Do you know what happens when you Sleep?

 

By Courtney Johnson

How does sleep change throughout the night? 

Researchers used to believe that people were both physically and mentally inactive during sleep. Now, with further knowledge, we know that is not the case! 

There are four stages of sleep that we cycle through throughout the night. The first three stages make up what is called non-rapid eye movement (REM) sleep, and the fourth is rapid-eye movement (REM) sleep, the stage in which dreams occur. 

This cycle occurs multiple times throughout the night and varies in duration, typically from 70 to 120 minutes.  

Stage 1: Awake / falling into non-REM light sleep 

This phase is the cross-over period from wakefulness to sleep. During this brief period (typically lasting around 7 minutes), we experience very light sleep, the heartbeat, breathing, and eye movements slow, and the muscles relax. Brain waves also begin to slow. 

Stage 2: Non-REM light sleep

This stage is a period of light sleep before entering deep sleep. At this point, body temperature drops, eye movements cease, heartbeat and breathing slow even further, and the muscles relax more deeply. Here, brain wave activity briefly spikes and then continues to slow. 

We spend most of our sleep cycle in stage 2 sleep. 

Stage 3: Non-REM deep sleep

Stage 3 non-REM sleep is the phase that allows us to feel refreshed in the morning. It occurs in longer stretches during the first half of the night. In this phase, heart rate, breathing, and brain activity drop to their lowest levels, and it may be difficult to wake up. 

This type of sleep is restorative and is the time when the body repairs tissues, muscles, and cells, and restores its energy.  

Stage 4: REM deep sleep

REM sleep first occurs about 90 minutes after falling asleep. During this phase, as its name suggests, the eyes move rapidly behind closed eyelids. In REM sleep, brain activity, breathing, blood pressure, and heart rate increase to near their waking levels. 

Most of our dreaming occurs during stage 4, as does the processing of information by the brain, making it an important phase for memory and learning. 

What happens to the body and brain while we sleep? 

Almost every part of the body undergoes changes during sleep. Once we fall asleep, switching mechanisms in the brain activate, triggering thousands of neurons to go from a waking to sleeping state, which sends signals throughout the body. 

While scientists are still unclear about the sleep process and the purpose of sleep, we do know that sleep aids the immune and cardiovascular systems and helps to balance metabolism.  

We can observe changes in a number of key bodily processes while we sleep, such as: 

Brain function 

When measured in a clinical setting, our brain waves demonstrate clear patterns linked to each sleep stage. In early non-REM sleep, brain activity slows; however, in stage 2 and 3, there are brief spikes of brain energy.  

In REM sleep, brain activity speeds up and different types of brain waves can be observed, which is why this stage is most associated with dreaming. Scientists think that REM sleep supports critical cognitive functions, such as memory consolidation. 

Hormone levels 

Both sleep and the circadian rhythm (the body’s internal clock) are a key player in the production of hormones in the body, such as: 

• Melatonin, the sleep hormone 
• Cortisol, which plays a role in stress response 
• Growth hormone, which supports metabolism and bone and muscle development 
• Leptin and ghrelin, which regulate appetite 

Levels of these hormones fluctuate during the various sleep stages throughout the night, and the quality of a person’s sleep can potentially affect their production during the day. 

Muscle tone 

As the body goes through each stage of non-REM sleep and the body’s energy expenditure drops, the muscles gradually relax. While in REM, many of the muscle groups experience atonia, a temporary state of paralysis, which keeps the limps from moving in response to the content of our dreams.

The respiratory system and the eyes are unaffected, however, so we continue to breath and our eyes dart back and forth behind closed eyelids, giving us the name for REM sleep. 

Dreaming

Dreaming is most common and intense during REM sleep, though it can occur during any other sleep stage. However, dreams that occur during REM and non-REM sleep typically demonstrate different brain wave patterns, with dreams during REM being more immersive, imaginative, or bizarre in content. 

Heart rate

Our heart rate starts to slow during stage 1 of sleep and attains its slowest pace at stage 3. However, during REM sleep, our heart rate quickens to nearly the same rate as when we are awake. 

Breathing

As with the pulse, breathing also slows during non-REM sleep and reaches its lowest rates during stage 3. It can speed up and become irregular during REM sleep. 

