What Is Emotion?
Although feelings of love, hate, anger, and joy are common responses for most people, emotions have always been thought to be subjective feelings that vary depending on the person. For example, two people engaging in an argument will have different levels of response and may experience different sensations. Emotions are a difficult field of study for scientists because their complexity and uniqueness make them nearly impossible to measure.
Neuroscientists studying the brain have narrowed down the areas most active during an emotional response. Feelings of happiness and pleasure are linked to the prefrontal cortex, while anger, fear, and other negative emotions are linked to the amygdala. Expressive behavior, such as smiling or laughing, is the outward sign of emotion. Most people also have physiological responses to emotion, such as turning red, a pounding heart, or adrenaline release. Different chemicals in the brain control the level of emotion a person experiences. At any moment, dozens of neurotransmitters, or chemical messengers, travel through individual cells throughout the entire brain. If a person is in danger, the brain releases stress hormones, flooding certain regions with adrenaline. These measurable signs of emotion differ between individuals, however, again suggesting that emotion is subjective. But according to a new study by Cornell neuroscientist Adam Anderson, that is not exactly the case. Two people who have a similar reaction to a sunset share a similar pattern of activity in the orbitofrontal cortex, a region of the prefrontal cortex. “Despite how personal our feelings feel, the evidence suggests our brains use a standard code to speak the same emotional language,” Anderson explains.
Whether emotions are objective or subjective, scientists are still not entirely sure why we feel what we feel, or why we express it in particular ways. Anderson calls emotions “the last frontier of neuroscience.” Most people consider emotions a necessary part of being human. They add depth to the human experience. Empathy, in particular, is an important by-product of emotion. Scientists trace the feeling of empathy to mirror neurons, cells in the brain that fire when we see someone else in a situation that we can imagine ourselves in. People with autism spectrum disorders have difficulty showing empathy, and researchers believe that a better understanding of the physical processes behind emotion can solve these and other psychological disorders.
Is It True That You Use Only 10 Percent of Your Brain?
Historians have traced the earliest reference to this rumor back to the beginning of the 20th century, when it was perpetuated by self-help gurus promising to expand people’s mental abilities. However, like so many things hucksters have told us, the brain claim is false. “There’s no question,” says Marcus Raichle, a neurologist and professor of radiology at Washington University in St. Louis, “you’re using every little bit of this thing.”
Even when you’re sleeping or just watching TV, your brain is burning a surprising amount of energy for its size. Although your brain constitutes about 2 percent of your body weight, it accounts for 20 percent of the total energy that your body consumes.
Scientists know that most of your brain’s energy is used for basic upkeep and communication between neurons. The rest, they speculate, might go toward preparing the brain to receive information by making predictions based on past experiences. For example, instead of scanning your entire fridge each time you want to grab some milk, you can reach directly for the shelf where you last left it—because your brain is working hard to remind you of its location and shoot your hand in that direction. This preprocessing helps you deal with the enormous amount of detail you encounter every day.
You can be certain that all of your brain is working hard, even when you’re not thinking hard. “We should back away from the notion that the only thing the brain is doing is sitting around waiting for something to happen,” Raichle says. “Every piece of it is running full-tilt all the time.”
What Causes Déjà Vu?
Few of us ever experience significant supernatural phenomena, but 60 to 80 percent of us do report having the strange sensation that we’ve already experienced something that we consciously we are actually experiencing for the first time. Like feeling you’ve had the same exact conversation with someone before. Or walking into a room you have never been in before, and sensing that you’ve been there in the past.
If you’ve ever had feelings such as these, you’ve experienced déjà vu, the sense of having experienced something previously, although it is, in reality, entirely new. Déjà vu comes from the French term meaning “already seen.”
The phenomenon of déjà vu is difficult to study because it occurs only briefly and without notice, and it fades quickly. In addition, there is no physical manifestation of the experience, leaving scientists little to work with other than self-reported descriptions. So although researchers have been studying déjà vu for more than 100 years and theories to explain it abound, there is no single conclusive explanation for why it happens or what processes are involved in its occurrence.
Many modern researchers believe déjà vu is a memory-based cerebral experience. The precise interplay of brain functions, however, remains uncertain. One prevalent hypothesis, called the cellphone theory, or divided attention, proposes that a brief distraction might explain the feeling that we have experienced something before. Imagine walking down a street while chatting with a friend on your cellphone. Engrossed in your conversation, you pass a brand-new restaurant for the first time, your brain subliminally, shallowly acknowledging the new eatery. Moments later, when the conversation has ended and you focus your complete attention on your surroundings, you become fully conscious of the restaurant—and are struck with a feeling of déjà vu. What’s happened? Your brain, while observant of all your surroundings, had been working below conscious awareness, and when you returned your full attention to the restaurant, you got the feeling you were familiar with it. In fact, you were: You just hadn’t been paying attention.
