Severe stress can damage a child`s brain, say researchers at the Stanford University School of Medicine and Lucile Packard Children`s Hospital. The researchers found that children with post-traumatic stress disorder and high levels of the stress hormone cortisol were likely to experience a decrease in the size of the hippocampus - a brain structure important in memory processing and emotion.

斯坦福大学医学院和Lucile Packard儿科医院的研究人员声称，严重应激能够损伤儿童的大脑。这些研究者发现患有创伤后应激障碍的儿童和体内应激激素皮质醇含量高的儿童可能出现海马体积的缩小（海马是参与记忆过程和情绪反应的重要脑结构）。

Although similar effects have been seen in animal studies, this is the first time the findings have been replicated in children. The researchers focused on kids in extreme situations to better understand how stress affects brain development.

尽管已经在动物研究中观察到类似的作用，但是该现象在儿童体内得以复制尚属首次。研究者关注的是极端环境中的儿童，以便更好地了解应激如何影响脑的发育。

"We`re not talking about the stress of doing your homework or fighting with your dad," said Packard Children`s child psychiatrist Victor Carrion, MD. "We`re talking about traumatic stress. These kids feel like they`re stuck in the middle of a street with a truck barreling down at them."

“我们谈论的并非做家庭作业或与父亲争吵之类的应激”Packard 医院儿童精神病专家维克多.卡里昂博士说，“我们讨论的是创伤性应激，这些孩子们觉得他们好像被卡在马路中间，卡车要向他们碾过来一样。”

Carrion, assistant professor of child and adolescent psychiatry at the medical school and director of Stanford`s early life stress research program, and his collaborators speculate that cognitive deficits arising from stress hormones interfere with psychiatric therapy and prolong symptoms.

卡里昂是该医学院儿童和青少年精神病学助理教授，同时是斯坦福大学生命早期研究项目主任。卡里昂博士与其同事推测应激激素引起的认知缺损干扰精神病的治疗并能拖延症状。

The children in the study were suffering from post-traumatic stress disorder, or PTSD, as a result of undergoing physical, emotional or sexual abuse, witnessing violence or experiencing lasting separation and loss. This type of developmental trauma often impairs the child`s ability to reach social, emotional and academic milestones.

该研究中的儿童因经历生理的、情感的或性的虐待、目击暴力或体验持久的分离和失落感而罹患创伤后应激障碍（PTSD）。此类型的发展性创伤通常损害儿童获取社会方面、情感方面或学习方面等重要事件的能力。

"We`d really like to understand why some children are more resilient than others, and what the long-term effects of extreme stress are," said Carrion, who is the first author of the research, to be published in the March issue of Pediatrics. "We know, for example, that these children are at higher risk of developing depression and/or anxiety as adults."

卡里昂是该项研究的第一位作者，他的研究论文发表在《儿科学》第三期上，他说，“我们非常想了解某些儿童比其它儿童更容易复原的原因，以及极端应激的长期作用，比如说，我们已经知道这些儿童成年后发生抑郁和/或焦虑的风险相对较高。

One theory posits that everyone carries an ongoing stress burden that accumulates throughout life. Once a certain threshold is reached, either through one or two very traumatic events or through chronic, high levels of stress, adults and children can begin to exhibit PTSD symptoms such as re-experience (including flashbacks, intrusive thoughts or nightmares), avoidance and emotional numbing, and physiological hyperarousal (such as an elevated resting heart rate). These behavioral symptoms make PTSD difficult to differentiate from other conditions such as attention deficit/hyperactivity disorder.

理论认为每个人一生中时刻都在承受着应激负担。一旦经受一项或两项创伤性事件或慢性高水平应激后达到某个阈限，成人和儿童便开始出现PTSD的症状如再体验（包括重现、侵入性思维或梦魇）、回避和情感麻木，以及生理的高觉醒状态（如静止时心率加快）。这些行为方面的症状使PTSD难以与其它疾病区分比如注意缺陷/多动障碍。

Children predisposed by genetics or environment to be more anxious than their peers are also more likely to develop PTSD in response to emotional trauma, perhaps because their responses to other life experiences simply left them closer to that threshold than less-anxious children.

因遗传或环境因素而易于产生焦虑的儿童与其它同龄儿童相比，在遭受情感创伤时更可能发生PTSD，可能的原因在于他们对其它生活经历的反应使得他们比低焦虑儿童更接近发生PTSD的阈值。

The researchers studied 15 children from ages 7 to 13 suffering from PTSD. They measured the volume of the hippocampus at the beginning and end of the 12- to 18-month study period. After correcting for gender and for physiological maturity, they found that kids with more severe PTSD symptoms and higher bedtime cortisol levels (another marker of stress) at the start of the study were more likely to have reductions in their hippocampal volumes at the end of the study than their less-affected, but still traumatized peers.

研究人员对15名7～13岁罹患PTSD的儿童进行了研究。他们在为期12～18个月的研究期间的开始和结束时分别测量了海马的体积。校正了性别和生理成熟度因素之后，发现起始阶段PTSD症状较严重且在睡眠期间皮质醇水平（应激的另一个标志物）较高的儿童比其他受影响较小但依然受到创伤的同龄儿童在研究结束时海马体积缩小。

It is significant that the change in the hippocampal volume corresponds to both PTSD symptom severity and increased cortisol levels. Cortisol belongs to a class of human hormones known as glucocorticoids that have been shown to kill hippocampal cells in animals. In a vicious cycle, a reduction in hippocampal size can make it more difficult for a child to process and deal with traumatic events, which in turn may raise both stress and cortisol levels that cause even more damage.

显然，海马体积的变化与PTSD症状的严重程度和皮质醇水平的升高一致。已知糖皮质激素能够杀伤动物的海马细胞，皮质醇属于糖皮质激素的一种。海马体积的缩小使得儿童在处理创伤性事件时更为困难，而这些创伤性事件又可提高应激和皮质醇水平，进而导致海马更严重的损伤，从而构成恶性循环。

"Although everyday levels of stress are necessary to stimulate normal brain development, excess levels can be harmful," said Carrion, likening the biological effects of increasing amounts of stress to an inverted U. "One common treatment for PTSD is to help a sufferer develop a narrative of the traumatic experience. But if the stress of the event is affecting areas of the brain responsible for processing information and incorporating it into a story, that treatment may not be as effective."

“尽管每天一定水平的应激是刺激正常大脑发育所必需的，但是过度的应激水平却是有害的。”卡里昂博士说，可把应激水平增加的生物学效应比作倒写的 U，“PTSD通常的治疗是帮助罹患者把创伤性体验改编成故事。但是，如果对该事件的应激影响到信息加工和把信息整合到某个故事的脑区的话，治疗不一定是有效的。”

Carrion and his colleagues are now using an imaging technique known as functional MRI to visualize whether and how the children`s brains differ when performing emotional and cognitive tasks.

现在卡里昂与其同事正使用影像学技术即功能性核磁成像（功能性MRI）来对儿童大脑在完成情绪性和认知性任务时是否出现不同和怎样出现不同进行可视化研究。

"What we have now is basically a snapshot," said Carrion. "We can`t yet say much about function. But we know that PTSD is chronic and pervasive. Hopefully with further research we can develop more effective, targeted interventions to help these kids."

卡里昂说，“我们现在得到的只是一些基本的简单印象，对其作用还没有更多的了解。但是我们知道PTSD是一种慢性和普遍性的疾病。随着研究的不断深入，我们希望能找到更有效、针对性更强的干预方法来帮助这些儿童。”

（编辑：Cherry 包红）

来源：中国教育人博客