A new model for understanding how nerve cells in the brain control movement may help unlock the secrets of the motor cortex, a critical region that has long resisted scientists’ efforts to understand it, researchers report June 3 in Nature.

Scientists at Washington University in St. Louis, Stanford University and Columbia University have shown that the motor cortex’s effects on movement can be much more easily understood by looking at groups of motor cortex neurons instead of individual nerve cells. In the study, scientists identified rhythmic brain cell firing patterns coordinated across populations of neurons in the motor cortex. They linked those patterns to different kinds of shoulder muscle movements. 

Cunningham

Until now, scientists had based their studies of the motor cortex on decades-old insights into the workings of the visual cortex. In this region, orientation, brightness and other characteristics of objects in the visual field are encoded by individual nerve cells.

However, researchers could not detect a similar direct encoding of components of movement in individual nerve cells of the motor cortex.

“We just couldn’t look at an arm movement and use that to reliably predict what individual neurons in the motor cortex had been doing to produce that movement,” Cunningham says.

For the new study, conducted at Stanford University, scientists monitored motor cortex activity as primates reached for a target in different ways. They showed that the motor cortex generated patterns of rhythmic nerve cell impulses.

“Finding these brain rhythms surprised us a bit, as the reaches themselves were not rhythmic,” says co-first author Mark Churchland, PhD, who was a postdoctoral researcher at Stanford at the time of the study and is now assistant professor of neuroscience at Columbia University. “In fact, they were decidedly arrhythmic, and yet underlying it all were these unmistakable patterns.”

Cunningham compares the resulting picture of motor cortex function to an automobile engine. The engine’s parts are difficult to understand in isolation but work toward a common goal, the generation of motion.

“If you saw a piston or a spark plug by itself, would you be able to explain how it makes a car move?” Cunningham asks. “Motor-cortex neurons are like that, too – they are understandable only in the context of the whole.”

Researchers are applying their new approach to understanding other puzzling aspects of motor cortex function.

“With this model, the seemingly complex system that is the motor cortex can now be at least partially understood in more straightforward terms,” says senior author Krishna Shenoy, PhD, associate professor of electrical engineering at Stanford.

John Cunningham is a member of Washington University’s Center for Biological Systems Engineering. His research is supported by the UK Engineering and Physical Sciences Research Council and the McDonnell Center for Systems Neuroscience.

This research was supported by funding from the Helen Hay Whitney Foundation, the National Institutes of Health (NIH), the Burroughs Wellcome Fund Career Awards in the Biomedical Sciences, the Engineering and Physical Sciences Research Council, the National Science Foundation, Texas Instruments, a Paul and Daisy Soros Fellowship, the Stanford Medical Scientist Training Program, the Defense Advanced Research Projects Agency, the Stanford Center for Integrated Systems, the Office of Naval Research and the Whitaker Foundation.

Washington University School of Medicine’s 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children’s hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked sixth in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children’s hospitals, the School of Medicine is linked to BJC HealthCare.

Vanessa Ruta

A four-neuron circuit in the male fruit fly brain, called the sex circuit, transforms chemical scents into a physical response. A group of scientists at Washington University in St. Louis have found an ion channel they think activates neurons that feed into the sex circuit, releasing male courtship behavior. The image, which was published in Nature in 2010, was produced by Vanessa Ruta, PhD, a postdoctoral fellow at Columbia University in New York.

Fruit fly courtship is so highly stylized and repetitive, it is as instantly recognizable as the knee jerk or Achilles reflex.

A male lines himself up behind a female and then chases her, licking her and tapping her with his forelegs while vibrating his wings to sing to her. If she responds to these blandishments, the male attempts to mount her. (To hear the song, click here.)

Scientists at Washington University in St. Louis have found a gene that seems to unleash the courtship ritual. Males missing this gene are capable of courtship; they just have trouble getting started.

This lackadaisical behavior is remarkable because males are usually “highly sexed,” to the point that they will court and mount “perfumed dummies,” decapitated females coated in waxy pheromones.

The problem seems to be that the males with a mutation in this gene, which codes for an ion channel, can’t “taste” the waxy pheromone on the female’s cuticle and without that trigger, the courtship ritual isn’t released, says Yehuda Ben-Shahar, PhD, assistant professor of biology in Arts & Sciences, who led the team.