Sleep plays a crucial role in our health, giving the brain and body the time to repair and reenergize after a long day. 

If we don’t get enough sleep, we may experience certain side effects like mood changes, focus and memory issues, and weakened immunity. 

Most adults need around 7-9 hours of sleep, though this can change depending on the person and the phase in life. If you’re having trouble sleeping, make sure to talk to your doctor. He or she may refer you to a sleep specialist or centre, who will be able to identify the underlying cause and help improve your sleep quality. 

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FAVORITE IMAGES OF THE WEEK - 9

Gerardo Aizpuru

Jewel Caterpillar

The Jewel Caterpillar--probably, though it hasn't been formally confirmed, an Acraga coa, belonging to a family of moths known as Alceridae--is sometimes known as a "slug caterpillar" due to gooeyness. This one was photographed near Cancun, Mexico. [via BoingBoing]

NASA/JPL-Caltech

Super Earth

This artist's concept of a so-called "super Earth" is a representation of a first-of-its-kind view that NASA's Spitzer Space Telescope caught this week. For the first time, we've seen direct light from a super Earth, "using its sensitive heat-seeking infrared vision." The planet is incredibly close to the star it orbits, and probably has a rocky core surrounded by both liquid and gaseous water. Read more here.

Wikimedia Commons

London Rooftop Missiles

We learned last week that, to protect the games or possibly just freak us the hell out, some London residents will play host to rooftop missiles during the Olympics. Here's what that missile will look like: a Starstreak High Velocity Missile. Read more here.

Tony LaCasse/New England Aquarium

Calico Lobster

This is a calico lobster. Caught off the coast of Maine, it was originally going to be eaten, because obviously, lobsters are delicious, that's what you do with them. But it's weird coloration (only 1 in 30 million are colored this way) led it to the New England Aquarium instead. Read more here.

Reuters/Darley Shen

DIY Double-Seater Sub

Zhang Wuyi, a farmer, created this double-seater sub--one of six. To see more photojournalism like this, head over to American Photo Mag.

USGS

Earth as Art

The U.S. Geological Survey occasionally exhibits some of the amazing satellite imagery taken of our planet--even though the satellite is for scientific purposes, sometimes it produces just stunningly beautiful images. Read more here.

BIG

Skyscraper

A Danish architecture firm called BIG have designed an apartment building, or group of buildings, or something, that is/are shaped like a hashtag. #Unlikely but #supercool. Read more here.

NASA/JPL-Caltech

Black Hole Revs Up

This artist's concept of the galaxy Arp 220 is based on data picked up by the Hubble Space Telescope. It's meant to show how a black hole that's revving up in power can suppress a galaxy's ability to birth new stars. Read more here.

Wenceslao T. Medina, Andre ́s A. de la Llera, Juan L. Condori, and Jose ́ M. Aguilera

Cereal Science

In one of our favorite stories of the week, a team of scientists sought to answer a question that has plagued absolutely nobody for absolutely no time: why does cereal taste better with milk than with water? Included in the article (which had amazing quotes) were these precise/hilarious magnified shots of soggy breakfast cereal.

Brain areas responsibility

Why Sex Feels Good: Neuroscientist Finds Orgasms Enhance Brain Activity, Leading To Altered State Of Consciousness

Repetitive sexual stimulation can lead to a trance-like state of mind during an orgasm.Photo courtesy of Pexels, Public Domain

The slightest touch from our partner can send shivers down our spine and travel through the most erogenous zones of the human body. Repeated stimulation can make our toes curl, our breath short, and our body move rhythmically to this touch. Before we know it, we’ve entered a trance-like state, and orgasm. Researchers at Northwestern University suggest orgasms feel so good because sexual stimulation sends the brain into an altered state of consciousness; it blocks out everything else, and allows us to solely concentrate on the sensation.

"Sex is a source of pleasurable sensations and emotional connection, but beyond that, it's actually an altered state of consciousness" said Adam Safron, study author, a neuroscientist, and a Ph.D candidate in the psychology department's Brain Behavior Cognition program in the Weinberg College of Arts and Sciences at Northwestern, in a statement.

