To test the effectiveness of the drug, researchers created bad memories by giving mice electric shocks while a loud noise was played. Over time, the creatures learned to associate the sound with the shock, and hearing the noise alone was enough to make them freeze. But when they were given a drug called brain-derived neurotrophic factor, or BDNF, they lost their fear.

　　为了测试此种药物的效果，研究人员制造噪音，同时电击小白鼠，以此制造小白鼠的“痛苦记忆”。一段时间后，光是听到噪音就足以让这些小动物们害怕到“僵住”。但是当给他们使用一种含有脑源性神经营养因子的药物后，恐惧消失了。

　　BDNF is naturally produced in the brain, and experiments showed that rats with a shortage of the compound struggled to overwrite bad memories. Failure to overwrite fear is thought to contribute to many psychological problems.

　　据了解，脑源性神经营养因子是大脑产生的一种物质，实验表明缺乏这种物质的小白鼠很难消除“痛苦回忆”。而不能消除痛苦则会导致许多心理疾病。