Another hypothesis, the hologram theory, proposes that some feature in our environment, such as a sight or a sound that resembles a distant memory, triggers the brain to create a complete scene of the déjà vu experience. As you study a small portion of a painting you’ve never seen before, for instance, a distant memory surfaces from deep within your brain. According to the hologram theory, this occurs because memories are stored in a form like holograms, and with holograms you need only one fragment in order to see the full picture. Your brain identifies the portion of the painting with the past memory, perhaps a similar painting or a comparable photograph you’ve seen. However, instead of remembering that you’ve seen something similar in the past, your brain recalls the old memory without identifying it, leaving you with a sense of familiarity with the painting—your déjà vu experience—but no recollection of the original memory.
Researchers are hopeful that advances in brain imaging technology will allow us to better understand how the human brain works and to pinpoint exactly how the déjà vu phenomenon occurs.
The Y chromosome is small in comparison to other chromosomes, containing only 27 unique genes as compared to thousands on others. A result of natural selection, this indicates that it is stripped down to its essential purpose.
Is the Y Chromosome Doomed?
Humans store their genes in 23 pairs of chromosomes, 22 of which are identically matched. The 23rd is a two-sided biological coin—twin Xs mean you’re female; an X and a Y, male. Chromosome pairs often trade bits of DNA in a process called recombination, the purpose of which is to keep genes functioning properly.
Talk of men’s path toward extinction began in the late 1990s, when it was discovered that the human Y chromosome, which is stumpy compared with the X, does not share enough genetic material with the X to practice recombination. Left without a way to renew damaged genes, the Y would continue to degrade and would eventually disappear, geneticists announced. They slapped an expiration date on the male half of the species of sometime in the next 5 to 10 million years.
To get a perspectiv
e on this prediction, scientists looked to our closest genetic relatives—the chimps. Because humans and chimpanzees shared a common ancestor 6 million years ago, geneticist David Page of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, studied how the chimp Y chromosome and its human Y counterpart have evolved differently in the intervening years. What he found surprised him: The chimp Y chromosome is far more degraded than the human Y chromosome.
Page and his colleagues speculate that chimps’ promiscuity—females mate with multiple partners—has led to enhancement of the Y genes that produce sperm, to the detriment of other genes. Among chimps, “there are sperm wars going on. Each male is trying to pass his own genes down,” says Jennifer Hughes, who coauthored the study. Neglected, the chimp Y chromosome’s nonreproductive genes have declined.
The Whitehead Institute scientists think that although the human Y chromosome also lost genes at first, in recent eons it has been relatively stable. The human Y has eluded the chimp Y’s fate, they suggest, because humans are largely monogamous. Human sperm don’t face the same competition as chimps’, so there isn’t as much pressure on the human Y to produce good sperm.
Not all geneticists are convinced that the human Y has stopped deteriorating. Jenny A. Marshall Graves of the Australian National University in Canberra, believes that the Y chromosome’s days are numbered. “The human Y has been degenerating since it was born, 300 million years ago,” she says. And so the controversy continues. Rest assured, though; the Y chromosome—and the guys—will be around for a while.
Do Men and Women Have Different Brains?
While it’s not exactly true that men are from Mars and women from Venus, scientific evidence shows they are wired differently. Anecdotally speaking, men tend to gravitate toward math and science disciplines, while women lean toward excellence at language.
To study brain connectivity, researchers use a type of scan called DTI, a technique that maps the diffusion of water molecules within brain tissue, tracing fiber pathways that connect different regions of the brain. Female brains contain about 9.5 times as much white matter, the substance that connects various parts of the brain. The bridge of nerve tissue that connects the right and left side of the brain is stronger in women, perhaps explaining why they are more equipped for multitasking. Women activate both the left and right hemispheres when listening to language. The frontal area and the temporal area of the cortex are bigger and better organized, helping women score better on attention, facial recognition, and social cognition. Women are faster and more accurate when identifying emotions and seem better at controlling them.
In contrast, men tend to focus on a single issue and excel at it. Studies of male brains show fewer connections between the right and left hemispheres. Male brains are about 10 percent larger than female brains and contain about 6.5 times more gray matter, or “thinking matter.” Men appear to be better at special processing, meaning that they are more aware of where they sit on a map (and also that they are less likely to ask for directions). They rely on the hippocampus to place where they are, whereas women tend to rely on landmarks. But it’s not all good news for the male sex—men are more susceptible to attention deficit disorder and lack of impulse control.
Despite these differences, women and men still have a lot in common. “All of these things have overlapping distributions. There are many women with better-than-average spatial skills, and men with good writing skills,” says David Geary, professor of psychological services at the University of Missouri. Some researchers argue that exercising one’s brain, especially at a young age, can enhance areas of difficulty. Most importantly, while men and women take different routes, they perform equally well on broad measures of cognitive ability.
Why Do We Sleep?