During sex, our brain acts as a “pleasure center” to let us know what is enjoyable and what is not. The various nerves in the genitalia communicate with the brain about the sensation experience; this is why sensations can be perceived differently depending on what part of the body is being touched. The “cloud nine” feeling reported by many during sex is linked to the nerves sent to the brain’s pleasure center, or reward circuit.

Sexual pleasure floods the brain with a surge of neurochemicals — chemical messengers that forge emotions, feelings of attachment, and even love, according Psychology Today. The level of pleasure we feel is connected to the release of the chemicals, which can be used to measure the intensity of our orgasm. The areas of the brain impacted by sexual stimulation include the amygdala, nucleus accumbens, ventral tegmental area (VTA), cerebellum, and the pituitary gland.

In the study, published in the journal Socioaffective Neuroscience & Psychology, Safron and his colleague Victoria Klimaj, reviewed related studies and scientific literature to come up with a model in which rhythmic sexual activity likely influences brain rhythms. The model showed stimulating certain nerves in a particular way at a particular speed over and over again focuses our neurons. They begin to synchronize their activity in a process known as neural entrainment.

Eventually, if stimulation continues long enough, this synchronization can spread throughout the brain, which helps us become more focused than ever. If sexual stimulation is intense enough and goes on long enough synchronized activity could spread throughout the brain. This intense focused attention outcompetes usual self-awareness for access to consciousness, and so produces a state of sensory absorption and trance.

“This then caused me to hypothesize that rhythmic entrainment is the primary mechanism by which orgasmic thresholds are surpassed," said Safron.

The researchers were surprised to find parallels between sexual climax and seizures as well as with music and dance, In both orgasm and reflex seizures, rhythmic inputs into high-bandwidth sensory channels result in an explosive process after certain stimulation thresholds are surpassed. This could potentially be an evolutionary advantage.

The ability to keep rhythm may serve as a test of fitness for potential mates. Safron believes this is consistent as rhythmic song and dances are nearly universal parts of mating; dating back to hundreds of millions of years to our common ancestors with pre-vertebrate animals such as insects.

The trance-like state of mind could also have an evolutionary aspect. For example, the entrainment during sexual stimulation could be nature’s way of saying to continue having sex with this person because they are attending to your sexual needs, which means they’re more likely to be attentive in a relationship.

“Before this paper, we knew what lit up in the brain when people had orgasms, and we knew a lot about the hormonal and neurochemical factors in non-human animals, but we didn’t really know why sex and orgasm feel the way they do,” Safron said

So, this is why sex and orgasms feel so damn good.

How To Fall Asleep In 60 Seconds: I Practiced The 4-7-8 Breathing Technique For One Month

Tossing and turning, eyes opening and closing, and the inability to keep my mind from wandering while I try to sleep, are what most of my nights are made of. After midnight, I grow restless and disgruntled in my dark and silent bedroom as I’m unable to ease my mind and body into a deep slumber. Before I realize, it’s morning, and I’ve clocked in a maximum of five hours of poor sleep.

On a Sunday night, I decided to try something that would eventually give me one of the best sleeps of my life — breathing.

This is what happened when I tried the 4-7-8 breathing technique each night for a month.Pixabay, Public Domain

THE 4-7-8 BREATHING EXERCISE

Simple inhales and exhales can help you get the good night’s rest you deserve — in just 60 seconds. In May of last year, Dr. Andrew Weil, a physician and a “guru” for holistic health and integrative medicine, popularized the sleep technique known as the “ The 4-7-8 Breathing Exercise,” or the “Relaxing Breath.”

This holistic breathing technique is based on pranayama, an ancient Indian practice that means “regulation of breath.” While sitting in an upright position, you simply place the tip of your tongue against the ridge of tissue behind the upper front teeth and keep it there through the entire exercise (this will make a “whoosh” sound as you exhale). This is followed by breathing in through your nose for four seconds, holding your breath for seven seconds, and exhaling through your mouth for eight seconds. Weil suggests repeating this for three breathing cycles, for a total of four breaths. Eight breathing cycles is the absolute maximum.

