From birth, we spend a third of our lives asleep. After decades of research, we’re still not sure why. (…)

If we don’t know why we can’t sleep, it’s in part because we don’t really know why we need to sleep in the first place. We know we miss it if we don’t have it. And we know that no matter how much we try to resist it, sleep conquers us in the end. We know that seven to nine hours after giving in to sleep, most of us are ready to get up again, and 15 to 17 hours after that we are tired once more. We have known for 50 years that we divide our slumber between periods of deep-wave sleep and what is called rapid eye movement (REM) sleep, when the brain is as active as when we’re awake, but our voluntary muscles are paralyzed. We know that all mammals and birds sleep. A dolphin sleeps with half its brain awake so it can remain aware of its underwater environment. When mallard ducks sleep in a line, the two outermost birds are able to keep half of their brains alert and one eye open to guard against predators. Fish, reptiles, and insects all experience some kind of repose too.

All this downtime comes at a price. An animal must lie still for a great stretch of time, during which it is easy prey for predators. What can possibly be the payback for such risk? “If sleep doesn’t serve an absolutely vital function,” the renowned sleep researcher Allan Rechtschaffen once said, “it is the greatest mistake evolution ever made.”

The predominant theory of sleep is that the brain demands it. This idea derives in part from common sense—whose head doesn’t feel clearer after a good night’s sleep? But the trick is to confirm this assumption with real data. How does sleeping help the brain? The answer may depend on what kind of sleep you are talking about. Recently, researchers at Harvard led by Robert Stickgold tested undergraduates on various aptitude tests, allowed them to nap, then tested them again. They found that those who had engaged in REM sleep subsequently performed better in pattern recognition tasks, such as grammar, while those who slept deeply were better at memorization. Other researchers have found that the sleeping brain appears to repeat a pattern of neuron firing that occurred while the subject was recently awake, as if in sleep the brain were trying to commit to long-term memory what it had learned that day.

Such studies suggest that memory consolidation may be one function of sleep. Giulio Tononi, a noted sleep researcher at the University of Wisconsin, Madison, published an interesting twist on this theory a few years ago: His study showed that the sleeping brain seems to weed out redundant or unnecessary synapses or connections. So the purpose of sleep may be to help us remember what’s important, by letting us forget what’s not.

{ National Geographic | Continue reading }

related { Fatal familial insomnia | Thanks Anthony! }

That post was about sleep researcher Jerry Siegel, who argues that sleep evolved as a state of “adaptive inactivity”. According to this idea, animals sleep because otherwise we’d always be active, and constant activity is a waste of energy. Sleeping for a proportion of the time conserves calories, and also keeps us safe from nocturnal predators etc.

Siegel’s theory in what we might call minimalist. That’s in contrast to other hypotheses which claim that sleep serves some kind of vital restorative biological function, or that it’s important for memory formation, or whatever. It’s a hotly debated topic. (…)

Dreams are simply a result of the “awake-like” forebrain - the “higher” perceptual, cognitive and emotional areas - trying to make sense of the input that it’s receiving as a result of waves of activation arising from the brainstem. A dream is the forebrain’s “best guess” at making a meaningful story out of the assortment of sensations (mostly visual) and concepts activated by these periodic waves. There’s no attempt to disguise the shameful parts; the bizarreness of dreams simply reflects the fact that the input is pretty much random. (…)

While Hobson’s theory is minimalist in that it reduces dreams, at any rate in adulthood, to the status of a by-product, it doesn’t leave them uninteresting. Freudian dream re-interpretation is probably ruled out (”That train represents your penis and that cat was your mother”, etc.), but if dreams are our brains processing random noise, then they still provide an insight into how our brains process information. Dreams are our brains working away on their own, with the real world temporarily removed.

{ Neuroskeptic | Continue reading }

{ Sleep, say US feminists, is the next big issue for women to address — doing less and enjoying more duvet time is the way to go. | Times | Full story }

photo { Abbey Drucker }

Sounds played as you sleep can reinforce memories.

Ken Paller and his colleagues at Northwestern University in Evanston, Illinois asked people to memorise which images and their associated sounds – such as a picture of a cat and a miaow – were associated with a certain area on a computer screen and then to take a nap. They played half the group the sounds in their sleep, and these people were better at remembering the associations than the rest when they woke up.

How can you boost your sleep learning capacity?

As a rule, hit the hay after learning something new – late-night TV and Xbox marathons are a no-no.

That is, of course, unless the skill you hope to learn is a computer game: when Sidarta Ribeiro of the Edmond and Lily Safra International Institute of Neuroscience in Natal, Brazil, got people to play shoot-’em-up video game Doom before bed, those who dreamed about the game during their sleep were better players the next day.

{ NewScientist | Continue reading | Cosmos magazine | Read more }

photo { Malerie Marder }

Anyone who can remember a vivid dream knows that at times the strange nighttime scenes reflect real hopes and anxieties: the young teacher who finds himself naked at the lectern; the new mother in front of an empty crib, frantic in her imagined loss.

But people can read almost anything into the dreams that they remember, and they do exactly that. In a recent study of more than 1,000 people, researchers at Carnegie Mellon University and Harvard found strong biases in the interpretations of dreams.

For instance, the participants tended to attach more significance to a negative dream if it was about someone they disliked, and more to a positive dream if it was about a friend.

In fact, research suggests that only about 20 percent of dreams contain people or places that the dreamer has encountered. Most images appear to be unique to a single dream.

Scientists know this because some people have the ability to watch their own dreams as observers, without waking up. This state of consciousness, called lucid dreaming, is itself something a mystery. But it is a real phenomenon.

{ NY Times | Continue reading }