11~20 題 (請以代號作答，一個選項限用一次)     FFI, fatal familial insomnia, is an awful disease, the main symptom of which is the inability to sleep. First the ability to napdisappears, then the ability to get a full night’s sleep, until the patient cannot sleep at all. The syndrome usually 11 when thesufferer is in his or her late 50s, ordinarily lasts about a year, and always ends in death, as the name indicates     erer is in his or her late 50s, ordinarily lasts about a year, and always ends in death, as the name indicates.To make matters worse, so little about how it works is known to researchers after years of study. So far researchers have onlyfigured out that in a patient with FFI, 12 proteins called prions attack the sufferer’s thalamus, a structure deep in the brain, and13 a damaged thalamus interferes with sleep. But they don’t know why this happens, or how to stop it, or ease its 14symptoms. Before FFI was investigated, most researchers didn’t even know the thalamus had anything to do with sleep. FFI is 15rare, known in only 40 families worldwide. But in one respect, it’s a lot like the less serious kinds of insomnia 16 millions ofpeople today: It’s pretty much a mystery    If we don’t know why we can’t sleep, it’s 17 because we don’t really know why we need to sleep in the first place. Weknow we miss it if we don’t have it. And we know that no matter how much we try to resist, sleep conquers us in the end. We haveknown for 50 years that we divide our slumber between periods of deep-wave sleep and what is called rapid eye movement (REM),when the brain is as active as when we are awake, but our voluntary muscles are 18 . Furthermore, we know all mammals andbirds sleep. Fish, reptiles and insects all experience some kind of repose too.      Yet all this 19 comes at a price. An animal must lie still for a great stretch of time, during which it is easy prey forpredators. So what possibly is the payback for such risk? As the renowned sleep researcher Allan Rechtschaffen once said, “If sleepdoesn’t serve an absolutely vital function, it is the greatest mistake evolution ever made.” Not surprisingly, the 20 theory ofsleep is that the brain demands it.
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