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7 Surprising Facts About the Breast

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The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

Of all the organs of the body, the humble breast has come to represent so much more than its essential functions. American culture places undue value on size, shape, and appearance of breasts, which can make it easy to forget the essential function of the breast, from an evolutionary standpoint, which is primarily for feeding our offspring. Mental Floss spoke to a pair of specialists about the breasts. Here are seven things we learned.

1. BREASTS ARE GLANDS.

Beneath the fleshy mound that we think of as a breast is the less glamorously named mammary gland, a complex network of fat cells and tubes that are capable of producing milk for babies. If a woman becomes pregnant, the milk ducts, sac-like structures, fill first with colostrum before the baby is born and then breast milk after, and send it via little channels called lobules to the nipple, where the milk exits.

2. BREASTS ARE SISTERS, NOT TWINS.

According to Constance Chen, a plastic and reconstructive surgeon and director of microsurgery at New York Eye & Ear Infirmary of Mount Sinai Hospital, two breasts are rarely, if ever, identical. "Breasts come in all shapes and sizes," she tells Mental Floss. "There are lots of different ways to be normal." The same is also true for nipples and their areolae, the darker colored skin around the nipples.

3. INVERTED NIPPLES ARE NORMAL.

An inverted nipple is a normal occurrence "caused by adhesions at the base of the nipple that bind the skin to the underlying tissue," according to a team of specialists at Columbia University that answers medical questions in a column called “Go Ask Alice.” It's possible to have one inverted nipple and not the other, or both. In general, it should cause very little discomfort or problems, with the exception of breastfeeding. Sometimes an inverted nipple can be difficult for an infant to latch onto, but there are methods to help the nipple protrude again, such as nipple shields. In very rare cases, a nipple that becomes inverted may be a sign of breast cancer, in which a tumor is pulling on the tissue and causes it to invert.

4. SMOKING CAN CAUSE BREASTS TO DROOP, BUT BREASTFEEDING DOESN'T.

Many women blame breastfeeding for breast droop, but the facts don’t bear that out. While pregnancy can change the elasticity of ligaments in the breasts, breastfeeding merely changes the size of the breasts, but has little impact on the elasticity of the skin. Smoking, on the other hand, is a direct antagonist to elastin, the substance that makes all skin supple, which can lead to drooping breasts.

5. BREAST CANCER DOES NOT DISCRIMINATE.

People often believe that the only way they’re likely to get breast cancer is if they have a family history. According to Chen, this is not accurate: "Most people who get breast cancer have no family history," she notes. Beyond genetics, risk factors include "getting older, benign breast problems, more exposure to estrogen, drinking alcohol, and exposure to radiation."

And men can get breast cancer, too. "It makes up less than 1 percent of all cancers in men, but it's not a part to be ignored," Jay Harness, a breast cancer and reconstructive surgeon at St. Joseph Hospital in Orange, California, tells Mental Floss. Women and men should both seek preventative cancer screenings, especially if there is a family history of the aggressive BRCA1 gene that carries a significant risk of cancer in men and women. Early detection is key to helping treat breast cancer.

6. MIDWIVES OF OLD READ BREASTS LIKE BOOKS.

According to a class at Stanford titled "A History of the Body," early midwives and medical practitioners made meaning of the colors of women’s breasts. A 17th-century midwife, Jane Sharp, wrote about the English women she tended to: "The Nipples are red after Copulation, red as a Strawberry, and that is their Natural colour: But Nurses Nipples, when they give Suck, are blue, and they grow black when they are old." 

7. IT’S NOT JUST MEN WHO STARE AT WOMEN'S BREASTS.

Psychologists from the University of Nebraska-Lincoln did a study in 2013 to determine whether men were alone in their alleged fascination with women's breasts. For the study, titled "My Eyes Are Up Here: The Nature of the Objectifying Gaze Toward Women," 29 women and 36 men were fitted up with eye-tracking technology and shown women with "body shapes that fit cultural ideals of feminine attractiveness to varying degrees." They were told to focus on the appearance versus the personality of the women. Both male and female participants spent more time looking at the women's breasts than they did their faces, especially if a woman had a "high ideal" body shape: hourglass, with a small waist and large breasts.

