There is no scientific consensus on the purpose of sleep – a curious fact considering that it accounts for a third of every human's life. Over the next day, the world's population will spend 58 billion hours in slumber.Sleep has been implicated in the secretion of vital hormones, neurogenesis (the creation of new neurons), memory consolidation, immune system maintenance, and some theorists think sleep is a kind of "adaptive inactivity," just a good way to stay out of harm and conserve precious calories. Evidence for each of these claims has been consistently building for decades, both confusing the matter and painting sleep to be some kind of magically adaptive cure-all.Whatever sleep is for, there's one thing we can all agree on: It's weird. Take snoring: snoring is weird because it can make petite people sound like mythical beasts. Dreams are weird too – like that one where Genghis Khan forces you and your 6th grade social studies teacher to make pancakes for his thousands of children. And don't forget that eerie feeling when you wake up from a late afternoon nap, it's dark outside, and you have no fucking idea what is going on.Sleepwalking has to be the weirdest though – If you have ever encountered a sleepwalker, as I have, the zombie resemblance is uncanny.Some new research out of Paris, published in the Public Library of Science, provides some really striking data about sleepwalkers and the role of sleep in general. Delphine Oudiette, et al, studied 19 people who were diagnosed with various parasomnias ( that translates to "beside sleep"), specifically disorders involving chronic sleepwalking. The researchers hoped that by studying sleepwalkers they could find clear, observable evidence for the idea that during sleep we "replay" behavioral sequences we encountered while we were awake. [This idea has been pretty well supported in animal research].The "replay" argument contends that sleep functions as a sort of quiet study period during which our brain softly recapitulates the events of the day, sharpening and consolidating our memories. Using a simple motor task, that can be seen in the video above, the authors showed that sleep not only acted as a learning enhancer in all the subjects (they performed better after a night of sleep), but, in one incredible subject, it acted as a kind of mental stage for the literal replay of the movements in the task (see video). While the researchers found such obvious evidence of "replay" in only one subject, it is still pretty amazing considering that, even in chronic sleepwalkers, sleepwalking only occurs an average of one minute per night.The reason they had to study chronic sleepwalkers is simple. When non-parasomniacs (I think that's a new word) sleep, several crucial neurotransmitters are down-regulated and a partial paralysis of the muscles occurs. This is why normal sleepers don't move very much or walk around. The sleepwalkers described in this study, however, do not regulate these chemicals and are prone to acting out their dreams, walking about, and, in this particular case, physically replaying newly learned motor movements. Non-sleepwalkers, presumably, also replay newly learned movements, but the replaying is confined to the mind.So, next time you sleepwalk, remember that you may be inadvertently broadcasting to your roommates that you’ve been practicing medieval lute for three days.
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