By Rocío de la Vega de Carranza -
The Conversation
As the song from the musical
Les Miserables
, based on Victor Hugo's novel, says, "the tigers come out at night, with their voices soft as thunder."
We have all been miserable some night, when we find ourselves tossing and turning in bed, staring at the ceiling due to unbearable back pain (or tooth, ear, knee...).
It was there during the day, but now it won't let us rest and bites us like a tiger.
Why is the pain felt more intensely at night?
What does science have to say about this?
Let's start at the beginning: what is pain?
We have all been hurt by something at some time – many of us are sure at this very moment – so it is not a strange phenomenon for anyone.
However, if we have to define it, it begins to complicate the matter.
After numerous modifications over the years, the International Association for the Study of Pain (IASP) agreed in 2020 to define it as “an unpleasant sensory and emotional experience associated with, or similar to that associated with, actual or potential tissue damage.
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Therefore, the current consensus is that it is an experience of the senses, that it has an unpleasant emotional component and is related to (or reminiscent of) what is felt when there is some damage.
What is it for?
We tend to think of this feeling as something negative, since, by definition, it is an unpleasant experience.
But the human being is a complex and well geared machine, which rarely has functions that are there “just because”.
The purpose of pain is to warn us that something is wrong;
it is a survival mechanism that helps keep us safe from the dangers that can threaten our physical integrity.
To put a simile:
it is an alarm system that our brain has to tell us that we are at risk
and that urges us to get safe.
And it's unpleasant for us to feel the need to avoid it.
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However, it is not a response to a stimulus, as was thought in the days of Descartes (for example: I touch something hot and the pain saves me from being singed because it makes me withdraw my hand).
The modern conception understands it as a product of our brain: it is this organ that tells us where, how much and in what way it hurts.
Of course, external stimuli (such as the heat that we mentioned before) send a signal to the peripheral nerves that connect to the brain.
Then, it will process it and turn it into something else: the so-called nociception.
But that is only part of the experience, since the concept of pain includes our cognitive and emotional interpretation of that nociception.
Maria Korneeva/Getty Images
In short, pain is not always directly related to the amount of painful stimuli that we are receiving, since it can be perceived in the absence of them.
An extreme example is the phantom limb phenomenon: there are people whose brain is producing very real pain in a body part that has been amputated.
The control gate theory
So why does the feeling increase at night, when we are
safe
in our bed?
How does that help survival?
The explanation has to do with our brain's processing systems and with the science of perception.
Back in the 1960s, Roland Melzack and Patrick Wall proposed their
Gate Control Theory
, in which they proposed that there is a gate in the spinal cord that allows or does not allow painful stimuli to pass to the brain.
In other words: there will be certain things that make the door close and we feel less pain and others will make it open and we feel it more intensely.
An example is the mechanical act of rubbing our skin if we have been hit: the sensation of friction competes with that of pain and is felt less.
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In the silence of the night, the voices of those tigers are heard more, in the same way that we remember some uncomfortable situation that we experienced during the day and had almost forgotten.
There alone, in the dark, there is nothing to distract us and help close the door: no images, no sounds, no interactions with others.
The worst moment, at 4 in the morning
Since the 1960s, new theories, new techniques, and new findings have been nurturing the science of pain.
Thus, a study published in
Brain
last September also points to circadian rhythms as a possible key agent in the phenomenon of nocturnal accentuation.
Inès Daguet and her collaborators carried out a novel laboratory study in which they discovered that the time of day when pain (experimentally induced, in this case) is most intensely perceived is at 4 in the morning.
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A possible explanation is lack of sleep, since its influence has also been demonstrated, but in Daguet's model, the weight of circadian rhythms was much greater.
These changes may be related to the cyclical levels of hormones that we have during the day, such as cortisol, related to the immune system and inflammation, and melatonin.
Despite everything, we must not forget that this is an experimental study, in a laboratory environment, where the participants are not in their natural environment (sleeping in their bed) and receive painful stimuli artificially (using a machine that induces heat).
Alerts to the threat of predators
Researchers Hadas Nahman-Averbuch and Cristopher D. King have published a comment to the previous study where they point out that from an evolutionary perspective,
we are more vulnerable to predators at night, since that is when we sleep
.
Therefore, it makes sense that a lower intensity of stimuli is enough to wake us up to potential danger.
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In short,
more research is still needed to understand why we feel more pain at night
, but it seems that our brain is still trying to protect us from being eaten by tigers (in this case real ones) while we sleep.
[The author of this article is a researcher at the University of Malaga and holds a doctorate in Health Psychology]
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