National Geographic

Our brains aren’t less active when we sleep, aswas long thought, just diferently active. Spin-dles, it’s theorized, stimulate the cortex in sucha way as to preserve recently acquired informa-tion—and perhaps also to link it to establishedknowledge in long-term memory. In sleep labs,when people have been introduced to certainnew tasks, mental or physical, their spindle fre-quency increases that night. The more spindlesthey have, it seems, the better they perform thetask the next day.The strength of one’s nightly spindles, someexperts have suggested, might even be a predic-tor of general intelligence. Sleep literally makesconnections you might never have consciouslyformed, an idea we’ve all intuitively realized.No one says, “I’m going to eat on a problem.” Wealways sleep on it.The waking brain is optimized for collectingexternal stimuli, the sleeping brain for consol-idating the information that’s been collected.At night, that is, we switch from recording toSLEEP 51