Sleep and the Brain
A picture of the night sky with a cresent moon in the center. No stars are visibile.
Sleep is essential in our lives! I believe that science has sufficiently proved that and, frankly, many of us could speak it from our own experiences. Caregivers raising children and missing sleep have trouble focusing the next day. Students who stay up all night finishing a big paper struggling to stay awake and learn the next day. What about the athlete who stays up all night before a big game and sees a dip in their performance? Chances are we can all agree that sleep is a need that we all have. It is also suicide prevention. This week’s post will have some neuroscience in it, which you can skip, but will also talk about how the brain controls sleep, reasons people need sleep and dreams.
The Brain Structures Involved in Sleep
Similar to previous weeks, if it helps, pull up the 3D brain by clicking here and dive right in! Also, feel free to skip this section and move on if you are over the neuroscience.
Hypothalamus
It contains groups of nerve cells that act as control centers affecting sleep and arousal. The suprachiasmatic nucleus (SCN), located in the anterior hypothalamus above the optic chiasm, is composed of clusters of thousands of cells that take in information about light exposure from the eyes and control your behavioral rhythm (National Institute, n.d.).
Brain Stem
The brain stem is responsible for communicating with the hypothalamus to control wake and sleep transitions. It also plays a role in REM sleep as it sends signals to the muscles to relax so that we don’t end up acting out our dream (National Institute, n.d.).
The combination of sleep-promoting cells within the hypothalamus and the brain stem are responsible for the production of GABA which acts to help reduce the activity of the arousal centers in both structures (National Institute, n.d.).
Thalamus
This structure acts as a relay station for the information incoming from the senses to the cerebral cortex and during most stages of sleep the thalamus becomes quiet so that people can tune out the external world. The interesting piece, however, is that during the REM sleep phase the thalamus is active and has a role in sending the cortex images, sounds, and other types of sensations that fill our dreams (National Institute, n.d.).
Pineal Gland
Located within the brain’s two hemispheres, it receives signals from the SCN and increases melatonin production which is responsible for putting people to sleep once the lights go down. It is believed that the peaks and valleys of melatonin over the course of the day are important for matching the body’s circadian rhythm to the external light and dark cycle (National Institute, n.d.).
Basal Forebrain
This structure helps promote sleep and wakefulness. The release of adenosine from the cells in this structure in combination with other regions supports a person’s sleep drive. If someone is a caffeine drinker, the caffeine acts by blocking the actions of adenosine (National Institute, n.d.).
Amygdala
The amygdala, during REM sleep, becomes increasingly active (National Institute, n.d.).
Reticular Formation
A complex bundle of nerves that relays information to the thalamus for action by the cerebrum, it helps filter out unnecessary noise that has the potential to interfere with message process or slow down the processing of messages during sleep (Peters, 2020).
Locus Coeruleus
The locus coeruleus is responsible for releasing norepinephrine throughout the brian except during REM sleep and prior to each non-REM sleep spindle when it falls silent (Swift et al., 2018).
Reticular Thalamic Nucleus
This structure plays a role in local sleep control and during non-REM sleep blocks transmission of sensory information to cerebrum and limbic system (Vantomme, 2019; Wilson, 2013).
How the Brain Controls Sleep
Now that the brain structures have been laid out, we can look at how the brain controls sleep. This discussion will open with a look at the raphe system.
The raphe system holds the role of being the principal source of serotonin in the brain. Unlike other neurons in the brain, the neurons in the raphe fire spontaneously at a slow, steady rate and the rate of firing changes in response to the level of consciousness alterations (Wilson, 2013).
The next piece that we will look at is the biological clock and how the SCN plays a key role (Wilson, 2013). The SCN is thought to hold the pacemaker for what is called the circadian rhythm. This rhythm is important as it regulates now only our levels of sleepiness and wakefulness but also controls hormone levels, body temperature, and metabolism. Not only does the body temperature follow a specific rhythm but the brain activity and sensory abilities do as well. Despite changes in lighting, diet, hormonal state, drugs, and illness, this rhythm continues. However, environmental events, light, etc. can reset the biological clock.
The SCN plays another role as well. The retina relays light information to the SCN through the retinohypothalamic tract which takes this information and sends it to the pineal gland (Wilson, 2013). This information directly affects the release of melatonin from the pineal gland which in term lets the rest of the brain know about the environmental light/dark cycle. The melatonin receptors in the SCN also permit melatonin to influence the circadian rhythm.
Reasons People Sleep
Sleep is an essential function (Berger et al., 2020). According to Eidelman (2002), the recovery and regeneration of cells, tissues, and organs is a constant, ongoing involuntary process that happens both day and night. However, the recovery and regeneration is not the only necessary recovery phase. Eidelman (2002) discussed the process of daily realignment, in an integrated manner, which is facilitated during sleep. While people sleep it is believed that it is a way to conserve energy expenditure as the metabolic rate of sleep may allow biological processes happening during sleep to be completed at a lower overall energy cost (Assefa, 2015). Four other interesting functions of sleep include: (1) sleep acting as an adjuvant to enhance early stage immune responses; and that both long, (2) short sleep durations are associated with increased risks of all-cause mortality, (3) sleep as essential for motor skill learning, and (4) memory formation (Assefa, 2015). It also is important to look at not only the positive effects of sleep but how sleep loss can impact the body. One example is the striking and acute effects on neurocognitive performance (Assefa, 2015).
