Inception or Reality?
Can external cues shape our dream worlds?
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Dall-e 3 representation of this post
Some days ago I had an interesting dream where I was traveling between the ruins of ancient cities seemingly located in Egypt. I can’t remember all the details, but I vividly remind the names of at least two cities, and that I was trying to interpret some hieroglyphs to discover the next place to visit. If it sounds like a plot for an Indiana Jones movie, I agree: I love those movies and, furthermore, I am fascinated by the ancient Egyptian culture.
Why is this relevant for writing a post? Well, the context behind the dream was interesting. I was so tired that i felt asleep without switching off the TV while watching a peaceful documentary about weird animals living in the deep oceans. Likely because it was not in the most comfortable setup for a nightly sleep, I woke up about two hours later, while the same channel was still streaming a documentary about the ancient Egyptians.
Just a coincidence? Maybe, but it triggered a question: is it possible that unconsciously listening about ancient Egyptians in the early stages of my sleep the brain was driven to elaborate a dream about them? Provided that I have a lot of memories about my trip to Egypt and I have watched Indiana Jones movies several times (but not recently).
As a complexity scientist, my hypothesis is rather simple. Since I am still studying the mechanisms for controlling a dynamical system (smaller than the brain) with one of our PhD students, I am just assuming that the TV acted as an external driver signal for my brain’s sensory input, thus interfering with its natural activity by forcing it to process the signal.
I am not an expert at all about the sleeping brain, so I ask my fellow neuroscientist friends and colleagues to read this piece as an attempt to find answers to a specific question, rather than a way to formulate a definitive answer. I have discovered that there are literally thousands of scientific papers with hypotheses about why the brain should dream. Here there is what I have found.
I won’t bother you with the sleep cycle and EEG recordings, since this is something that can be easily found everywhere. Instead, I am going to focus first on why we should dream, and later I will discuss about the possibility to force dreams with external stimuli.
Dreaming is primarily associated with the Rapid Eye Movement (REM) stage of sleep, with various brain structures and neurotransmitters implicated in the generation and experience of dreams.
Activation-Synthesis Hypothesis
According to Hobson and McCarley, dreaming is essentially the brain's way of interpreting random electrical impulses generated during REM sleep. In this stage, the pons, a region at the base of the brain, sends random signals to the cerebral cortex, the brain's "control center" for thought and perception. The cortex, which is involved in logical reasoning and sense-making, takes these random signals and tries to weave them into a coherent narrative, much like trying to find shapes in clouds or patterns in static noise. The final result is a dream: a narrative constructed out of the brain's attempt to make sense of these random signals. This theory, known as the Activation-Synthesis Hypothesis, can be used to explain the often surreal and illogical nature of dreams, as the brain is essentially improvising a story from electrical noise. The work by Hobson and McCarley has the main merit of providing a potential neurobiological explanation for dreaming, shifting the focus from psychoanalytic interpretations to the workings of the brain itself.
However, I am struggling to reconcile this theory with the famous work by Dobzhansky, according to which “Nothing in Biology Makes Sense except in the Light of Evolution”. After all, interpreting random electrical noise seems like quite an expensive activity for a brain, e.g., for regulating the corresponding metabolism. I can't believe in such an inefficient management of resources, although evolutionary arguments alone might not be sufficient to explain a complex process like dreaming.
Social Simulation Theory
To give some evolutionary meaning to the act of dreaming, other theories have been proposed. Revonsuo, Tuominen and Valli proposed the Social Simulation Theory, according to which the primary function of dreaming is to simulate social interactions and problem-solving scenarios, essentially serving as a kind of "rehearsal" for real-life social situations. It follows that dreams allow individuals to practice and refine their social skills by navigating complex, imagined interpersonal interactions, which may improve their ability to effectively deal with social challenges in waking life.
Really interesting, since individuals able to deal with social-driven problems might have some evolutionary advantage with respect to the ones who are not able to do so. Since some dreams appear to unfold in some “universal” situations or scenarios, recurring themes of social interactions and problem-solving provide some preliminary validation for the hypothesis. Nevertheless, one can argue that to provide a real evolutionary advantage, this simulation should be as realistic as possible, and this seems to be in sharp contrast with the crazy things that sometimes happen during a dream. Experimental tests are needed.
Threat Simulation Theory
Revonsuo proposed another interesting hypothesis, known as the Threat Simulation Theory, according to which one of the primary evolutionary functions of dreaming is to simulate threatening events. This serves as a kind of cognitive rehearsal for real-life threatening situations, thereby providing an evolutionary advantage in terms of survival. According to the theory, the brain would activate to consolidate memories related to such threats, making them easier to access and act upon in the future.