When I first started practicing this method, I chose to lay in my bed, and would speed up my counting after inhaling for four seconds and holding my breath for seven. I thought to myself at 1 a.m. (my usual sleep time): "If I count faster, I can be done faster." Alas, I knew I would only be cheating myself in the end, so I decided to stick with it, and repeat the 4-7-8 breathing cycle, without taking breaks, or going back to regular breathing.

After two nights of this type of breathing, I could feel myself drifting away, as if my mind was wandering away while my body remained still. I could feel my heart rate begin to slow down, my mind start to ease, and my body physically relax as if it were one with the mattress. I was overpowered by the feeling of sedation — not being able to remember getting past the second breathing cycle. Before I realized it, I went from counting to four and waking up the next day at 7 a.m., wondering if I reached my eight-count exhalation.

Painting of girl sleeping.Pixabay, Public Domain

My sedative-like state is a typical symptom of the breathing exercise. Weil describes the technique as a “a natural tranquilizer for the nervous system” that eases the body into a state of calmness and relaxation. This slows down heart rate and increases oxygen in the bloodstream, relaxing the heart and the brain, because I’m in control of the breath in this situation.

Dr. Lindsay Bira, a clinical health psychologist and clinical researcher in San Antonio, Texas, says when we adjust our breath to be deeper, longer, and more controlled, we directly call into action the parasympathetic nervous system — the part of the nervous system that calms things down like heart rate, blood pressure, digestion, capillaries, and overall anxiety.

“Basically, breathing in this way and making the out-breath longer than our in-breath tells our brain the environment is safe and it is ok to calm down,” she told Medical Daily.

BREATHING AND THE NERVOUS SYSTEM

The rush hour commutes, deadlines, and living in the city can make it hard for anyone to catch their breath. These everyday triggers of stress activate the sympathetic nervous system, which is responsible for the stress response. Usually when I try to fall asleep, my mind thinks about how my day went and what I have to do the next day, meaning I tend to always live in the sympathetic nervous system. According to Bira, if we make a conscious effort to adjust the breath and let our parasympathetic take control, we can experience the benefits of stress reduction and relaxation.

So, when we choose to extend our inhale count to four, we're allowing ourselves to take in more oxygen, which affects the bloodstream as we hold our breath for seven seconds, and then emit carbon dioxide from our lungs as we exhale steadily for eight seconds. Moreover, the way our tongue is positioned during this exercise helps activate a pressure point, according to Dan Ferguson, an acupuncturist in Vancouver, Wa.

It “completes a circuit of two acupuncture channels that were made by the very first split of cells of you as an embryo,” he told Medical Daily.

This completes the circuit, which sets the foundation for relaxing the body, calming the nervous system and centering the mind.

Person sleeping.Pixabay, Public Domain

BREATHING AWAY SLEEPING DISORDERS

I’m no stranger to sleepless nights — as a child and currently in adulthood, I suffer from night terrors. The parasomnia, which affects 2.5 percent of the adult population, has been linked to triggers such as anxiety, poor sleep, and fever. However, these episodes are usually infrequent and benign, occurring only once or twice a month. Deep breathing in yoga has helped calm me down and remove feelings of anxiety, while the sleep breathing technique has led me to get a better night’s rest — no night terrors included.

These exercises can benefit people with sleep disorders like insomnia. Evidence-based treatments forinsomnia and other sleep issues usually include cognitive behavior therapy. It “focuses on adjusting the sleep environment, adjusting sleep behaviors, teaching the body how to relax effectively (e.g., diaphragmatic breathing) and addressing maladaptive thoughts that tend to promote anxiety at bedtime,” said Bira.

The focus on breath control and counting allows me to focus on something benign and exert control over stress-induced impulses like shallow breathing. The ability to control my breath, and not have it control me, has let me regain control of my body as I fall sleep.

IS 4-7-8 THE MAGIC NUMBER?

Weil has a magic formula that has proven to work, but does this mean we should all abide by this?

The breathing technique is supposed to be practiced twice a day — once in the morning, and once at night, but my yogi-like nature decided to save it for yoga. Yoga has plenty of breathing exercises that have allowed me to focus on my breathing and not my surroundings. Inhaling and exhaling as I stretch my limbs has given me a better sense of self control. Although breathing in yoga isn't based on the 4-7-8 method, it has helped me feel relaxed.

