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.
回想一段很鮮活的回憶。想到了嗎？好。現在試著想想你三個禮拜前吃了什麼午餐。第二個記憶大概不會印象很深，但為什麼呢？為什麼我們記得某些事情，卻忘掉某些事情呢？為什麼回憶最終會模糊消失呢？讓我們先看看記憶在一開始是怎麼形成的。
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 hippocampus and finally to several storage regions across the brain.
當你經歷某件事，例如像是撥電話號碼，這個經驗會轉換成一道電能脈衝，快速沿著神經元網路移動。資訊首先停留在短期記憶區，留存幾秒或幾分鐘。接著會透過像是海馬迴的部位轉換成長期記憶，最後到達整個頭腦裡的幾個記憶儲存區域。
Neurons throughout the brain communicate at dedicated sites called synapses, using specialized neurotransmitters. 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.
大腦裡的神經元在稱作「突觸」的特定區塊內相互聯繫，運用專門的神經傳導物質。如果兩個神經元反覆聯繫，奇妙的事情就會發生：兩者之間的聯繫效率會提高。這個過程就稱作「長期增強作用」，被認為是記憶儲存在長期記憶裡的一種機制。
But how do some memories get lost? 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 deterioration, from actual brain shrinkage, the hippocampus loses five percent of its neurons every decade for a total loss of 20 percent by the time you're 80 years old, to the drop in the production of neurotransmitters like acetylcholine, which is vital to learning and memory. These changes seem to affect how people retrieve stored information.
但有些記憶為什麼會消失呢？年紀是一個因素。隨著我們年齡增長，突觸會開始退化與衰弱，影響我們找回記憶的能力。針對這種退化，科學家已有幾個理論，其中之一是實際的腦部萎縮，海馬迴每十年會失去百分之五的神經元，到了八十歲，你總共會失去百分之二十的神經元，另一理論則是如乙醯膽鹼等神經傳導物質的生產降低，這種物質對對學習與記憶有很重要的影響。這些變化似乎會影響人們找回儲存資訊的能力。
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.
年紀也會影響記憶生成的能力。記憶編碼最為強烈有效的時刻是我們專心一志、全心投入或資訊意義非凡的時候。心理與生理問題通常會隨著年齡增長而增加，也會影響我們專注的能力，就如同記憶的小偷一樣。
Another leading cause of memory problems is chronic 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 any crisis. Stress chemicals help mobilize energy and increase alertness. 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.
另一個主要影響記憶的問題是長期壓力。若我們長期負擔過多工作和個人責任，身體會處於高度警覺狀態。這種反應由生理機制演化而成，為了確保我們能在任何危機下生存。壓力化學物質幫助我們驅動能量和增加危機感。然而，若有長期壓力，身體會被這些化學物質填滿，導致腦細胞損失，失去形成新細胞的能力，進而影響我們保留新資訊的能力。
Depression is another culprit. People who are depressed are 40 percent more likely to develop memory problems. Low levels of serotonin, a neurotransmitter connected to arousal, 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.
憂鬱也是另一個罪魁禍首。有憂鬱情緒的人擁有記憶問題的機率比一般人高百分之四十。憂鬱症患者血清素濃度較低，而與快感相關的血清素是種神經傳導物質，血清素不足可能會使憂鬱的人較不留心新的資訊。沉浸在過去的悲傷中也是憂鬱的另一個症狀，使患者很難專注於當下，影響儲存短期記憶的能力。
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.
孤獨感也與憂鬱息息相關，可稱作另一種記憶小偷。哈佛公共衛生學院的一個研究發現，六年的研究期間中，社交頻率高的老年者記憶減退的速度較慢。確切的原因雖未知，但專家懷疑社交互動也會給予大腦智力上的活動。就像肌力一樣，我們必須運用大腦，否則就有失去功能的風險。
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 intact.
但不要絕望。以下是一些你可以幫助腦袋保存記憶的方式。一定要保持身體活動。增加大腦血液流動是有助益的。還要吃得好。你的頭腦需要對的營養保持正常運作。最後，讓大腦活動。給大腦多一點挑戰，像是學習新語言，這是種保持記憶完整最好的防衛方式。
- 「沉浸、老是想著」- dwell on
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.
沉浸在過去的悲傷中也是憂鬱的另一個症狀，使患者很難專注於當下，影響儲存短期記憶的能力。
