Why don't we remember being babies?
为什么我们不记得自己是婴儿了？

Your mother's smile as you say your first word or the smell of the candles on your second birthday cake are memories many people would love to hold onto. But almost nobody can recall memories from very early childhood — a phenomenon known as infantile amnesia.
当你说出第一句话时母亲的微笑，或者你第二次生日时蛋糕上蜡烛的香味，都是许多人希望留住的记忆。但是，几乎没有人能回忆起幼年时期的记忆--这种现象被称为婴儿遗忘症。

So why do we tend to forget these very early memories? It's not because we don't retain information as young children. Rather, it's likely because at that age our brains don't yet function in a way that bundles information into the complex neural patterns that we know as memories.
那么，为什么我们容易忘记这些幼年记忆呢？这并不是因为我们无法保留幼年时期的信息。相反，这很可能是因为在那个年龄，我们的大脑还不能将信息捆绑成复杂的神经模式，也就是我们所知的记忆。

Young children do remember facts in the moment, such as who their parents are, or that one must say "please" before mom will give you candy. This is called "semantic memory."
幼儿确实能记住当时的事实，比如父母是谁，或者必须说 "请 "妈妈才会给你糖吃。这就是所谓的 "语义记忆"。

Until sometime between the ages 2 and 4, however, children usually lack "episodic memory" — memory regarding the details of a specific event. Such memories are stored in several parts of the brain's surface, or "cortex." For example, memory of sound is processed in the auditory cortexes on the sides of the brain, while visual memory is managed by the visual cortex at the back. A region of the brain called the hippocampus ties all the scattered pieces together.
但是，在 2 到 4 岁之前，儿童通常缺乏 "情节记忆"--对具体事件细节的记忆。这种记忆存储在大脑表面的几个部分，即 "皮层"。例如，声音记忆由大脑两侧的听觉皮层处理，而视觉记忆则由后部的视觉皮层管理。大脑中一个名为海马体的区域将所有分散的部分连接在一起。

"If you think of your cortex as a flower bed, there are flowers all across the top of your head," Patricia Bauer, a professor of psychology at Emory University told Live Science. "The hippocampus, tucked very neatly in the middle of your brain, is responsible for pulling those all together and tying them in a bouquet." The memory is the bouquet — the neural pattern of linkages between the parts of the brain where a memory is stored.
"埃默里大学心理学教授帕特里夏-鲍尔对《生活科学》说："如果把大脑皮层想象成一个花坛，那么你的头顶上到处都是花朵。"海马体整齐地排列在大脑中央，负责将这些花朵组合在一起，并扎成花束。记忆就是花束--存储记忆的大脑各部分之间的神经联系模式。

Related: How accurate are our first childhood memories?
相关内容我们最初的童年记忆有多准确？

Kids may fail to record specific episodes until the 2-to-4 age range because that's when the hippocampus starts tying fragments of information together, Nora Newcombe, a professor of psychology at Temple University in Philadelphia told Live Science.
费城坦普尔大学（Temple University）心理学教授诺拉-纽科姆（Nora Newcombe）告诉《生活科学》。

Newcombe said that, for children younger than that age range, episodic memory may be unnecessarily complex at a time when a child is just learning how the world works.
纽科姆说，对于小于这个年龄段的儿童来说，在他们刚刚了解世界如何运作的时候，外显记忆可能会变得不必要的复杂。

"I think the primary goal of the first two years is to acquire semantic knowledge and from that point of view, episodic memory might actually be a distraction," Newcombe said. 
"纽科姆说："我认为，头两年的主要目标是获取语义知识，从这个角度来看，外显记忆实际上可能会分散注意力。

However, another theory suggests that we actually store these early memories as kids but struggle to recall them as adults. For example, a 2023 study, published in the journal Science Advances, found that "forgotten" childhood memories could be reinstated in adult mice by stimulating neural pathways that are relevant to specific memories with light. 
然而，另一种理论认为，我们在孩童时期实际上储存了这些早期记忆，但成年后却很难回忆起它们。例如，2023 年发表在《科学进展》（Science Advances）杂志上的一项研究发现，通过用光刺激与特定记忆相关的神经通路，可以恢复成年小鼠 "遗忘 "的童年记忆。

The authors of the study first set out to explore developmental factors that could influence infantile amnesia. They found that mice with characteristics of the neurodevelopmental condition autism spectrum disorder (ASD) were able to recall memories from their pup days.
这项研究的作者首先着手探索可能影响婴儿遗忘症的发育因素。他们发现，具有自闭症谱系障碍（ASD）神经发育特征的小鼠能够回忆起幼年时期的记忆。

Autism has many causes, but it has been previously linked to the over-activation of the mother's immune system during pregnancy. So, to make mice with ASD, the researchers stimulated the immune system of female mice during pregnancy.
自闭症的病因有很多，但以前曾被认为与母亲在怀孕期间过度激活免疫系统有关。因此，为了制造出患有自闭症的小鼠，研究人员在怀孕期间刺激了雌性小鼠的免疫系统。

This immune activation helped prevent the loss of early memories in these offspring by influencing the size and plasticity of specialist memory cells in their brains. When these cells were optically stimulated in adult mice without autism, forgotten memories could be restored.
这种免疫激活通过影响这些后代大脑中专业记忆细胞的大小和可塑性，有助于防止它们丧失早期记忆。当这些细胞在没有自闭症的成年小鼠体内受到光学刺激时，被遗忘的记忆就能恢复。

"These new findings suggest that immune activation during pregnancy results in an altered brain state that alters our innate, yet reversible 'forgetting switches' that determine whether the forgetting of infant memories will occur," study co-author, Tomás Ryan, an associate professor of biochemistry at Trinity College Dublin in Ireland, said in a statement. 
"这项研究的共同作者、爱尔兰都柏林圣三一学院生物化学副教授托马斯-瑞安（Tomás Ryan）在一份声明中说："这些新发现表明，怀孕期间的免疫激活会导致大脑状态发生改变，从而改变我们与生俱来但可逆的'遗忘开关'，这种开关决定着婴儿记忆的遗忘是否会发生。

While the research is in mice and has yet to be studied in humans, it "holds significant implications for enhancing our comprehension of memory and forgetting across child development, as well as overall cognitive flexibility in the context of autism," Ryan said.
虽然这项研究是在小鼠身上进行的，尚未在人类身上进行研究，但它 "对提高我们对整个儿童发育过程中的记忆和遗忘以及自闭症背景下的整体认知灵活性的理解具有重要意义"，瑞安说。

Editor's note: Originally published on Feb. 7, 2011 and updated on Nov. 27, 2023 to include the new study about autism. 
编者注：原文发表于2011年2月7日，并于2023年11月27日更新，以纳入有关自闭症的新研究。