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Why Is Your First Instinct After Hurting Your Finger to Put It in Your Mouth?
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If you close your fingers in a car door or slam your funny bone into a wall, you might find your first reaction is to suck on your fingers or rub your elbow. Not only is this an instinctive self-soothing behavior, it's a pretty effective technique for temporarily calming pain signals to the brain.

But how and why does it work? To understand, you need to know about the dominant theory of how pain is communicated in the body.

In the 17th century, French scientist and philosopher René Descartes proposed that there were specific pain receptors in the body that "rang a bell in the brain" when a stimulus interacted with the body, Lorne Mendell, a professor of neurobiology and behavior at Stony Brook University in New York, tells Mental Floss. However, no study has effectively been able to identify receptors anywhere in the body that only respond to painful stimuli.

"You can activate certain nerve fibers that can lead to pain, but under other circumstances, they don't," Mendell says. In other words, the same nerve fibers that carry pain signals also carry other sensations.

In 1965, two researchers at MIT, Patrick Wall and Ronald Melzack, proposed what they called the gate control theory of pain, which, for the most part, holds up to this day. Mendell, whose research focuses on the neurobiology of pain and who worked with both men on their pain studies, explains that their research showed that feeling pain is more about a balance of stimuli on the different types of nerve fibers.

"The idea was that certain fibers that increased the input were ones that opened the gate, and the ones that reduced the input closed the gate," Mendell says. "So you have this idea of a gate control sitting across the entrance of the spinal cord, and that could either be open and produce pain, or the gate could be shut and reduce pain."

The gate control theory was fleshed out in 1996 when neurophysiologist Edward Perl discovered that cells contain nociceptors, which are neurons that signal the presence of tissue-damaging stimuli or the existence of tissue damage.

Of the two main types of nerve fibers—large and small—the large fibers carry non-nociceptive information (no pain), while small fibers transmit nociceptive information (pain).

Mendell explains that in studies where electric stimulation is applied to nerves, as the current is raised, the first fibers to be stimulated are the largest ones. As the intensity of the stimulus increases, smaller and smaller fibers get recruited in. "When you do this in a patient at low intensity, the patient will recognize the stimulus, but it will not be painful," he says. "But when you increase the intensity of the stimulus, eventually you reach threshold where suddenly the patient will say, 'This is painful.'"

Thus, "the idea was that shutting the gate was something that the large fibers produced, and opening the gate was something that the small fibers produced."

Now back to your pain. When you suck on a jammed finger or rub a banged shin, you're stimulating the large fibers with "counter irritation," Mendell says. The effect is "a decrease in the message, or the magnitude of the barrage of signals being driven across the incoming fiber activation. You basically shut the gate. That is what reduces pain."

This concept has created "a big industry" around treating pain with mild electrical stimulation, Mendell says, with the goal of stimulating those large fibers in the hopes they will shut the gate on the pain signals from the small fibers.

While counter irritation may not help dull the pain of serious injury, it may come in handy the next time you experience a bad bruise or a stubbed toe.

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10 Surprising Ways Senses Shape Perception
The American Museum of Natural History
The American Museum of Natural History

Every bit of information we know about the world we gathered with one of our five senses. But even with perfect pitch or 20/20 vision, our perceptions don’t always reflect an accurate picture of our surroundings. Our brain is constantly filling in gaps and taking shortcuts, which can result in some pretty wild illusions.

That’s the subject of “Our Senses: An Immersive Experience,” a new exhibition at the American Museum of Natural History in New York City. Mental Floss recently took a tour of the sensory funhouse to learn more about how the brain and the senses interact.

