人們往往認(rèn)為打呵欠是因?yàn)槔Ь牖蚱v。美國(guó)研究人員發(fā)現(xiàn),，打呵欠可能也是大腦過(guò)熱的跡象,，人通過(guò)打呵欠吸入外界空氣給大腦降溫。
美國(guó)普林斯頓大學(xué)生態(tài)學(xué)和進(jìn)化生物學(xué)學(xué)院博士后安德魯·蓋洛普帶領(lǐng)研究小組,，研究季節(jié)對(duì)人打呵欠的影響,。研究人員在亞利桑那州圖森市隨機(jī)攔住80名行人，向他們展示打呵欠的圖片,，觀察行人是否跟著打呵欠,。測(cè)試分別在冬季和夏季各進(jìn)行一次。結(jié)果顯示,，冬季一半研究對(duì)象跟著打呵欠,，夏季只有四分之一研究對(duì)象“受傳染”。
美國(guó)每日科學(xué)網(wǎng)站9月20日援引蓋洛普的話報(bào)道,，過(guò)去數(shù)十年中,，研究人員對(duì)打呵欠的控制機(jī)制提出諸多假設(shè)，但鮮有研究揭示打呵欠的生物學(xué)功能,，至于打呵欠的目的或作用尚沒(méi)有一致結(jié)論,，“這項(xiàng)研究給打呵欠的控制機(jī)制涉及體溫調(diào)節(jié)生理機(jī)能這種觀點(diǎn)提供了更多支持”,。
這一研究結(jié)果由本月出版的《進(jìn)化神經(jīng)學(xué)前沿》發(fā)表。
根據(jù)體溫調(diào)節(jié)假設(shè),，打呵欠由大腦溫度升高引起,。先前研究結(jié)果顯示，在打呵欠前后,，小鼠大腦溫度發(fā)生變化,。打呵欠時(shí)，下頜拉伸增加了流向大腦的血流,，這些血流與吸入的外界空氣進(jìn)行熱量交換,，最終幫助大腦降溫。
按照這一假設(shè),，打哈欠應(yīng)有反作用,，即當(dāng)外界空氣溫度等于或高于體溫時(shí)，打呵欠吸入的空氣無(wú)法冷卻大腦,。
這在蓋洛普的研究中得到印證,。夏季外界溫度等于甚至高于體溫，無(wú)助于讓過(guò)熱的大腦休息,，因此研究對(duì)象打呵欠頻率降低,。
按照體溫調(diào)節(jié)假設(shè)，當(dāng)環(huán)境溫度處于一定范圍時(shí),，打呵欠頻率最高,。
蓋洛普說(shuō)，他們的研究結(jié)果與假設(shè)一致,。綜合考慮濕度,、置身室外時(shí)間、睡眠時(shí)間等因素后,，無(wú)論夏季還是冬季,，研究對(duì)象初到室外5分鐘內(nèi)，近40%打呵欠,，隨后,，夏季研究對(duì)象打呵欠比例降至10%以下，冬季打呵欠比例升高較多,。
他說(shuō)：“這是第一份顯示打呵欠頻率隨季節(jié)變化的報(bào)告,。”
研究人員認(rèn)為，這項(xiàng)研究增加了人們的生理知識(shí),，有助解釋人在高熱環(huán)境中容易思維混亂,、不知所措的原因，有助更好地理解運(yùn)動(dòng)神經(jīng)元疾病或癲癇患者緣何常打呵欠,。(生物谷 Bioon.com)
doi:10.3389/fnevo.2011.00003
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Contagious yawning and seasonal climate variation
Andrew C. Gallup and Omar T. Eldakar
Recent evidence suggests that yawning is a thermoregulatory behavior. To explore this possibility further, the frequency of contagious yawning in humans was measured while outdoors in a desert climate in the United States during two distinct temperature ranges and seasons (winter: 22oC; early summer: 37oC). As predicted, the proportion of pedestrians who yawned in response to seeing pictures of people yawning differed significantly between the two conditions (winter: 45%; summer: 24%). Across conditions yawning occurred at lower ambient temperatures, and the tendency to yawn during each season was associated with the length of time spent outside prior to being tested. Participants were more likely to yawn in the milder climate after spending long periods of time outside, while prolonged exposure to ambient temperatures at or above body temperature was associated with reduced yawning. This is the first report to show that the incidence of yawning in humans is associated with seasonal climate variation, further demonstrating that yawn-induced contagion effects can be mediated by factors unrelated to individual social characteristics or cognitive development.
