“What I’m trying to understand is: How are the brain cells different between the healthy people and those with schizophrenia and autism?” Kristen Brennand. Credit: Joe Belcovson/Salk Institute

To figure out how your brain cells behave, scientist Kristen Brennand would first look at the skin on your hand. As a postdoctoral fellow in the lab of Fred Gage at the Salk Institute for Biological Studies in San Diego, Brennand transforms skin cells into brain cells to study how the brain behaves in health and disease. It sounds like magic, but it’s not: Before brain cells become full-grown neurons, they start out as immature stem cells. Stem cells have the ability to become any type of cell. In her lab, Brennand takes skin cells back in time, transforming them into stem cells. She then coaxes them to become brain cells. She’s using this approach to compare healthy brain cells to those in people with schizophrenia, a common mental illness, and to those of people with autism.

Here, Brennand, who earned her Ph.D. from Harvard University, describes her research to science writer Susan Gaidos.

Susan Gaidos: How can you study someone’s brain by looking at his or her skin cells?

Kristen Brennand:  About four years ago, some scientists in Japan discovered that you can turn skin cells into stem cells. In fact, the stem cells that you get are almost identical to embryonic stem cells, which means that they can make every cell type found in the adult body. For our experiment, we first turn the skin cells into stem cells. Then we can make brain cells from the stem cells. So we have to go: skin cells to stem cells to brain cells.

As a result, we have an incubator full of brain cells that should, in theory, have the same characteristics as the brain cells in the brain.

How do you get the skin cell to go back in time and become a stem cell?

It’s amazing to me that we can do this. It turns out that by turning on four genes — that’s all it takes — you can turn the skin cell into stem cells. These four specific genes are highly active in embryonic stem cells. By activating those genes in skin cells, the cells acquire all the abilities to grow and to differentiate, which means to make all the cell types that we know of. We turn on these four genes for a period of three weeks. Then, when we then go back and turn them off, the cells have made the change.

How do you go about making the stem cells to turn into brain cells?

We try to do it the same way that the embryo does. And we have information on that process, thanks to studies of animals such as mice. Over the past 20 years, scientists have been learning about this process by looking at mice embryos to see how they make brain cells. So we have an idea of some of the proteins, or growth factors, that turn on as an embryo makes a brain, and we try to add the same growth factors in the same order.

Can any type of cell become a brain cell?

Using those four genes, any kind of cell in the body can be turned into a stem cell in the laboratory. Once they become a stem cell, they can be coaxed into making brain cells. We use skin cells because they are easier to get than are a lot of the other cell types.

How do you collect the skin cells?

We have a dermatologist take a small punch biopsy. It’s the same thing that you would do if you had a mole that you wanted to remove.

“Most of my day, every day, is spent in a tissue culture hood, feeding my cells and taking care of them.” Kristen Brennand. Credit: Joe Belcovson/Salk Institute

How do you keep the skin cells alive?

That’s actually really easy. Skin cells love to grow and are some of the easiest cells to keep alive. I can keep them alive for much longer than four weeks. The cells are kept in our incubators and the incubators are kept at 37° Celsius — the same temperature as our bodies. The air in the incubator is five percent carbon dioxide, which is a lot higher than the air that we breathe but closer to what you have in your body. To feed them, we give them a mixture that includes a specific mix of amino acids and vitamins and minerals and sugars — all the things that are needed to keep cells alive.

Once the cells are transformed into brain cells, how are they used to study disease?

I take skin cells from healthy people, and also from people with schizophrenia and autism. The fact that I start with skin cells is not important; skin cells just happen to be on the outside of every person and are pretty easy to take a small sample of. Every cell in our body contains a complete copy of our DNA, so we know that the skin cells from my patients contain all the genes that cause their disease. While the skin cells from healthy people have no mutations and should make normal brain cells, the skin cells from patients with schizophrenia and autism should have all the mutations necessary to cause the disease. This means that the brain cells that I generate from patient skin cells should be identical to the brain cells inside their brain. So what I wind up with is brain cells from healthy people and from people with schizophrenia and autism to study in the laboratory. What I’m trying to understand is: How are the brain cells different between the healthy people and those with schizophrenia and autism?

The things we look at include how well the neurons, or mature brain cells, ‘talk’ to each other, how mature they are, how functional they are, or how many branches they have. We’re trying to understand, at the level of an individual brain cell, how that cell matures and how it talks to its neighbors. So that might be different.

Did you always want to be a scientist?

