Neurological Disorders Part 1: REM Sleep

Written By: Diyanka Lahane

Introduction 

People can spend up to one-third of their lives sleeping. 

The brain while awake and while asleep can remain equally as active, indicating that dreaming can take place in REM-sleep and non-REM sleep. REM sleep is a period of sleep that is uniquely characterized by rapid eye movement while the eyes are still closed. While brain activity is still the same as when someone is awake, muscle activity is greatly decreased. Arm and leg muscles can become temporarily “paralyzed” and diaphragm muscles become more erratic (Steck, A., Steck, B., 2016).

Eugene Aserinsky and Nathaniel Kleitman (Silber M.H., 2023) are recognized for discovering REM sleep in an experiment that served as a foundation for the modern understanding of dreams. They discovered rapid eye movement occurring over 3-4 cycles in 20 adults during a regular sleep schedule. An in-depth experiment was published by the same researcher years later that indicated the same cycles in sleeping infants. However, medical student William Dement and researcher Kristina Denisova coined the term “REM sleep” and analyzed the original sleep experiments to explain the body physiology behind REM sleep, as Kleitman was accused of not thoroughly detailing their research (Silber M.H., 2023). During REM sleep, participants exhibited increased and irregular breathing, changes in body temperature, body twitching, and both horizontal and vertical eye movement.

This two-part paper will discuss the current research behind dreams and nightmares, including the neurobiology and if dreams or nightmares can be interpreted to physiological or neurological disorders within the body. 

Stages of Sleep

REM sleep is more than a time to have dreams and nightmares. It allows for the body to repair itself and prepare for the next day. This includes converting food to energy and storing any extra “resources” the body cells do not need. It is even said that sleeping allows for the brain to process all the information input from the day without taking in any new information (Steck, A., Steck, B., 2016). The sleep cycle is not one long cycle, but rather 4 or 5 repeated cycles that each last around 90-120 minutes. To start, there are two sleeping stages: REM sleep and non-REM (NREM) sleep. When initially falling asleep, the body enters stage 1 of NREM sleep and continues to stage 2 and 3 before entering a REM cycle. Dreaming occurs only during REM sleep. The cycle repeats by going back to stage 1 of NREM sleep (Cleveland Clinic, 2023). 

Stage 1 is the shortest stage and of the lightest sleep. A person can be easily awoken in this stage. Stage 2 is when the signals in the brain are slower and there is not nearly as much electrical activity as Stage 1 or as being awake. Researchers believe these small bursts of energy could be the brain trying to organize the memories/thoughts of the day. Stage 3 is the deepest stage where the brain waves are very slow. This is the time where the body does the most repairing for injuries on the outside and inside of the body. To wake up feeling rested, someone must complete a Stage 3 cycle. If awoken in the middle of this stage, someone might feel more drowsy than before going to bed. Light sleepers tend to spend more time in REM sleep which is the last stage before waking up. Deep sleepers tend to spend more time in deep sleep such as NREM stage 3 (Cleveland Clinic, 2023). 

Neurobiology of REM Sleep: Current Findings

Brain Lesions 

Brain lesions are different parts of the brain tissue that have been damaged and either do not work at all or have drastically decreased  function effectiveness. When taking a brain scan such as MRI or CT, brain lesions can be identified as either an extremely dark spot or light spot compared to the rest of the scan. Brain lesions can occur for a variety of reasons, the most common being blunt injury, infections, and fetal developmental issues. 

A recent article in the “Trends in Cognitive Science” journal explains that waking cognitive ability can determine the extent of dreams. If someone has a brain lesion that harms their ability to perceive new faces while awake, their dreams will not have any faces present in them. In other cases, lesions that impair more physical characteristics like motor control can cause erratic movement while dreaming. This can explain severe twitching while asleep that may not occur while awake (Nir, Y., Tononi, G., 2010). This can even occur with processing color if there is a restricted lesion in a part of the brain that affects visual perception. Brain lesions may impair or limit cognitive ability, but they do not always have negative effects on dreaming. During an experiment, patients with a lesion in the basal forebrain and medial prefrontal cortex reported that dreams were more vivid and increased in frequency, meaning multiple dreams within one REM cycle. It is concluded that dreams have a specificity regarding which part of the brain is affected by lesions (Nir, Y., Tononi, G., 2010). 