The 4-7-8 breathing pattern has led people to benefit from it, including me, but like anything, it’s not a one-size-fits-all approach.

“The point behind the sensationalized promise is to promote consistent practice. It is true that the most benefit comes with consistent practice of slowing the breath and breathing from the diaphragm,” said Bira.

She suggests practicing diaphragmatic breathing twice per day, 10 minutes each time. Doing so will allow us to exercise the diaphragm muscle, train our body how to relax effectively and on demand, and reduce emotional anxiety. Diaphragmatic breathing can be used as a “life line” for times of stress and to combat maladaptive thoughts.

The practice of breathing definitely helps the body and brain go to sleep.

So, did I really go to sleep in a minute or less?

Yes, but like any skill, it takes time to master. The key is to be mindful about breathing technique.

Next time you go to sleep, take a couple of breaths, and allow yourself to fall into a deep slumber.

20 Things You Didn't Know About... Sweat

Eunika Sopotnicka / Shutterstock

Your health, feelings and diet can change your sweat composition — but your unique sweat fingerprint is distinctly yours.

By Jessica Festa

1. Composed of about 99 percent water, sweat evaporates on the skin’s surface, cooling the body and keeping it from overheating.

2. Sweat secretions help you in other ways, too. They include dermcidin, an antibiotic peptide that appears to regulate bacteria growth on the skin and may fight infection.

3. Not all humans sweat equally. Men sweat up to twice as much as women, and both sexes sweat less with age.

4. The sensation of touch can trigger a “sweat reflex” on the opposite side of the body from the spot that is touched. 5 Sweat can trigger other responses: People with atopic dermatitis, a skin condition, can experience an immediate and serious allergic reaction to a fungal protein called MGL_1304 that’s found in sweat.

6. Aside from humans, horses are one of the few mammals that thermoregulate by sweating. Horse sweat is high in latherin, a protein that helps the water in sweat travel from the skin, past the animals’ heavy waterproof pelt and to the air, where it can evaporate and keep them cool.

7. Hippos actually produce a red-colored sweat, which acts as an antibiotic and sunscreen.

8. If you’re sweating red and you’re not a hippo, you might have a rare condition called hematohidrosis. Blood vessels rupture and run into sweat glands in affected individuals, causing them to actually sweat blood.

9. Another rare condition, chromhidrosis, causes humans to sweat orange, blue or other colors. While the condition can sometimes be traced to ingesting certain drugs, the cause often remains a mystery in otherwise healthy people.

10. It’s no mystery, however, why the sweat of healthy people often smells different from that of sick individuals. The body emits volatile organic compounds based on metabolic condition, which can change when disease or infection is present.

11. Cystic fibrosis can be detected with a sweat test. Sodium and chloride are much more concentrated in the sweat of individuals with the condition.

12. Emotions can trigger changes in the composition of your sweat. In an Austrian study, participants wore pads that collected their sweat while watching scary films first, and then neutral films the next day. A second group of volunteers smelled the pads and was able to distinguish which pads were worn during the scary movie.

13. In a similar experiment, female participants judged the sweat of non-meat-eating men to be more attractive than that of meat eaters.

14. Regardless of your health, feelings or diet, your sweat is distinctly yours. While other components of sweat may fluctuate, an individual’s sweat “fingerprint,” a unique blend of 373 volatile compounds, remains consistent over time.

15. Each of us has a unique sweat fingerprint, but the two types of sweat glands, apocrine and eccrine, are universal to humans. We have eccrine glands over most of our bodies, but apocrine glands only in our armpits and genital region.

16. Our bodies produce very little apocrine perspiration, but it’s responsible for most of the odor because it’s high in water and waste products that promote the growth of smelly bacteria.

17. Clear, fluid eccrine sweat, produced in much larger quantities, spreads the apocrine over a larger surface area — and the stench along with it.

18. What to do with all that sweat? UNICEF and Swedish engineer Andreas Hammar teamed up in 2013 to draw attention to millions of people without clean drinking water by creating the Sweat Machine, which pulled sweat from clothing and turned it into potable water through a process of spinning, heating and filtering.

