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Why Does Music Give You Chills?

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When your playlist strikes all the right chords, your body can go on a physiological joyride. Your heart rate increases. Your pupils dilate. Your body temperature rises. Blood redirects to your legs. Your cerebellum—mission control for body movement—becomes more active. Your brain flushes with dopamine and a tingly chill whisks down your back.

About 50 percent of people get chills when listening to music. Research shows that’s because music stimulates an ancient reward pathway in the brain, encouraging dopamine to flood the striatum—a part of the forebrain activated by addiction, reward, and motivation. Music, it seems, may affect our brains the same way that sex, gambling, and potato chips do.

Strangely, those dopamine levels can peak several seconds before the song’s special moment. That’s because your brain is a good listener—it’s constantly predicting what’s going to happen next. (Evolutionarily speaking, it’s a handy habit to have. Making good predictions is essential for survival.)

But music is tricky. It can be unpredictable, teasing our brains and keeping those dopamine triggers guessing. And that’s where the chills may come in. Because when you finally hear that long awaited chord, the striatum sighs with dopamine-soaked satisfaction and—BAM—you get the chills. The greater the build-up, the greater the chill.

Gray Areas

But there are competing theories. Neuroscientist Jaak Panksepp, for example, discovered that sad music triggers chills more often than happy music. He argues that a melancholy tune activates an ancient, chill-inducing mechanism—a distress response our ancestors felt when separated from family. When a ballad makes us feel nostalgic or wistful, that evolutionary design kicks into gear.

What’s interesting about Panksepp’s theory, though, is that chills don’t sadden most people. The experience is overwhelmingly positive. Recent research shows that sad music actually evokes positive emotions—sadness experienced through art is more pleasant than the sadness you experience from a bad day at the office.  

And this may hint at another theory. The amygdala, which processes your emotions, responds uniquely to music. A somber tune may activate a fear response in the amygdala, making your hair stand on end. When that happens, your brain quickly reviews whether there’s any real danger. When it realizes there’s nothing to worry about, that fear response becomes positive. The fear subsides but the chill remains.

Anything Goes

You can feel chills from any genre, whether it’s Mozart, Madonna, tango, or techno. It’s the structure—not the style—that counts. Goosebumps most often occur when something unexpected happens: A new instrument enters, the form shifts, the volume suddenly dims. It’s all about the element of surprise.

Well, maybe.

The most powerful chills may occur when you know what’s coming next. When our expectations are being met, the nucleus accumbens becomes more active. This ties back to that dopamine-inducing guessing game our brain likes to play. As a result, being familiar can enhance the thrill of the chill. (Perhaps that’s why 90 percent of musicians report feeling chills.)

Your personality matters, too. Scientists at UNC Greensboro found that people who are more open to new experiences are more likely to feel a quiver down their spine (possibly because open individuals are more likely to play instruments). Meanwhile, researchers in Germany found that people who felt chills were less likely to be thrill seekers, but were more reward-driven.

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Big Questions
Do Bacteria Have Bacteria?
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Drew Smith:

Do bacteria have bacteria? Yes.

We know that bacteria range in size from 0.2 micrometers to nearly one millimeter. That’s more than a thousand-fold difference, easily enough to accommodate a small bacterium inside a larger one.

Nothing forbids bacteria from invading other bacteria, and in biology, that which is not forbidden is inevitable.

We have at least one example: Like many mealybugs, Planococcus citri has a bacterial endosymbiont, in this case the β-proteobacterium Tremblaya princeps. And this endosymbiont in turn has the γ-proteobacterium Moranella endobia living inside it. See for yourself:

Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)
Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)

I don’t know of examples of free-living bacteria hosting other bacteria within them, but that reflects either my ignorance or the likelihood that we haven’t looked hard enough for them. I’m sure they are out there.

Most (not all) scientists studying the origin of eukaryotic cells believe that they are descended from Archaea.

All scientists accept that the mitochondria which live inside eukaryotic cells are descendants of invasive alpha-proteobacteria. What’s not clear is whether archeal cells became eukaryotic in nature—that is, acquired internal membranes and transport systems—before or after acquiring mitochondria. The two scenarios can be sketched out like this:


The two hypotheses on the origin of eukaryotes:

(A) Archaezoan hypothesis.

