If, when you see someone yawning you can’t hold back a yawn, if you yawn when you sleep, when you get bored and even when you’re tired, maybe it’s not so bad because, according to a recent study conducted at the University of the State of New York, it is likely you have a larger and more complex brain. Conversely, those with smaller brains are likely to yawn less.
These researchers analyzed the yawning duration of 109 individuals belonging to 19 different species, humans, elephants, mice, monkeys and rabbits. So they discovered that the more the yawn lasts, the greater is the size of the brain and more numerous are the cortical connections.
To test this theory, they measured the duration of yawning in several animal species and discovered that the key was not the size of their mouth or jaw. In fact, the yawns of mice last on an average of 0.8 seconds, 2.4 seconds those of the dogs, 1.97 seconds the cats, 4.8 seconds the camels and humans 6.5 seconds.
Yawning is a mechanism to cool the brain
The relationship between the amount of yawning and the duration with the size of the brain could be supported by a hypothesis advanced by the same researchers in 2007, when they discovered that yawning will expand and contract the sinus walls to pump air to the brain, in order to reduce the temperature.
The “theory of the yawning thermoregulation” says that yawning we aspire air, and that this serves to cool the brain. In fact, it is no coincidence that the jaw is one of the four largest cavities of our head.
These researchers first analyzed the brain of rats and observed temperature changes in the brain, before, during and after the yawns. In fact, the temperature of the brain suffered little abrupt changes before a yawn.
Later the researchers asked some patients who yawned often and excessively, to measure the temperature before and after yawning. The results showed that their body temperature was high prior to yawn and then fell.
Another theory of some French researchers suggests that the yawn serves to bring out the brain from what is called the “default mode”, a state in which we aren’t fully awake or fully asleep, and makes sure that we pass to the phase of full attention.
Thus, the yawn would serve as a kind of switch which allows activating our level of alert. This mechanism would be triggered by the increase in circulation of the cerebrospinal fluid.
From this point of view, it would be logical thinking that if the brain is larger, the person will need to yawn more often and longer to cool it. In fact, neuroscientists claim that the duration of yawning is linked to brain size and its complexity, given that as many neurons the more complex will be the networks that they form, and the higher the blood flow necessary to cool them.
Sources:
Gallup, A. C. (2016) Yawn duration predicts brain weight and cortical neuron number in mammals. Biology Letters; 12(10).
Shoup-Knox, M. et. Al. (2010) Yawning and stretching predict brain temperature changes in rats: support for the thermoregulatory hypothesis. Front. Evol. Neurosci.; 24(2): 108.
Gallup, A. C. & Gallup, G. G. (2007) Yawning as a Brain Cooling Mechanism: Nasal Breathing and Forehead Cooling Diminish the Incidence of Contagious Yawning. Evolutionary Psychology; 5(1):92-101.
Walusinski, O. (2014) How yawning switches the default-mode network to the attentional network by activating the cerebrospinal fluid flow. Clinical Anatomy; 27(2): 201–209.
