How Your Brain Fights Sleep Even When You're Exhausted

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iStock

Maybe you’ve got an exam in the morning, or there’s just one more episode left in this season. Whatever the reason, tonight you ignore your body’s demands and stay up instead. It’s an impressive feat, if you think about it—sleep is essential—and now scientists may be closer to understanding how we do it. They published a report on their findings in the journal Neuron.

There’s a little section of your brainstem called the dorsal raphe nucleus (DRN). This region is responsible for making serotonin and other brain chemicals.

Lead researcher Viviana Gradinaru of Caltech says previous studies have also suggested that the dorsal raphe nucleus plays a role in helping keep us awake.

"People who have damage in this part of their brain have been shown to experience excessive daytime sleepiness,” she said in a statement, “but there was not a good understanding of the exact role of these neurons in the sleep/wake cycle and whether they react to internal or external stimuli to influence arousal."

Within the dorsal raphe nucleus lies a little-understood group of dopamine cells called the dorsal raphe nucleus neurons (DRNDA).

Color image of dorsal raphe nucleus neurons
Dorsal raphe nucleus neurons responding to light (green) and chemical (red) signals.
Viviana Gradinaru

Gradinaru and her colleagues wanted to know if voluntary wakefulness had anything to do with dopamine activity within these cells. They started by studying mouse brains, which are similar to our own in many ways.

The researchers monitored the rodents’ DRNDA action while the mice were fed, met new potential mates, or experienced sudden unpleasant sensations—all experiences for which the mice would want or need to stay awake. Throughout the experiences, the mice’s DRNDA cells kept very busy, sending bursts of dopamine to other parts of the brain.

Next, the scientists tracked DRNDA cell activity as the mice slept and woke. They found that the cells seemed to sleep when the mice did, and revved up when the mice got up.

So far, the researchers knew that the sleeping mouse/sleeping neurons and waking mouse/waking neurons pairs existed, but they couldn’t tell if the neurons caused the waking or vice versa.

To find out, they engineered DRNDA cells that could be switched on and off by light. They then bred mice with these light-sensitive cells and let them sleep. As the mice snoozed, the researchers switched on the lights and their DRNDA cells using a technique called optogenetics. Sure enough, the mice woke up.

Shutting off DRNDA cells had the opposite effect: Mice with no DRNDA activity couldn’t keep their eyes open, even when faced with danger, loud noises, or the possibility of mating.

The authors note that their experiments included only mice, and that it’s too soon to draw conclusions about what this might mean for people.

“Further work is necessary to establish causation in humans,” Gradinaru said, “and to test the potential of the DRNDA as a therapeutic target for insomnia or oversleeping, and for sleep disturbances that accompany other psychiatric disorders such as depression, bipolar disorder, and schizophrenia."

How Did 6 Feet Become the Standard Grave Depth?

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iStock

It all started with the plague: The origins of “six feet under” come from a 1665 outbreak in England. As the disease swept the country, the mayor of London literally laid down the law about how to deal with the bodies to avoid further infections. Among his specifications—made in “Orders Conceived and Published by the Lord Mayor and Aldermen of the City of London, Concerning the Infection of the Plague”—was that “all the graves shall be at least six feet deep.”

The law eventually fell out of favor both in England and its colonies. Modern American burial laws vary from state to state, though many states simply require a minimum of 18 inches of soil on top of the casket or burial vault (or two feet of soil if the body is not enclosed in anything). Given an 18-inch dirt buffer and the height of the average casket (which appears to be approximately 30 inches), a grave as shallow as four feet would be fine.

A typical modern burial involves a body pumped full of chemical preservatives sealed inside a sturdy metal casket, which is itself sealed inside a steel or cement burial vault. It’s less of a hospitable environment for microbes than the grave used to be. For untypical burials, though—where the body isn’t embalmed, a vault isn’t used, or the casket is wood instead of metal or is foregone entirely—even these less strict burial standards provide a measure of safety and comfort. Without any protection, and subjected to a few years of soil erosion, the bones of the dearly departed could inconveniently and unexpectedly surface or get too close to the living, scaring people and acting as disease vectors. The minimum depth helps keep the dead down where they belong.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article originally appeared in 2012.

One Good Reason Not to Hold in a Fart: It Could Leak Out of Your Mouth

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iStock/grinvalds

The next time you hold in a fart for fear of being heard by polite company, just remember this: It could leak out of your mouth instead of your butt. Writing on The Conversation, University of Newcastle nutrition and dietetics professor Clare Collins explains that pent-up gas can pass through your gut wall and get reabsorbed into your circulation. It's then released when you exhale, whether you like it or not.

“Holding on too long means the build up of intestinal gas will eventually escape via an uncontrollable fart,” Collins writes. In this case, the fart comes out of the wrong end. Talk about potty mouth.

A few brave scientists have investigated the phenomenon of flatulence. In one study, 10 healthy volunteers were fed half a can of baked beans in addition to their regular diets and given a rectal catheter to measure their farts over a 24-hour period. Although it was a small sample, the results were still telling. Men and women let loose the same amount of gas, and the average number of “flatus episodes” (a single fart, or series of farts) during that period was eight. Another study of 10 people found that high-fiber diets led to fewer but bigger farts, and a third study found that gases containing sulphur are the culprit of the world’s stinkiest farts. Two judges were tapped to rate the odor intensity of each toot, and we can only hope that they made it out alive.

Scientific literature also seems to support Collins’s advice to “let it go.” A 2010 paper on “Methane and the gastrointestinal tract” says methane, hydrogen sulfide, and other gases that are produced in the intestinal tract are mostly eliminated from the body via the anus or “expelled from the lungs.” Holding it in can lead to belching, flatulence, bloating, and pain. And in some severe cases, pouches can form along the wall of the colon and get infected, causing diverticulitis.

So go ahead and let it rip, just like nature intended—but maybe try to find an empty room first.

[h/t CBS Philadelphia]

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