(B) Symbiotic hypothesis.

The shapes within the eukaryotic cell denote the nucleus, the endomembrane system, and the cytoskeleton. The irregular gray shape denotes a putative wall-less archaeon that could have been the host of the alpha-proteobacterial endosymbiont, whereas the oblong red shape denotes a typical archaeon with a cell wall. A: archaea; B: bacteria; E: eukaryote; LUCA: last universal common ancestor of cellular life forms; LECA: last eukaryotic common ancestor; E-arch: putative archaezoan (primitive amitochondrial eukaryote); E-mit: primitive mitochondrial eukaryote; alpha:alpha-proteobacterium, ancestor of the mitochondrion.

The Archaezoan hypothesis has been given a bit of a boost by the discovery of Lokiarcheota. This complex Archaean has genes for phagocytosis, intracellular membrane formation and intracellular transport and signaling—hallmark activities of eukaryotic cells. The Lokiarcheotan genes are clearly related to eukaryotic genes, indicating a common origin.

Bacteria-within-bacteria is not only not a crazy idea, it probably accounts for the origin of Eucarya, and thus our own species.

We don’t know how common this arrangement is—we mostly study bacteria these days by sequencing their DNA. This is great for detecting uncultivatable species (which are 99 percent of them), but doesn’t tell us whether they are free-living or are some kind of symbiont. For that, someone would have to spend a lot of time prepping environmental samples for close examination by microscopic methods, a tedious project indeed. But one well worth doing, as it may shed more light on the history of life—which is often a history of conflict turned to cooperation. That’s a story which never gets old or stale.

This post originally appeared on Quora. Click here to view.

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Big Questions
Why Do Cats 'Blep'?
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As pet owners are well aware, cats are inscrutable creatures. They hiss at bare walls. They invite petting and then answer with scratching ingratitude. Their eyes are wandering globes of murky motivations.

Sometimes, you may catch your cat staring off into the abyss with his or her tongue lolling out of their mouth. This cartoonish expression, which is atypical of a cat’s normally regal air, has been identified as a “blep” by internet cat photo connoisseurs. An example:

Cunning as they are, cats probably don’t have the self-awareness to realize how charming this is. So why do cats really blep?

In a piece for Inverse, cat consultant Amy Shojai expressed the belief that a blep could be associated with the Flehmen response, which describes the act of a cat “smelling” their environment with their tongue. As a cat pants with his or her mouth open, pheromones are collected and passed along to the vomeronasal organ on the roof of their mouth. This typically happens when cats want to learn more about other cats or intriguing scents, like your dirty socks.

While the Flehmen response might precede a blep, it is not precisely a blep. That involves the cat’s mouth being closed while the tongue hangs out listlessly.

Ingrid Johnson, a certified cat behavior consultant through the International Association of Animal Behavior Consultants and the owner of Fundamentally Feline, tells Mental Floss that cat bleps may have several other plausible explanations. “It’s likely they don’t feel it or even realize they’re doing it,” she says. “One reason for that might be that they’re on medication that causes relaxation. Something for anxiety or stress or a muscle relaxer would do it.”

A photo of a cat sticking its tongue out
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If the cat isn’t sedated and unfurling their tongue because they’re high, then it’s possible that an anatomic cause is behind a blep: Johnson says she’s seen several cats display their tongues after having teeth extracted for health reasons. “Canine teeth help keep the tongue in place, so this would be a more common behavior for cats missing teeth, particularly on the bottom.”

A blep might even be breed-specific. Persians, which have been bred to have flat faces, might dangle their tongues because they lack the real estate to store it. “I see it a lot with Persians because there’s just no room to tuck it back in,” Johnson says. A cat may also simply have a Gene Simmons-sized tongue that gets caught on their incisors during a grooming session, leading to repeated bleps.

Whatever the origin, bleps are generally no cause for concern unless they’re doing it on a regular basis. That could be sign of an oral problem with their gums or teeth, prompting an evaluation by a veterinarian. Otherwise, a blep can either be admired—or retracted with a gentle prod of the tongue (provided your cat puts up with that kind of nonsense). “They might put up with touching their tongue, or they may bite or swipe at you,” Johnson says. “It depends on the temperament of the cat.” Considering the possible wrath involved, it may be best to let them blep in peace.

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