While this theory makes sense from an evolutionary perspective, putting the focus on survival to threats, it fails at explaining why we also have peaceful and enjoyable dreams. After all, going back to the beginning of this piece, I was really enjoying my adventure through ancient cities of Egypt while traveling like Indiana Jones.
Defensive Activation Theory
A similar theory posits that the primary function of dreaming is to engage the brain's defense mechanisms, essentially preparing the individual for potential threats in the waking world. On the one hand, works by Hartmann and Perogamvros and Schwartz, suggest that dreams serve to stimulate and exercise the emotional and cognitive systems used for coping with stress and danger: a clear defensive strategy against potential threats. However, as for TST, this does not really account for the full spectrum of dream experiences, which can also include positive, neutral, or abstract experiences. I think that another work aligned with this aspect, is Blumberg's theory arguing that REM sleep and its associated neural activities are essential for the development and calibration of neural circuits and motor systems.
While, on the one hand, the psychotherapy hypothesis proposed by Hartmann suggests a clear cognitive defensive mechanism and the Blumberg’s work suggest a clear developmental defensive mechanism, on the other hand another recent theory has been proposed in terms of a biological defensive mechanism: the Defensive Activation Theory. This is related to the concept of "livewiring," which refers to the brain's ability to reconfigure its neural pathways (i.e., brain plasticity) in nearly real-time. In fact, the brain’s flexibility allows it to adapt to new conditions quickly: e.g., in people who have lost their sight, the visual cortex can be repurposed for processing auditory information. DAT builds on this concept, suggesting that REM sleep serves to keep the visual cortex active for preventing a takeover of its functions by other senses, particularly in the absence of visual input, as in darkness. The theory is backed by the observation that specialized neurons trigger activity in the visual cortex during REM sleep, underlining the biological importance of dreaming.
Thus, sleep is the price we have to pay for plasticity, and its goal is the homeostatic regulation of the total synaptic weight impinging on neurons — G. Tononi and C. Cirelli
Poorly speaking, we could argue that DAT is related to internal threats, rather than external ones (as in TST). I have found this paper reporting a rather interesting result:
We investigated the effect of sudden, complete and prolonged visual deprivation (five days) in normally sighted adult individuals while they were immersed in an intensive tactile training program. Following the five-day period, blindfolded subjects performed better on a Braille character discrimination task. In the blindfold group, serial fMRI scans revealed an increase in BOLD signal within the occipital cortex in response to tactile stimulation after five days of complete visual deprivation. This increase in signal was no longer present 24 hours after blindfold removal. Finally, reversible disruption of occipital cortex function on the fifth day (by repetitive transcranial magnetic stimulation; rTMS) impaired Braille character recognition ability in the blindfold group but not in non-blindfolded controls. This disruptive effect was no longer evident once the blindfold had been removed for 24 hours.
Overall, our findings suggest that sudden and complete visual deprivation in normally sighted individuals can lead to profound, but rapidly reversible, neuroplastic changes by which the occipital cortex becomes engaged in processing of non-visual information. The speed and dynamic nature of the observed changes suggests that normally inhibited or masked functions in the sighted are revealed by visual loss …
To some extent, this theory shifts the focus from life-threatening external stressors to a simple biological argument. The brain evolved to quickly respond to a changing environment and the temporary inhibition of one of its input circuitry can lead to the takeover of other circuitries, within hours, aiming at filling the gap.
If I got it correctly, then the theory suggests that without dreaming our brain would lose a specific function: keeping the brain active (via dreaming) avoids that loss.
In terms of explanatory power, there is some value in DAT, but I refer to the ending of this article for details. I like this theory, but to which extent the brain evolved to keep a so potentially dangerous self-regulating activity?
Going back to the original question
It seems that the brain can effectively process surrounding information even during sleep and, in the REM phase, it is possible that the external signals can act as an input for specific memories. I think that without those memories, it could barely build dreams based on those external signals.
There is some value in all the theories described above, but I think that the question remains wide open, although the subject of controlled dream manipulation is not new at all and “information processing during sleep is active, ongoing and accessible to engineering”. Furthermore, thanks to Luiz Pessoa, I have discovered a recent work on real-time communication about a dream, reporting that during REM sleep individuals can perceive and even answer an experimenter’s questions.
Dreaming represents the interplay of complex processes within one of the most intricate systems known: the brain. Understanding its role in neural functionality is nothing short of fascinating.
Dreams are a most remarkable experiment in psychology and neuroscience, conducted every night in every sleeping person — Y. Nir and G. Tononi