The study results appeared in PLoS Genetics.

A mysterious family of ion channels

Ben-Shahar’s team started out with the observation of a simple discrepancy. Fruit flies have 31 genes that code for a specific kind of ion channel, called a degenerin/epithelial sodium ion channel (DEG/ENaC). Mammals have eight or nine, depending on the species.

“I began wondering why this superfamily of channels is so diversified, especially in the fruit fly,” Ben-Shahar says.

Ion channels are pore-forming proteins that regulate the flow of ions (in this case sodium ions) across the membrane in cells. Many are involved in the transmission of nerve impulses, which is why most animal venoms disable them in various ways.

Very little is known about the DEG/ENaC superfamily of channels, but Ben-Shahar and his team suspected for various reasons that some of them might be involved in chemosensory-driven behaviors in the fly.

The bodies of insects are covered with hairs that are actually sensory bristles, Ben-Shahar says. Each of these hairs has several neurons in it that are tuned for very specific stimuli. Some are tuned to mechanical stimulation, and others to chemosensory (olfactory or gustatory) cues.

“The term gustatory is actually a bit of a misnomer,” he says. “These bristles aren’t necessarily used to sense food but rather chemicals in a liquid or solid form —such as perfumed waxes that serve as sexual attractants.”

Channel gene Pickpocket 23

Because the scientists knew some DEG/ENaC channels are expressed in fruit fly chemosensory organs, they reasoned they might be able to find genes in this superfamily by comparing wild-type flies (flies as they exist in nature) with flies with a mutation that causes them to have only mechanosensory bristles.

When they looked at the genes the two types of flies expressed, they found that one ion channel, called pickpocket 23, or ppk23, was markedly reduced in that mutant flies, suggesting this ion channel involved in chemosensation.

By linking the ppk23 gene to one that makes cells glow green, postdoctoral fellow Beika Lu, PhD, was able to see where it was expressed. It turned out to be abundant in the forelegs of male flies, which sported twice as many ppk23-expressing neurons on their legs as did females.

“We knew that the male uses his forelegs in the courtship ritual,” Ben-Shahar says. “The male hugs the female, rubbing his legs and proboscis on her cuticle to test how she tastes. So it made sense that they have something in their legs that could detect the waxy pheromones she secretes.”

When they looked closely at the neurons expressing ppk23, it turned out that they also branch differently in male flies than they do in female flies.

Ben-Shahar et al.

Neurons expressing ppk23, here revealed by a protein that fluoresces green, branch differently in the male (left) than in the female (right). In the male, they cross the midline of the thoracic ganglion, considered part of the fruit fly brain.

They may be feeding into a male-specific neural circuit, called the sex circuit, which determines sexual behaviors and whether an individual fly behaves as a male or a female.

“Courtship is like a reflex with these males,” Ben-Shahar says. “You put a wild-type male in with a virgin female and it takes two seconds and he’s courting and trying to mate with her.”

A courtship assay

At this point, Ben-Shahar and his team had lots of circumstantial evidence that ppk23 was somehow involved in fruit fly courtship, but they didn’t really know for sure how it affected fly behavior. To find out, they would need to disable ppk23 and compare the behavior of the flies without functioning ppk23 to that of the wild type.

They designed several different behavioral assays for this purpose, including assays for feeding, tasting and courtship. The feeding and tasting assays showed that the ppk23-disabled flies behaved like wild-type flies, so clearly ppk23 didn’t have to do with feeding behavior.

The courtship assay, however, clearly separated the ppk23-deficient flies from the wild-type flies.

The assay was carried out under red light, which left the flies essentially blind. The targets were decapitated females that had been carefully washed in a solvent and then coated with the pheromone 7,11 HD.

“In the assays, the ppk23-deficient males run and run and run, and bump into the female, but never get interested,” Ben-Shahar says. “Wild-type flies, the moment they bump into a female, they start courting.”

Ben-Shahar et al.

Intriguingly, most ppk23-expressing cells in the male fruit fly’s forelegs also express a gene called fruitless. Discovered in 1996, this gene seems to govern almost the entire courtship repertoire. Mutations in fruitless prevent courting entirely or disrupt parts of the repertoire. The ppk23 neurons probably play a role in stimulating the fruitless-dependent circuit to produce sex-appropriate behaviors in males.