Yes. For a while I thought that I wanted to be medical doctor as well. But I’ve loved science since I was in elementary school, and I always knew that I wanted to work in the medical field or science field.

What made you decide you wanted to study the brain?

When I was an undergraduate, I worked in a lot of different labs. One of them studied mouse brain development and I found the work interesting and exciting. I then went on to graduate school, where I worked in a pancreas lab studying diabetes. This was a laboratory that carried out some of the earliest studies on embryonic stem cells. From my work in this lab I knew that I wanted to use stem cells to model disease. I went back to studying the brain because the timing just seemed right. There are a lot of interesting diseases that can be studied using stem cells today, not five or 10 years from now. It was the right time to start using stem cells to study the brain.

How do you spend your days in the lab?

Usually the first thing that I do is I feed my cells. Some days that takes the entire day, other days it takes just a few hours. But my cells get fed every day, and all the different types of cells get fed different types of food.

The cells require other care, too, because they are growing all the time. So every few days I have to put them into bigger plates. That’s called splitting — when you take cells that have been growing and multiplying and spread them out on the new plate. I have to split my stem cells about every five days, and I have to split my neural progenitor cells about every week and my skin cells about every week. So all the cells are always growing, except for the neurons — they’re the only ones that don’t keep growing. So you just have to feed those, which is kind of nice. So most of my day, every day, is spent in a tissue culture hood, feeding my cells and taking care of them.

How can information from your studies be used to treat brain disorders or disease?

If I can find a difference between the schizophrenic brain cells or the autistic brain cells and the healthy ones, then I can start putting drugs on them to see if I can reverse the damage. For example, if I see that the neurons are a different size or if they don’t talk as well, I could try different drugs to identify ones that fix it. In theory, if I can fix the differences I see in a cell in a dish, those same drugs might work in people.

How did you prepare for your science career?

I grew up in a small town in Canada, so I didn’t have access to any laboratories in high school. I simply studied hard and then got my lab experience when I entered college. I think students who live in cities near universities should feel free to contact researchers to volunteer to help in the lab. Contact lots of them if necessary and be persistent. Somebody will say yes. High school students are incredibly useful and are always welcomed in the lab.

What do the students in your lab do?

One thing I have them do is look for differences between the neurons. One student is looking to see if the neurons talk differently. Another is trying to see if they are a different size. Another student is looking to see if they are as functional, and looking to see if different genes are turned on in the schizophrenic neurons versus the healthy neurons. So my students do real experiments for me all the time, experiments that I wouldn’t have time to do.

Power words

Embryonic stem cell A stem cell that comes from a human in the early stages of development. Embryonic stem cells have two distinctive properties: 1) they are pluripotent, meaning they can generate every cell type found in adults; and 2) they can replicate indefinitely in the laboratory. Embryonic stems cells are derived from four-day-old human embryos prior to implantation in the uterus, when they consist of just 50–150 cells.

Gene Any one of the tiny units that make up a section of a chromosome. Genes carry qualities and characteristics that are passed on to a person’s children, such as hair color and eye color.

Turn on a gene A gene that is activated is said to be turned “on.” The human genome contains more than 20,000 genes, but only some are ever turned on. Each cell type in the body, from brain cells to heart cells to skin cells, has different genes turned “on” and “off.”

Model disease To study how a disease occurs and what happens in a cell or body over the course of a disease. Some diseases and health problems involve processes that can be studied only in a living organism, so scientists frequently use cells or animals as research subjects.

Neuron A mature brain cell.

Neural proginator cell Unlike neurons, neural progenitor cells can still divide. They cannot function like mature brain cells. With time (in the laboratory, usually a few months), neural progenitor cells can become neurons.

Neurogenesis: The birth of new brain cells.

Some people with synesthesia always see the letters in the alphabet as a certain color. The color of each letter is always the same.

The number “6” is a bright shade of pink. Listening to a cello smells like chocolate. And eating a slice of pizza creates a tickling sensation on the back of your neck.

If you have experiences like this, you may be one of the special people with an unusual sensory condition called synesthesia (pronounced sin-uhs-THEE-zha).

People with synesthesia experience a “blending” of their senses when they see, smell, taste, touch or hear. Such people have specially wired brains, so that when something stimulates one of the five senses, another sense also responds. This blending can cause people to see sound, smell colors or taste shapes.

Dozens of different sensory combinations exist. In the most common form of synesthesia, numbers, letters or even days of the week appear in their own distinct color.