19. The Sweat Machine was more awareness-raising stunt than solution. A sweaty T-shirt yielded just 2 teaspoons of purified water, and organizers admitted there were no plans to mass-produce the gizmo.

20. Maybe the Sweat Machine would have been more productive if they’d used socks instead. A pair of human feet has 250,000 sweat glands, emitting a half pint of liquid every day.

WHAT DOES YOUR GUT MICROBIOME LOOK LIKE?

Katherine Harmon Courage

SCIENTISTS CAN NOW SEE HOW DIET IMPACTS THE GUT AND ITS MICROBES—AND YOU CAN, TOO

Inside your gut

Quantitative Imaging of Gut Microbiota Spatial Organization

Your large intestine may not usually be a pretty place, but for scientists wielding a new technique to map out every last bacterium and undigested food particle, it can become a marvel. The results, described in the October issue of Cell Host & Microbe paint a stunning visual picture of a delicate dance between necessary microbes and the sensitive gut wall—kept in balance by a crucial layer of mucus. This image shows a detail taken from a mouse's gut that has been colonized with human gut microbes; the mucus layer is dyed green, the gut wall cells are tinted blue, and two phyla of bacteria common in a human gut are also marked: Firmicutes in yellow and Bacteroidetes in fuchsia. Such never-before-seen detail will help researchers better understand how diet can impact gut microbes and our health.

The microbes in your gut depend on you to feed them well. A steady diet of complex fibers keeps them happy—and by extension, may keep you healthier. The microbiota have been linked to weight, gut health, allergies and even mood. Studies have shown that when the host (you) fails to supply the hungry hordes of beneficial microbes with what they want, the populations can change, and can even start to threaten the gut's thin lining. But we have been unable to see exactly whether—and how—these shifts were happening.

Fiber-deprived

Quantitative Imaging of Gut Microbiota Spatial Organization

We depend on the mucus layer (pictured in green) to protect our gut wall. Even beneficial microbes in our gut can cause the immune system to activate if they get too close. A normal, healthy mucus layer is pictured on the left, showing the microbes (red) and food particles (yellow) far away from the host tissue (blue) when mice were on a standard diet. But when mice didn't eat any fiber (a favorite food of gut microbes, also known as "microbiota-accessible carbohydrates" or "MACs"), the mucus wall shrank, allowing microbes uncomfortably close to the gut tissue. Why the shrinkage? When microbes don't have dietary fibers to munch on, they eat the mucus instead.

Now a team at Stanford University has created an elegant method of peering inside the gut—at cell-level resolution—to see what is going on. The researchis in the October issue of Cell Host & Microbe.

The big picture

Quantitative Imaging of Gut Microbiota Spatial Organization

This slice shows how the mucus lining (green) surrounds undigested food (blue)—in this case plant matter—in the large intestine. This comprehensive, high-resolution view of a tiny (9-millimeter) sample was made by stitching together 40 different images.

Most of our understanding about gut microbes—and any impact diet has on them—has come from poop. Researchers can run a quick genetic scan on a smudge of a fecal sample, assessing which microbes are there, and in what abundances. But from this mixed-up pile, there is no way to know where in the gut the microbes are living—or how they are interacting with one another or with you. "Mapping the spatial organization of this microbial community is a fundamental aspect of understanding its biology," says Justin Sonnenburg, a microbiologist at Stanford and coauthor of the new paper. "Without this information, we will struggle to make sense of how these microbes are contributing to our health or why interactions go awry and cause disease."

Missing clusters

Quantitative Imaging of Gut Microbiota Spatial Organization

Researchers found that mice colonized with human gut microbes and fed a normal, healthy diet had clusters of different types of bacteria (Bacteroidetes in red andFirmicutes in green). When mice lacked fiber in their diet, however, this organization disappeared, and members of these two microbe phyla were scattered randomly within the large intestine. You can also see that the space (black) between the microbes and the host tissue (blue) is thinner in the no-fiber diet.