To wrap up this discussion on the reasons people sleep, I felt it important to at least list out the numerous theories about sleep. If you are curious to learn more details about them, I encourage you to explore them. They are all different perspectives and all, to me, have value in understanding sleep.
Theories
Adaptive, Immobilization, Ethological Theory
Protective and Restorative Theory
REM Sleep Function
Restorative or Recuperative Theory
Function of REM Sleep
Energy Conservation Hypothesis
Neuronal Network Reorganization or Plasticity Theory
Activity Dependent Sleep Function (1994) and REM sleep Function (1996)
Restoration of Brain Energy Metabolism
The Free Radical Flux
Neurotoxic Clearance that Results in Sleep Restorative Function
Energy Allocation Theory
Dreams
Dreams are hallucinations that occur during certain stages of sleep and are strongest during REM sleep (Sullivan, 2017). The purpose of dreams is not universally agreed upon, but we will discuss a few beliefs about why we dream and learn some fun facts. The ancient Egyptians built temples to the goddess Isis where congregants and priests gathered to perform dream interpretations. Throughout history, dreams were variously considered to be messages from seemingly or unseemly supernatural entities. In later times the study of the human mind developed and looked at dreams as a reflection of “inner” unexpressed human desires or psychic traits (Assefa, 2015). Other more recent ideas about why we dream include: dreams as therapists, as fight-or-flight training, as muse, and memory aids (Sullivan, 2017).
Sleep is fascinating! Hopefully, you learned something about the role of sleep in your life. Happy sleeping!
take action today moment:
Prioritize sleep. Do some research (or use some of the resources below in the Learn More section) on good sleep hygiene and make sure to practice what you learn. Protect your sleep!
Learn More About sleep and the brain:
Brain Basics: Understanding Sleep
Sleep tips: 6 steps to better sleep
6 tips for better sleep | Sleeping with Science, a TED series (YouTube)
References
Assefa, S. Z., Diaz-Abad, M., Wickwire, E. M., & Scharf, S. M. (2015). The functions of sleep. Neuroscience, 2(3), 155–171. doi:10.3934/Neuroscience.2015.3.155
Berger, F., Zieve, D., & Conway, B. (2020, August 4). Sleep and your health. MedLine Plus. https://medlineplus.gov/ency/patientinstructions/000871.htm
Di Domenico, S. I., & Ryan, R. M. (2017). The emerging neuroscience of intrinsic motivation: A new frontier in self-determination research. Frontiers in Human Neuroscience, 11, 1-14. doi: 10.3389/fnhum.2017.00145
Eidelman, D. (2002). What is the purpose of sleep?. Medical Hypotheses, 58(2), 120-122. doi: 10.1054/mehy.2001.1472
Lee, W., Reeve, J., Xue, Y., & Xiong, J. (2012). Neural differences between intrinsic reasons for doing versus extrinsic reasons for doing: an fMRI study. Neuroscience Research, 73(1), 68–72. https://doi.org/10.1016/j.neures.2012.02.010
National Institute of Neurological Disorders and Stroke. (n.d.). Brain basics: Understanding sleep. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep
Peters, B. (2020, August 5). Reticular activating system and your sleep: How brain Disturbances disrupt sleep patterns. Very Well Health. https://www.verywellhealth.com/definition-of-reticular-activating-system-3015376
Simpson, E. H., & Balsam, P. D. (2016). The behavioral neuroscience of motivation: An overview of concepts, measures, and translational applications. In E. H. Simpson & P. D.
Dalsam, Behavioral neuroscience of motivation (pp. 1–12). Springer. https://doi.org/10.1007/7854_2015_402
Sullivan, D. (2017, August 22). Why do we dream?. Healthline. https://www.healthline.com/health/why-do-we-dream
Swift, K. M., Gross, B. A., Frazer, M. A., Bauer, D. S., Clark, K. J. D., Vazey, E. M., Aston-Jones, G., Yong, Y., Pickering, A. E., Susan J. Sara, S. J., & Gina R. Poe, G. R. (2018). Abnormal locus coeruleus sleep activity alters sleep signatures of memory consolidation and impairs place cell stability and spatial memory. Current Biology, 28, 3599–3609. https://doi.org/10.1016/j.cub.2018.09.054
Vantomme, G., Osorio-Forero, A., Lüthi, A., & Fernandez, L. (2019). Regulation of local sleep by the thalamic reticular nucleus. Frontiers in Neuroscience, 13, 576. https://doi.org/10.3389/fnins.2019.00576
Wilson, J. F. (2013). Biological basis of behavior. Bridgepoint Education.
Wypych, M., Michałowski, J. M., Droździel, D., Borczykowska, M., Szczepanik, M., & Marchewka, A. (2019). Attenuated brain activity during error processing and punishment anticipation in procrastination - a monetary Go/No-go fMRI study. Scientific Reports, 9(1), 11492. https://doi.org/10.1038/s41598-019-48008-4
Zhang, W., Wang, X. & Feng, T. (2016). Identifying the neural substrates of procrastination: A resting-state fMRI study. Scientific Reports, 6, 33203. https://doi.org/10.1038/srep33203