If you’ve encountered these types of events, you’re not alone. Scientists say as many as one in every 200 people may be a synesthetes, as people with this condition are called. The phenomenon is known to run in families, and may occur more often among women than men. Many famous people have had synesthesia, including Russian writer Vladimir Nabokov and physicist Richard Feynman.

One thing is certain; most synesthetes treasure their unusual ability to take in the world with an additional sense. After all, who wouldn’t want to experience the world in full, glorious color or sound?

“It’s absolutely a positive experience,” says Patricia Lynn Duffy, a synesthete who has talked to hundreds of others with the condition while writing a book on the subject. “If you proposed to take away someone’s synesthetic ability, I think they would say, ‘No, I like it this way.’’’

When people with certain types of synesthesia look at the image on the left, they can easily detect the six figures facing the opposite way, as shown in the image on the right. To these people, the “S” figures appear in a different color than the “2″ figu

What Color is my “i”?

Most synesthetes learn about their amazing gift by accident. They are surprised to learn that everyone does not experience the world as they do.

Though it may sound strange to many people, Duffy says the experiences are not scary. The people who have synesthesia have always experienced life that way.

“For as long as I could remember, each letter of the alphabet had a different and distinct color. This is just part of the way alphabet letters look to me,” says Duffy. “Until I was 16, I took it for granted that everyone shared those perceptions with me.”

Synesthetes do not actively think about their perceptions — they just happen. Some synesthetes report that they see such colors internally, in “the mind’s eye.” Others, such as Duffy, see their visions projected in front of them, like watching an image on a movie screen.

Scientists know that in synesthesia, those colors are real, not just figments of an active imagination. How? Studies show that the colors synesthetes see are highly specific and consistent over time. If the letter “b” is lime green, it will always be lime green.

Studies done in the mid-1990s showed that synesthesia also can be measured by brain-scanning techniques. For synesthetes who perceive colors when hearing words, a certain part of the brain involved with vision is active in response to sound. That type of activity didn’t occur in non-synesthetes.

Making Connections

So how can the sound of a musical instrument lead to color?

Scientists are still trying to discover exactly how information from the senses merge together in the brain. But this much is known:

Messages gathered from the eyes, ears, mouth, nose and nerves involved in the sense of touch travel to the brain for processing. Much of this sensory processing occurs in an area of the brain called the cortex, the outermost part of the brain that organizes and enables us to respond to the incoming messages.

Information from each of senses is first processed in its own special region. It’s then sent on to “higher” regions in the cortex for further processing. At certain points in the brain, these various senses converge.

One theory is that synesthesia may be caused by “cross-wiring” between areas of the brain that process different sensations, such as color, sound or taste. This theory draws on the fact that children are born with many nerve connections between nearby parts of the brain.

“During our first few years of life, our brain makes more connections than it needs, and then eventually prunes some of those away,” says Edward Hubbard, a post-doctoral researcher at the French National Institute for Health and Medical Research who studies what causes synesthesia.

One thing that may happen in synesthesia, Hubbard says, is that some of these connections don’t get pruned away. If so, then people may see specific colors with particular letters because they have extra connections between the brain areas involved in word and color perception.

Last summer, a group of scientists in the Netherlands found direct evidence of these types of extra connections.

The researchers used a method called DTI to scan the brains of 18 people with synesthesia. They also looked at the brains of 18 non-synesthetes.

Using a kind of magnetic resonance imaging called DTI (an example is shown above) to look at the brains of synesthetes and non-synesthetes, scientists showed that synesthetes who see colored letters have higher levels of white matter in three different br

DTI (which stands for diffusion tensor imaging) measures how water flows in the brain. Within certain brain tissues, or nerve fibers, water flows more freely in one direction than the other. This is especially true in a type of nerve fiber, or axon, that carries messages from brain cell to brain cell. Commonly called “white matter,” these axons connect different parts of the brain to each other.

By measuring the water flow through these tissues, the scientists could measure how many of these axons there were in each brain region. Brain regions that are highly connected will have more white-matter axons.

In synesthetes who saw colored letters, the scientists found higher levels of white matter in three different brain regions. One was in the letter and word region of the brain, known as V4. The other highly connected areas were found in brain regions involved in consciousness — the awareness that you’re thinking, feeling, seeing, hearing or any number of other things your brain enables you to do.

“We have lots of things impinging upon our senses, and some of them become conscious and some of them don’t,” says Hubbard. “Activity in this area might make a person more consciously aware of a synesthetic experience.”