The ppk23-less males were capable of courtship, Ben-Shahar says, they just weren’t very good at it. “If you put them in a vial with lots of females, they will mate and you’ll get living offspring, so they’re not sterile in any way.”

“But if you put them in competition with wild-type flies, they wouldn’t stand a chance. By the time they decided to court a female, she will already have mated with somebody else.

“We don’t know what these ion channels do in females, Ben-Shahar says, but at least in males, the ppk23 neurons are critical in the decision to chase and court a female.” “

The inevitable question

What does it mean for people and human sexual behavior? “I’d be shocked,” Ben-Shahar says, “if humans were such an anomaly in nature that sensory cues didn’t affect sexual behavior.”

On the other hand, he says, “Human sexual behavior is very plastic and not at all categorical. It’s never all or nothing, probably extremely complex genetically and strongly affected by the environment.”

The American Academy of Microbiology has named two Washington University in St. Louis faculty members as fellows: Robert Blankenship, PhD, and John Heuser, MD.

Heuser

Heuser devised a way to freeze cells in about one-ten-thousandth of a second by driving them onto a block of copper cooled to minus 450 degrees Fahrenheit.

These “quick-frozen” cells can then be split open, “deep etched” to remove some of the ice, and coated with an ultrathin film of metallic platinum so they can be imaged with an electron microscope.

For decades, Heuser has used this technique to capture details of the molecular mechanisms that underlie many basic biological activities, including nerve cell signal-transmission, muscle contraction, and most recently, the fusion of viruses with cells during the spread of infection.

His “Heusergrams” have won praise not only for the scientific insights they reveal but also for their unexpected artistic merit.

Heuser’s colleagues recently arranged an exhibit of his work on the School of Medicine campus. The images are now permanently displayed on the third floor of the Farrell Learning and Teaching Center, near the histology labs where medical students will have some of their first encounters with the cells and tissue structures seen in Heuser’s micrographs. 

Blankenship

Blankenship, the Lucille P. Markey Distinguished Professor of Arts and Sciences and professor of biology, studies the highly interdisciplinary subject of photosynthesis.

He has studied energy transfer and electron transfer processes in antenna and reaction center complexes (the two major components of photosynthetic systems) from all major groups of photosynthetic organisms, with primary emphasis on the anoxygenic photosynthetic bacteria.

He also has done genome sequencing and annotation along with molecular evolutionary studies aimed at understanding the origin and early evolution of photosynthesis.

Recent work is targeted to improving the efficiency of photosynthesis in bio-energy contexts.

The author of over 300 scientific publications in the area of photosynthesis, in 2009, he became the founding director of the Photosynthetic Antenna Research Center (PARC), a DOE Energy Frontier Research Center at WUSTL.

He also is organizer for the 16th International Congress on Photosynthetic Research, which will be held in St. Louis in August 2013.

Wikipedia Commons

Missouri has two species of box turtle, the Ornate box turtle (Terrapene ornata ornata) shown here and the Three-toed box turtle shown below. Box turtles get their name from a special hinge on the bottom part of their shell (the plastron) that allows them to close or “box up" as a form of protection against predators. Box turtles are omnivorous and typically eat worms, snails, berries, fungi, and arthropods. Because they have few offspring, are slow-moving and late in maturing, are particularly susceptible to human-related extinction.

Sixteen St. Louis youth were in Forest Park today tracking box turtles, fitted with telemetry devices — all to help with a project aimed at studying box turtle movements and their health.

The 12- and 13-year-olds are participating in a pilot study designed by scientists from the Saint Louis Zoo and Washington University in St. Louis to document box turtle movements and their health status in urban and rural areas in and around St. Louis.

This study comes at a critical time as previous studies conducted across the globe show that many populations of turtles are being threatened by vehicles, habitat loss, and disease. However, the conservation status of box turtles in Missouri is not well-understood.

The Zoo and WUSTL launched the Box Turtle Project this spring as turtles were coming out of hibernation. To begin this pilot project, 20 turtles — 10 in Forest Park and eight at WUSTL's Tyson Research Center — were fitted with radio tags that emit unique frequencies so they can be tracked over the coming year. In addition, the turtles have been marked with small, v-shaped notches on their upper shells to provide individual identification.

