2023届高三英语三轮复习冲刺押题外刊阅读理解专项训练 (26)

2023届高考英语三轮复习·冲刺押题 外刊阅读理解训练26 ——改编自How adult brains learn the new without forgetting the old 【文章】 Learning is a challenging process, but retaining what one has learned can often be harder. For any successful learning system- whether it's in the brain or AI software, there must be a balance between stability and flexibility. This means that it needs to be stable enough to remember important old things while also flexible enough to learn new ones without destroying old memory traces. Learning is a result of changes in the pattern of neural connectivity in the brain. Synapses, which are tiny gaps between nerve cells, are what help messages jump across these gaps in the form of molecules called neurotransmitters. There are around 600 trillion synapses in a human brain. To deal with the stability-plasticity dilemma, scientists at the Massachusetts Institute of Technology (MIT) have found a way to preserve a type of memory-forming synapse found in children into adulthood. These synapses are called "silent synapses" - so-called because they don't transmit signals from one nerve cell to another. Silent synapses are often found on slender protrusions called filopodia found near nerve cells. Previously, it was thought that these disappeared as the brain matured. But the MIT researchers have shown that not only are they present in adulthood, but they are also quite common. Just over a quarter of the connections sampled in the visual cortexes of adult mice were silent synapses on filopodia. Murine and human brains are similar enough that something similar almost certainly applies to people. The researchers used a sensitive microscopy technique called eMAP to study synapses between cortical nerve cells of a type called pyramidal neurons. They discovered that mature synapses generated electrical activity when exposed to glutamate, the brain's main excitatory neurotransmitter. Filopodia, on the other hand, did not because their synapses are silent. However, the researchers were