1. LIGHTING REVEALS HIDDEN IMAGES.

Woman and child looking at pictures on a wall

Under normal lighting, the walls of the first room of “Our Senses” look like abstract art. But when the lights change color, hidden illustrations are revealed. The three lights—blue, red, and green—used in the room activate the three cone cells in our eyes, and each color highlights a different set of animal illustrations, giving the viewers the impression of switching between three separate rooms while standing still.

2. CERTAIN SOUNDS TAKE PRIORITY ...

We can “hear” many different sounds at once, but we can only listen to a couple at a time. The AMNH exhibit demonstrates this with an audio collage of competing recordings. Our ears automatically pick out noises we’re conditioned to react to, like an ambulance siren or a baby’s cry. Other sounds, like individual voices and musical instruments, require more effort to detect.

3. ... AS DO CERTAIN IMAGES.

When looking at a painting, most people’s eyes are drawn to the same spots. The first things we look for in an image are human faces. So after staring at an artwork for five seconds, you may be able to say how many people are in it and what they look like, but would likely come up short when asked to list the inanimate object in the scene.

4. PAST IMAGES AFFECT PRESENT PERCEPTION.

Our senses often are more suggestible than we would like. Check out the video above. After seeing the first sequence of animal drawings, do you see a rat or a man’s face in the last image? The answer is likely a rat. Now watch the next round—after being shown pictures of faces, you might see a man’s face instead even though the final image hasn’t changed.

5. COLOR INFLUENCES TASTE ...

Every cooking show you’ve watched is right—presentation really is important. One look at something can dictate your expectations for how it should taste. Researchers have found that we perceive red food and drinks to taste sweeter and green food and drinks to taste less sweet regardless of chemical composition. Even the color of the cup we drink from can influence our perception of taste.

6. ... AND SO DOES SOUND

Sight isn’t the only sense that plays a part in how we taste. According to one study, listening to crunching noises while snacking on chips makes them taste fresher. Remember that trick before tossing out a bag of stale junk food.

7. BEING HYPER-FOCUSED HAS DRAWBACKS.

Have you ever been so focused on something that the world around you seemed to disappear? If you can’t recall the feeling, watch the video above. The instructions say to keep track of every time a ball is passed. If you’re totally absorbed, you may not notice anything peculiar, but watch it a second time without paying attention to anything in particular and you’ll see a person in a gorilla suit walk into the middle of the screen. The phenomenon that allows us to tune out big details like this is called selective attention. If you devote all your mental energy to one task, your brain puts up blinders that block out irrelevant information without you realizing it.

8. THINGS GET WEIRD WHEN SENSES CONTRADICT EACH OTHER.

Girl standing in optical illusion room.

The most mind-bending room in the "Our Senses" exhibit is practically empty. The illusion comes from the black grid pattern painted onto the white wall in such a way that straight planes appear to curve. The shapes tell our eyes we’re walking on uneven ground while our inner ear tells us the floor is stable. It’s like getting seasick in reverse: This conflicting sensory information can make us feel dizzy and even nauseous.

9. WE SEE SHADOWS THAT AREN’T THERE.

If our brains didn’t know how to adjust for lighting, we’d see every shadow as part of the object it falls on. But we can recognize that the half of a street that’s covered in shade isn’t actually darker in color than the half that sits in the sun. It’s a pretty useful adaptation—except when it’s hijacked for optical illusions. Look at the image above: The squares marked A and B are actually the same shade of gray. Because the pillar appears to cast a shadow over square B, our brain assumes it’s really lighter in color than what we’re shown.

10. WE SEE FACES EVERYWHERE.

The human brain is really good at recognizing human faces—so good it can make us see things that aren’t there. This is apparent in the Einstein hollow head illusion. When looking at the mold of Albert Einstein’s face straight on, the features appear to pop out rather than sink in. Our brain knows we’re looking at something similar to a human face, and it knows what human faces are shaped like, so it automatically corrects the image that it’s given.

All images courtesy of the American Museum of Natural History unless otherwise noted.

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