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" After only a few weeks of treatment, his patients would return to the clinic and, with puzzled amazement, say things like, “Doc, it’s the strangest thing, my dreams don’t have those flashback nightmares anymore. I feel better, less scared to fall asleep at night.” It turns out that the drug prazosin, which Raskind was prescribing simply to lower blood pressure, also has the fortuitous side effect of suppressing noradrenaline in the brain. "
― Matthew Walker , Why We Sleep: Unlocking the Power of Sleep and Dreams
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" Things get even more interesting when birds group together. In some species, many of the birds in a flock will sleep with both halves of the brain at the same time. How do they remain safe from threat? The answer is truly ingenious. The flock will first line up in a row. With the exception of the birds at each end of the line, the rest of the group will allow both halves of the brain to indulge in sleep. Those at the far left and right ends of the row aren’t so lucky. They will enter deep sleep with just one half of the brain (opposing in each), leaving the corresponding left and right eye of each bird wide open. In doing so, they provide full panoramic threat detection for the entire group, maximizing the total number of brain halves that can sleep within the flock. At some point, the two end-guards will stand up, rotate 180 degrees, and sit back down, allowing the other side of their respective brains to enter deep sleep. "
― Matthew Walker , Why We Sleep: Unlocking the Power of Sleep and Dreams