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7 Things We Can Turn Off and On in the Brain

iStock / Rebecca O'Connell
iStock / Rebecca O'Connell

As much as we’d like to think we’re always in control of our own actions, a lot of human behavior, mood, and habit can be traced to involuntary reactions in the brain. As researchers learn more about what’s going on inside our heads, they’re finding the light switches that control some of our most basic functions—many of which can be turned off. 

1. Thirst

Researchers know the control center for thirst is somewhere in the hypothalamus, an almond-sized section of the human brain that regulates a number of our basic functions (hunger, sex drive, temperature). But recently, neuroscientists at Columbia University identified two specific populations of neurons in the hypothalamus of mice that control the impulse to hydrate, and they wanted to know what happens when they’re activated. By using a process called optogenetics, they manipulated these cells to make them sensitive to certain wavelengths of light. Then, fiber-optic cables were implanted in the brains of mice that when illuminated, turned the corresponding neurons on or off.

They found that one group of thirst neurons “evokes intense drinking behavior” when activated. How intense? Mice drank up to eight percent of their body weight in water when these neurons were switched on. That’s the equivalent of a human drinking a gallon and a half of water in 10 minutes.

The second group of neurons reduces the desire to drink, even when the animal is deprived of water. You can see video of some very thirsty mice from this study here.

2. Hunger

Using the same optogenetics technique, scientists at Johns Hopkins University have pinpointed the brain cells that control our impulse to eat. When these cells are activated in mice, the rodents are compelled to stuff themselves well beyond the point of being full. But when they’re shut down, the mice ignore food, even when they should be hungry. Researchers think this information could potentially help treat eating disorders in humans.

3. Consciousness

We consider consciousness and self-awareness to be defining characteristics of human life. So it may surprise you to know that such sacred traits can be turned off and on like a light switch in a lab setting. At George Washington University, Mohamad Koubeissi and his team accidentally flipped the switch while using electrodes to stimulate different parts of the brain in an epileptic woman.

When they stimulated a section called the claustrum, the patient lost consciousness, but she didn’t pass out. Instead she sat motionless with a blank stare and showed no response to cues around her. She snapped out of her trance when the stimulation stopped, and had no memory of the lapse. "Ultimately, if we know how consciousness is created and which parts of the brain are involved then we can understand who has it and who doesn't," says Christof Koch at the Allen Institute for Brain Science in Seattle. "Do robots have it? Do fetuses? Does a cat or dog or worm?” The caveat: because of her epilepsy, this woman had part of her hippocampus removed, so her brain is far from that of a “normal” person.

Other studies have shown the human brain may switch off self-awareness when we’re stressed, without any help from researchers. In 2006, neurobiologists from the Weizmann Institute of Science in Rehovot, Israel observed that when humans are forced to focus on a difficult task (particularly under a strict deadline), the area of our brains associated with introspection, the cortex, becomes quiet, and we go into a sort of robotic mode until the task is done. This ability could have evolved for purposes of self-defense. "If there is a sudden danger, such as the appearance of a snake, it is not helpful to stand around wondering how one feels about the situation," researcher Ilan Goldberg told New Scientist.

4. Pain

We can already ease pain with certain drugs, but many treatments come with side effects like dependency and tolerance. Saint Louis University researcher Daniela Salvemini and her team think they’ve found a way to treat chronic pain caused by nerve damage, including the physical agony caused by chemotherapy and bone cancer. By turning on the “A3 adenosine receptor” in the brain and spinal cord, Salvemini and her team were able to block pain caused by nerve damage in rodents, without any of the side effects associated with drug treatments.

5. Violence

What if we could reduce the human urge to fight? Dayu Lin from New York University zoomed in on the hypothalamus, the previously-mentioned hub of bodily functions, to look at the specific neurons that fire during acts of physical violence. By stimulating those neurons using optogenetics, Lin was able to turn male mice into vicious fighters that attacked anything in their vicinity—including inanimate objects, and both male and female mice. She could also calm them, quelling their violent urges by silencing these neurons. Could this strategy one day be used on people? "I think there's every reason to think that this would be true in humans," says Newton Canteras, a neuroscientist at the University of São Paulo in Brazil, and a co-author of this study.

