Attention, this article may cause more than one yawn. And not because of its lack of interest – we hope – but because it deals with one of the most contagious behaviors that exist. Science is still trying to explain such enigmatic behavior.
The jaw tightens, the mouth opens and inhales a large amount of air. This is followed by a rapid exhalation, accompanied by a feeling of well-being. It is enough to read this description to feel like yawning, a gesture as common as it is misunderstood by science. Eating, talking, looking … many of the actions that are done on a daily basis have an obvious function. It is not the case.
“Seeing a dog or horse yawning makes me feel like all animals are built with the same structure.” This is how Charles Darwin expressed in his notes of 1838 the universality of gesture.Caused by tiredness, boredom, or digestion, It appears in practically all vertebrates, which suggests a very ancient origin; it probably goes back to the common ancestor of all these living things. The survival of yawning, practically unchanged for millions of years, indicates that it must have a fundamental evolutionary function. In fact, 15-week-old human fetuses already experience it. Does it serve to? Cool the brain? To arouse attention? Or is it more related to sexual arousal? So far no definitive answers have been found.
The patriarch of physicians, the Greek Hippocrates, was the first to write something about it. According to his hypothesis, it is a system to expel “bad air” from the lungs or to irrigate the brain. HisTreaty of the WindsHe tried to show that the origin of all diseases was the air, which is why he considered this act as a bad sign, an omen of fever. Then other theories followed, but it was relegated as a minor issue in medicine. A new point of view only appeared in the mid-nineteenth century, when French neurologists Jean-Martin Charcot and Georges Gilles de la Tourette began to study cases of women in which compulsive yawning accompanied what was then called “hysteria.” Charcot’s work inaugurated a very fruitful approach in this field: that of neuroscience.
Parkison’s patients hardly experience it
Opening your mouth involuntarily triggers a realwhirlwind of biochemical signals in the brain. Dopamine, oxytocin, acetylcholine, serotonin or hypocretin are some of the substances that intervene in the complex and misunderstood neural process that is activated when we yawn. Dopamine, in particular, seems to play a crucial role. Indeed, this substance is scarce in the brain of Parkinson’s patients, who also present an almost total disappearance of this behavior. Some drugs that relieve motion sickness by inhibiting acetylcholine also significantly reduce its frequency. Finally, scientists have detected lthe appearance of sex hormones and opioid substances during the process. The former could be related to the erections that sometimes occur in men, while the latter would attenuate our ability to react, making yawning impossible to stop.
But does all this brain machinery kick in to trigger a simple boredom signal? Driving, reading, waiting, traveling in public transport … monotonous and repetitive activities are the situations in which we are assaulted most often. Other occasions that favor this manifestation do not seem more complex: the moments before going to bed and those that follow after waking up, the after-dinner of a large meal, the hours of fasting or the dizziness on travel. None of these scenarios seems to justify the complexity of the brain and the age-old permanence of yawning.
There is a set of circumstances that are not characterized by boredom, fatigue or gastric fullness and that also cause it: athletes before competitions, paratroopers in the moments before their first jump, students when they have to face an exam , the musicians preparing to give a concert … It seems thatthe brain machinery that triggers yawning is activated before a major event, in conjunction with alertness and vigilance. These same circumstances occur in the animal world.In many species, yawning precedes mating. Male Siamese fighting fish experience it before attacking a rival. In zoos, it is very common to see lions or apes opening their mouths when there is less than an hour to eat. Also, predators often do it before hunting and hyenas while surrounding a carrion.
It is not true that it serves to oxygenate the brain
Such observations have provided the clues for developing the most widely used theory today. The old argument – which is still circulating – according to which it would serve to “oxygenate the brain” has been totally discredited. In the 1980s, Robert R. Provine, a psychologist at the University of Maryland (USA), went to the trouble of putting it to the test. He asked a group of students to think about the act he was trying to study while inhaling air with different concentrations of CO2. On average, the volunteers reacted by yawning about 24 times per hour, regardless of the carbon dioxide concentration. Therefore, the experiment excluded oxygen input as an explanation for the behavior. A Provine colleague, Ronald Baenninger of Temple University in Philadelphia, decided to attack the problem head-on. He provided several people with a portable computer by asking them to press a button on the device each time he yawned. After collecting data for two weeks, Baenninger found that the highest frequency was recorded about 15 minutes before some activity that required special attention or delivery.
The body thus resists disconnecting from the environment
The experiment confirmed that it must be a system to increase alertness in animals. This seems obvious for sexual acts or hunting, but its manifestation during times of tiredness or boredom could also be explained as aattempt by the body to resist falling into a state of disconnection from the environment.
However, this theory does not explain the most suggestive phenomenon:the “contagious” yawn, which only humans and certain primates experience. Also, no matter how much parents express their fatigue in this way, they will never be emulated by the baby who keeps them awake with their crying. An experiment carried out in 2003 by psychologists James Anderson and Pauline Meno, from the University of Stirling, in the United Kingdom, showed that this behavior does not appear before the age of 5 or 6.
Other research conducted in 2007 by a team coordinated by psychologist Atsushi Senju, from the University of London, revealed that autistic children are not infected either. The total disappearance of the phenomenon in individuals with little empathy would therefore link it with the ability to connect with others. Blissempathyit has a fundamental evolutionary function. For example, when a pigeon senses a pedestrian approaching, it takes flight and the entire flock immediately follows, although most birds ignore the cause of the alarm.
Yawning in a group can be an evolutionary advantage
In 2005, a group of German and Swedish neuroscientists, coordinated by Riita Hari of the Helsinki University of Technology in Finland, discovered that during “contagious yawning” the superior temporal sulcus of the brain is activated, the same structure that functions in the brain. perception of the movement of eyes and mouth. As the use of emoticons in emails and text messages shows, such gestures are the main vehicle for perceiving the emotions of our peers. Thus, this collective drive could have been consolidated throughout evolution as a tool to “propagate” the state of vigilance in a group. It is still unknown if this is the case, but what no one can deny is the irrepressible force that pushes us to yawn.Have you not opened your mouth more than usual while reading this article?
Michele Catanzaro
