Old Memories Appear to Fade to Make Room for Stronger Ones
舊記憶淡出 更強的進駐
By Pam Belluck

What happens to forgotten memories – say, old computer passwords, friends’ old phone numbers?
原來記得的事，比方說舊的電腦密碼和朋友的舊電話號碼，忘到哪兒去了？

Scientists have long held two different theories. One is that older memories do not diminish but do not diminish but get obscured by new memories. The other is that older memories become weaker, that pulling to mind new passwords or phone numbers degrades old recollections so they do not interfere.
科學界一向有兩種理論。一是舊記憶並未減弱，是被新記憶搞模糊了。另一則為舊記憶會變弱，放在心上的新密碼或電話號碼削弱了舊記憶。

If old memories stay strong and are merely obscured by new ones, they may be easier to recover. That could be positive for someone trying to remember an acquaintance’s name, but difficult for someone trying to lessen memories of abuse.
如果舊記憶強度未減，只是被新記憶搞模糊了，也許比較容易恢復。這對想記起熟人名字的人也許是好事，而想要拋開受虐記憶的人可就不好過了。

Now, a study claims to show that people’s ability to remember something and the pattern of brain activity that cognition shows appear to diminish when a competing memory gets stronger.
現在，一項研究宣稱能展示，當競爭的記憶較強時，人們記得某件事物的能力，以及認知顯示的腦部活動模式，顯然減弱。

Using brain scans, authors of the study, published in the journal Nature Neuroscience, appear to have identified neural fingerprints of specific memories, distinguishing brain activity patterns produced when viewing a picture of a necklace, say, from a picture of binoculars. The experiment, conducted by scientists in Birmingham and Cambridge, England, involved several stages with 24 participants first trained to associate words to two unrelated pictures. They then completed several tasks in a brain scanner. First, they were shown a cue word and asked to recall the image they had been trained to link to that word so that image would become the dominant memory.
研究發表在「自然神經科學」期刊，作者利用腦部掃描似已找到特定記憶的神經指紋，區分看一張項鍊的照片，與看一張雙目望遠鏡的照片，產生的腦部活動模式有何不同。由英格蘭的伯明罕和劍橋的科學家進行的實驗分幾個階段，24名參與者先被訓練把一些字與兩張不相關的照片產生連結。接著他們在腦部掃描機內完成任務。首先，給他們看一個提示的字，並要求他們回憶他們被訓練與那個字相連的圖像，讓那個圖像變成主要的記憶。

For example, if “sand” was associated first with Marilyn Monroe and then with a hat, scientists wanted participants to indicate that they were recalling Monroe. Each cue word was sprinkled into the test four times, so scientists could see if participants looking at the word “sand” increasingly chose Monroe over the competing memory of the hat. They did.
例如，如果「沙」這個字先與瑪麗蓮夢露相連，再與一頂帽子相連，科學家要參與者表示他們記得夢露。每個提示字在測驗中出現四次，科學家可以觀察，參與者是否看到「沙」這個字，選擇夢露的次數增多，而不是選擇與之競爭的帽子的次數增多。他們的確如此。

Next, scientists wanted to see what happened to the hat memory. They showed people two different pictures of Monroe and two hat pictures, asking them which version they had been trained to recognize. If the hat memory had not degraded, scientists reasoned, people would pick the right hat as often as they picked the right Monroe.
接著，科學家想看看帽子的記憶到哪兒去了。他們給參與者看兩張不同的夢露照片與兩張帽子照片，問他們被訓練認識哪一張。科學家推論，如果帽子的記憶未減弱，人們選擇正確帽子的次數，會與選擇正確夢露的次數一樣多。

