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How stress affects your brainStress isn't always a bad thing; it can be handy for a burst of extra energy and focus, like when you're playing a competitive sport or have to speak in public. But when it's continuous, it actually begins to change your brain. Madhumita Murgia shows how chronic stress can affect brain size, its structure, and how it functions, right down to the level of your genes. [Directed by Andrew Zimbelman, narrated by Addison Anderson, music by Josh Smoak].
Madhumita Murgia Journalist Madhumita is a journalist, editor and speaker with expertise in the fields of science, health and technology. She is the European Technology Correspondent at The Financial Times. 6,539,409 views | Madhumita Murgia • TED-EdAre you sleeping restlessly, feeling irritable or moody, forgetting little things, and feeling overwhelmed and isolated? Don't worry. We've all been there. You're probably just stressed out. Stress isn't always a bad thing. It can be handy for a burst of extra energy and focus, like when you're playing a competitive sport, or have to speak in public. But when its continuous, the kind most of us face day in and day out, it actually begins to change your brain. Chronic stress, like being overworked or having arguments at home, can affect brain size, its structure, and how it functions, right down to the level of your genes. Stress begins with something called the hypothalamus pituitary adrenal axis, a series of interactions between endocrine glands in the brain and on the kidney, which controls your body's reaction to stress. When your brain detects a stressful situation, your HPA axis is instantly activated and releases a hormone called cortisol, which primes your body for instant action. But high levels of cortisol over long periods of time wreak havoc on your brain. For example, chronic stress increases the activity level and number of neural connections in the amygdala, your brain's fear center. And as levels of cortisol rise, electric signals in your hippocampus, the part of the brain associated with learning, memories, and stress control, deteriorate. The hippocampus also inhibits the activity of the HPA axis, so when it weakens, so does your ability to control your stress. That's not all, though. Cortisol can literally cause your brain to shrink in size. Too much of it results in the loss of synaptic connections between neurons and the shrinking of your prefrontal cortex, the part of your brain the regulates behaviors like concentration, decision-making, judgement, and social interaction. It also leads to fewer new brain cells being made in the hippocampus. This means chronic stress might make it harder for you to learn and remember things, and also set the stage for more serious mental problems, like depression and eventually Alzheimer's disease. The effects of stress may filter right down to your brain's DNA. An experiment showed that the amount of nurturing a mother rat provides its newborn baby plays a part in determining how that baby responds to stress later in life. The pups of nurturing moms turned out less sensitive to stress because their brains developed more cortisol receptors, which stick to cortisol and dampen the stress response. The pups of negligent moms had the opposite outcome, and so became more sensitive to stress throughout life. These are considered epigenetic changes, meaning that they effect which genes are expressed without directly changing the genetic code. And these changes can be reversed if the moms are swapped. But there's a surprising result. The epigenetic changes caused by one single mother rat were passed down to many generations of rats after her. In other words, the results of these actions were inheritable. It's not all bad news, though. There are many ways to reverse what cortisol does to your stressed brain. The most powerful weapons are exercise and meditation, which involves breathing deeply and being aware and focused on your surroundings. Both of these activities decrease your stress and increase the size of the hippocampus, thereby improving your memory. So don't feel defeated by the pressures of daily life. Get in control of your stress before it takes control of you.
Shoudong He, Translator Tianchang Luo, Reviewer 00:06 你是否睡觉不安稳， 感到易躁或者情绪化， 总是忘记一些小事情， 以及感到不堪重负和孤独？ 别担心，我们都经历过这些。 你可能仅仅是压力太大。 压力并不总是件坏事， 它会在某些时候帮助你 爆发额外的能量和专注力， 比如，在进行一项竞技性的运动 或者必须在公众面前发言时。 但如果压力一直持续， 每天我们都接连不断地承受着压力， 它就开始实实在在地改变你的大脑。 慢性压力， 比如过度工作或家庭纷争， 会影响大脑尺寸、 大脑结构 和大脑功能， 甚至会影响你的基因。 压力开始于一种叫做 下丘脑垂体肾上腺轴的东西， 一连串的相互作用， 在大脑的内分泌腺和肾脏之间， 它会控制身体对压力的反应。 当你的大脑检测到压力情况， 你的下丘脑垂体肾上腺轴立刻会被激活， 并释放一种叫做皮质醇的激素， 提醒你的身体做好立即行动的准备。 但是高水平的皮质醇在一段长时间过后 会严重破坏你的大脑。 例如，慢性压力会增加你大脑的活动水平 和大脑恐惧中心——杏仁体 的神经连接数量。 随着皮质醇水平的上升， 你海马体里面的电信号 即大脑中和学习、记忆、压力控制相关的部分， 开始恶化。 海马体也抑制了下丘脑肾上腺轴的活动， 所以当它变弱， 你控制压力的能力也随之变弱了。 但是，这还不是全部。 皮质醇实际上可以引起你大脑在尺寸上的萎缩， 过多的皮质醇导致神经原之间突触连接减少， 和你额叶前部皮质层的萎缩。 这是你大脑里管理精力集中、 决策制定、 判断 和社交互动的部分。 它也致使海马体中新生的脑细胞更少， 这意味着长期的压力可能使学习和记忆 对你而言更困难， 同时也留下了其他更严重的精神问题的隐患， 比如抑郁和最后的老年痴呆症。 压力的影响可能直接渗透到你脑部的DNA。 实验表明， 一个雌鼠对她的孩子培育的情况， 对于她的孩子在以后的生活中 会如何应对压力有一定影响。 被妈妈照顾得细致的鼠宝宝 会变得对压力比较不敏感， 因为他们的大脑里发展了更多的皮质醇受体， 和皮质醇紧密相关的皮质醇受体抑制了应激反应。 被妈妈粗心大意喂养大的鼠宝宝就有相反的结果， 所以 这些鼠宝宝在随后的一生里 都会对压力更加敏感。 这些被认为是表观遗传变异， 就是说它们在不直接更改基因代码的前提下， 影响了哪些基因被表现出来。 如果雌鼠妈妈被交换，这些变化就会对调。 但是，还有个令人惊讶的实验结果。 一个鼠妈妈导致的表观遗传变异 会被传递给她后面的好几代老鼠。 换句话说，这些行为是会遗传的。 但是，也不都是坏消息。 有许多不同的方式 可以改变皮质醇对你紧张的大脑的影响。 最有力的武器是锻炼和冥想， 因为做这些事情的时候你同时也会深呼吸， 并关心和关注到你的周遭环境。 这些活动减少了你的压力 增加了海马体的大小， 从而改善你的记忆。 所以不要因为日常生活中的压力而感到挫败， 人们只有控制好自己的压力 才不会反过来被它控制。 Madhumita Murgia: How stress affects your brain | TED Talk
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