提升成年人大脑记忆力的方法(上)

How adult brains learn the new without forgetting the old.

成年人的大脑如何在不忘记旧内容的情况下学习新内容。

Learning new things is hard.

学习新事物很难。

Remembering what has already been learned is harder.

记住已经学过的东西更难。

Any successful learning system, be it a brain or a piece of artificial-intelligence software, must strike the right balance between stability and flexibility.

任何成功的学习系统，无论是大脑还是人工智能软件，都必须在稳定性和可塑性之间取得适当的平衡。

It must be stable enough to remember important old things yet flexible enough to learn new ones without destroying old memory traces - preferably for as long as it exists.

它必须足够稳定，能够保留过往重要的记忆，也必须足够可塑，以便在不影响过往记忆痕迹的情况下学习新事物——最好是在过往记忆存在的时间内。

Learning is a result of changes in the pattern of neural connectivity in the brain.

学习是大脑中神经连接模式改变的结果。

Each connection between nerve cells, called a synapse, is a tiny gap between the ends of branches ramifying from such cells.

神经细胞之间的连接被称为突触，突触是神经细胞末梢的分支之间的微小间隙。

Messages jump across these gaps in the form of molecules called neurotransmitters.

信息以被称为“神经递质”的分子形式跳过这些缝隙。

Current estimates suggest there are 600 trillion synapses in a human brain.

根据目前的估计，人类大脑中有600万亿个突触。

How, then, to deal with the stability-plasticity dilemma - particularly as brains age and, as it were, fill up?

那么，我们该如何平衡大脑的稳定性和可塑性——特别是在大脑老化并且已经“被信息填满”的情况下——我们该如何应对这种两难境地？

Research by Dimitra Vardalaki, Kwanghun Chung and Mark Harnett at the Massachusetts Institute of Technology, just published in Nature, suggests one way is to preserve into adulthood a type of memory-forming synapse found in children.

麻省理工学院的迪米特拉·瓦达拉基、钟光勋和马克·哈内特的研究表明，一种方法是将儿童大脑中发现的一种形成记忆的突触保留到成年时期。

These are called silent synapses.

这些被保留下来的突触名为沉默突触。

Silent synapses - which, as their name suggests, transmit no signal from one nerve cell to another - are often found on the ends of slender, immature protrusions from nerve cells, called filopodia.

沉默突触——顾名思义，它不会将信号从一个神经细胞传递到另一个神经细胞——通常出现在神经细胞细长的未成熟突起的末端，称为树突丝。

Until now, it had been thought that these disappeared as a brain matured.

到目前为止，人们一直认为，这些东西会随着大脑的成熟消失。

But Drs Vardalaki, Chung and Harnett have shown not only that they are present in adulthood, but also that they are common, at least in mice.

但瓦达拉基、钟光勋和哈内特博士已经证明，它们不仅能够存在于成年期的大脑中，而且十分常见，至少在老鼠身上是这样。

Just over a quarter of the connections they sampled in adult mouse visual cortices were silent synapses on filopodia.

他们在成年小鼠的视皮层中采样的突触中，略多于四分之一是树突丝上的沉默突触。

And murine and human brains are sufficiently alike that something similar almost certainly applies to people.

老鼠大脑和人类大脑非常相似，因此几乎可以肯定类似的东西也存在于人类大脑之中。