Sleep Paralysis

Sleep paralysis can be caused by several variables: trauma, genetics, stress, physical illnesses, and disorders (either neurological or specifically sleep related) (Denis, D., French, C.C., Gregory, A.M., 2018). It is when the body maintains all muscle paralysis that occurs during REM sleep while the person is still fully conscious. This is due to the body having an increased “sympathetic tone,” which causes a disconnect between perception and motor control (Farooq, M., Anjum, F., 2023). Sympathetic tone is the body’s ability to react in a fight or flight mode, the engagement of the sympathetic nervous system in the body. Females tend to have a higher level of sleep paralysis occurrence than men, although no scientific explanation has been discovered yet for  this discrepancy. During sleep paralysis, people tend to wake up with feelings of dread and intense fear, sometimes before they have realized they are incapable of moving their body. This is due to the body being in the “hypervigilant state” during REM sleep which instantly triggers the brain to feel fear (Farooq, M., Anjum, F., 2023). Additionally, those who experience sleep paralysis feel a weight on their chest resembling the inability to take deep breaths. Through several experiments, various researchers believe that when breathing becomes irregular during REM sleep, there is a reduction in tidal volume and how much air is let into the alveoli within lungs (Farooq, M., Anjum, F., 2023). 

Sleep paralysis is a common symptom for narcolepsy, which is a neurological disorder that limits the brain’s ability to manage sleep-wake cycles. Narcolepsy is associated with loss of body muscle, extreme weight loss, and feeling exhausted during the daytime (Denis, D., French, C.C., Gregory, A.M., 2018). Unfortunately, there is no cure or tactic to prevent sleep paralysis for the entirety of someone’s life. Some factors may increase the likelihood, however it can still occur for anyone. Once in a sleep paralysis stage, someone must wait for the episode to finish on its own and focus on grounding your body such as consistent breathing and paying attention to items that are certainly in your reality.

What can affect REM sleep?

Melatonin

Melatonin is a hormone produced within the body primarily from the pineal gland, though production can also occur from secondary organs. It is converted from serotonin through a two step process that starts with the activation of norepinephrine binding to adrenergic beta-1 receptors (Claustrat, B., Brun, J., Chazot, G., 2005). Melatonin secretion is not directly associated with stages and peaks in REM sleep, but rather through an endogenous clock within the suprachiasmatic nuclei (SCN) in the hypothalamus. The SCN controls other bodily processes–essentially all circadian rhythms–like sleep-wake cycles, temperature changes, and levels of cortisol (Claustrat, B., Brun, J., Chazot, G., 2005). In other words, melatonin secretion occurs in the dark stage of a light-dark cycle. Instead of something “activating” secretion during the dark, the retino-hypothalamic fibers in the retina sense the presence of light and send an output to the hypothalamus which will “inhibit” secretion during the light stages. However, most people in modern society do not have constant patterns of melatonin secretion due to stress, use of drugs, late-night work shifts, or even aging. When artificial light from light bulbs are present, melatonin levels can still be reduced by a certain amount even during night hours, such as airport lights during an overnight flight or staring at a phone screen when trying to fall asleep- specifically the blue light (Claustrat, B., Brun, J., Chazot, G., 2005, Alghamdi, B.S., 2018). 

Changes in the sleep-wake cycle controlled by the SCN can cause low melatonin production, resulting in sleeping difficulties. Irregular sleeping patterns then disrupt the homeostatic balance of sleep levels in the body. For example, if someone’s routine doom scrolling causes lower levels of melatonin during the night, they would still feel the need to nap during the day: the body needs to adequately rest, regardless of the level of melatonin at that point in the day (Hardeland, R., 2012). Sleeping issues are often associated with depressive disorders as well. Lack of a consistent sleep schedule can be a predictor of a group of disorders like insomnia (Hardeland, R., 2012).