At the end of the pilot study, the scientists will compare data from urban (Forest Park) and rural (Tyson Research Center) turtle populations and use the results to develop a larger scale research program.

Many aspects of the box turtle project, particularly the combination of animal tracking research with outreach for school-age children, were initiated by Stephen Blake, PhD, a co-investigator on the project and visiting scientist at WUSTL, who is also coordinating an on-going study of the movements and ecology of giant tortoises on the Galapagos Islands (www.gianttortoise.org). On Galapagos, local school children are introduced to conservation by direct involvement in the research program.

“Through this study, the Forest Park box turtles, though they are 100 times smaller than their distant giant cousins in Galapagos, can offer a similar window into nature and conservation science for St. Louisans,” said Blake.

Led by Zoo and WUSTL cientists, students from the Ecology Club of South City Preparatory Academy will join three Washington University undergraduates in a search for some of the 10 Forest Park turtles that have been fitted with telemetry devices. They will use receivers to hear chirps from the small transmitters anchored on the backs of the tagged turtles. The students will also help scientists weigh each turtle and perform the weekly veterinary checks, as part of the health and movement ecology monitoring program. 

Wikipedia Commons

The Three-toed turtle (Terrapene carolina triunguis) is named for the number of toes on its back feet. The official reptile of the state of Missouri, they are popular in the pet trade and so sometimes found far outside their home range.

The WUSTL undergraduates are Joanna Wang, a rising senior majoring in environmental studies, Jenny Fung, a rising junior majoring in environmental biology and international sustainable development and Chika Akiyamamajoring in biology.

Meredith Hessling and Amber Stout, high school seniors who are participating in the Tyson Environmental Research Fellowship (TERF) program are also working on the turtle project.

The South City Preparatory Academy students have been preparing for the June 13 monitoring effort by discussing turtle biology and ecology and practicing tracking the turtles using plush toys equipped with radio tags.

“One of the most important goals of a conservation project, like this one, is to use all the natural wonder of Forest Park to develop empathy in children toward animals and nature,” said Alice Seyfried, curator of the Emerson Children’s Zoo and director of the Zoo’s WildCare Institute Center for Conservation in Forest Park, which is funding this study.

“We know from earlier studies that conservation-minded adults were likely to have spent time in nature as children and that playing in nature has a profound effect on childhood development.”

Sharon Deem, PhD, director of the Institute for Conservation Medicine, who is co-directing the research end of the study, said that blood drawn from the turtles in both rural and urban areas will be monitored for stress hormones, in addition to indicators of disease. “This pilot program will result in a database that may show the value of box turtles as sentinels for health issues that may affect both animal and human urban dwellers.

“Essentially, we are studying box turtle health to better understand environmental factors that may be affecting the health of wildlife and humans, alike,” she said, adding that another goal is to address the nature deficit seen in children today — a deficit that affects their health and well-being. This project involves environmental education, ecological and health sciences and offers a holistic approach that we believe will help us achieve strong conservation results.”

Partners in the project are Forest Park Forever, WUSTL's Tyson Research Center, the Zoo’s WildCare Institute Center for Conservation in Forest Park and the Zoo’s Institute for Conservation Medicine.

During the day, David L. Wright, PhD, is chairman of the Department of Mathematics in Arts & Sciences at Washington University in St. Louis; at night, he is assistant director of Ambassadors of Harmony, a men’s a cappella chorus that has won international competitions. 

http://www.youtube.com/watch?v=QmDGntpZC3I&feature=related

Collage of Wikimedia Commons images

Whodunnit? The scientists had found squirrel-like DNA in ticks also carrying pathogen DNA but couldn’t tell which animal the tick had bitten. Was it (clockwise from top left) a thirteen-line ground squirrel, a fox squirrel, a red squirrel, an eastern chipmunk, an eastern gray squirrel, a prairie dog, a flying squirrel or the woodchuck? Yes, even the woodchuck, or whistle-pig, is a member of the squirrel family.

