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SLEEP AND BRAIN

Updated: Jun 29

Author: Jeevitha Ramesh


If sleep does not serve a vital function, then it is the biggest mistake the evolutionary process ever made”.

-A.Rechtschaffen (Sleep science researcher)


Our quality of life can be disrupted for many reasons. One of the major yet unrealised causes for that is sleep loss. In our fast-paced world, working hours are always increasing which cuts down on active leisure time. Jobs in healthcare, security and transportation require working at night and restricting sleep hours.


Although the amount of sleep needed by everyone varies, the average human requires between 7 to 8.5 hours per day to function optimally. Sleep is modulated by two internal biological mechanism processes - a homeostatic process and a circadian process. These two work together to regulate the awake and sleep cycle.

  • Circadian rhythms perform various functions from wakefulness to body temperature, metabolism, and the release of hormones. It controls the timing of sleep by causing sleepiness at night and tends to wake us in the morning without an alarm. Circadian rhythms may concur with environmental cues like light, temperature etc.

  • Sleep-wake homeostasis keeps track of the need for sleep. It prompts the body to sleep after a particular time and manages sleep intensity.

Across the average 85-year lifespan, we may sleep about 250,000 hours or over 10,000 full days. People often consider the time spent sleeping as “lost” time, but it is important to know that sleep is purposeful. Sleep is an essential part of our day to day routine.


Sleeping enough and on time is as important as food and water to survive. Without proper sleep, our brain would be unable to form neural pathways or maintain them in the brain which will help us to learn and create new memories, and it would become harder to concentrate and respond quickly.


There are stages in sleep. Firstly, non-REM sleep has three stages and then, rapid eye movement (REM) sleep. Each of these is linked to particular brain waves and neuronal activity. We cycle through all stages of non-REM and REM sleep several times during the night, with increasingly longer, deeper REM periods occurring toward morning.

Sleep Cycle

Let us look into structures within the brain that are involved with sleep.

  • The Hypothalamus It acts as control centres affecting sleep and arousal. Hypothalamus has a suprachiasmatic nucleus – which is a cluster of cells that receive information about light exposure from the eyes and control our sleep behavioral rhythm.

  • The Brain Stem It controls the transitions between wake and sleep. Brain stem produces a chemical in the brain named GABA, which will help by reducing the activity of arousal centres and inducing sleep.

  • The Thalamus It induces the release of melatonin, which modulates and influences sleep onset and maintenance.

  • The Pineal Gland Gland receives signals from the suprachiasmatic nucleus and increases the melatonin hormone production, which will help in inducing sleep.

  • The Amygdala This is involved in processing emotions, becoming increasingly active during REM sleep.



Brain structures involved in sleep

Sleep is important for tissue restoration inside the brain, metabolism, neuronal communications, immune function, mood, and disease resistance and many other important functions. Research also links sleep’s role in cognitive functioning. Sleep loss has long been known to affect performance, weaken attention and executive control tasks. Recent findings suggest that sleep plays a major role in removing toxins in the brain that build up while we are awake. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of various disorders like high blood pressure, cardiovascular disease, diabetes, depression, obesity and effects of cognitive reserve in the long run.


As we age, there are considerable changes to sleep quantity and quality. Changes that occur in sleep physiology can affect cognition and its processes, for example, it may affect memory consolidation. Hence it is said that Sleep and cognition are often interrelated, with the maintenance of good sleep quality, during young adulthood or in middle age, we can ensure better cognitive functioning and we can protect ourselves against age-related cognitive declines.


Many factors influence sleep including medical conditions, medications, stress, sleep environment, what we eat and drink and also the influence of exposure to light. Dedicated cells in the retina of our eye process light and signal the brain whether it is day or night. This can advance or delay our sleep-wake cycle. Opening more hours to light can make it difficult to fall asleep or even return to sleep when awakened. For example, night shift workers often have trouble falling asleep when they go to bed, and also have trouble staying awake at work because their natural sleep-wake cycle is disrupted.


