When humankind was young, this process offered a sociobiological evolutionary advantage: If Early Man got especially freaked out by a tiger attack, that hardwiring taught him to stay out of tiger country. However, tigers are no longer a pressing issue in Modern Man's life. Today, adrenaline more often makes Modern Man remember the events he'd most like to forget.
If a surplus of adrenaline makes us remember, it stands to reason that a deficit of adrenaline would help us forget. And this is what propranolol does. It inhibits the chemical rush that makes memories hyperconcrete. It doesn't erase memories, but it makes them more abstract and less painful.
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