A team of scientists at Washington University in St. Louis has been keeping a wary eye on emerging tick-borne diseases in Missouri for the past dozen years, and they have just nailed down another part of the story.

They knew from earlier work that the animal reservoirs for the diseases included white-tailed deer, wild turkey and a species in the squirrel familiy, but the DNA assay they had used wasn’t sensitive enough to identify the species.

Squirrels belong to a large family called the Sciuridae, which includes chipmunks, fox squirrels, red squirrels, flying squirrels, ground hogs and prairie dogs.

In the May issue of the Journal of Medical Entomology the scientists, led by Robert E. Thach, PhD, professor of biology in Arts & Sciences, report that a more sensitive assay has allowed them to identify the major species in question as the eastern gray squirrel.

Yes, the friendly neighborhood seed thief and dog tease is also a mobile tick blood supply and bacteria incubator.

The work is important because tick-borne diseases can be efficiently controlled only if all of the animal reservoirs that might contribute to transmission of the disease have been identified.

Not your New England tick

The most prevalent tick-borne disease in North America is Lyme disease, which is transmitted by the bite of an infected black-legged tick. In the southeastern United States, however, the most common diseases are ehrlichioses and STARI, which are transmitted by the bite of a different tick, the lone star tick.

Until 1986, ehrlichia bacteria were thought to cause disease only in animals. But in that year, a physician noticed mulberry-shaped aggregates characteristic of the bacteria in the blood of a gravely ill man.

The lone star tick, similarly, was thought to be merely a nuisance species until 1993, when the DNA of one of the ehrlichia species was found in lone star ticks collected in Missouri and several other states.

Ehrlichiosis typically begins with vague symptoms that mimic those of other bacterial illnesses. In a few patients, however, it progresses rapidly to affect the liver and other organs, and may cause death unless treated with antibiotics. STARI is similar to Lyme disease but seems to be less virulent.

The reservoirs

By 2010, with the pathogens and their vector identified, the WUSTL team was trying to find the animal reservoirs.

Looking for pathogens and host species, they ran two assays on the ground-up ticks: one to identify the DNA of pathogens and the other to identify the DNA of animals that had provided blood meals.

David Kilper/WUSTL

Lisa Goessling and Robert Thach setting up an assay that identifies the animal that provided an infected tick's last blood meal.

The blood meal assay on ticks carrying pathogens identified white-tailed deer blood and the blood of a species in the squirrel family, but it couldn’t distinguish among 20 or so possible squirrel species.

So the team was very interested when they read a paper in the Journal of Medical Entomology about a new assay that could identify tick blood meals down to the species level.

The assay, developed by scientists at the University of Neuchatel in Neuchatel, Switzerland, used a segment of mitochondrial DNA instead of nuclear DNA as a species marker.

Mitochondria, organelles within the cells that convert energy into forms cells can use, have their own DNA, probably because they were once free-living bacteria.

For reasons that are not entirely clear, mitochondrial DNA mutates faster than DNA tucked away in the cell nucleus. It may be that the mitochondria simply have more primitive DNA repair mechanisms and so cannot fix mistakes if they occur.

In any case, the more mutations, the greater the difference between the DNA of two different species, and the greater the power of the assay to distinguish among species, Thach says.

To tailor the assay for their purposes, the team retrieved the DNA sequences for possible North American host species from Genbank, an open-access sequence database. Sequences not available in the database were determined by the lab.

Thach et al.

The squirrel species was identified with an assay in which short sequences of mitochondrial DNA unique to a host animal, called probes (red), were deposited in lines on a membrane. The membrane was then rotated 90 degrees and DNA from a tick that had been tagged with a light-generating dye (blue) was laid down in lines perpendicular to the probe lines. Wherever two lines crossed, DNA from the tick sample mixed with probes for animal DNA. If the two matched, the molecules “hybridized” together and stuck to the membrane, showing up, after further treatment, as glowing spots (black).

Lisa S. Goessling, now a research lab supervisor in the School of Medicine, used the sequences to make a palette of probes for 11 species and — just to make sure the net was cast wide enough — several higher taxonomic orders.

The scientist then re-ran old samples and newly collected ticks through the new assay. Spots on the assay where the tick blood and the gray squirrel probe overlapped lit up, signaling the presence of gray squirrel blood in the ticks.