Interestingly, Lin and her team found violence-inducing neurons overlap and compete with neurons associated with sex. In fact, the act of sex temporarily suppresses the violent urges in mice.

6. Bad habits

Can’t stop biting your nails? Plagued by an urge to crack your knuckles? Neuroscientists have found the brain cells responsible for habit formation, at least in rats. By turning these neurons on or off, they are able to eliminate or encourage the formation of new habits. To test this, they gave lab rats a new habit. With a little help from a tasty reward, scientists trained the rodents to navigate a maze until it became so habitual that they’d do it even after the reward was replaced by punishment. But when the neurons were inhibited in the lab, the habit disappeared.

Right now, this kind of procedure would be too invasive to try on humans, says Professor Ann Graybiel, a member of the McGovern Institute for Brain Research at MIT. But it does pave the way for similar, more advanced treatments in the future.

7. Parkinson’s, depression—and maybe Alzheimer’s

Using electrodes embedded in the brain, a neurosurgeon from the University of Toronto named Andres Lozano is harnessing electricity to treat some of humanity’s most vexing ailments. For example, Lozano knows which neurons in the brain are misfiring to cause the severe shaking associated with Parkinson’s disease. In his TED Talk, he explains, “we use electricity to dictate how they fire, and we try to block their misbehavior using electricity. So in this case, we are suppressing the activity of abnormal neurons.” As a result of this suppression, tremors can be dramatically reduced.

Lozano has done similar work with areas in the brain that cause severe depression and is “seeing very striking results in these patients,” he says. Can this approach work for memory? In 2014, he launched a clinical trial to treat 50 people with mild Alzheimer’s with electrical stimulation “to get these areas of the brain that were not using glucose to use glucose once again.” We’ll know in April if the treatment worked.

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DNA Analysis of Loch Ness Could Reveal the Lake's Hidden Creatures
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Stakeouts, sonar studies, and a 24-hour video feed have all been set up in an effort to confirm the existence of the legendary Loch Ness Monster. Now, the Associated Press reports that an international team of scientists will use DNA analysis to learn what's really hiding in the depths of Scotland's most mysterious landmark.

The team, led by Neil Gemmell, who researches evolutionary genetics at the University of Otago in New Zealand, will collect 300 water samples from various locations and depths around the lake. The waters are filled with microscopic DNA fragments animals leave behind as they swim, mate, eat, poop, and die in the waters, and if Nessie is a resident, she's sure to leave bits of herself floating around as well.

After extracting the DNA from the organic material found in the water samples, the scientists plan to sequence it. The results will then be compared to the DNA profiles of known species. If there's evidence of an animal that's not normally found in the lake, or an entirely new species, the researchers will hopefully spot it.

Gemmell is a Nessie skeptic, and he says the point of the project isn't necessarily to discover new species. Rather, he wants to create a genetic profile of the lake while generating some buzz around the science behind it.

If the study goes according to plan, the database of Loch Ness's inhabitants should be complete by 2019. And though the results likely won't include a long-extinct plesiosaur, they may offer insights about other invasive species that now call the lake home.

[h/t AP]

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How Long to Steep Your Tea, According to Science
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The tea in your cabinet likely has vague instructions about how long to steep the leaves. Bigelow, for instance, suggests two to four minutes for black tea, and one to three minutes for green tea. According to Lipton, you should "try singing the National Anthem" while waiting for black tea leaves to infuse.

But while it's true that tea brewed for 30 seconds is technically just as drinkable as a forgotten mug of tea that's been steeping for 30 minutes, drinkable shouldn't be your goal. Taste and—depending on the tea you're drinking—antioxidant and caffeine levels all depend on the amount of time the leaves are in contact with the water. So how early is too early to pluck out a tea bag, and how long can you leave it in before passing the point of no return?

