The journey towards a better understanding of the role light plays in our physiological equilibrium continues. Using Enlighten your clock: How your body tells time
, a comic book written and illustrated by the neuroscientist Coline Weinzaepflen, we are explaining certain keywords regarding our biological mechanisms and the effects light has on all our lives. In the second part of this small visual dictionary, we are focusing on light and the effect it has on how we sleep and why we sometimes don’t recharge the way we should.
Light is the key to understanding the relationship between our bodies and time. Our biological rhythms, our internal clock, are not the same as the twenty-four hour system we divide our day into. Our eyes filter the visible light detected by our brain, which tells us that outside it is daytime and therefore time to be awake or nighttime and therefore time to go to sleep. To match up these two rhythms and synchronise our circadian rhythm with the environment around us, light is therefore fundamental. It is the main tool for regulating our sleep-wake cycle. This explains why looking at bright lights or screens at night or late in the evening can affect our rest. The light of our iPhone screen tells us that it is time to be awake even if it is pitch-black outside.
The state of our physical and mental health depends largely on the quality and quantity of the sleep we enjoy.
But our level of sleep is not the same all night long. Over time, scientists have discovered that sleep varies throughout the night and can be divided into different stages: REM (Rapid Eye Movement) phases that coincide with the periods of most intense cognitive activity in which dreams are formed, and alternate non-REM phases that are characterised by the presence of specific brain waves with different frequencies. The cyclical nature of these phases is fundamental for effective relaxation and recharging and all the stages must be concluded, which usually takes between six and nine hours.
Narcolepsy is a condition that provokes excessive daytime sleepiness with patients suffering from unexpected and instant impulses to close their eyes and sleep. It is a disturbance that makes working or studying very difficult. Science tells us that narcolepsy can be caused by a lack of hypocretin, also known as orexin, in the brain. This is a neurotransmitter that regulates the REM phase and controls the alternation of our sleeping and waking patterns. In narcoleptics, for example, the REM phase is reached much faster than in other people. Narcolepsy has nothing to do with the more common disorder of insomnia and even if this may have many causes, the main one is stress. An inability to enjoy regular sleep may also be the result of various clinical conditions, including Alzheimer’s disease and epilepsy.