Why not the others?

Lone star ticks are famously aggressive and indiscriminate biters, so why hadn’t they attacked other animals? Is there something special about deer or gray squirrels that makes the ticks prefer them?

This isn’t the kind of question the scientists can answer definitively, but Thach doesn’t think so. He has a simpler answer.

“If you think of an inventory of the animals in the woods and the amount of blood in each, well, most of the available blood in the woods is in deer, and next to that in turkeys and squirrels, because turkeys are so big and there are so many squirrels. So I suspect it’s mainly just a mass phenomenon,” he says.

Neighborhood, neighborhood, neighborhood

Wikimedia Commons

The eastern gray squirrel dunnit. The white-tailed deer and  the eastern gray squirrel are the major animal reservoirs for tick-borne diseases prevalent in Missouri. You won’t get sick from a squirrel, but you might get sick if it drops a tick that bites you.

Having found gray squirrel DNA in tick blood, the scientists attacked the problem from a different angle to see if they could confirm their results. They trapped gray squirrels rather than ticks.

Were the gray squirrels carrying tick-borne pathogens? The answer, it turned out, depends on where you are. Only 5 percent of the squirrels in a relatively urban suburb (University City, Mo.) were carrying a pathogen, but 25 percent of the squirrels in a wooded “garden suburb” (Kirkwood, Mo.) were infected.

Why the difference? Thach suspects it comes down to white-tailed deer. There are few, if any, in University City, but they cruise backyards in Kirkwood. Wherever deer go they shed ticks.

This also is the likely answer to another conundrum: the absence or near absence of ticks in Forest Park, the 1,371-acre urban park that adjoins Washington University. Thach says an exhaustive search turned up only one tick.

Why so few ticks? Perhaps because the only deer in Forest Park are the ones in the Saint Louis Zoo. 

Travis Mohrman/Tyson Research Center

Male blue dasher (Pachydiplax longipennis), is one of about 10 dragonfly species commonly seen buzzing the artificial pond systems at the Tyson Research Center, WUSTL’s field station for ecosystem studies. A new study showed that the dragonflies were the liaisons that connected aquatic to terrestrial ecosystems, allowing the plant purple loosestrife to “tug” on the interconnections between organisms in both ecosystems.

An elementary school science activity asks children who have each been assigned a wetland plant or animal to connect themselves with string and tape to other “organisms” their assigned plant or animal interacts with in some way.

Once an ecosystem web has been created, the teacher describes an event that affects one "organism." That “organism” tugs on its string. Other “organisms” that feel the tug then tug on their strings in turn.

The lesson is that every organism is important to the health and balance of a wetland and that every organism in the wetland is connected to every other organism in some way.

That’s more or less an article of faith among ecologists, but how true is it really? Ecologists rarely have the time or resources to test this foundational concept through experiment.

Now a summer-long study shows that the flowering invasive plant purple loosestrife (Lythrum salicaria) triggers a chain of interactions that ultimately alters the diversity of zooplankton populations in artificial ponds.

The interactions cross traditional ecosystem boundaries, connecting aquatic to terrestrial systems on the wings of dragonflies that exploit, at different times in their lives, the resources of both the water and the land.

“It’s easy to say that everything is connected in some way, but how much these connections matter is something that we don’t always know,” says Kevin G. Smith, PhD, adjunct professor of biology in Arts & Sciences at Washington University in St. Louis and associate director of the Tyson Research Center, WUSTL’s 2,000-acre field station.

By verifying one of the foundational ideas of ecology, the experiment, published electronically May 24 by the journal Oecologia in advance of print, will help inform decisions about biological control of invasive species, restoration of degraded habitats and similar ecological issues.

A study long meditated

Smith says the experiment was inspired by work his colleague Tiffany Knight published in 2005. Knight, PhD, associate professor of biology at WUSTL, had showed that plants do better if they are near ponds with fish, because the fish eat dragonfly larvae, reducing the population of dragonflies that prey on plant pollinators.

Smith was intrigued by the study because the effect was indirect and cut across ecosystems as traditionally defined. “Ecologists tend to study forests, or ponds, or glades, but there is a lot of border crossing going on,” he says, “and Tiffany’s study demonstrated that.”