THE SCIENCE OF STEEPING

To achieve the perfect timing, you first need to understand the chemical process at work when you pour hot water over tea leaves. Black, green, white, and oolong tea all come from the leaves and buds of the same plant, Camellia sinensis. (Herbal teas aren't considered "true teas" because they don't come from C. sinensis.) The teas are processed differently: Green and white tea leaves are heated to dry them, limiting the amount of oxidation they get, while black and oolong tea leaves are exposed to oxygen before they're dried, creating the chemical reactions that give the tea its distinct color and flavor. Damaging the tea leaves—by macerating them, rolling them gently, or something in between—helps expose the chemicals inside their cells to varying levels of oxygen.

Both green and black teas contain a lot of the same chemical compounds that contribute to their flavor profiles and nutritional content. When the leaves are submerged in hot water, these compounds leach into the liquid through a process called osmotic diffusion, which occurs when there's fluid on both sides of a selectively permeable membrane—in this case, the tea leaf. Compounds on the surface of the leaf and in the interior cells damaged by processing will diffuse into the surrounding liquid until the compounds in both the leaf and the water reach equilibrium. In other words, if given enough time to steep, the liquid in your mug will become just as concentrated with tea compounds as the liquid in your tea leaves, and the ratio will stay that way.

Osmotic diffusion doesn't happen all at once—different compounds enter the water at different rates based on their molecular weight. The light, volatile chemicals that contribute to tea's aroma and flavor profile dissolve the fastest, which is why the smell from a bag of tea leaves becomes more potent the moment you dunk it in water. The next group of compounds to infuse with the water includes the micronutrients flavanols and polyphenols, which are antioxidants, and caffeine. They're followed by heavier flavanols and polyphenols such as tannins, which are the compounds responsible for tea's bitter flavor. (They're also what make your mouth feel dry after drinking a glass of wine.) Tea also has amino acids like theanine, which can offset the sharpness of tannins.

Water temperature is another factor to take into consideration when steeping your tea. High water temperature creates more kinetic energy, which encourages the compounds to dissolve. "The heat helps you to extract the compounds out of the tea leaves," Shengmin Sang, a North Carolina A&T State University researcher who studies the chemistry of tea, tells Mental Floss. "If you put it into cold water or low-temperature water, the efficiency to extract these compounds out of the leaves will be much lower." But not all water is equal: Bigelow Tea recommends using water at a rolling boil for black tea, and barely boiling water for green tea.

LOOSE LEAF VS. TEA BAGS

Osmotic diffusion takes place whether you use loose leaves or tea bags, but there are some notable differences between the two. When given room to expand, loose tea leaves swell to their full capacity, creating more room for water to flow in and extract all those desirable compounds. Tea that comes prepackaged in a bag, on the other hand, only has so much room to grow, and the quality suffers as a result. This is why some tea companies have started selling tea in roomier, pyramid-shaped bags, though the size matters more than the shape.

But even before the tea touches the water, there's a difference in quality. Loose leaf tea usually consists of whole leaves, while most teabags are filled with broken pieces of tea leaves called dust or fannings, which have less-nuanced flavors and infuse fewer antioxidants than whole leaves, no matter how long you let them steep.

So if you have a choice, go with loose leaf. But if tea bags are all you have on hand, don't bother adjusting your brewing method: The difference in taste and antioxidants isn't something that can be fixed with a few extra minutes, and according to Sang, you should follow the same steeping times for both tea bags and loose leaf.

To calculate the perfect brew times for what's in your mug, first consider what you want most out of your drink.

IF YOU DRINK TEA TO BE HEALTHY

Suggested steeping time: 2 minutes, 30 seconds to 5 minutes

Tea leaves are packed with beneficial compounds. Research indicates that flavanols such as catechins and epicatechins, found in both green and black teas, help suppress inflammation and curb plaque build-up in arteries. Drinking tea may improve vascular reactivity, which dictates how well blood vessels adjust to stress. According an analysis of multiple tea-related studies published in the European Journal of Epidemiology in 2015, drinking three cups of tea a day reduces your risk of coronary heart disease by 27 percent, cardiac death by 26 percent, and total mortality by 24 percent. Polyphenolic antioxidants in tea may also protect against diabetes, depression, and liver disease.