"This is a huge advance," says Eric Martens, an assistant professor of microbiology at the University of Michigan Medical School, who also studies the impact of fiber on gut microbes and the gut's mucus layer and was not involved in the new research. "Since we are just beginning to understand the mechanisms and functions of the hundreds of species of bacteria that inhabit the gut, understanding how these organisms pack together, organize, and reproduce in such a dense and tightly confined space provides enormous insight," he says.

Up-close companions

Quantitative Imaging of Gut Microbiota Spatial Organization

A closer look comparing the healthy diet (left) and the fiber-deficient diet (right) shows how different the distributions of the microbe types are. Bacteria in theBacteroidetes phylum are in red, and those in the Firmicutes phylum are in green. The standard diet on the left also appears to contain more Firmicutes overall than the fiber-free diet on the right, which could have implications for what happens in the gut—and by extension, the host.

Sonnenburg and his colleagues fed mice (colonized with human gut microbes) standard and fiber-deficient diets. They then carefully preserved thin slices of the mouse intestines and added special dyes to mark different microbes, undigested food, the essential mucus layer and the gut wall. With so many minute sample slices to analyze, they also developed software to help compute the spatial relationships.

Building the barrier

Quantitative Imaging of Gut Microbiota Spatial Organization

The crucial mucus layer that protects our gut is constantly being renewed. This image of a standard mouse gut shows a close-up of mucus (green) being formed by goblet cells (in pockets surrounded by blue host tissue) and then released into the mucus barrier. "The mucus forms sheets that build on top of each other, forming a boundary," explains Kristen Earle, a graduate researcher in microbiology and immunology at Stanford University and co-author of the new study. "On top of this layer is a looser layer, that forms a habitat for bacteria."

In being able to actually see what was happening on these different diets, the researchers found that when the fiber was reduced, the mucus layer shrank—likely due to starved microbes eating it—from approximately 51 micrometers to just 31, allowing the microbes closer to the sensitive wall of the intestine. And as Sonnenburg notes, "we know that part of maintaining harmony between our resident microbes and our intestinal tissue is separation of the two"—namely by the mucus layer.

Crowded field

Quantitative Imaging of Gut Microbiota Spatial Organization

The highest concentrations of bacteria are found in the large intestine, where they break down fibers and other compounds our body couldn't process on its own. This image shows a mat of bacteria in a normal mouse fed on a healthy diet.

As this mucus layer shrank, mice missing the fiber in their diet also had more markers of inflammation. This can be triggered by the immune system attempting to keep bugs where they belong—in the gut. "Over long periods of time, low levels of inflammation can lead to many different types of problems, including colitis or even cancer," Sonnenburg says. (But, he cautions, the experiments have only been in mice—and over a short time period—so how the findings translate to us and our long-term health remain to be seen.)

Strange powers

Quantitative Imaging of Gut Microbiota Spatial Organization

Although fewer and farther-between, bacteria in the small intestine seem to play a role in shaping the landscape there. The small intestine is lined with protrusions called villi, which help increase the body's ability to absorb nutrients from food passing through. In mice fed a standard diet, there was a small amount of an antimicrobial compound (called REG3B, noted by coloring antibodies to this compound in red) at the base of the villi. But this microbe-deferring compound was prevalent through the villi when mice ate a fiber-free diet. Researchers are still investigating what this might mean for health.

In addition to the shrinking mucus layer, the researchers were also able to see that changing the diet altered the way bacteria were organized in the gut. On a standard diet, two categories of bacteria were usually found in clumps of similar cells. But without fiber, these groupings vanished, and the microbes were more evenly distributed.

Ronan O'Connell, of University College Dublin's Conway Institute of Biomolecular and Biomedical Research, has been using laser microscopy to parse the structure of the gut microbiota in healthy people as well as those with diseases of the intestinal tract. He notes that the new imaging technique "beautifully illustrates the complexity of the host-microbiome interface," adding that it might some day be able to be used to study the differences in healthy and diseased guts in humans. Sonnenburg and his group are, in fact, already looking to expand the work to humans.

In the meantime, the new software used for this work (called BacSpace) is available to other groups, and, Sonneburg notes, he hopes sharing it will "propel this field forward rapidly." Martens, for one, is enthusiastic about the potential for this visual approach. "One can imagine turning up the resolution to the species level, instead of just phyla."

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