Most people could benefit from a few extra hours of sleep every night. But some people habitually sleep much less than the recommended amount, yet report feeling no ill effects. A new University of Utah study, published Sept. 15 in Brain and Behavior, 研究发现，所谓的“习惯性短睡眠者”大脑中的神经连接模式表明，其中一些人可能是高效睡眠者, but may also be more tired than they realize.
“这是一个诱人的证据，可以解释为什么有些人觉得自己不需要睡那么多," says study co-author and radiologist Jeff Anderson. “也许有些人的大脑能够在白天的一小段时间里做睡眠所做的事情."
Why we sleep
The reasons for sleep are still a mystery. “这是所有科学中最有趣的问题之一：大发娱乐首先为什么要睡觉？?" Anderson says. "It's incredibly disadvantageous to spend a third of our life asleep. 这样做一定有一个重要的原因，但为什么仍然是一个活跃的研究领域."
一些主要的假设认为，睡眠可以清除大脑中一整天积累的化合物, and allows memories to move from short-term to long-term memory storage.
For most people, 如果每晚睡眠时间少于建议的7到9小时，就会导致疲劳, irritability and some impairment in judgment and reasoning. 长期的短睡眠时间与许多精神和身体健康的后果有关, including diminished cognitive performance, mood disturbance, obesity, coronary disease and all-cause mortality risk.
但是一些每晚睡眠时间少于6小时的人却没有感觉不适. 2009年，犹他大学的神经学家克里斯托弗·琼斯和他的同事 found 一种罕见的基因突变与短时间高效睡眠有关. Many genetic factors are involved in sleep, 这些因素的结合可能会导致一些人觉得他们需要的睡眠比其他人少.
"Most people feel terrible when they get less than six hours of sleep," says study co-author and psychology professor Paula Williams. "What's different about these short sleepers who feel fine? Is there something different going on in terms of brain function? Although they report no daytime dysfunction from short sleep, what if their perceptions are inaccurate?"
The brain's wiring diagram
To begin answering those questions, Williams, Anderson, Jones and psychology graduate student Brian Curtis, who is first author on the new study, looked into how people's brains are wired together. “大脑中的大多数细胞只是表面的一层薄薄的灰质细胞," Anderson says. “中间的所有东西都是表面上这些点之间的连接，以及中间的几个小站. So figuring out where those connections go, 灰质中哪些点是相连的，哪些点不是，这真的是大脑工作的全部吗."
The set of brain connections, 也被称为“连接体”，目前正在人类连接体项目中进行探索, a multiuniversity consortium analyzing the network of connections in 1,200 people through MRI scans. So far, data from about 900 people have been released, 这使得犹他大学的研究人员能够访问大量的大脑连接数据集.
Cat-napping?
研究小组比较了过去一个月里睡眠时间正常的人和每晚睡眠时间不超过6小时的人的数据. 他们进一步将短睡眠者分为两组：报告白天功能障碍的人, 比如感觉太困，无法完成日常任务或保持热情, and those who reported feeling fine.
在MRI扫描中，两组短睡眠者都表现出了比清醒时更典型的睡眠连接模式. 安德森说，尽管人们被要求在扫描仪中保持清醒, some short sleepers may have briefly drifted off, even those who denied dysfunction. 他说：“众所周知，人们很难知道自己是否睡着了一两分钟。. For the short sleepers who deny dysfunction, 一种假设是，他们唤醒的大脑系统永远处于超速运转状态. "This leaves open the possibility that, 在无聊的功能磁共振成像扫描仪中，他们没有任何事情可以让他们保持清醒，从而入睡," says Jones. This hypothesis has public safety implications, according to Curtis. "Other boring situations, 比如在没有足够视觉或听觉刺激的情况下在夜间驾驶汽车, 也可能使睡眠时间短的人有困倦的危险，甚至在开车时睡着," he says.
专门研究大脑区域之间连通性的差异, 研究人员发现，否认功能障碍的短睡眠者感觉皮质之间的连通性增强, which process external sensory information, and the hippocampus, a region associated with memory. “这很诱人，因为它表明，短睡眠者在扫描仪中做的事情之一，可能是比非短睡眠者更有效地进行记忆巩固。," Anderson says. In other words, 一些睡眠时间短的人可能一整天都能进行类似睡眠的记忆巩固和大脑任务, reducing their need for sleep at night. 或者他们可能在白天低刺激条件下入睡, often without realizing it.
Testing perceptions of dysfunction
The next phase of the team's research, to be conducted at the University of Utah, 将直接测试否认功能障碍的短睡眠者是否真的做得很好. “大多数睡眠不足的人表现出与醉酒相似的认知障碍," Williams says. 然而，先前的研究主要涉及对正常睡眠者的实验性睡眠限制. 研究人员计划招募每晚自然睡眠不足6小时的人, regardless of whether it is the weekend, workday or vacation. In addition to brain imaging, they will examine cognitive performance, including driving simulator testing, to get objective information about functioning. 威廉姆斯说，睡眠不足可能会影响人们对自身功能障碍的认知. “大发娱乐特别感兴趣的是了解人们对自己功能的感知与实际功能之间的差异. Not everyone is equally accurate.该团队未来的工作还将纳入研究对象的家庭成员或伴侣的报告, to provide an additional evaluation of daytime function.
What it means
In analyzing connectome data, 研究小组发现，自我报告的前一个月平均睡眠时间是最能解释人们休息时连通性特征差异的因素. 安德森说，这一结果表明，未来的功能磁共振成像研究在解释结果时应该考虑睡眠. "Sleep is central to everything we do," he says. "All psychiatric disorders are impacted by sleep."
威廉姆斯希望这个正在进行的研究项目能够回答关于个体睡眠需求差异的关键问题. 她说：“两个人可以睡同样的时间，一个人会感到神清气爽，而另一个人则不会。. "What's the difference? Are there some people who can get away with less sleep? We don't know. Amazingly, we still don't know."
The full study can be found here.