for something, that something must be with reference to some part of evolutionary theory.

We situate our approach to understanding dream phenomenology and dream function within that part of evolutionary theory known as Costly Signaling Theory. CST is concerned primarily with understanding animal signaling behaviors. The basic idea is simple: for signals between two parties to be workable or believable by both parties they must be reliably unfake-able. Only signals that can't be faked can be trusted to carry honest information. Un-fakeable signals are those signals that are metabolically, motorically, or behaviorally difficult to produce (costly). Their production costs or 'costliness' is their certification of honesty. Costly signals are preferred by animals under conditions where the animals are capable of deception but require reliable and honest signaling between the parties (e.g., between the two sexes during mating season). For a signal to classify as a handicap, the net benefits for displaying the signal (REM sleep intensity in our case) must be higher for a high-quality individual than a low-quality individual (or the costs of high REM intensity must be higher for low-quality individuals). Thus a low-quality signaler must be able to send a signal suggesting high quality; i.e. must be able to fake 'high REM'. The signal must be costly to fake but not impossible to fake. The handicap principle asserts that low-quality signalers generally don't send false signals because it simply does not pay; the net costs are too high.

Humans, of course, engage in a range of signaling behaviors, but can REM sleep and dreams plausibly be considered one of them? Human signaling behaviors include everything from speech and language exchanges to emotional displays, 'body-language' (e.g. clothes, postures, tattoos etc) and other non-verbal behaviors. Dreams associated with so-called rapid eye movement or REM sleep can function as signals. Dreams can also function to facilitate production of signals when they produce some daytime effect such as a memory or a mood (or both) or a behavior that communicates a message to an observer. A person, for example, who awakens from a disturbing dream may behave differently during the day from a person who awakens from, for example, an erotic dream or a bizarre dream and so on. Many dreams, even un-remembered dreams create background moods and behavioral dispositions that linger through much of the subsequent daytime period. While it is difficult to demonstrate that un-recalled dreams can influence daytime mood and behavior, we know that depriving a person of his or her REM/dream sleep can significantly alter daytime mood states –at least in some vulnerable individuals.

Patrick McNamara, Ph.D. is Professor of Psychology at Northcentral University, Associate Professor of Neurology and Psychiatry at Boston University School of Medicine and Research Associate Professor of Neurology at Department of Neurology, University of Minnesota School Of Medicine in Minneapolis. He is the author of over 60 papers on sleep and dreams several single author books and co-edited volumes on sleep and dreams. His most recent book is 'The Neuroscience of Sleep and Dreams'. He maintains a blog on sleep and dreams for Psychology Today online. He has been awarded grants from the National Institutes of Health to study evolutionary biology and functions of sleep and dreams as well as REM and NREM dream differences. In 2009-10 he appeared on the PBS (NOVA), program ‘What Are Dreams?’ In 2012-13 he appeared in PBS 'Closer to Truth' series on sleep and dreams. In 2013 he was named Chief Science Advisor to Dreamboard.com. He is regularly interviewed on sleep and dreams in international media forums including online blogs, traditional radio and TV, and traditional print magazines/newspapers such as Time magazine, Science Weekly, and the Daily Mail in London. His work on nightmares and dreams has been turned into a theater production and an art installation in Washington DC.

Michelle Carr, Ph.D. is a Postdoctoral Associate at the University of Rochester in the Department of Psychiatry, working in the Sleep and Neurophysiology Research Laboratory with Dr. Wilfred Pigeon. She previously completed postdoctoral training at the Swansea University Sleep Laboratory with Dr. Mark Blagrove, and received her PhD in Biomedical Sciences from the University of Montreal in 2016, conducting research with Dr. Tore Nielsen at the Dream and Nightmare Laboratory. Her research interests center on sleep psychophysiology, disturbed dreaming, and dream engineering - applying technologies to influence sleep and dreams to benefit memory, creativity, emotional or physical well-being. She led the organization of the Dream Engineering Workshop at MIT Media Laboratory in January 2019, and guest edited a Special Issue on Dream Engineering with the journal Consciousness and Cognition. She also translates dream science research to the public by writing for Psychology Today.

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