Melatonin can affect the body in ways not involving sleep. In a study written by Alghamdi, rats were observed to test reactions to ischemic strokes, or when there is some obstruction or blockage in the cerebral arteries that affect blood circulation and therefore limit the work done by that area of the brain. It was concluded that rats that received a pineal gland transplant, and therefore had an increased production of melatonin,had a huge improvement in motor ability and a shorter recovery time, as well as smaller obstructions in the artery (Alghamdi, B.S., 2018). That being said, more research should be conducted on the long-term effects of consuming supplemental melatonin for longer than 4-5 months and how this heavy consumption impacts REM sleep.

What Does Science Say for Dream Interpretation?

Researchers debate whether dreams are a “top-down” or “bottom-up” process in the brain. In other words, do dreams form from low-sensory areas in the brain such as abstract thought and then form high-level organized thinking? Or do they form piece together distinct memories stores in long-term memory with strong sensory and perceptual cues? Different scientists have suggested different findings , as dream experiments are mainly done through verbal reports from participants (Nir, Y., Tononi, G., 2010). Some support the idea that ponto-geniculo-occipital (PGO) waves generated in the brainstem during REM sleep can trigger the visual cortex. The output is later synthesized to a higher-processing level in the brain resulting in a dream. Others, such as Sigmund Freud, believe that dreams originate from psychological underlying motives in the brain that interact with sensory perception and form a dream (Nir, Y., Tononi, G., 2010). While dreaming, the brain can create illusions and figures that are not present in their everyday reality. The ability to mentally create new imagery can explain some neural mechanisms that form dreams (Desseilles, M., Thanh Dang-Vu, T., Sterpenich, V., Schwartz, S., 2011). 

Resources

Alghamdi, B.S. (2018). The neuroprotective role of melatonin in neurological disorders. Journal of Neuroscience Research, 96(7); 1136-1149. https://doi.org/10.1002/jnr.24220 

Claustrat, B., Brun, J., Chazot, G. (2005). The basic physiology and pathology of melatonin. Sleep Medicine Reviews, 9(1); 11-24. https://doi.org/10.1016/j.smrv.2004.08.001

Cleveland Clinic. (2023). Sleep. https://my.clevelandclinic.org/health/body/12148-sleep-basics 

Denis, D., French, C.C., Gregory, A.M. (2018). A systematic review of variables associated with sleep paralysis. Sleep Medicine Reviews, 38; 141-157. https://doi.org/10.1016/j.smrv.2017.05.005

Desseilles, M., Thanh Dang-Vu, T., Sterpenich, V., Schwartz, S. (2011). Cognitive and emotional processes during dreaming: A neuroimaging view. Consciousness and Cognition, 20(4), 998-1008. https://doi.org/10.1016/j.concog.2010.10.005. 

Farooq, M., Anjum, F. (2023). Sleep Paralysis. StatPearls Publishing (Internet). https://www.ncbi.nlm.nih.gov/books/NBK562322/ 

Hardeland, R. (2012). Neurobiology, Pathophysiology, and Treatment of Melatonin Deficiency and Dysfunction. The Scientific World Journal. https://doi.org/10.1100%2F2012%2F640389 

Nir, Y., Tononi, G. (2010). Dreaming and the brain: from phenomenology to neurophysiology.Trends in Cognitive Science. 14(2):88-100.  https://doi.org/10.1016/j.tics.2009.12.001 

Silber M.H. (2023). Who discovered REM sleep? Sleep, 47(1). https://doi.org/10.1093/sleep/zsad232 

Steck, A., Steck, B. (2016). Dreams and the Dreaming Brain. Brain and Mind, 219-240. https://doi.org/10.1007/978-3-319-21287-6_15