视听｜记忆：如何形成又如何消失

大家是否注意到，对于过去许久的重要时刻，人们往往记忆犹新，而对于近期的琐碎细节，人们却难以回忆——这样的反差中潜藏着怎样的秘密？Catharine Young的教育短片将带我们一探究竟。

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How Memories Form and How We Lose Them

里面一

Think back to a really vivid memory. Got it? Okay, now try to remember what you had for lunch three weeks ago. That second memory probably isn't as strong, but why not? Why do we remember some things, and not others? And why do memories eventually fade?

Let's look at how memories form in the first place. When you experience something, like dialing a phone number, the experience is converted into a pulse of electrical energy that zips along a network of neurons. Information first lands in short term memory, where it's available from anywhere from a few seconds to a couple of minutes. It's then transferred to long-term memory through areas such as the hippocampus①, and finally to several storage regions across the brain. 

① hippocampus /ˌhɪpəʊˈkæmpəs/ n. either of the two areas of the brain thought to be the centre of emotion and memory 海马（大脑中被认为是感情和记忆中心的部分）

Neurons throughout the brain communicate at dedicated sites called synapses using specialized neurotransmitters②. If two neurons communicate repeatedly, a remarkable thing happens: the efficiency of communication between them increases. This process, called long term potentiation, is considered to be a mechanism by which memories are stored long-term, but how do some memories get lost? 

② neurotransmitter /ˌnjʊərəʊtrænzˈmɪtə/ n. a chemical by which a nerve cell communicates with another nerve cell or with a muscle 神经传递素

Age is one factor. As we get older, synapses begin to falter and weaken, affecting how easily we can retrieve memories. Scientists have several theories about what's behind this deterioration③, from actual brain shrinkage, the hippocampus loses 5% of its neurons every decade for a total loss of 20% by the time you're 80 years old to the drop in the production of neurotransmitters, like acetylcholine④, which is vital to learning and memory. These changes seem to affect how people retrieve stored information.

③ deterioration /dɪˌtɪriəˈreɪʃn/ n. the fact or process of becoming worse 恶化

④ acetylcholine /ˌæsɪtaɪlˈkəʊliːn/ n. a chemical substance secreted at the ends of many nerve fibres, esp in the autonomic nervous system, and responsible for the transmission of nervous impulses. Formula: CH3CO2(CH2)2N (CH3)3 + 乙醯胆碱

Age also affects our memory-making abilities. Memories are encoded most strongly when we're paying attention, when we're deeply engaged, and when information is meaningful to us. Mental and physical health problems, which tend to increase as we age, interfere with our ability to pay attention, and thus act as memory thieves.

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Another leading cause of memory problems is chronic⑤ stress. When we're constantly overloaded with work and personal responsibilities, our bodies are on hyperalert. This response has evolved from the physiological mechanism designed to make sure we can survive in a crisis. Stress chemicals help mobilize energy and increase alertness. 

⑤ chronic /ˈkrɒnɪk/ adj. A chronic illness or disability lasts for a very long time. 慢性的; 长期的

However, with chronic stress our bodies become flooded with these chemicals, resulting in a loss of brain cells and an inability to form new ones, which affects our ability to retain new information. 

Depression is another culprit⑥. People who are depressed are 40% more likely to develop memory problems. Low levels of serotonin⑦, a neurotransmitter connected to arousal⑧, may make depressed individuals less attentive to new information. Dwelling on sad events in the past, another symptom of depression, makes it difficult to pay attention to the present, affecting the ability to store short-term memories. 

⑥ culprit /ˈkʌlprɪt/ n. When you are talking about a problem or bad situation, you can refer to its cause as the culprit. （造成问题或麻烦的）原因

⑦ serotonin /ˌsɛrəˈtəʊnɪn/ n. Serotonin is a chemical produced naturally in your brain that affects the way you feel, for example, making you feel happier, calmer, or less hungry. 血清素

⑧ arousal /əˈraʊzəl/ n. Arousal is a state in which you feel excited or very alert, for example, as a result of fear, stress, or anger. 兴奋

Isolation, which is tied to depression, is another memory thief. A study by the Harvard School of Public Health found that older people with high levels of social integration had a slower rate of memory decline over a six-year period. The exact reason remains unclear, but experts suspect that social interaction gives our brain a mental workout. 

Just like muscle strength, we have to use our brain or risk losing it. But don't despair. There are several steps you can take to aid your brain in preserving your memories.

☞ Make sure you keep physically active. Increased blood flow to the brain is helpful. 

☞ And eat well. Your brain needs all the right nutrients to keep functioning correctly.

☞ And finally, give your brain a workout. Exposing your brain to challenges, like learning a new language, is one of the best defenses for keeping your memories intact⑩.

⑩ intact /ɪnˈtækt/ adj. Something that is intact is complete and has not been damaged or changed. 完整无缺的

文章来源：TED-Ed官网

大连外国语大学高级翻译学院实习生

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