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.

12 Fantastic Facts About the Immune System

monkeybusinessimages/iStock via Getty Images
monkeybusinessimages/iStock via Getty Images

If it weren't for our immune system, none of us would live very long. Not only does the immune system protect us from external pathogens like viruses, bacteria, and parasites, but it also battles cells that have mutated due to illnesses, like cancer, within the body. Here are 12 fascinating facts about the immune system.

1. The immune system saves lives.

The immune system is a complex network of tissues and organs that spreads throughout the entire body. In a nutshell, it works like this: A series of "sensors" within the system detects an intruding pathogen, like bacteria or a virus. Then the sensors signal other parts of the system to kill the pathogen and eliminate the infection.

"The immune system is being bombarded by all sorts of microbes all the time," Russell Vance, professor of immunology at University of California, Berkeley and an investigator for the Howard Hughes Medical Institute, tells Mental Floss. "Yet, even though we're not aware of it, it's saving our lives every day, and doing a remarkably good job of it."

2. Before scientists understood the immune system, illness was chalked up to unbalanced humors.

Long before physicians realized how invisible pathogens interacted with the body's system for fighting them off, doctors diagnosed all ills of the body and the mind according to the balance of "four humors": melancholic, phlegmatic, choleric, or sanguine. These criteria, devised by the Greek philosopher Hippocrates, were divided between the four elements, which were linked to bodily fluids (a.k.a. humors): earth (black bile), air (blood), water (phlegm) and fire (yellow bile), which also carried properties of cold, hot, moist, or dry. Through a combination of guesswork and observation, physicians would diagnose patients' humors and prescribe treatment that most likely did little to support the immune system's ability to resist infection.

3. Two men who unraveled the immune system's functions were bitter rivals.

Two scientists who discovered key functions of the immune system, Louis Pasteur and Robert Koch, should have been able to see their work as complementary, but they wound up rivals. Pasteur, a French microbiologist, was famous for his experiments demonstrating the mechanism of vaccines using weakened versions of the microbes. Koch, a German physician, established four essential conditions under which pathogenic bacteria can infect hosts, and used them to identify the Mycobacterium tuberculosis bacterium that causes tuberculosis. Though both helped establish the germ theory of disease—one of the foundations of modern medicine today—Pasteur and Koch's feud may have been aggravated by nationalism, a language barrier, criticisms of each other's work, and possibly a hint of jealousy.

4. Specialized blood cells are the immune system's greatest weapon.

The most powerful weapons in your immune system's arsenal are white blood cells, divided into two main types: lymphocytes, which create antigens for specific pathogens and kill them or escort them out of the body; and phagocytes, which ingest harmful bacteria. White blood cells not only attack foreign pathogens, but recognize these interlopers the next time they meet them and respond more quickly. Many of these immune cells are produced in your bone marrow but also in the spleen, lymph nodes, and thymus, and are stored in some of these tissues and other areas of the body. In the lymph nodes, which are located throughout your body but most noticeably in your armpits, throat, and groin, lymphatic fluid containing white blood cells flows through vein-like tubules to escort foreign invaders out.

5. The spleen helps your immune system work.

Though you can live without the spleen, an organ that lies between stomach and diaphragm, it's better to hang onto it for your immune function. According to Adriana Medina, a doctor who specializes in hematology and oncology at the Alvin and Lois Lapidus Cancer Institute at Sinai Hospital in Baltimore, your spleen is "one big lymph node" that makes new white blood cells and cleans out old blood cells from the body.

It's also a place where immune cells congregate. "Because the immune cells are spread out through the body," Vance says, "eventually they need to communicate with each other." They do so in both the spleen and lymph nodes.

6. You have immune cells in all of your tissues.

While immune cells may congregate more in lymph nodes than elsewhere, "every tissue in your body has immune cells stationed in it or circulating through it, constantly roving for signs of attack," Vance explains. These cells also circulate through the blood. The reason for their widespread presence is that there are thousands of different pathogens that might infect us, from bacteria to viruses to parasites. "To eliminate each of those different kinds of threats requires specialized detectors," he says.

7. How friendly you're feeling could be linked to your immune system.

From an evolutionary perspective, humans' high sociability may have less to do with our bigger brains, and more to do with our immune system's exposure to a greater number of bacteria and other pathogens.

Researchers at the University of Virginia School of Medicine have theorized that interferon gamma (IG), a substance that helps the immune system fight invaders, was linked to social behavior, which is one of the ways we become exposed to pathogens.

In mice, they found IG acted as a kind of brake to the brain's prefrontal cortex, essentially stopping aberrant hyperactivity that can cause negative changes in social behavior. When they blocked the IG molecule, the mice's prefrontal cortexes became hyperactive, resulting in less sociability. When they restored the function, the mice's brains returned to normal, as did their social behavior.

8. Your immune system might recruit unlikely organs, like the appendix, into service.

The appendix gets a bad rap as a vestigial organ that does nothing but occasionally go septic and create a need for immediate surgery. But the appendix may help keep your gut in good shape. According to Gabrielle Belz, professor of molecular immunology at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, research by Duke University's Randal Bollinger and Bill Parker suggests the appendix houses symbiotic bacteria that are important for overall gut health—especially after infections wipe out the gut's good microbes. Special immune cells known as innate lymphoid cells (ILCs) in the appendix may help to repopulate the gut with healthy bacteria and put the gut back on track to recovery.

