The Science of Dreams: What Happens In The Brain When We Dream
Why Do We Dream?
Dreaming and the meaning of dreams have been hot topics for centuries. Ancient civilizations believed that dreams contained prophecies and connected humans to the messages of the gods (6). In the late 1800s, Sigmund Freud popularized the theory that dreams represented repressed desires (6).
Even some modern psychologists believe that there could be some metaphorical insights gained from dreaming. Still to this day, there is no precise answer to whether dreaming actually serves a purpose, but there has been an abundance of theories.
We know that sleeping, in general, produces many benefits, and those who are sleep deprived or have poor sleep quality are subject to a higher risk of developing some pretty concerning health conditions (4). Yet we haven’t quite figured out what purpose dreaming has.
Modern Theories on Dreams
Some modern theories have introduced the belief that perhaps dreaming doesn’t actually mean anything—instead, dreams are bits and pieces of different memories that we have that get strung together.
These memories are often the ones that are at the forefront of our minds or are the things that we think about frequently. Others, however, insist that dreaming has a deeper and more complex function:
1. Memory Consolidation
We know that sleep in general plays a role in memory consolidation. Those who lack proper sleep appear to have worse memory recall and lower ability to focus.
Dreaming may contribute to building memory storage in a different way. REM sleep and dreaming could be a place where your brain gets rid of the memories it doesn’t need (or could be harmful) in order to make space for more useful information (1).
2. Evolutionary Purpose
Some insist that since dreaming occurs in other mammals as well, an evolutionary purpose must exist. It may allow us to simulate threatening situations and be better prepared to deal with it in real life, or that it allows us to solve problems while in an altered state (2).
3. Emotional Processing
One emerging theory of why we dream has to do with processing emotions. We have learned that some parts of the brain responsible for dreaming correspond with the parts that process visual memories and emotions.
We know that sleep plays a role in mood because those who are sleep deprived are more likely to have higher reactivity to anger and fear during the day.
A study conducted at the Sleep and Neuroimaging Laboratory at Berkeley University demonstrated that during REM sleep, the limbic system (the part of the brain that governs fear and emotions) may be partly responsible for blocking negative emotions such as fear and anger, as well as resetting the brains emotional reactivity (3).
So, dreams may be connected to one’s emotional state since those who get less REM sleep (and therefore dream less), appear to have more difficulty processing emotions in their waking hours (3). These theories have yet to be 100% proven, and so we are left with the assumption that if dreaming has a purpose, it may play a role in many different processes.
Dreams & What’s Happening in the Brain
Dreaming is such a fascinating topic because everyone dreams (even if you don’t remember them), but the experience of dreaming can vary from person to person. We do know that most dreams last about 5-20 minutes, and you can have multiple dreams in a night. The variability is in the experience of dreaming, recollection, and intensity.
Some people remember their dreams vividly, and others do not. Some have the same dream over and over while others rarely repeat a dream. Some remember only a handful of dreams in their lifetime but others can recall dreams nightly. Some are lucid dreamers, and most of us are not. Others dream in color, while some dream in black and white (4).
Muse’s EEG Spectogram image above shows the intensity of brainwave activity over time. High-intensity regions are indicated by tones of red, yellow, green, and low-intensity regions are indicated by tones of blue.
Up until the advent of the electroencephalogram (EEG), researchers were unable to access or measure electrical activity that occurs in the brain during all states of consciousness. Previously, it was believed that sleep was a fully resting state, when in fact there are varying levels of brain activity that occur during different stages of sleep. Our brain fluctuates between four main types of waves depending on the level of wakefulness or relaxation (alpha, theta, delta, beta).
Dreams in REM
You can dream in any stage, but most dreaming appears to occur during the REM stage. During REM sleep, brain activity most closely resembles that of a wakeful state (5). Dreaming during the REM stage seems to be the most intense, and people tend to remember more of their dreams when they wake up right after REM sleep. In fact, people generally seem to be sharper cognitively right after REM sleep.