His idea was to see if he could find links that went the other way, connecting land to water instead of water to land. If fish affected land plants, could plants affect fish —or at any rate aquatic communities? 

York County Soil & Water Conservation District

Purple loosestrife, seen here encroaching on a golf course in Maine, is an invasive plant that was probably imported by early European settlers. Once established, it is difficult to eradicate; each plant can produce as many as three million seeds a year and the plants grow clonally, with many stems emerging from a single root mass.

One plant that might tug hard on ecosystem connections, Smith thought, was the purple loosestrife, which produces many showy flowers and displaces native plants such as cattails that produce few or none.

“The flowers make it functionally different from the native plants,” Smith says, “so it seemed possible its presence would cause a disturbance that would ripple through the wetland communities.”

But it took a few years for Smith to start the experiment.

“Everybody I talked to about it thought that one of the links would fail; that it wasn’t possible for every connection from the plant to the aquatic system to hold as I had hypothesized it would,” Smith says. “I sort of felt that way, too. It seemed like a long shot.”

Eight artificial wetlands

Travis Mohrman/Tyson Research Center

Stock tanks at the Tyson Research Center hold artificial pond communities that are manipulated in various ways to explore ecological interactions. Scientists also survey natural ponds at the research center and in its vicinity.

But the tradition at Tyson Research Center is to challenge fundamental ecological ideas with the methods and tools of science, and so in the summer of 2009, Smith finally undertook what he knew would be a labor-intensive experiment.

He and colleagues Laura A. Burkle, PhD, then a postdoctoral fellow who is now a faculty member at Montana State University, and Joseph R. Mihaljevic, then a WUSTL undergraduate and now a graduate student at the University of Colorado, Boulder, created eight artificial wetlands at Tyson, each consisting of a central stock tank and four smaller surrounding pools.

The tanks were stocked with six species of aquatic plants and three species of snails and inoculated with the smaller zooplankton and phytoplankton drawn from local ponds. The remainder of the aquatic community, such as frogs, dragonflies, flies, beetles and bugs, was allowed to assemble naturally.

Loosestrife plants in pots were placed in each of the four small pools. The pools were separated from the tanks so that only the flowers — and notplant litter and pollen — would play a role in the ecosystem of the central pool.

The eight “wetlands” thus created were divided into four treatment groups and the number of loosestrife flowers in each “wetland” was manipulated to mimic differences in loosestrife density.

The loosestrife in two wetlands were left alone but flowers at the other wetlands were picked to reduce their numbers to 75 percent, 50 percent or 25 percent of the flowers at the untouched wetlands.

During the course of the experiment, the small insects visiting the pools were regularly counted and categorized, as were the dragonflies and their behaviors.

At the end of the summer and the experiment, the zooplankton and phytoplankton in the eight central tanks were sampled and identified.

What happened?

The scientists were able to track the effect of the loosestrife flowers across four trophic levels, or levels in the food web, and two ecosystems, the terrestrial and the aquatic ones. 

Travis Mohrman/Tyson Research Center

Here’s looking at you, kid. Dragonfly larvae are voracious predators and can grow to be three inches long.

The links worked as follows: Wetlands with abundant flowers attracted more pollinating insects; the insects in turn attracted more of the carnivorous dragonflies; the well-nourished dragonflies laid more eggs in the central ponds; the voracious dragonfly larvae that hatched from the eggs altered the diversity of the zooplankton communities in the ponds.

In an unexpected turn, flowering loosestrife actually increased zooplankton species richness, perhaps, speculates Smith, because they preferentially ate a dominant zooplankton species, releasing others from competition.

“To be honest,” Smith says, “although the increase in zooplankton diversity is interesting and surprising, I don’t think that specific detail matters too much. Nor, is the point simply that purple loosestrife might be affecting aquatic ecosystems, although that is important from a management perspective.

“What matters is that we showed the interconnections are actually strong enough to transmit disturbances through and across webs. We pushed on one link and something four links away in another ecosystem moved.”

Anyone who has looked at the jagged recording of the electrical activity of a single neuron in the brain must have wondered how any useful information could be extracted from such a frazzled signal.

But over the past 30 years, researchers have discovered that clear information can be obtained by decoding the activity of large populations of neurons.

