A neuroscientist at the University of Wisconsin has discovered that, contrary to prevailing opinion, sleep is not to reinforce memories, but to weaken memories so that we can forget unneeded information.
The theory is unorthodox, but it does make a certain amount of sense. Without the ability to pare away unneeded information as we sleep, our brains would face a serious energy shortage as well as a space crunch: Stronger synapses are typically bigger, and real estate in the brain is precious. By proportionally weakening synapses, the brain ensures that they retain the same strength relative to each other. So when we wake up each morning, all of our synapses are weaker, and some have vanished. With them, our smallest memories from each day may be lost forever.