These findings don’t rule out other possible causes of synesthesia, says Hubbard. Still, he is now working to see if this type of “cross-wiring” occurs in other forms of synesthesia. Other scientists are looking to see whether other parts of the brain are also involved in synesthesia.

Hubbard is also developing better ways to identify the various processing regions of the brain. “Everybody’s brain differs a little bit in its exact organization,” he says.

Duffy notes that these variations in nerve connections occur not only in synesthetes, but in all people.

“Everybody develops a neural pattern that’s kind of unique, just like a fingerprint,” she says. “That’s why no two people are seeing the world in exactly the same way.”

Going Deeper:

For most mammals, puberty is marked by an increase in aggression. As animals reach reproductive age, they often have to establish themselves in their herd or social group. In species where males compete for access to females, signs of aggressive behavior

Breakouts, mood swings and sudden growth spurts: Puberty can be downright awkward. Even if you’re not of the human species.

Puberty is a period in which humans move from childhood to adulthood. During this transition, the body goes through many physical and emotional changes.

But humans aren’t the only creatures to experience dramatic changes as they mature. Jim Harding, a wildlife information specialist at Michigan State University, says all animals — from aardvarks to zebra finches — go through a period of transition as they take on adult characteristics and reach sexual maturity, or the ability to reproduce.

“If you look at it that way, you could say that animals go through a kind of puberty, too,” he says.

For animals, the awkwardness of growing up is also not just a physical phenomenon. It’s social and chemical, as well. While they may not have zits to contend with, many animals change their coloring or body shape as they mature. Others take on a whole new set of behaviors. In some cases, animals are forced to leave their social group once they reach sexual maturity.

Just as in humans, the process of moving from a juvenile animal to a full-fledged adult is driven by changes in the body’s hormones, says Cheryl Sisk, a neuroscientist at Michigan State University. Hormones are important messenger molecules. They signal to cells when to turn on or off their genetic material, and play a role in every aspect of growth and development.

When the time is right, certain hormones tell the body to start the changes that come with puberty. In humans, this process begins when the body sends a chemical signal from the pituitary gland in the brain to the sex organs.

This brings about many changes in the body. Girls start to gain curves and menstruation begins. Boys develop facial hair and may hear their voice crack from time to time. Boys and girls also go through all sorts of emotional changes at puberty.

Animals go through a similar process. In nonhuman primates, it’s not all that different from humans. Monkeys, chimpanzees and gorillas — all genetically similar to humans — go through many of the same biological changes as humans do. Females begin having monthly menstrual cycles, and males become larger and more muscular.

Some primates go through a change that humans, fortunately, don’t go through: Their rump color changes to red. This happens when the animals gain sexual maturity, Sisk says. “That’s a sign of being fertile or receptive.”

The age at which the maturation process begins in an animal depends on the species. In rhesus monkeys, for example, pubertal changes start around 3 to 5 years of age. Just as in humans, the maturation process can take years, Sisk says.

Fighting for status

For most mammals, puberty is marked by an increase in aggression, says Ron Surratt, director of animal collections at the Fort Worth Zoo in Texas. The reason? As animals reach reproductive age, they often have to establish themselves in their herd or social group. In species where the males have to compete for access to females, signs of aggressive behavior can begin at a young age.

Monkeys, for example, often give up the rough-and-tumble play they engaged in as juveniles and begin showing more interest in the opposite sex. And male gorillas between the ages of 12 and 18 become much more aggressive as they begin to compete for access to mates.

This punky, teenage period in male gorillas is a time to try to test boundaries, says Kristen Lukas, a psychologist who specializes in animal behavior. She should know: Her job at the Cleveland Metroparks Zoo is to keep these unruly apes in line.

During puberty, these cocky young male gorillas may try to pick fights with older males, or threaten other guys in the group. Often, they act as if they have more power or control than they actually have, Lukas says.

In the wild, such behavior is rewarded with the right to breed. But in zoos, managers must try to manage or prevent such aggression in young males.

“It can be a very difficult time to manage the males through,” she says. “But once they get past puberty and they’re more mature, they settle down and they make good parents.”

Gorillas aren’t the only animals that get a bit testy during puberty.

Male antelopes, for example, will use their horns to spar with one another beginning at the age of 12 to 15 months. When puberty hits, such play-fighting may give way to all-out aggression. As the males get older and larger, they may take on the older males, knowing that the strongest animal gets the herd.

