ps 3-13-13 Today I saw a patient who once again confirmed by hypothesis that yawning developed as a mechanism to stall sleep. This young man is not getting along with his girlfriend. In the session when he broached this issue within a short time he was flooded with painful emotions and instead of going further with what he had to tell he indulged in a giant yawn. From his expressions I could not help but notice that as soon as his conflict with his girlfriend emerged in his consciousness he first tried to talk about it but as the pain associated with the memory followed in to consciousness he lost interest in the talking and tried to withdraw in to sleep where he could turn the painful memories into pleasant ones through the mediation of dreams but on realizing that it would be not appropriate to fall asleep in front of me he yawned to activate the neuronal circuits connected with wakefulness.
ps. In the Wall Street Journal 7-16-2013 I read a small write up titled "Why you may yawn less in the summer." It quoted a study which conducted an experiment with two groups of people. One in early summer and the other in winter. They were made to look at pictures of yawning and encouraged to talk about their own yawning behavior. It was found that people were more likely to yawn during winter than early summer months. The reasoning given was that in winter yawing would reduce the brain temperature more. This is not a joke. The study was published in impressive sounding Frontiers in Neuroscience so it got to be true. Yet the question arises why would anybody want to reduce his or her brain temperature especially in winter when you would want to conserve heat. The article claimed in summer the outside temperature was closer to body temperature so the cooling effect was not as robust as during the winter so there was less benefit from yawning.
Now my own experience is that in uncomfortably hot weather too the tendency to yawn increases. And the explanation may be simpler. When it is uncomfortably hot in the present then a person wants to go to sleep so he can dream of being in the Alps or better still on the peaks of Himalayas. If one is in cold weather the desire to go to sleep and conserve energy is even stronger. So whenever one is in unpleasant surroundings one way to escape from it is to go to sleep. But if it inappropriate to fall asleep in the situation then the yawning mechanism kicks in to activate the wakefulness centers of the brain. Since cool air is a sharper stimulant than air that is nearer to more comfortable temperature it acts as a sharper arousing agent and is gulped in larger quantity through yawning.