What is Worthy Enough of Our Sleep?

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Dream is not what you see in sleep, Dream is something which doesn’t let you sleep.

Dr. A.P.J Abdul Kalam

But, should we really chase our dreams at the cost of our sleep?

 We have never asked this question, have we? “The less time you sleep, the more dedicated you are.” has been the motto running deep down the veins of our society. Glorifying sleeplessness and demeaning sleep as unproductive has been our convention. Are we doing this right? Is sleep not crucial for us? To answer that, let’s start with the fundamental question: what is sleep?

We can define sleep as a rapidly reversible state of immobility and greatly reduced sensory responsiveness. We don’t consider the anatomical and neurochemical properties of sleep, since it changes between phyla due to the neural system’s structural differences. One must keep in mind that sleep is distinct from hibernation, torpor, and rest since they have different physiological correlates. It was believed that every organism has a sleep-like state. However, it is debatable as we haven’t studied every organism to confirm behavioural sleep. Nevertheless, all terrestrial mammals ever examined have exhibited sleep activity, and unihemispheric sleep has been reported in marine mammals indicating the possible significance of sleep in mammals [1].

In mammals, age, body size, diet, and predation risk can influence sleep behaviours [2]. In terrestrial mammals, sleep has two crucial stages: REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement). Though named based on eye movement, the two states are characterised based on their distinct EEG activity. NREM states exhibit slow-wave activity (a measurement of sleep depth) with minimal cortical acetylcholine release, resulting in reduced brainstem and forebrain activation. In contrast, REM sleep is characterised by waking pattern activity shown by cortical and brainstem neurons, but the noradrenergic, serotonergic and histaminergic neurons are silent, making it distinct from the waking states [1]. Considering these characteristic features of sleep in mammals, let’s discuss how crucial sleep is in humans based on the studies in human and mouse models.

The sleep homeostasis and circadian rhythm directly regulate this highly adaptive trait in mammals. The sleep homeostasis mechanism acts by increasing the time and intensity of sleep in the subsequent sleep to recover from sleep deprivation. However, when we consider the increase in the depth of sleep (slow-wave activity during NREM) along with the time, it adds up to the total EEG activity lost for short-lasting sleep deprivation.The circadian regulation of sleep, on the other hand, is controlled by the Suprachiasmatic Nucleus (SCN) in a light and endogenous rhythm dependent manner. Interestingly, new evidence suggests that in humans, these two mechanisms of rest-activity regulate each other as well. Both endogenous clock and the duration of prior waking and sleep were shown to influence our body’s activities [3]. Thus, alterations in circadian rhythm might affect the NREM and cause sleep load in mammals.

In humans, various functions, including cognitive processes such as schematic thinking, perception, concentration, attention, vision, reaction time, and emotion processing, are impaired due to sleeplessness. Thus, sleeplessness leaves the individual in a less vigilant and alert state with deteriorated interpersonal responses and increased aggressiveness [4][5][6]. Though most of these defects can be restored with sleep compensation, higher cognitive abilities such as attention and memory remain degraded due to continuous sleep deprivation [6]. From an evolutionary point of view, these critical cognitive abilities imply the adaptive significance of sleep. 

However, humans are no longer abiding by the day and night cycle of nature. Artificial light at night, travelling across time zones, usage of alarm calls to wake up are few of the many ways we alter our natural rhythm. In developed nations, 75% of people use an alarm clock to wake up on workdays resulting in chronodisruption and causing ‘social jetlag’ (equivalent to travelling across multiple time zones) [7]. Research has equipped us with information such as the effect of small nap schedules in overcoming jet lags and on faster adaptation to zeitgebers to increase the susceptibility to light by the circadian clock [2]. Hence, understanding our sleep cycle and connecting it with our knowledge about the cross-talk between sleep homeostasis and circadian rhythm would lead to a more productive life. Neuroimaging studies have shown the prefrontal cortex (the most prominent region of the human brain) as more susceptible to the effects of sleeplessness, indicating the resulting cognitive deficits along with the previously mentioned problems [5]. Experiments on humans have shown an increase in the onset of sleep in pregnant females, indicating the link between circadian rhythm and reproductive physiology [8]. Consistent with this, studies on chronodisruption showed an increased risk for night shift working women to have a miscarriage and pre-term birth than the rest. Thus, the intrinsic circadian rhythm in the foetus, which kicks in by the last ten weeks of gestation, plays a significant role in different aspects of an individual throughout life [9].

Thus, scientific evidence indicates the crucial role of sleep and circadian rhythm in an individual’s normal functioning. Then what is stopping us from applying this understanding in our daily life? To ensure a healthy sleep pattern in our population, necessary steps have to be taken by officials who schedule day-night shifts as well as by the common man who sets the daily alarm. The change in society at multiple levels based on scientific data has been proven possible by the COVID-19 pandemic. We must take up the same spirit and apply it in other science fields for a better, healthier tomorrow because science aims to enhance society with a better-quality life for everyone.

So, as President Kalam said, you should have a dream that won’t let you sleep but make sure you have adequate sleep to have a healthy mind and body to achieve those dreams. 

References

  1. Siegel, Jerome M. “Do all animals sleep?” Trends in neurosciences 31.4 (2008): 208-213
  2. Siegel, Jerome M. “Clues to the functions of mammalian sleep.” Nature 437.7063 (2005): 1264-1271
  3. Deboer, Tom. “Sleep homeostasis and the circadian clock: Do the circadian pacemaker and the sleep homeostat influence each other’s functioning?.” Neurobiology of sleep and circadian rhythms. 5 (2018): 68-77
  4. Palchykova, Svitlana, et al. “Sleep deprivation impairs object recognition in mice.” Neurobiology of learning and memory 85.3 (2006): 263-271
  5. Orzeł-Gryglewska, Jolanta. “Consequences of sleep deprivation.” International journal of occupational medicine and environmental health. (2010)
  6. Killgore, William DS. “Effects of sleep deprivation on cognition.” Progress in brain research. Vol. 185. Elsevier, 2010. 105-129
  7. McCarthy, Ronald T., et al. “Riding the rhythm of melatonin through pregnancy to deliver on time.” Frontiers in endocrinology. 10 (2019): 616
  8. Martin-Fairey, Carmel A., et al. “Pregnancy induces an earlier chronotype in both mice and women.” Journal of biological rhythms. 34.3 (2019): 323-331
  9. Reschke, Lauren, et al. “Chronodisruption: An untimely cause of pre-term birth?.” Best Practice & Research Clinical Obstetrics & Gynaecology. 52 (2018): 60-67

Footnote

  1. Homeostasis: process of regulating the  physiological variables to remain near a defined value constantly over time [2].
  2. Circadian regulation: Regulating the level of each variable for the optimal functioning of the body at the proper time of the day [2].