9. Gut bacteria has been shown to boost immune systems in mice.

Researchers at the University of Chicago noticed that one group of mice in their lab had a stronger response to a cancer treatment than other mice. They eventually traced the reason to a strain of bacteria—Bifidobacterium—in the mice's guts that boosted the animals' immune system to such a degree they could compare it to anti-cancer drugs called checkpoint inhibitors, which keep the immune system from overreacting.

To test their theory, they transferred fecal matter from the robust mice to the stomachs of less immune-strengthened mice, with positive results: The treated mice mounted stronger immune responses and tumor growth slowed. When they compared the bacterial transfer effects with the effects of a checkpoint inhibitor drug, they found that the bacteria treatment was just as effective. The researchers believe that, with further study, the same effect could be seen in human cancer patients.

10. Scientists are trying to harness the immune system's "Pac-Man" cells to treat cancer.

Aggressive pediatric tumors are difficult to treat due to the toxicity of chemotherapy, but some researchers are hoping to develop effective treatments without the harmful side effects. Stanford researchers designed a study around a recently discovered molecule known as CD47, a protein expressed on the surface of all cells, and how it interacts with macrophages, white blood cells that kill abnormal cells. "Think of the macrophages as the Pac-Man of the immune system," Samuel Cheshier, lead study author and assistant professor of neurosurgery at Stanford Medicine, tells Mental Floss.

CD47 sends the immune system's macrophages a "don't eat me" signal. Cancer cells fool the immune system into not destroying them by secreting high amounts of CD47. When Cheshier and his team blocked the CD47 signals on cancer cells, the macrophages could identify the cancer cells and eat them, without toxic side effects to healthy cells. The treatment successfully shrank all five of the common pediatric tumors, without the nasty side effects of chemotherapy.

11. A new therapy for type 1 diabetes tricks the immune system.

In those with type 1 diabetes, the body attacks its own pancreatic cells, interrupting its normal ability to produce insulin in response to glucose. In a 2016 paper, researchers at MIT, in collaboration with Boston's Children's Hospital, successfully designed a new material that allows them to encapsulate and transplant healthy pancreatic "islet" cells into diabetic mice without triggering an immune response. Made from seaweed, the substance is benign enough that the body doesn't react to it, and porous enough to allow the islet cells to be placed in the abdomen of mice, where they restore the pancreatic function. Senior author Daniel Anderson, an associate professor at MIT, said in a statement that this approach "has the potential to provide [human] diabetics with a new pancreas that is protected from the immune system, which would allow them to control their blood sugar without taking drugs. That's the dream."

12. Immunotherapy is on the cutting edge of immune system research.

Over the last few years, research in the field of immunology has focused on developing cancer treatments using immunotherapy. This method engineers the patient's own normal cells to attack the cancer cells. Vance says the technique could be used for many more conditions. "I feel like that could be just the tip of the iceberg," he says. "If we can understand better what the cancer and immunotherapy is showing, maybe we can go in there and manipulate the immune responses and get good outcomes for other diseases, too."

Why Do People Get Ice Cream Headaches?

CharlieAJA/iStock via Getty Images
CharlieAJA/iStock via Getty Images

Reader Susann writes in to ask, "What exactly is the cause of brain freeze?"

You may know an ice cream headache by one of its other names: brain freeze, a cold-stimulus headache, or sphenopalatine ganglioneuralgia ("nerve pain of the sphenopalatine ganglion"). But no matter what you call it, it hurts like hell.

Brain freeze is brought on by the speedy consumption of cold beverages or food. According to Dr. Joseph Hulihan—a principal at Paradigm Neuroscience and former associate professor in the Department of Neurology at the Temple University Health Sciences Center, ice cream is a very common cause of head pain, with about one third of a randomly selected population succumbing to ice cream headaches.

What Causes That Pain?

As far back as the late 1960s, researchers pinned the blame on the same vascular mechanisms—rapid constriction and dilation of blood vessels—that were responsible for the aura and pulsatile pain phases of migraine headaches. When something cold like ice cream touches the roof of your mouth, there is a rapid cooling of the blood vessels there, causing them to constrict. When the blood vessels warm up again, they experience rebound dilation. The dilation is sensed by pain receptors and pain signals are sent to the brain via the trigeminal nerve. This nerve (also called the fifth cranial nerve, the fifth nerve, or just V) is responsible for sensation in the face, so when the pain signals are received, the brain often interprets them as coming from the forehead and we perceive a headache.

With brain freeze, we're perceiving pain in an area of the body that's at a distance from the site of the actual injury or reception of painful stimulus. This is a quirk of the body known as referred pain, and it's the reason people often feel pain in their neck, shoulders, and/or back instead of their chest during a heart attack.

To prevent brain freeze, try the following:

• Slow down. Eating or drinking cold food slowly allows one's mouth to get used to the temperature.

• Hold cold food or drink in the front part of your mouth and allow it to warm up before swallowing.

• Head north. Brain freeze requires a warm ambient temperature to occur, so it's almost impossible for it to happen if you're already cold.

This story has been updated for 2019.

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