21 What would be the best title of this passage?
(A) Possible Causes of Memory Loss.
(B) Post-traumatic Stress Disorder.
(C) Studies of Trauma in Humans.
(D) Suppressing Fearful Memories.

Suppressing Fearful Memories.抑制恐懼的記憶。

Post-traumatic stress disorder創傷後壓力症候群 is a malady of memory. Sufferers are often haunted by recurrent經常性的 nightmares, distressing thoughts and flashbacks so intense in color, smell and sound that they feel as if they are reliving重溫 the trauma.
創傷後壓力症候群是一種記憶疾病。 患者經常被反復出現的噩夢、令人痛苦的想法和倒敘所困擾，這些回憶在顏色、氣味和聲音上如此強烈，以至於他們感覺好像正在重溫創傷。

But what if these unbearable memories could be selectively erased? Sheena Josselyn, a professor of physiology and psychology, who studies how the brain encodes, stores and uses information, is intrigued感興趣 by the idea and has been investigating how to “silence” memories --make them temporarily inaccessible-- in mice. She thinks it’s possible that a variation of this technique could one day help treat post-traumatic stress disorder in humans. 
但如果這些難以忍受的記憶可以被選擇性地抹去呢？ 研究大腦如何編碼、儲存和使用信息的生理學和心理學教授 Sheena Josselyn 對這個想法很感興趣，並一直在研究如何在老鼠身上“沉默”記憶——讓它們暫時無法進入。 她認為有朝一日這種技術的變體可能有助於治療人類的創傷後壓力症候群。

Studies with mice have found that although their brains contain billions of neurons, only a few are necessary to form a fearful memory. Researchers working with mice began by teaching them to fear a tone: when it sounds, they feel a mild shock to their feet (not to hurt them, just to scare them). The next time the mice hear the tone, they crouch and freeze, signaling fear.
對小鼠的研究發現，儘管它們的大腦包含數十億個神經元，但只需要少數幾個就可以形成可怕的記憶。 與老鼠打交道的研究人員首先教它們害怕一種音調：當它響起時，它們的腳會感到輕微的震動（不是為了傷害它們，只是為了嚇唬它們）。 下次老鼠聽到這種聲音時，它們會蹲下並僵住，表示害怕。

The researchers discovered that they could trigger the memory of that fear even without presenting the tone. They did this by stimulating the small group of nerve cells holding that memory through a technology called optogenetics. Using the same technology, they found they could also suppress the fearful memory. With optogenetics, scientists insert proteins into neurons to make them sensitive to light. Depending on the type of protein and color of light used, these cells can then be activated or deactivated by shining pulses of the light directly into the brain.
研究人員發現，即使不說出語調，他們也能觸發對恐懼的記憶。 他們通過一種叫做光遺傳學的技術刺激了一小群持有這種記憶的神經細胞來做到這一點。 使用同樣的技術，他們發現他們也可以抑制可怕的記憶。 通過光遺傳學，科學家們將蛋白質插入神經元，使它們對光敏感。 根據蛋白質的類型和所用光的顏色，這些細胞可以通過將光脈衝直接照射到大腦中來激活或停用。