Similar struggles for dominance occur among elephants, Surratt says. “As the young, immature bulls start to mature, you’ll see them pushing each other around. This becomes much more intense as they start to reach adulthood. They’re basically fighting for the right to breed.”

Taking shape

For some animals, size is just as important as age when it comes to reaching sexual maturity. Turtles, for example, have to reach a certain size before they can take on adult characteristics. Once they reach the right proportions, their bodies begin to transform.

Male wood turtles, for example, look just like the females until they reach about 5 1/2 inches in length. At that time, the males’ tails become longer and thicker. Their bottom shell changes shape, too, taking on an indentation that makes it look somewhat concave. The change in males’ shell-shape allows them to mount females during mating without falling off.

Male slider turtles and painted turtles go through a different, more bizarre kind of change as they mature: In these species, the males develop long fingernails. The nails grow gradually, over a period of about a month. They are then used to tap out vibrations on the face of the females during courtship.

Some animals go through two major transition periods as they mature. Frogs and salamanders, for example, go through metamorphosis — moving from a larval stage to a tadpole — before they take on their adult form. They then have to grow to a certain size before they can reproduce. That may take several months to a year, says Harding, who specializes in herpetology — the study of amphibians and reptiles.

Some animals go through two major transition periods as they mature. Frogs, for example, go through metamorphosis — moving from a larval stage to a tadpole — before they take on their adult form.

Simon Colmer / Nature Picture Library

The average frog, for example, will remain a tadpole over the summer months and may not breed until the following year. Before it’s able to reproduce, the frog goes through a growth spurt, getting larger in size. Its spot pattern or color pattern may also change.

Salamanders follow a similar growth pattern. A young salamander will metamorphose, but not get its full adult coloration for some time, says Harding.

“I get a lot of calls from people who say, ‘I found this weird salamander. It’s kind of small and I’ve looked at the field guides and can’t find anything that matches it,’ ” Harding says. He explains, “That’s probably because it has a juvenile coloration, which will gradually change into the adult color pattern.”

Looking good

Many types of birds develop elaborate plumage when they hit puberty. In some species, such as birds of paradise, males gain colorful, eye-popping feathers while females remain rather drab-looking by comparison.

oariff/iStockphoto

For all critters, the changes that occur during puberty have evolved for a single reason: to help them reproduce. In order to succeed at this task, they first have to attract a mate. No problem.

While animals can’t go to the mall to purchase image-boosting accessories to attract the opposite sex, they’ve developed some clever strategies of their own. Many types of birds, for example, develop elaborate plumage when they hit puberty.

In some species, such as birds of paradise, the males gain colorful, eye-popping feathers while the females remain rather drab-looking by comparison. In other species, both males and females take on a flashier hue. In flamingos, for example, both sexes turn a bright shade of pink when they hit puberty.

In flamingos, both sexes turn a bright shade of pink when they hit puberty.

jlsabo/iStockphoto

Along with these new adornments come behavioral changes. Even before they’re in full adult plumage, most birds start learning new postures, calls or moves that are used to communicate with other members of their species.

With all this growth and learning taking place so quickly, pubescent animals, like humans, can appear a little klutzy at times. But just like their human counterparts, animals eventually fill out, shape up and make their way through it.

Going Deeper:

As part of the carbon cycle, leaves decompose and the carbon in their bodies is broken down and recycled. Some of it is released into the air as carbon dioxide, or CO2. The rest moves into the soil.

Each year, spring comes, plants bloom and the trees leaf out in their full green glory. Come fall, while diving into piles of fallen leaves, you may think the life cycle of the leaf has come to an end.

But that’s not so. Once a leaf hits the dirt, a new cycle begins. All those brightly colored leaves are like candy for fungi and bacteria on the ground. These decomposers, organisms that feed on dead matter, go to work breaking down leaves to create energy-filled food for themselves. In the process, decomposers also make nutrients available for other organisms.

This recycling scheme is not just a plot to produce a mob of mushrooms and other eensy entities. It’s part of a complex chemical cycle that helps regulate the Earth’s climate. And it’s all based on carbon, a kind of element, or tiny substance.

Carbon is the building block for all life on Earth. Every single cell in every living thing — including plants, animals and humans — contains at least some of the stuff.

Carbon isn’t found only in living matter. It’s also found inside the Earth’s mantle, the layer between the crust and the core, and in seawater, air, rocks and soil. The planet’s carbon is constantly flowing from one of these to another, creating what is known as the carbon cycle.

