Light, architect of life

Light, architect of life

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Russian pianist and composer Alexander Scriabin once said: “I am a moment of enlightened eternity, I am affirmation, I am ecstasy.” A contemporary of his, the Valencian painter Joaquín Sorolla was drawn by light in fleeting impressions of what would later become painting on immaculate canvas. Mythical are also the shadows cast in the depths of Plato’s cave, who never ceases in his efforts to find the light that guides human knowledge.

From the initial explosion of the big Bangthe abstraction implied by the idea of ​​brushing against infinity materialized in a universe where the constant evolution of seasons, equinoxes, solstices, day, night follows one another in an eternal cyclical return whose promise underlies the possibility of present contemplation.

In this rhythmic succession of events, the human being began to seek his niche on Earth, like the planet its place in the inconceivable immensity of the universe. And he began to play in a race against time, in favor of the light. That’s right, light articulates our day-to-day with surprising skill, being one of the main stimuli that coordinates, regulates and synchronizes our organic activity over time.

Cardiac rhtyms

The British evolutionary biologist William Hamilton argued that the maintenance of a species depends on its versatility and that only those who change remain true to themselves and, we could add, to the environment that surrounds them. Evolution has matched the internal workings of living things with the changing condition of the outside world in cyclical fluctuations in time known as circadian rhythms.

Circadian rhythms are cycles of endogenous regulation, lasting approximately 24 hours – the word circadian It comes from the Latin circa diemWhat does it mean about a day–. They arise as an evolutionary adaptation that allows us to anticipate, anticipate changes in the environment to be able to respond more effectively.

These rhythms guide or dictate processes such as the time of hibernation, courtship and reproduction, weight variations or hormonal changes in animals and plants. In addition, in humans they control important processes with molecular implications (gene expression), metabolic, physiological (regulation of body temperature, heart rate, sleep and production of melatonin, insulin, glucagon) and behavioral (mood, functions and cognitive activity).

How do we receive light information?

The most spiritual minds and souls would say that “we are beings of light”. For us mammals, the alternation between light and darkness, controlled by the binomial day/night, represents, as we have said, the most important adjustment signal of our circadian rhythms.

The suprachiasmatic nucleus, a tiny structure located in the anterior hypothalamus, one of our brain areas, works as a master or central clock, monitoring the intensity of light that we receive.

This stimulus is also perceived at the ocular level, in the retina, and, via the retinohypothalamic tract (an eye-brain highway), the information flows into the aforementioned nucleus, in charge of controlling the functions of our peripheral organs thanks to the regulation of the release of hormones such as melatonin.

Through this cascade of events, the conductor, the suprachiasmatic nucleus, baton in hand, coordinates his instrumentalist subjects, the peripheral organs.

Evolution of the circadian system

The regularity in the internal temporal order of the human being requires a maturation process from birth to adulthood.

The fetus, strongly connected to the mother, constantly receives cyclical signals produced by her, informing it of the day/night time according to, for example, the circulating concentrations of melatonin in the blood. Fetal circadian rhythms, such as melatonin and cortisol, are still mostly regulated by the mother.

Birth is the critical moment. New nerve connections are established within the suprachiasmatic nucleus and towards other regions of the brain of the already independent newborn, which must progressively adapt to the new environmental signals to which it is exposed.

At three months of age, their sleep-wake rhythm begins to consolidate. At two years old, he reaches the maximum of nerve connections of the central clock. During the first years of life, circadian rhythms will achieve the daily periodicity that characterizes the adult stage.

Light-dark-disease

At the time when our ancestor Homo sapiens decided to hunch his back and prostrate himself in front of a computer from his upright posture, we set foot in the global, technological and overstimulated world that governs us. In our current lifestyle, we often take the opposite direction to what our circadian rhythms dictate (disruption of the sleep-wake cycle, eating at odd hours, being exposed to artificial light at night), which is called chronodisruption.

These behavior patterns, it is believed, could be closely related to the risk of developing diseases such as cancer. In fact, the World Health Organization (WHO) and the International Agency for Research on Cancer (IARC) have classified shift work (where the break in the light/dark, sleep/wake cycle is continuous in time) as a possible human carcinogen.

The maladjusted tick-tock of the circadian clock would predictably have more severe effects on organs such as the liver or the intestine, given that they present 24-hour rhythms in many of their functions. It is known that animals with mutated circadian clock genes such as Bmal1, Per1 and Per2 develop tumor processes more frequently, since these seem to act as tumor suppressors.

Light at the end of the tunnel

Studying the role of chronodisruption and the alteration of our synchronization with the cycles of light and darkness could lead to an advance in the knowledge of diseases such as cancer.

We are an ecosystem intimately linked to the environment, and light, in an exquisite biological promise, acts as a gear and circumscribes the activity of our central and peripheral clocks to the rhythmic beat of the same beat.

The light, like the musician, the painter and the philosopher, directs us, coordinates us, unquestionably shapes us in this life, in the unforgivable clockwise direction.


This article was the winner of the 2nd edition of the youth disclosure contest organized by the Lilly Foundation and The Conversation Spain.


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