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7 Amazing Facts About the Amygdala

We tend to think of our brains as one big organ inside our skulls, but it’s actually comprised of many, small structures that make it possible for us to walk, talk, think, and feel. Of these, one of the more well-known structures, the amygdala, has been found to play a hugely important role in many social and emotional processes—influencing everything from health to addiction.

Mental_floss spoke to Rahul Jandial, a neurosurgeon and neuroscientist at City of Hope Cancer Center in Los Angeles, California, and Brandon Brock, a staff clinician at the Cerebrum Health Centers Brain Initiative Group in Texas, about this fascinating part of the brain.

1. IT'S NOT REALLY ONE STRUCTURE …

One of the more well-known structures, the amygdala is located within the depths of the anterior-inferior temporal lobe. The almond-shaped region is part of the limbic system and is actually a paired structure, with parts in each temporal lobe, according to Jandial.

He says you can survive with only one of the two: “How do I know? I can surgically remove one as part of a brain surgery called selective amygdalohippocampectomy.” In fact, in studies where rats, monkeys, or rabbits have their amygdala removed, the animals live normal lives except for one notable new development: They don’t feel fear.

2. … BECAUSE THE AMYGDALA IS YOUR BRAIN'S FEAR FACTORY.

Your fear of snakes and scary movies is in large part due to the function of your amygdala, which “responds before frontal lobes weigh in,” Jandial says. It’s part of your instinctive brain and serves as your “emotional thermostat.” He adds, “It’s not in charge of just fear, but all deep and visceral emotions—one of those ancient brain regions that can defy the frontal lobe request.”

According to a 2007 study in Social Cognitive and Affective Neuroscience, “amygdala activity may represent the generation of emotional experience itself, and/or it may reflect sundry aspects of emotional information processing correlated with emotional experience.”

3. THE AMYGDALA ALSO HAS A TRUE MIND-BODY CONNECTION.

And yet the amygdala has purposes beyond fear. It has been shown to assist in emotional learning, “whereby cues acquire significance through association with rewarding or aversive events,” according to a paper in Current Opinion Neurobiology. More recent research, the authors write, suggest that the amygdala regulates additional cognitive processes, such as memory or attention.

With its ability to interpret sensory stimuli in the world and translate them into physical reactions, the amygdala, as a research paper in Social Cognitive and Affective Neuroscience suggests, “may thus represent embodied attention—the crucial link between central (mental) and peripheral (bodily) resources.”

4. DAMAGE TO THE AMYGDALA CAN LEAVE YOU HORNY AND HUNGRY.

An injured amygdala can leave a person “super hungry, sexually aroused, and fixated with putting things in their mouth,” says Jandial. In other cases, it can lead to a reduced fear of risks, and thus an increase in risky behavior. Researchers found that adult monkeys who were given amygdalectomies “showed more pro-social cues and less avoidance behaviors toward other (healthy) monkeys.” In one extreme case, damage to the amygdala shut down one woman’s ability to feel fear altogether.

5. IT ALSO PLAYS A ROLE IN PAIN.

Fibromyalgia is a disease characterized by "widespread musculoskeletal pain with diffuse tenderness at multiple tender points,” as a study in Clinical Neuroscience describes. Brock says that changes in the amygdala’s volume and function play a role in both fibromyalgia and chronic pain syndromes. This appears to be a consequence of the amygdala becoming hypervigilant and oversensitized to internal sensations of pain or trauma, according to a study in Explore. “This results in exhaustion of the neuro-endocrine and immune systems and chronic physical and mental exhaustion, as well as many secondary symptoms and ongoing complications.”

6. THE AMYGDALA IS KEY TO UNDERSTANDING ADDICTION.

Addiction is considered a brain disease by the medical community rather than a lack of willpower or a character defect. According to a study in Brain Research, a common addiction cycle comprises three stages—“preoccupation/anticipation, binge/intoxication, and withdrawal/negative affect—in which impulsivity often dominates at the early stages and compulsivity dominates at terminal stages.” The amygdala becomes recruited in the final withdrawal stage, where it sends stress signals to the body, driving a person to crave more of their substance.

7. DESPITE ADVANCES IN BRAIN-IMAGING TECHNOLOGY, IT'S STILL DIFFICULT TO STUDY.

Though we know much more about the amygdala since it was first discovered in the 1930s in monkeys, there’s still much to learn. Because of the amygdala’s deep brain location and its entanglement with other neighboring brain structures, it’s difficult to find “exact ways to monitor its function, output and all regions that it has a synaptic influence on. Time and further scientific research will hopefully unveil that,” Brock explains.

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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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