Advancing age is correlated with complex changes in sleep patterns and to increased risk of cognitive decline. Older individuals exhibit shorter sleep time, a lower percentage of rapid eye movement, an increased proportion of lighter sleep and reductions in a deeper sleep. Sleep restriction due to workload or any other kind of pressures may contribute to the accumulation of amyloid-β which is the main cause of Alzheimer’s dementia. Without proper sleep, the brain struggles to function properly. Because the brain does not get time to recover, neurons may become overworked eventually resulting in impaired cognitive functioning.


Poor quality sleep, less sleep or fragmented sleep can affect us in many forms. If poor sleep continues for the long term it may put anyone at high risk. Let us see the short-term implications of inadequate or poor-quality sleep on the brain and cognition,

  • Poor or interrupted sleep causes harm to certain parts of the brain with distinct effects on different types of cognition. Research shows that memory and sleep are linked very closely. Lack of sleep hampers immediate memory capacity, which is necessary to remember things for instant use. Sleep is very crucial in the process of memory formation, it will help in consolidation and reinforce the information in the brain so that it can be recalled when needed.

  • Poor sleep decreases one’s ability to perform cognitive tasks. For example, the ability to carry out a sequence of instructions, or perform tasks that need motor skills, or maintaining the rhythm. Studies have found that a lack of sleep reduces our cognitive flexibility, the ability to adapt to uncertain circumstances.

  • Poor sleep sometimes adds to the symptoms of mental health disorders like depression. Research firmly confirms the concept that poor sleep disturbs us from effective thinking. Without sound sleep, we may tend to make mistakes, fail to take in new facts, suffer from memory deficits, or may face impaired decision-making.


Most importantly inadequate sleep may cause health risks, including life-threatening dangers.

  • Recent studies have found that there is a significantly higher threat of cognitive dysfunction and dementia in people with sleep problems. It is known that 15% of Alzheimer’s, Dementia cases are due to poor sleep.

  • Research studies show that sleep is very important in maintaining the brain to conduct important functions, such as removing possible life-threatening substances, for example, b- amyloid proteins, which form clusters called plaques, that degrade cognitive function. Studies have shown that even a single night of sleep deprivation can aggravate the level of beta-amyloid in the brain.


Lack of sleep harms attention, working memory and many other cognitive abilities. This worsens as we age as it takes a toll on mental capacities and physical health. Due to ageing, one’s ability to cope with sleep loss decreases. Hence, it is important to maintain good sleep during adulthood so that a strong cognitive reserve is built and maintained during old age.


References

1. Patel, A. K., Reddy, V., & Araujo, J. F. (2020, April). Physiology, Sleep Stages. StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK526132/

2. National Institute of Neurological Disorders and Stroke (NINDS). (2019b, August 13). Brain Basics: Understanding Sleep. Retrieved December 2, 2020, from

https://www.ninds.nih.gov/Disorders/patient-caregiver-education/understanding-sleep

3. Division of Sleep Medicine at Harvard Medical School. (2007, December 18). Natural Patterns of Sleep. Retrieved December 2, 2020, from

http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem

4. Division of Sleep Medicine at Harvard Medical School. (2007, December 18). Sleep, Learning, and Memory. Retrieved December 2, 2020, from HTTP: // healthysleep .med.harvard.edu/healthy/matters/benefits-of-sleep/learning-memory

5. Poudel, G. R., Innes, C. R., Bones, P. J., Watts, R., & Jones, R. D. (2014). Losing the struggle to stay awake: divergent thalamic and cortical activity during microsleeps. Human brain mapping, 35(1), 257–269.

6. Dawson, D., & Reid, K. (1997). Fatigue, alcohol and performance impairment. Nature, 388(6639), 235. https://www.nature.com/articles/40775

7. Alhola, P., & Polo-Kantola, P. (2007). Sleep deprivation: Impact on cognitive performance. Neuropsychiatric disease and treatment, 3(5), 553–567.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2656292.


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