Got it? Okay, now try to remember what you had for lunch three weeks ago. 想起来了吗？好的，现在想想你三周前午餐吃了什么。

　　That second memory probably isn't as strong, but why not? 这个回忆可能就不是那么栩栩如生了吧，为什么会这样呢？

　　Why do we remember some things, and not others? 为什么我们会记住一些事情，而忘却另外一些事情？

　　And why do memories eventually fade? 为什么记忆最终会一点一点褪色？

　　Let's look at how memories form in the first place. 让我们先来看一下，记忆是如何产生的。

　　When you experience something, like dialing a phone number, 当你经历事情的时候，比如拨电话号码，

　　the experience is converted into a pulse of electrical energy that zips along a network of neurons. 这个体验会被转化成一种脑电波脉冲，这种脉冲快速地沿着神经网络前进。

　　Information first lands in short term memory, 信息首先到达短期记忆处理中心，

　　where it's available from anywhere from a few seconds to a couple of minutes. 这是一个存储几秒钟到几分钟记忆的区域。

　　It's then transferred to long-term memory through areas such as the hippocampus, 然后，信息通过海马体等区域被转成长期记忆，

　　and finally to several storage regions across the brain. 最终保存到大脑几个记忆储存区域。

　　Neurons throughout the brain communicate at dedicated sites called synapses using specialized neurotransmitters. 大脑里的神经元在专门地点交流，这些地点利用的是特殊神经传递的突触。

　　If two neurons communicate repeatedly, a remarkable thing happens: 如果两个神经元重复连接，就会发生一件重要的事：

　　the efficiency of communication between them increases. 两者间的交流变得更加有效率。

　　This process, called long term potentiation, 这个过程被称为长程增强效应，

　　is considered to be a mechanism by which memories are stored long-term, but how do some memories get lost? 它被认为是记忆被长期储存的机制，但是，有些记忆怎么会丢失呢？

　　Age is one factor. 年龄是个影响因素。

　　As we get older, synapses begin to falter and weaken, affecting how easily we can retrieve memories. 随着我们年龄增大，神经元突触开始衰退和变弱，影响了我们读取记忆的难易程度。

　　Scientists have several theories about what's behind this deterioration, 科学家们有几个原理解释了这种退化背后的原因。

　　from actual brain shrinkage, the hippocampus loses 5% of its neurons every decade 从真正的大脑萎缩开始，海马体每十年失去5%的神经元，

　　for a total loss of 20% by the time you're 80 years old to the drop in the production of neurotransmitters, 当你80岁的时候，你一共失去20%的神经元，这导致神经传递产物的下降，

　　like acetylcholine, which is vital to learning and memory. 比如对学习和记忆至关重要的乙酰胆碱。

　　These changes seem to affect how people retrieve stored information. 这些改变可能影响人们读取那些存储的信息。

　　Age also affects our memory-making abilities. 年龄也影响了我们产生记忆的能力。

　　Memories are encoded most strongly when we're paying attention, 当我们集中精力、完全投入的时候，

　　when we're deeply engaged, and when information is meaningful to us. 当信息对我们来说非常重要的时候，深刻记忆就会生成。

　　Mental and physical health problems, which tend to increase as we age,  当年纪变大，精神和身体的健康问题就变得越来越多，

　　interfere with our ability to pay attention, and thus act as memory thieves. 干扰我们注意力的集中度，也因此成为我们记忆的小偷。