美科學家發現新療法 清除改寫記憶或將成真

Roadside bombs, childhood abuse, car accidents—they form memories that can shape (and damage) us for a lifetime. Now, a handful of studies have shown that we’re on the verge of erasing and even rewriting memories. The hope is that this research will lead to medical treatments, especially for addiction and post-traumatic stress disorder (PTSD).

Researchers have known for decades that memories are unreliable. They’re particularly adjustable when actively recalled because at that point they’re pulled out of a stable molecular state. Last spring, scientists published a study performed at the University of Washington in which adult volunteers completed a survey about their eating and drinking habits before age 16. A week later, they were given personalized analyses of their answers that stated—falsely—that they had gotten sick from rum or vodka as a teen. One in five not only didn’t notice the lie, but also recalled false memories about it and rated that beverage as less desirable than they had before.

Studies like these point to possible treatments for mental health problems. Both PTSD and addiction disorders hinge on memories that can trigger problematic behaviors, such as crippling fear caused by loud noises or cravings brought about by the sight of drug paraphernalia.

Several studies have found chemical compounds that can be used to subdue or even delete memories in mice (and maybe someday in people). In June, a report led by an Emory University researcher showed that SR-8993, a drug that acts on the brain’s opioid receptors, can prevent a fear memory from forming. Researchers strapped mice to a wooden board for two hours—a stressful experience that later gave them a heightened sense of fear similar to PTSD. But mice given SR-8993 before or after the stressful incident were less likely to end up this way.

Another study identified a drug, Latrunculin A, that can erase memories days later. The researchers trained rodents to consume methamphetamine in an environment with distinctive visual, tactile, and scent cues such as black walls, gridded floors, and the scent of vanilla or peppermint. Rodents that were injected with Latrunculin A two days later didn’t seek out meth when returned to that environment, but others did.

To make more targeted treatments, researchers will ultimately need to understand how the brain’s neurons encode each memory. Last year, Susumu Tonegawa at the Massachusetts Institute of Technology reported that individual memories in mice leave telltale molecular signatures in the brain’s hippocampus region. In July, his group caused mice to falsely associate an old memory with a new context—essentially creating a false memory.

The idea of scientists manipulating memory does, naturally, sound a bit creepy. But it also points to some possible good: treatment for millions of people tormented by real memories. And that’s something worth remembering.路邊炸彈、童年受虐、慘烈車禍……這些可怕的場景會成爲記憶，然後帶來一生的陰影。據美國媒體報道，現有研究顯示清除甚至改寫記憶即將成爲可能，這將爲醫治上癮和創傷後應激障礙（PTSD）等心理病症提供一種全新的治療方法。

早在幾十年前，科學家就發現記憶是不可靠的。尤其當人們主動喚起某種記憶時，該記憶被迫脫離一種穩定的分子狀態，進而變得更加容易調整。去年春天，美國科學家公佈了在華盛頓大學進行的一項研究成果。在此研究中，多名成年志願者就其16歲之前的飲食習慣填寫調查問卷。一週後，他們各自收到一份個性化分析報告，其中故意加入他們年少時曾因飲用朗姆酒或者伏特加酒而患病的內容。然而令人意外的是，1/5的志願者不僅沒有察覺到報告中的錯誤，他們還回想起當時並不存在的糟糕場景。並且，這些志願者與之前相比，變得對酒水飲料更加沒有興趣。

諸如此類的研究爲治療心理健康疾病提供了一個全新的視角。包括上癮和創傷後應激障礙在內，類似的心理疾病都與能夠激發問題行爲的記憶緊密相關，例如噪音會使患者感到恐懼、看到吸毒用具則會勾起毒癮。

還有一些研究發現，化合物可以被用來抑制甚至消除老鼠的負面記憶。今年6月，美國埃默裏大學的研究人員發佈了一篇研究報告，報告稱一種名爲“SR-8993”的藥物可作用於大腦中的阿片樣物質受體，從而阻止形成恐懼記憶。實驗過程中，研究人員把老鼠捆綁在木板上長達兩個小時，對於受試老鼠而言，這是一種可怕的經歷，它們會產生類似創傷後應激障礙的心理恐懼。而服用了“SR-8993”藥物的老鼠，產生恐懼心理的機率比沒有服用藥物的老鼠要低。

另一種名爲“拉春庫林A”的藥物，則能夠在事後清除記憶。在這個實驗中，科學家對受試老鼠進行訓練，令其一旦處於特定的幽閉環境就會食用冰毒。兩天後，受訓成功的老鼠被注射了“拉春庫林A”藥物，當它們被再次放入幽閉環境時，卻沒有食用病毒。而那些沒有注射的老鼠則如常食用。

爲了令治療方法更具針對性，科學家還需要了解掌握大腦神經元究竟是如何生成記憶的。去年，麻省理工學院教授、1987年諾貝爾生理或醫學獎得主利根川進發現，老鼠的個體記憶會在大腦海馬區留下分子標籤。今年7月，利根川進研究團隊成功在老鼠的舊記憶與新內容間建立起虛構的聯繫，從本質上講，這相當於創造了一個虛假的新記憶。

由此看來，儘管操縱記憶聽上去有些令人毛骨悚然，但科學家的這種嘗試是有益的：因真實記憶而備受折磨的數百萬心理疾病患者或將因此痊癒。