A yawn is a reflex of deep inhalation and exhalation associated with tiredness, stress, over-work, lack of stimulation, or boredom. Pandiculation is the term for the act of stretching and yawning. Yawning is a powerful non-verbal message with several possible meanings, depending on the circumstances.
The exact causes of yawning are still undetermined. A recent hypothesis by Gordon Gallup of the University of Albany states that yawning may be a means to keep the brain cool. Mammalian brains operate best when they are cool. In an experiment, he showed several groups of people videos of other people yawning.
When the subjects held heat packs up to their heads while viewing the videos, they yawned often. But when they held cold packs up to their heads or breathed through their noses (another means of brain cooling), they did not yawn at all. Another recent hypothesis is that yawning is used for regulation of body temperature. Another hypothesis is that yawns are caused by the same chemicals (neurotransmitters) in the brain that affect emotions, mood, appetite and other phenomena. These chemicals include serotonin, dopamine, glutamic acid and nitric oxide. As more (or less) of these compounds are activated in the brain, the frequency of yawning increases. Conversely, a greater presence in the brain of opiate neurotransmitters such as endorphins reduces the frequency of yawning.
Patients taking the serotonin reuptake inhibitor Paxil (Paroxetine HCl) or Citalopram, another SSRI, have been observed yawning abnormally often.
Recent research carried out at by Catriona Morrison, a lecturer in psychology at the University of Leeds, involving monitoring the yawning behaviour of students kept waiting in a reception area, indicates a connection (supported by neuro-imaging research) between empathic ability and yawning. â€œWe believe that contagious yawning indicates empathy. It indicates an appreciation of other peopleâ€™s behavioural and physiological state,â€ said Morrison. Another theory is that yawning is similar to stretching. Stretching, like yawning, increases blood pressure and heart rate while also flexing many muscles and joints. It is also theorized that yawning helps redistribute surfactant, an oil-like substance which coats the lungs and aids breathing. The stretching of jaw and face muscles seems to be necessary for a satisfactory yawn.
Some people yawn when storms approach, which is a sure sign that changes in pressure affect them.