Some things are hard to remember. Others are hard to forget—especially things that are traumatic. But kids, it turns out, are better than adults at forgetting the bad stuff. Now scientists think they know why. According to an animal study in the September 4th issue of the journal Science, the brains of adults erect¹ physical barriers that keep painful memories intact.

As adults, events that emotionally disturb us tend to get seared into our brains. And those memories can resurface, causing anxiety, fear and even post-traumatic stress disorder². But young brains are much more resilient—and can even erase³ unpleasant memories.

To get a better handle on this youthful forgetting, scientists studied the brains of young and old rats. They found that in adult brains, a physical net forms around certain cells in the amygdala, a structure associated with emotional memories. Adults that had been trained to associate a mild foot shock with a specific sound would flinch⁴ when they just heard the sound. But using a drug to dissolve this barrier restored the older rats’ ability to extinguish fearful memories. So rats that got the net-busting treatment stayed calm when they heard the sound.

One of the few instances where a net loss is a real gain.有些事情很难记住。有些事情——尤其是那些带来巨大创伤的事情——则很难忘记。不过，有结果发现在忘记糟糕事情方面，小孩子要比成年人做得更好。现在科学 家们认为他们找到了答案。根据发表在9月4日《科学》（Science）杂志上的一项动物研究结果，成年人的大脑会竖立起有形的障碍，使得过去痛苦的记忆 保持原封不动。

对于成年人，那些在情感上扰乱我们的事情易于深深印在我们的大脑内。而且那些记忆能重现出来，从而导致我们焦虑、害怕甚至让我们患上创伤后精神紧张性障碍 （post-traumatic stress disorder）。但是年轻大脑的“柔韧性”要好的多---它们甚至能抹去那些不快的记忆。

科学家们为了更好的理解这种“年轻的遗忘”现象，他们研究了年轻和年老老鼠的大脑。科学家们发现，在成年老鼠大脑的杏仁核（杏仁核与情感记忆有关）的某些 细胞周围形成了一种有形的网。科学家对成年老鼠进行了训练，使得这些老鼠能把轻微的足部电击和一种特定的声音联系在一起，一旦这些老鼠听到这种声音，它们 就会退缩。但是当使用一种药物去掉这种障碍后，这些成年老鼠又恢复了它们消除可怕记忆的能力。因此对老鼠进行“消除障碍网”处理后，当这些老鼠在听到这种 特定声音的时候，它们仍然保持安静的状态。

这是完全失去变为真正获得的为数不多的例子之一。