Sleep is an interesting concept. When we are very busy with our lives it may not seem very necessary to us, whereas when we are exhausted all we can think about is how much we want to sleep. This week we will understand more about how sleep works, and how it affects our response to infectious pathogens. 

How do brain cells communicate?

When we perceive sensory stimulus, i.e. when we see or hear something, our brain makes adjustments according to the new information. So when we move or do anything, our brain adjusts itself accordingly by changing its electrical activity. However brilliant that is, pathologies related with brain electrical activity could also occur. The pathologies might include seizures as well as sleep disorders, which we will be talking about in a different blog.

When we are awake but do not have any mentation than imaging devices in our brain shows an alpha rhythm has been generated. It is a consistent wave that is related with decrease in attention levels. When we are awake and we are watchful then beta rhythm is generated, it can be formed by any sensory or mental concentration.

How does sleep work?

The time when we sleep and dream our brain enters a state called Rapid Eye Movement (REM), which is characteristic for the eye movements in this state. Another state of consciousness called Non-REM (NREM) which divides into four phases.

  1. Stage 1: The EEG shows theta waves and it is the first phase to be observed when a person sleeps.
  2. Stage 2: This phase consists of a complex of brain waves and is observed right after phase 1.
  3. Stage 3: Delta rhythm is dominant in this phase. It is observed right after phase 2.
  4. Stage 4: The velocity of brain waves is most decreased in this phase.

Here is an example of health brain waves. These waves are produced by electroencephalogram (EEG) which basically measures the electrical activity in the brain. Since the brain cells communicate with electrical signals EEG recordings show this communication as wavy lines as shown in the image above.

Continuing with the sleep phases, it is also important to understand how REM sleep works and how these phases are related to each other. In REM sleep the EEG shows waves as if we are awake, the waves are very fast as can be seen in the diagram below. Also this phase is famous for its dreams since the longer and more emotional dreams are seen when we are in the REM state, however we can dream both in NREM and REM phases.

A typical hypnogram showing sleep stages and cycles in adult sleep, closer to morning stages 4 and 5 are observed less whereas REM sleep is observed much more.

A health adult experiences 4-6 REM stages when they sleep. Exposure to light, our sleep hygiene, our hormones, all in all almost everything about our lives can influence our sleep. One of its influences is experienced in our immune system.

The Sleep-Immune Crosstalk

In a review research in 2020 by Silva et al. (3) it was found that the physiological problems that COVID-19 pandemic imposes, compromises the quality of sleep. And this has directly affected the immune system since sleep is an important regulator of immunological mediators and cells. However when COVID-19 compromises the quality of sleep, it then compromises the immune system as well.

Also another important article regarding the sleep and immune system crosstalk is the one by Prather et al. in 2015 (2). They have found by experimentally exposure to viral agents, that shorter sleep durations directly increased the susceptibility to common cold.

This relationship between sleep and immunity is interpreted by the effect of sleeps on inflammation, which is the immune response to pathogens. Sleep is an important factor for regulating the immune system’s markers such as cytokines and therefore directly affects the immune system.

For a healthier immune system we believe that you have understood deeply how it is important to have a better sleeping schedule. However when your immune system needs assistance in the comfort of your home, you can always use the FluAI App. Download the app in your smartphone in the App Store and Play Store.


  1. The Sleep-Immune Crosstalk in Health and Disease. Physiol Rev 99: 1325–1380, 2019. Published March 27, 2019; doi:10.1152/physrev. 00010.2018.
  2. Prather, A. A., Janicki-Deverts, D., Hall, M. H., & Cohen, S. (2015). Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep, 38(9), 1353–1359. https://doi.org/10.5665/sleep.4968
  3. Silva, Eduardo de Sousa Martins e, Ono, Ben Hur Vitor Silva, & Souza, José Carlos. (2020). Sleep and immunity in times of COVID-19. Revista da Associação Médica Brasileira, 66(Suppl. 2), 143-147. Epub September 21, 2020.https://dx.doi.org/10.1590/1806-9282.66.s2.143


Elif Başak Alço


Related Post

Leave a Comment