How memories form and fade

记忆如何形成并消失

上海译锐翻译   2019-9-10     13:20

Strong memories are encoded by teams of neurons working together in synchrony

深刻的记忆由许多组协同工作的神经元进行编码

Why is it that you can remember the name of your childhood best friend that you haven't seen in years yet easily forget the name of a person you just met a moment ago? In other words, why are some memories stable over decades, while others fade within minutes?

为什么即使多年没有见面，你也能够记得儿时最好朋友的名字？为什么和那个人见面才没多久，你就已经忘了他叫什么？换句话说，为什么有些记忆能够在数十年中留存，为什么有些记忆在几分钟内就会消失？

Using mouse models, Caltech researchers have now determined that strong, stable memories are encoded by "teams" of neurons all firing in synchrony, providing redundancy that enables these memories to persist over time. The research has implications for understanding how memory might be affected after brain damage, such as by strokes or Alzheimer's disease.

加州理工大学的研究人员通过利用老鼠模型发现，强烈持久的记忆由数组同时放电的神经元进行编码，这一过程会提供冗余并能够使这些记忆留存下来。研究有助于我们理解大脑在受到损害，比如中风或阿兹海默症后，大脑中的记忆可能会受到影响。

The work was done in the laboratory of Carlos Lois, research professor of biology, and is described in a paper that appears in the August 23 of the journal Science. Lois is also an affiliated faculty member of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech.

这项工作在生物研究教授Carlos Lois的实验室内进行，研究工作将以论文形式在8月23日的期刊《科学》中发表。Lois同时也是加州理工大学陈天桥雒芊芊脑科学研究院的附属教职人员。

Led by postdoctoral scholar Walter Gonzalez, the team developed a test to examine mice's neural activity as they learn about and remember a new place. In the test, a mouse was placed in a straight enclosure, about 5 feet long with white walls. Unique symbols marked different locations along the walls -- for example, a bold plus sign near the right-most end and an angled slash near the center. Sugar water (a treat for mice) was placed at either end of the track. While the mouse explored, the researchers measured the activity of specific neurons in the mouse hippocampus (the region of the brain where new memories are formed) that are known to encode for places.

在博士后Walter Gonzalez的带领下，研究团队制定出一个实验，以测定老鼠在了解并记住一个新地方后的神经活动。在实验中，老鼠被放在一个直筒型的围场中，围场四周为白色的墙，长度大约为5英尺。墙上独特的符号代表不同的位置-比如，围场最右边的尽头附近有粗体的加号，靠近中心位置则是带一定角度的斜线。糖水（给老鼠享用）被放在通道的任何一头。当老鼠开始探索时，研究人员测量老鼠海马体（大脑中形成新记忆的区域并会对地点进行编码）中特定神经元的活动。

hippocampus：海马体

When an animal was initially placed in the track, it was unsure of what to do and wandered left and right until it came across the sugar water. In these cases, single neurons were activated when the mouse took notice of a symbol on the wall. But over multiple experiences with the track, the mouse became familiar with it and remembered the locations of the sugar. As the mouse became more familiar, more and more neurons were activated in synchrony by seeing each symbol on the wall. Essentially, the mouse was recognizing where it was with respect to each unique symbol.

当老鼠被第一次放入后，它并不知道要做什么，它会朝左边和右边漫无目的地乱走直到遇见糖水。在这种情况下，当老鼠注意到墙壁上的符号时，单个的神经元就被激活了。但是，随着在通道内多次实践，老鼠开始熟悉这里并记住了糖水的位置。随着老鼠对周围变得越来越熟悉，当老鼠看到墙壁上的每个符号后，越来越多的神经元被同时激活。最后，老鼠会根据单独的符号认出自己所在的位置。

To study how memories fade over time, the researchers then withheld the mice from the track for up to 20 days. Upon returning to the track after this break, mice that had formed strong memories encoded by higher numbers of neurons remembered the task quickly. Even though some neurons showed different activity, the mouse's memory of the track was clearly identifiable when analyzing the activity of large groups of neurons. In other words, using groups of neurons enables the brain to have redundancy and still recall memories even if some of the original neurons fall silent or are damaged.

为了研究记忆如何随着时间慢慢淡化，研究人员将老鼠与通道隔离多达20天。在经过隔离并再次返回通道后，老鼠凭借由更多神经元所编码的深刻记忆迅速回忆起了任务。即使某些神经元显出不同的活性，当分析大量神经元的活性时，老鼠有关通道的记忆很容易辨别。换句话说，使用大量神经元能使大脑产生冗余并仍旧能够在某些原始神经元沉寂或受损后唤起记忆。

Gonzalez explains: "Imagine you have a long and complicated story to tell. In order to preserve the story, you could tell it to five of your friends and then occasionally get together with all of them to re-tell the story and help each other fill in any gaps that an individual had forgotten. Additionally, each time you re-tell the story, you could bring new friends to learn and therefore help preserve it and strengthen the memory. In an analogous way, your own neurons help each other out to encode memories that will persist over time."

Gonzalez解释道：“设想你要讲一个又长又复杂的故事。为了记住这个故事，你可以向5位朋友讲这个故事，然后把5位朋友聚在一起并把这个故事再讲一遍。当忘记故事中的某个细节时，朋友可以相互帮助把这个细节补充完整。此外，每次你重新讲这个故事时，你可以请新朋友来听这个故事并从而保留并强化记忆。通过类比的方式，你自己的神经元可以通过互相帮助来编码记忆并使其长期保留下来。”

Memory is so fundamental to human behavior that any impairment to memory can severely impact our daily life. Memory loss that occurs as part of normal aging can be a significant handicap for senior citizens. Moreover, memory loss caused by several diseases, most notably Alzheimer's, has devastating consequences that can interfere with the most basic routines including recognizing relatives or remembering the way back home. This work suggests that memories might fade more rapidly as we age because a memory is encoded by fewer neurons, and if any of these neurons fail, the memory is lost. The study suggests that one day, designing treatments that could boost the recruitment of a higher number of neurons to encode a memory could help prevent memory loss.

记忆对于人类行为至关重要，以至于任何记忆损害都会严重影响我们的日常生活。随着步入老年而出现的记忆缺失是老年人所面对的重大障碍。此外，由于数种疾病所导致的记忆缺失，最为人们熟知的就是阿兹海默症，会产生破坏性极大的后果，这一后果会影响最基本的日常行为，包括认识家人或记住回家的路。这一方式表明，随着我们步入老年，记忆可能会迅速衰退，因此对记忆进行编码的神经元变得更少了。此外，如果任何神经元无法工作，记忆就丢失了。研究表明，某一天，通过一种可以促进大量神经元加入并对记忆进行编码的治疗能帮助人们预防失忆。

"For years, people have known that the more you practice an action, the better chance that you will remember it later," says Lois. "We now think that this is likely, because the more you practice an action, the higher the number of neurons that are encoding the action. The conventional theories about memory storage postulate that making a memory more stable requires the strengthening of the connections to an individual neuron. Our results suggest that increasing the number of neurons that encode the same memory enables the memory to persist for longer."

“多年来，人们已经知道，对于某件事，你做得越多，你就越有可能在后面也记得。现在，我们认为，这很可能是因为，当你做得越多，就会有越多的神经元对行为进行编码。传统的关于记忆存储的理论假设，要想使记忆更加持久，需要加强与单个神经元之间的联系。我们的结果表明，编码相同记忆的神经元数量越多，记忆就会越持久。”

来源：科学日报   编辑：Susan