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Yawning involves opening the mouth involuntarily while taking a long, deep breath of air. It is commonly believed that people yawn as a result of drowsiness or weariness because they need oxygen.

However, researchers at the University of Albany in New York said their experiments on 44 students showed that drawing in air helps cool the brain and helps it work more effectively.

They said that their experiments showed that raising or lowering oxygen and carbon dioxide levels in the blood did not produce that reaction.

Study participants were shown videos of people laughing, being neutral and yawning, and researchers counted how many times the volunteers responded to their own 'contagious yawns,' reported the online edition of BBC News.

The researchers found that those who breathed through the nose rather than the mouth were less likely to yawn when watching a video of other people yawning. This was because vessels in the nasal cavity sent cool blood to the brain.

The same effect was found among those who held a cool pack to their forehead, whereas those who held a warm or room-temperature pack yawned while watching the video.

'Since yawning occurs when brain temperature rises, sending cool blood to the brain serves to maintain optimal levels of mental efficiency,' the authors wrote in the journal Evolutionary Psychology.