To measure success, scientists devised a standard: how well people recalled the correct picture of an unrelated famous person or object. These were images they had been shown early on but would have no reason to recall well because they had not been cued to remember them. For faces, a standard was two pictures of Albert Einstein, and people picked the right Monroe about as well as they picked the right Einstein. For objects, a standard was two pictures of goggles. People were better at remembered the correct goggles than they were the correct hat.
科學家設計了一種測量成功的標準：人們能正確記得不相關的名人或物件照片的能力有多強。他們之前看過一些圖像，但沒有被提示要去記住，因此沒有理由記得清楚。在臉孔方面，一種標準是兩張愛因斯坦的照片，人們選對夢露照片的次數，與選對愛因斯坦照片的次數相同。在物件方面，一種標準是兩張雙目望遠鏡的照片。人們比較記得正確的望遠鏡，比較不記得正確的帽子。

Brice Kuhl, a professor at New York University who was not involved in the study, said that those competing recollections get weaker. “You might think it would be better or at least the same” as the standard pictures “because you’ve just actually had a reminder for the hat, the cue word.” That people had trouble remembering the right hat, he said, makes it less likely the hat memory was just obscured by Monroe. “It’s pretty hard to think that your inability to pick the right hat has anything to do with Marilyn Monroe at that point.”
未參與實驗的紐約大學教授布萊斯．柯爾說，那些競爭的記憶變弱了。「你也許認為會記得更清楚，或至少與標準照片相同，因為你剛剛實際上有被提醒帽子，那個提示字。」他說，人們記不得正確的帽子，不太可能是帽子的記憶只是被夢露搞模糊了。「很難想像在那時間點上，你無法選出正確的帽子與瑪麗蓮夢露有任何關係。」

Next, researchers obtained a “neural signature” in the prefrontal cortex as participants viewed each picture six times, said a study author, Maria Wimber. Matching those signatures to brain patterns from the cue word test, researchers saw that when the word “sand” was first shown, people’s brains reflected both Monroe and hat patterns, but with subsequent “sand” cues, their brains produced fewer hat traces.
研究報告作者之一瑪莉亞．溫姆柏說，接下來參與者每張照片看六遍，研究人員在大腦前額葉皮質區取得「神經簽名」。把這些簽名與提示字測驗的腦部模式比對，研究人員看到，當「沙」字第一次出現時，人們的腦部反映夢露和帽子模式，但接下來「沙」提示字再出現時，他們腦部產生較少帽子的蹤跡。

“We watched the memories being suppressed, actively degraded,” Dr. Wimber said. “It’s not just that the target memories get stronger; the other memories get weaker.”
溫姆柏說：「我們看著記憶被壓抑，有效地減弱。不只是目標記憶變強；其他記憶也變弱。」

That interpretation is not necessarily accepted by proponents of memory overshadowing and similar theories.
支持記憶掩蓋理論和類似理論的人，未必會接受此一解釋。

“I buy that the brain patterns becomes less and less similar to the hat,” said David E. Huber of the University of Massachusetts, Amherst. “It’s also possible that increasingly, you’ve learned to think about something other than the hat.”
阿默斯特麻州大學的大衛．胡伯說：「我接受腦部模式對帽子愈來愈不熟悉。也有可能，逐漸地，你學會想到帽子以外的東西。」

Kenneth Norman, a neuroscientist at Princeton University in New Jersey, who was not involved in the study, said therapeutic applications of memory weakening could include extinguishing fears of something like snakes. “If you show someone a cartoon image of a snake, cute, funny,” he said, “in the moment you’ve caused liking the snake to overcome not liking the snake. If you want to actually weaken a memory, what you need to do is flush it out. It’s the process of the memory coming to mind as a competitor, but losing the competition.”
未參與研究的新澤西普林斯頓大學的神經學家肯尼斯．諾曼說，記憶減弱應用在治療上，可能包含根除對某些事物的恐懼，像是蛇。他說：「你若給某人看一條蛇的卡通圖片，可愛、好笑，當下你已造成喜歡蛇勝過不喜歡蛇。你若要實際上削弱一種記憶，你需要做的是把它沖掉。這是記憶以競爭者的身分進入心裡，但輸掉競賽的過程。」

原文參照：
http://www.nytimes.com/2015/03/20/business/international/japans-recovery-is-complicated-by-a-decline-in-household-savings.html

2015-04-07聯合報/G5版/UNITED DAILY NEWS 田思怡譯 原文參見紐時週報十版下