Past research has shown that it takes 100 to 150 seconds to extract half the polyphenol content from green and black tea leaves. According to a study published in 2016 in the journal Beverages, you can get more polyphenols into your drink if you allow the leaves more time to steep. However, the returns may not be worth the extra effort: Most of the compounds the researchers measured after 10 minutes of steeping were extracted in the first 5 minutes.

Sang makes another argument for not waiting too long to drink your tea. Antioxidants are slightly unstable, which means they will eventually break down and lose their healthy properties after infusing with water. “After you extract the compounds from the tea bag, you can not keep the solution for too long,” he says. “Because these compounds are not stable, they will be oxidized. So if you brew it in the morning, then you drink it in the afternoon, that's not good.” This oxidation can occur even after the tea leaves are removed from the cup, so if your tea has been sitting out for a few hours, it's better to brew a new batch than to pop it in the microwave.

IF YOU DRINK TEA FOR THE CAFFEINE BOOST

Suggested steeping time: 3 to 5 minutes

Though less potent than its rival coffee, a properly brewed cup of tea packs a caffeine punch. According to a 2008 study published in the Journal of Analytical Toxicology [PDF], letting your tea brew for at least a few minutes has a big impact on the caffeine content. The study found that after brewing for one minute, a cup of regular Lipton black tea had 17 milligrams of caffeine per 6 ounces of water, 38 milligrams per 6 ounces after three minutes, and 47 milligrams per 6 ounces after five. (The nutritional information for Lipton black tea says a serving contains 55 milligrams of caffeine per 8 ounces, so it's pretty accurate.)

Some people may use those numbers as an excuse to steep their tea past the five-minute mark in an attempt to reach 100 percent dissolution. But a longer brewing time doesn't necessarily equal a stronger caffeine kick. Yes, more caffeine molecules will enter the tea, but so will other compounds like thearubigins. Caffeine works because it's perfectly shaped to bind to certain neuroreceptors in your brain, thus blocking the chemicals that tell you to feel tired. But caffeine is the right shape to bind to thearubigins as well, and if that happens first, less caffeine will get to those neuroreceptors. So if you're looking for a highly caffeinated cup of tea, you should remove the leaves after most of the caffeine has been extracted—after about three to five minutes—rather than waiting for every last milligram of caffeine to dissolve.

IF YOU DRINK TEA BECAUSE IT TASTES GOOD

Suggested steeping time: 1 to 3 minutes

There's nothing wrong with enjoying a cup of tea for taste alone. Flavor is the most subjective factor influenced by steeping times, but for the sake of simplicity, let's assume you prefer a pronounced tea taste that's not overshadowed by bitterness. To extract those more delicate flavors, you don't need to steep your tea leaves for very long at all. Some of the first volatile organic compounds to break down in tea are geraniol and phenylacetaldehyde, tied to a tea's floral aroma, and linalool and linalool oxide, which give tea its sweetness.

The other compounds we associate with tea's distinctive taste are tannins. They're the difference between an aromatic, fruity cup of tea and a bitter cup that needs to be diluted with milk before it's palatable. But tannins aren't all bad: Some people prefer their tea to have a bracing astringency. Because tannins are some of the last molecules to dissolve into tea, if you want to add some bitter complexity to your drink, steep your tea for a minute or two longer than you normally would. A good way to keep track of the strength of your tea is to look at the color: Like tannins, pigments are heavy compounds, so if you see your tea getting darker, that means it's getting stronger as well.

And what about herbal teas? Feel free to leave the leaves in as long as you like. Because herbal teas are high in aromatic compounds and low in tannins, drinkers can be more liberal with their steep times without worrying about getting that astringent taste. Some teas, like rooibos and chamomile, also contain antioxidants, which is another reason to take your time.

And if you're new to the world of tea and aren't sure what your preferences are, put a kettle on the stove and start experimenting.

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