Interestingly, a study conducted by J. Allan Hobson at the Division of Sleep Medicine at Harvard Medical School proposed that “REM sleep dreaming can be viewed as a virtual reality created from our brain’s devise.” In other words, “we sense, we act and we feel” what we dream (7). The theory inspired a team of sleep engineers at MIT’s Sleep & Neurophysiology Lab to investigate if receiving sensory stimuli while sleeping could shape our dreams.
Muse’s sleep stages graph (hypnogram) above shows the different stages of sleep of participants during their session.
To do this, they recorded a group of participant’s body and brainwave patterns while sleeping and computed their sleep stages and sleep scores using Muse. While asleep, participants underwent sensory dream engineering techniques using Dormio, the first interactive interface for sleep. These techniques include; receiving a burst of scent or placing a heated eye mask over their eyes (8). So, what did the study uncover?
- Ameliorated Dream Valence – After introducing pleasurable or familiar scents and temperatures, participants showed positive affective responses (9) while dreaming that are associated with patterns of respiration, heart rate, and muscular activity (particularly during REM sleep), improved sleep quality, and mood.
- Alleviated Nightmares – Participants showed fewer biomarkers associated with nightmares, such as increased and elevated heart rate, increased eye movements, increased respiration rate, and the interference of REM sleep.
When you dream, your whole brain is active at some level. However, during REM sleep, your prefrontal cortex is less active. This is the part of the brain that is responsible for planning and logic. Since activity in the prefrontal cortex is lower during REM sleep, we often don’t recognize the strangeness or implausibility of a dream until we wake up (2). This is why your ability to fly or the appearance of monsters seems so realistic until you wake up from that dream (or nightmare).
It’s clear that we still have a lot to learn about what happens in the brain while we are sleeping and while we are dreaming. We have even more work to figure out why we dream in the first place. Until then, sweet dreams!
- Izawa et al. REM sleep-active MCH neurons are involved in forgetting hippocampus-dependent memories. Science, September 20, 2019 DOI: 10.1126/science.aax9238 https://science.sciencemag.org/content/365/6459/1308.abstract
- Yue, Carole. Khan Academy. Dreams. https://www.khanacademy.org/science/health-and-medicine/executive-systems-of-the-brain/sleep-and-consciousness-lesson/v/dreaming
- Gujar N, McDonald S, Nishida M, Walker M. A Role for REM sleep in Recalibrating the Sensitivity of the Human Brain to Specific Emotions. Cerebral Cortex January 2011; 21:115-123. https://walkerlab.berkeley.edu/reprints/Gujar-Walker_CC_2011.pdf
- National Institute of Neurological Disorders and Stroke. Brain Basics: Understanding Sleep https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep#2.
- Harvard University: Natural Patterns of Sleep. http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem
- Big Dreams: The Science of Dreaming and the Origins of Religion, https://books.google.ca/books?hl=en&lr=&id=_zh2CwAAQBAJ&oi=fnd&pg=PP1&dq=science+of+dreaming+scholarly+articles&ots=XhMok2QgJ1&sig=_RvNr2wjkwpQyug3LnoN8Z3I3mg#v=snippet&q=gods&f=false
- Hobson, J. REM sleep and dreaming: towards a theory of protoconsciousness. Nat Rev Neurosci 10, 803–813 (2009): https://www.nature.com/articles/nrn2716
- Carr, Michelle, Adam Haar, Judith Amores, Pedro Lopes, Guillermo Bernal, Tomás Vega, Oscar Rosello, Abhinandan Jain, and Pattie Maes. “Dream engineering: Simulating worlds through sensory stimulation.” Consciousness and cognition 83 (2020): https://dam-prod.media.mit.edu/x/2020/10/06/1-s2.0-S1053810020300325-main.pdf
- Horowitz H., A., Grover, I., Reynolds-Cuéllar, P., Breazeal, C., Maes, P., “Dormio: Interfacing with Dreams” Association for Computing Machinery (2018): https://dl.acm.org/doi/10.1145/3170427.3188403
- Shuman, V., Sander, D., and Scherer, K., R., “Levels of Valence” Frontiers in Psychology 4 (2013): https://www.frontiersin.org/articles/10.3389/fpsyg.2013.00261/full