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How Your Brain Fights Sleep Even When You're Exhausted

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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."

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'Lime Disease' Could Give You a Nasty Rash This Summer
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A cold Corona or virgin margarita is best enjoyed by the pool, but watch where you’re squeezing those limes. As Slate illustrates in a new video, there’s a lesser-known “lime disease,” and it can give you a nasty skin rash if you’re not careful.

When lime juice comes into contact with your skin and is then exposed to UV rays, it can cause a chemical reaction that results in phytophotodermatitis. It looks a little like a poison ivy reaction or sun poisoning, and some of the symptoms include redness, blistering, and inflammation. It’s the same reaction caused by a corrosive sap on the giant hogweed, an invasive weed that’s spreading throughout the U.S.

"Lime disease" may sound random, but it’s a lot more common than you might think. Dermatologist Barry D. Goldman tells Slate he sees cases of the skin condition almost daily in the summer. Some people have even reported receiving second-degree burns as a result of the citric acid from lime juice. According to the Mayo Clinic, the chemical that causes phytophotodermatitis can also be found in wild parsnip, wild dill, wild parsley, buttercups, and other citrus fruits.

To play it safe, keep your limes confined to the great indoors or wash your hands with soap after handling the fruit. You can learn more about phytophotodermatitis by checking out Slate’s video below.

[h/t Slate]

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Why Eating From a Smaller Plate Might Not Be an Effective Dieting Trick 
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It might be time to rewrite the diet books. Israeli psychologists have cast doubt on the widespread belief that eating from smaller plates helps you control food portions and feel fuller, Scientific American reports.

Past studies have shown that this mind trick, called the Delboeuf illusion, influences the amount of food that people eat. In one 2012 study, participants who were given larger bowls ended up eating more soup overall than those given smaller bowls.

However, researchers from Ben-Gurion University in Negev, Israel, concluded in a study published in the journal Appetite that the effectiveness of the illusion depends on how empty your stomach is. The team of scientists studied two groups of participants: one that ate three hours before the experiment, and another that ate one hour prior. When participants were shown images of pizzas on serving trays of varying sizes, the group that hadn’t eaten in several hours was more accurate in assessing the size of pizzas. In other words, the hungrier they were, the less likely they were to be fooled by the different trays.

However, both groups were equally tricked by the illusion when they were asked to estimate the size of non-food objects, such as black circles inside of white circles and hubcaps within tires. Researchers say this demonstrates that motivational factors, like appetite, affects how we perceive food. The findings also dovetail with the results of an earlier study, which concluded that overweight people are less likely to fall for the illusion than people of a normal weight.

So go ahead and get a large plate every now and then. At the very least, it may save you a second trip to the buffet table.

[h/t Scientific American]

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