Take those leaves, for example. As they decompose, or rot, the carbon in their bodies is broken down and recycled. Some of it is released into the air as carbon dioxide, or CO2. The rest moves into the soil.

Soil is a great place for carbon. There, it may remain locked up for hundreds, thousands or even millions of years, adding nutrients needed for growing food. Keeping carbon locked up in the soil also provides a way to keep it out of the atmosphere.

Dig in

Carbon has a very complicated cycle within the soil and in the atmosphere. The two cycles are intricately linked, says Patrick Drohan, a pedologist (scientist who studies soil) at Pennsylvania State University in University Park.

Though some of the carbon in soil comes from sedimentary rocks, such as limestone, most of it comes from organic matter, meaning waste from living organisms. Sounds a bit yucky, but it’s really cool. He explains the cycle like this:

A squirrel poops (or a plant or animal dies) and the waste then decomposes. Nutrients in the organic matter, including carbon, are released into the soil with the help of decomposers such as fungi and bacteria. Over the years, the nutrients are broken down further. Eventually, the nutrients get reabsorbed by a plant taking up water, or a human eating food grown in the soil or perhaps by a tiny organism called a microbe within the soil. When that microbe breathes, it releases CO2 into the atmosphere. Plants absorb the CO2 released from the microbe. From here, the cycle begins again.

Leaves on the ground are like candy for fungi and bacteria. These decomposers, organisms that feed on dead matter, go to work breaking down leaves to create energy-filled food for themselves. In the process, decomposers also make nutrients available for o

Karl Lipschitz/stock.xchng

Concern over the rapid buildup of carbon dioxide in the atmosphere has prompted scientists to look at ways to sequester, or contain, carbon in the soil and plants. The key to doing this is plant production.

Scientists say promoting and protecting the growth of forests and other plants may boost plants’ capacity to take up CO2 in the atmosphere. Such practices may also increase soils’ capacity to store carbon for long periods of time.

The power of plants

Most of the carbon on Earth is stored in plants and soil.

Where does all this carbon come from? Plants get all of their carbon from carbon dioxide, or CO2, in the atmosphere. The leaves on trees and crops soak up CO2 during photosynthesis, a chemical process that converts sunlight into food. Then plants spit some of the CO2 back out during another process called respiration, the way plants “breathe.”

Plants, especially trees, are so efficient at pulling carbon dioxide from the air that they take in more carbon than they release. That’s why they’re called “carbon sinks.”

Trees grouped together in forests are even more efficient. Scientists estimate that the Earth’s forests currently store more than 75 percent of the planet’s aboveground carbon. And the forests store almost that much of the planet’s soil carbon.

Scientists are working to develop forest management strategies to help absorb some of the extra CO2 in the atmosphere. But this task isn’t as straightforward as it may seem.

Not all forests actually store carbon, says Peter Curtis, a forest ecologist at Ohio State University in Columbus who studies the role of forests in the carbon cycle. “Some forests experience a net loss.”

That doesn’t mean that the trees have stopped photosynthesizing. It simply means that the respiration part, the loss, is greater than the gain, he explains.

Accounting for carbon

Curtis works to measure how much carbon can be held in forests in the Midwest and Great Lakes region. Working from the University of Michigan Biological Station in northern Michigan, he has two ways of doing that.

First, he uses a high-tech approach: Information is collected on and around two meteorological, or weather-measuring, towers, which look a lot like cell phone towers. Standing 150-feet-tall — about as high as a 15-story building — the towers loom over the forest’s canopy.

Instruments on the towers measure how much CO2 is being taken up by the leaves on the trees. The instruments also measure temperature and moisture levels in the air, recording information up to 10 times per second.

The scientists also use some “low-tech” methods to collect data. In other words, researchers spend lots of time on the ground measuring the trees and collecting leaves to see how much debris has decomposed.

Using this information, Curtis tracks how much carbon the forests take in through photosynthesis, and how much they lose through respiration.

Carbon is the building block for all life on Earth. Every single cell in every living thing — including flowers, frogs and humans — contains at least some of the element.

Keith Weller/USDA-ARS

“It’s like a bank account,” he says. “If you get $10 in allowance, but have $8 in expenses, then $2 is what goes into your account.”

The trees may take up a ton of CO2 per acre, but respire 1,500 pounds, leaving a “profit” of 500 pounds of carbon intake.

Fortunately, most forests take in more carbon than they loose. Generally speaking, the planet’s forests take in about 25 percent of the CO2 created by human activities, Curtis says.

