Introduction:
Research suggests that yawning began with the evolution of jawed fishes, which is believed to be 400 million years ago. Usually, yawning is considered by people as a sign that indicates feelings like tiredness, hunger, boredom, or sleep. Generally, people experience a feeling of relaxation instantly after yawning. An average adult is believed to yawn about 20 times a day.
What Is Yawning?
Yawning is a type of reflex that involves an involuntary wide mouth opening with a widening of the jaw accompanied by deep inhalation of air through the nose and mouth, followed by exhalation of the inhaled air which gives a feeling of comfort. Studies suggest that yawning is an involuntary response that is initiated in the brain stem (lower stalk-like part of the brain that connects the brain with the spinal cord). As the brain stem of human beings is similar to other vertebrae (animals including birds, reptiles, mammals, and fishes that have a backbone), most animals also tend to yawn. Yawning may be triggered by various changes that take place in the nervous system. Sometimes, yawning takes place during state change which is commonly seen following the transitions between sleeping and waking. Certain researchers suggest that yawning is triggered by an increase in brain temperature.
What Is the Reason Behind Yawning?
The definitive reason behind yawning has not been confirmed yet. However, various concepts or theories explaining the reason behind yawning have been proposed by many researchers. They are as follows:
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Yawning and Social Empathy:
This concept is based on the fact that yawning is caused as a result of social empathy. If an individual sees a person yawning or reads about yawning, there is a high chance for the individual to yawn. Researchers believe that an empathetic person has more possibility of yawning on seeing another person yawn than a non-empathetic person. If a person is very close and emotionally attached to a person, like his own family member or friend, there is a high chance for the person to yawn immediately after his family member or friend.
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Yawning and Ear Pressure:
This theory states that yawning occurs as a means to get rid of the hearing problems and ear discomfort that are experienced by people during altitude changes. When a person suddenly changes from a low altitude to a high altitude while traveling in an airplane or getting inside an elevator, the person may voluntarily and involuntarily yawn to equalize the pressure changes inside the ears. In such a situation, yawning is considered a defense mechanism of the ear that takes place during sudden altitude changes or other conditions which leads to air being trapped within the middle ear (part of the ear that is separated from the external ear by the eardrum and is joined to the back of the nose). Yawning helps to equalize the pressure inside the middle ear to the outside pressure at high altitudes.
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Yawning and Arousal:
This theory states that yawning occurs as a result of boredom or sleepiness. Boredom usually occurs when a person’s main source of stimulation that keeps him engaged is no longer able to sustain his attention. Hence drowsiness is induced by the activation of the sleep-generating system. As a result, yawning is generated as a reflex by the brain to make the person alert or wake up from the sleeping state. During yawning, a few hormones are released that increase alertness and heart rate. Thus, yawning can be considered a response that occurs to make the person alert if they are in a state of inattentiveness or feeling sleepy.
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Yawning and Brain Cooling:
According to this theory, yawning occurs as a reflex to cool the brain when the brain temperature rises. The relaxation of facial muscles that takes place during yawning elevates the facial blood flow resulting in the distribution of heat through the veins. The wide opening of the mouth, accompanied by inhalation of cool air, helps to change the temperature of the blood going to the brain from the lungs. Most people experience tears at the peak of yawning, which is thought to be a mechanism to distribute the heat coming from the skull.
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Yawning and Brain Hypoxia:
Brain hypoxia is a condition in which the brain does not get an adequate oxygen supply. This theory states that yawning occurs when the brain experiences oxygen deficiency. Yawning takes place with a deep breath and short exhalation of the inhaled air which brings in more oxygen and removes carbon dioxide. Hence, yawning is considered to eliminate the bad air from the lungs and increase the oxygen content in the brain.
Why Are Yawns Contagious?
Studies suggest that the possibility of a person yawning increases six-fold upon seeing another person yawn. This is based on a concept called social mirroring where an individual imitates the action of others. This could be associated with the mirror neurons present in the brain. Mirror neurons are a set of brain cells that reacts when an action is either performed by a person or when a person witnesses somebody else doing the same action. Yawning is thought to be contagious (spread from one person to another) also based on the fact that it acts as a way to increase the alertness of people within a group. Few studies suggest that the contagious nature of yawning is a means of showing empathy and equality in the emotional situation of the people. Contagious yawning is more commonly seen in a group of family members or friends than in a group of strangers.
Conclusion:
In most people yawning occurs as a normal reflex action. However, if there is an increased tendency to yawn which is not associated with lack of sleep, boredom, tiredness, or any related factors, it may be a symptom of any abnormality. Some medical problems are associated with excessive yawning including certain medications, brain tumors, bleeding around the heart, and heart attacks. Excessive yawning with no associated reasons should be taken care of immediately by visiting a physician and making sure that there is no underlying abnormality.