Catch 40 winks, nod off, hit the hay—we all sleep, spending roughly one-third of our lives doing it. Why humans need to sleep, though, is a question scientists still haven’t answered.
What’s obvious is that without sleep, we lack energy and our thinking process can become muddled. Sleep deprivation can also lead to accidents on the road or at work, various health ailments, decreased sex drive, and symptoms of depression, among other problems. And while reported cases of human beings directly dying from lack of sleep are rare, the physiological changes that occur from sleep deprivation can be more detrimental, and possibly fatal, than going without food.
Over the years, scientists have advanced several theories about the role sleep plays in human health. One theory suggests that sleep, and the conservation of energy that goes with it, helped humans and other species evolve. Using less energy for part of the day lowers the demand for food. For humans, sleeping at night meant they were conserving energy during the time when it would be hardest to find food. Some scientists see a link between this theory and one called the adaptive or evolutionary theory. Early humans saw the value of staying inactive at night in order to avoid drawing the attention of nocturnal predators. This prolonged inactivity evolved into sleep.
Another explanation for why we sleep is the restorative theory. During sleep, parts of the body restore themselves—tissues are repaired, hormones are released, proteins in brain cells are synthesized.
Neuroscientists talk about the brain’s plasticity—its ability to modify its internal structure as it encounters changes in the environment or the body itself. Sleep seems to play a role in this plasticity, as neurons forge new pathways during those hours, especially in young people. While asleep, the brain also processes memories so that they can be drawn upon for future use. Research suggests that the neural connections that create memories strengthen when we sleep.
A more recent theory about the importance of sleep has called it a “biological dishwasher.” During sleep, the brain flushes out waste products that accumulate there during the day. One of these substances is adenosine, which is found in all cells. In the brain it’s created during neural activity, and as it accumulates it makes us feel sleepy. When we actually do sleep, the body flushes the adenosine out of the brain, helping us feel revived when we wake.
In 2013, this idea of sleep and biological cleansing received a boost from research done on mice. Their brain cells shrank while they slept, creating pathways for spinal fluid to pass through. The fluid flowed ten times faster during sleep than when the mice were awake. The flow of the spinal fluid helped carry away the brain’s waste products as well as proteins that can harm the brain when too many of them accumulate there.
Today, scientists don’t agree that any one theory explains why we sleep. They continue to probe what exactly happens in the brain when we grab some shut-eye.
Why Do We Hiccup?
If you’ve ever chugged a carbonated drink, felt overwhelmed by fear, or experienced a bloated stomach, you might have hiccuped soon after. These and other actions and conditions can trigger hiccups, and sometimes they start for no clear reason at all.
Hiccups—singultus in the medical world—occurs during the breathing process when the diaphragm breaks out of its normal rhythm of moving up and down and suddenly contracts involuntarily. When this happens, air rushes down the throat and hits the vocal cords as they shut, creating the “hic” sound.
Although hiccups are a common occurrence, they don’t seem to have any real biological purpose. As to why they happen, one theory is that the nerves that control the vocal cords and the diaphragm get out of whack, for some reason scientists don’t understand. The malfunction could result from damage or irritation to those nerves. From an evolutionary standpoint, hiccups may have once been helpful in swallowing food or dislodging a stuck morsel.
Humans start hiccuping very early: A fetus may hiccup in the womb. Some scientists think hiccups could help developing infants prepare for breathing once they leave the womb. Whatever their purpose, fetal hiccups are common.
Hiccups be a sign of illness or hurt us on their own. Although most outbreaks last for only seconds or minutes, some people have endured nonstop hiccups for
days or weeks. In those extreme cases, a person could develop problems with eating, sleeping, or breathing, and doctors recommend seeking treatment if hiccups last more than 48 hours. In 2007, a Florida teenager made the news when she hiccuped for more than five weeks straight, sometimes 50 times per minute. She couldn’t go to school and had trouble sleeping, and doctors couldn’t explain what caused this severe hiccuping bout. The girl received various medical treatments, including acupuncture, but it isn’t clear whether the hiccups responded to the treatment or finally just stopped on their own.
Why Aren’t (Most) Humans Furry?
Ever since Darwin first made headlines, scientists have been pondering why humans lost their natural coats as they evolved from apes. The theories range from lice to cannibalism.
The traditional theory—refined by scientists over the past 40 years—proposes that humans gradually became furless in order to withstand the brutal heat of the African savanna or to prevent overheating while chasing prey.
One alternative idea, put forth in 2003 by evolutionary biologist Mark Pagel of the University of Reading in England, is that as humans learned to keep warm by making clothing and building shelters, they no longer needed heavy body hair. This hairlessness prevented parasites, such as mites and ticks, from sticking to their bodies. Avoiding parasites led to healthier humans, Pagel posits, and because there’s nothing as attractive as a bug-free hominid, hairlessness became a desirable feature in a mate, and natural selection drove the hairier folks into extinction.
100 Mysteries of Science Explained Page 7