Areas heavily populated with forests absorb even higher amounts of human-generated CO2. In some parts of Michigan or Maine, the oaks and pines found in hardwood forests take up about 60 percent of the carbon emitted by people that live in that area.

“A forest in one of these areas can soak up the yearly emissions of about 225,000 cars,” Curtis says. “We call that an ecological forest.”

But changes in rainfall and temperature can shift a forest’s ability to hold carbon from year to year. Unseasonably warm temperatures in a cool, wet forest, for example, can speed the rate of decomposition of soil matter. When that happens, carbon that has been stored in the soil for hundreds, even thousands of years, may be released back into the atmosphere.

Such changes have been documented in some Canadian forests, Curtis says. “This is one of the big worries with climate change. When temperatures increase, decomposition ramps up and the forest gets drier, and all that soil carbon starts to be lost.”

Small changes

Scientists don’t yet know all the effects climate change will have on soil’s ability to store carbon, Drohan says.

They do know, however, that even a small change in soil carbon storage can have a significant impact on the global carbon balance. To that end, researchers are looking at ways farmers might better manage their crops and soil.

Practices designed to keep carbon in the soil will benefit farmers, as well as the planet. Carbon adds organic matter, which helps soil retain nutrients and water. Soil carbon also improves the structure of soil, resulting in better drainage and aeration, or flow of gases, for roots. That means healthier plants and better yields for farmers.

You don’t have to be a farmer to benefit, or to help. Curtis spends some of his time working with government officials and landowners to help them manage forest areas for the benefit of the planet and its soil.

At Michigan Technological University, faculty and students are leading a community effort to return carbon to the soil. The group throws logs and other debris into a large container. These scraps are then burned slowly at a low temperature to create bioch

Michigan Technological University

Even small-scale, community efforts can help. At Michigan Technological University, faculty and students are leading a community effort to return carbon to the soil. Instead of just letting agricultural and plant wastes degrade on their own, the group throws logs and other debris into a large container. These scraps are then burned slowly at a low temperature.

This smoldering process produces a substance called biochar that resembles the char left by a campfire. More importantly, the slow burn prevents much of the carbon from getting released back into the air, says Michael Moore, who’s leading the effort. The char can then be tilled right into the soil, where the carbon stays locked for years.

Amazonian natives have used this technique for centuries to fertilize their soil, says Moore, who teaches writing and poetry. He learned about it while traveling in Honduras.

Biochar isn’t ready for large-scale agriculture yet, but Moore says such community efforts provide a way for ordinary citizens to help the planet. And that has benefits for all.

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Word Find: The Dirt on Carbon

This image shows a neuron as it responds to an electrical signal. The blue traces the path of the signal as it moves through synapses to the neuron.

Think back to the first time you rode a bike or the last time you had ice cream for dessert. Now, imagine a perfect summer day. What’s going on in your noggin’ that allows you to remember, dream and think?

Lots. And some of the world’s brainiest scientists are conducting experiments/doing research to figure out how it all works.

The human brain is amazing. It lets you remember the way to your friend’s house, and how to pedal your bike to get there. It can conjure up memories of the fish you saw while snorkeling and remind you to feed your goldfish at home. It even controls stuff you don’t have to think about, such as your heart rate, breathing and blinking.

In recent years, brain-imaging techniques such as functional magnetic resonance imaging (fMRI) have allowed scientists to watch the brain in action. Studies using fMRI show how different parts of the brain do different things, says neuroscientist Sam Wang, who studies the brain at Princeton University.

For example, one part of the brain, called the amygdala (ah-MIGG-duh-luh), handles emotional information, and another part of the brain, the prefrontal cortex, makes plans for the future. Yet another brain system, the cerebellum (SEHR-eh-BELL-um), helps control your movements and balance, while the hypothalamus (HI-poh-THAH-luh-muss) works to control your body’s temperature.

The brain contains other systems, too. Your hippocampus (HIP-poh-CAM-pus), for example, has the job of transferring information between short-term and long-term memory.

By working together, these systems let you think, remember, see, hear, smell, taste and touch. The goal of this teamwork is to get you through life.

Though the human brain is sometimes compared to a computer, it’s not one. It’s actually much more complex, Wang says.

Computers, for example, are designed to record everything perfectly. Rather than recording everything, the brain sorts through all the information taken in through the senses and decides what to hold on to. Because the brain does all this pre-sorting, things such as the pattern in your rug or sound of songbirds outside your window don’t constantly distract you.

