(c) flickr & Tambako the Jaguar
あくびには熱くなり過ぎた脳を冷やす機能がある，との説を支持する研究結果が発表された。あくびをすると顎が伸びて脳への血流が増え，深い吸気により外気との熱交換が起こる。そのため，この仮説によると高い気温ではあくびが少ないはずだ。アリゾナ州ツーソンで160名の通行人を対象とし，人々があくびをする映像を見せて何人がつられてあくびをするか調査したところ，結果がこの仮説と一致した。気温が体温以上になる夏は冬よりあくびが少なかったのだ。頻繁なあくびを伴う多発性硬化症や癲癇などの疾患の理解にも今回の研究が役立つと考えられる。（吉田素子）
More Than a Sign of Sleepiness, Yawning may Cool the Brain
Though considered a mark of boredom or fatigue, yawning might also be a trait of the hot-headed. Literally.
A study led by Andrew Gallup, a postdoctoral research associate in Princeton University's Department of Ecology and Evolutionary Biology, is the first involving humans to show that yawning frequency varies with the season and that people are less likely to yawn when the heat outdoors exceeds body temperature. Gallup and his co-author Omar Eldakar, a postdoctoral fellow in the University of Arizona's Center for Insect Science, report this month in the journal Frontiers in Evolutionary Neuroscience that this seasonal disparity indicates that yawning could serve as a method for regulating brain temperature.
Gallup and Eldakar documented the yawning frequency of 160 people in the winter and summer in Tucson, Ariz., with 80 people for each season. They found that participants were more likely to yawn in the winter, as opposed to the summer when ambient temperatures were equal to or exceeding body temperature. The researchers concluded that warmer temperatures provide no relief for overheated brains, which, according to the thermoregulatory theory of yawning, stay cool via a heat exchange with the air drawn in during a yawn.
Gallup describes the findings as follows:
This provides additional support for the view that the mechanisms controlling the expression of yawning are involved in thermoregulatory physiology. Despite numerous theories posited in the past few decades, very little experimental research has been done to uncover the biological function of yawning, and there is still no consensus about its purpose among the dozen or so researchers studying the topic today.
［単語和訳］
Sleepiness：眠気 Brain：脳
boredom：退屈 fatigue：疲労 trait：特徴 hot-headed：頭の熱い（通常は，「短気な」の意味） Literally：文字通り
postdoctoral：博士課程修了後の research associate：研究員 Ecology：生態学 Evolutionary Biology：進化生物学 frequency：頻度 varies with：～によって変化する exceeds：～を超える body temperature：体温 co-author：共著者 Evolutionary：進化の Neuroscience：神経学 seasonal：季節的な disparity：格差 regulating：～を調節すること
participants：参加者 as opposed to：～とは対照的に ambient temperatures：気温 researchers：研究者 overheated：過熱した according to：～によると thermoregulatory：体温調節の heat exchange：熱交換 drawn in：吸い込まれた
physiology：生理学 numerous：多数の posited：推測された experimental：実験的な uncover：～を明らかにする biological：生物学的 consensus：意見の一致 the dozen or so：十数人ほどの