This illustration shows how the billions of neurons in your brain are linked by a web of connections. Neurons interact through electrical connections similar to those in a computer.

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The human brain can also do things that are in many ways faster and better than what any computer can do. For instance, you brain enables you recognize your friends — just from the way they walk — even from a distance. Computers can’t do that. Nor can a computer tell the difference between a cat and a dog, even though most toddlers can.

Though your brain is not a computer, they do share something in common: Both brains and computers use electrical signals to transmit information.

All fired up

Your brain doesn’t get its electrical energy from a socket in the wall, the way a computer does. Instead, it creates and sends electrical signals through specialized cells called neurons.

A neuron’s axons and dendrites help it to transmit electrical signals. Dendrites bring information to the body of the neuron, and axons take information away from the cell body.

U.S. National Cancer Institute

Neurons look different from other cells. That’s because neurons have long extensions called dendrites and axons. These work like electrical wires to transmit messages from your brain throughout your whole nervous system. Dendrites bring information to the body of the neuron, and axons take information away from the cell body.

Information is passed along throughout the nervous system from neuron to neuron. The region where the information is transferred from one neuron to another is called the synapse. The synapse is actually a small gap located between two neurons. When information is transferred from one neuron to another, chemicals called neurotransmitters are released from the end of one neuron and travel across the synapse to reach the other neuron. There, these chemicals attach to special structures called receptors, which are located on the receiving neuron. This attachment creates a small electrical response within the receiving neuron.

These electrical signals race up and down the dendrites and axons at super speeds — up to several hundred feet per second. That’s fast enough to help you flee from a wild animal, or pull your hand away from a sizzling hot frying pan.

The human brain contains billions of neurons, and each individual neuron may receive information from thousands of other neurons. To keep the mental machinery running smoothly, the neurons specialize in doing certain tasks.

Sensory neurons, for example, carry messages from your eyes, ears and other sensory organs to your brain. They alert your brain when your nose picks up a whiff of cinnamon rolls coming from the kitchen. Motor neurons carry signals from your brain to your muscles and organs, enabling you to walk, talk, breathe and scramble to the kitchen to grab a hot roll.

Other types of neurons in the brain help in building social relationships. Mirror neurons, for example, are specialized cells that help you show empathy and understanding to others. They fire not only when you take action, but also when you watch others take action.

“Mirror neurons are active when I pick up a cup, and are also active when I watch someone else pick up a cup,” Wang says. “If you’ve ever winced when you watched a TV surgeon slice into a patient, you have your mirror neurons to thank.”

Some neurons have very specific tasks. Things and people that you see on a regular basis — your mother, your dog and even your favorite celebrities — all have a group of dedicated neurons that fire specifically in response to them.

By working together, all the various types of neurons help build our thoughts and actions, Wang says. “Thoughts are basically neurons like these acting together, being put together in patterns.”

Hold that thought

So, with all the various neurons racing through the different brain regions, how can a person think straight? Figuring out how the mind gives rise to thoughts, actions and emotions isn’t easy, and scientists are still working to put all the pieces together. Imaging studies such as those using fMRI have provided some clues.

For example, fMRI studies show that the prefrontal cortex acts as a kind of traffic cop, directing signals to and from different brain regions. Information that comes into the brain through eyes travels to the prefrontal cortex before it is distributed to other brain regions for additional processing. The same holds true for information coming from the other senses.

Other fMRI studies show that when people are sitting around just thinking about something, multiple brain regions are activated. When volunteers in a study were asked to imagine that they are looking at something, the parts of their brain that handle visual information lit up. “The same brain regions that are active during direct visual experience are also active by imagining a scene,” Wang says.

Scientists have also found that your memory plays a role in imagining new scenarios. In recent years, researchers have discovered that the brain regions used to store and retrieve memories are activated when envisioning the future. So all those facts and autobiographical data stored in your brain actually help you construct and predict possible future events.

When it comes to learning new information, one thing is certain: Practice makes perfect. When messages travel from neuron to neuron, over and over, the brain creates a connection between the neurons to form a memory. Once this happens, processing and recalling information becomes easier.

This holds true whether you are trying to learn a new language or learn a new dance move, Wang says. “Memory formation requires multiple steps,” he says. “Once an initial idea or motion is laid down, it must be reinforced both by repetitions and recall.”

Allowing time for rest breaks also aids learning. That’s why spacing out your study time works better than trying to cram information all at once. Wang says one possible reason for this is that breaks provide time for information consolidation.

Now that’s something to keep in mind.

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