Now, scientists at Washington University in St. Louis, who were decoding brain activity while monkeys reached around an obstacle to touch a target, have come up with two remarkable results.

Their first result was one they had designed their experiment to achieve: they demonstrated that multiple parameters can be embedded in the firing rate of a single neuron and that certain types of parameters are encoded only if they are needed to solve the task at hand.

Their second result, however, was a complete surprise. They discovered that the population vectors could reveal different planning strategies, allowing the scientists, in effect, to read the monkeys’ minds.

By chance, the two monkeys chosen for the study had completely different cognitive styles. One, the scientists said, was a hyperactive type, who kept jumping the gun, and the other was a smooth operator, who waited for the entire setup to be revealed before planning his next move. The difference is clearly visible in their decoded brain activity.

The study was published in the July 19 advance online edition of the journal Science.

All in the task
The standard task for studying voluntary motor control is the “center-out task,” in which a monkey or other subject must move its hand from a central location to targets placed on a circle surrounding the starting position.

To plan the movement, says Daniel Moran, PhD, associate professor of biomedical engineering in the School of Engineering & Applied Science and of neurobiology in the School of Medicine at Washington University in St. Louis, the monkey needs three pieces of information: current hand and target position and the velocity vector that the hand will follow. 

In other words, the monkey needs to know where his hand is, what direction it is headed and where he eventually wants it to go.

A variation of the center-out task with multiple starting positions allows the neural coding for position to be separated from the neural coding for velocity. 

Moran/Pearce

In the classic center-out reaching task, a monkey reaches from a central location to targets on a circle surrounding the starting position. This task does not allow the neural encoding for hand position to be separated from the neural encoding for hand velocity. If the starting position varies, however, as in the task shown here, hand position and initial hand velocity can be disambiguated.

By themselves, however, the straight-path, unimpeded reaches in this task don’t let the neural coding for velocity to be distinguished from the neural coding for target position, because these two parameters are always correlated. The initial velocity of the hand and the target are always in the same direction.

To solve this problem and isolate target position from movement direction, doctoral student Thomas Pearce designed a novel obstacle-avoidance task to be done in addition to the center-out task.

Moran/Pearce

The obstacle-avoidance task is a variation on the center-out reaching task in which an obstacle sometimes prevents the monkey from moving directly to the target. The monkey must first place a cursor (yellow) on the central target (purple). This was the starting position. After the first hold, a second target appeared (green). After the second hold an obstacle appeared (red box). After the third hold, the center target disappeared, indicating a “go” for the monkey, which then moved the cursor out and around the obstacle to the target.

Crucially, in one-third of the obstacle-avoidance trials, either no obstacle appeared or the obstacle didn’t block the monkey’s path. In either case, the monkey could move directly to the target once he got the “go” cue.

The population vector corresponding to target position showed up during the third hold of the novel task, but only if there was an obstacle. If an obstacle appeared and the monkey had to move its hand in a curved trajectory to reach the target, the population vector lengthened and pointed at the target. If no obstacle appeared and the monkey could move directly to the target, the population vector was insignificant. 

In other words, the monkeys were encoding the position of the target only when it did not lie along a direct path from the starting position and they had to keep its position “in mind” as they initially moved in the “wrong” direction.

“It’s all,” Moran says, “in the design of the task.”

And then some magic happens
Pearce’s initial approach to analyzing the data from the experiment was the standard one of combining the data from the two monkeys to get a cleaner picture.

“It wasn’t working,” Pearce says, “and I was frustrated because I couldn’t figure out why the data looked so inconsistent. So I separated the data by monkey, and then I could see, wow, they’re very different. They’re approaching this task differently and that’s kind of cool.”

The difference between the monkeys’ styles showed up during the second hold. At this point in the task, the target was visible, but the obstacle had not yet appeared.

The hyperactive monkey, called monkey H, couldn’t wait. His population vector during that hold showed that he was poised for a direct reach to the target. When the obstacle was then revealed, the population vector shortened and rotated to the direction he would need to move to avoid the obstacle.

The smooth operator, monkey G, in the meantime, idled through the second hold, waiting patiently for the obstacle to appear. Only when it was revealed did he begin to plan the direction he would move to avoid the obstacle.

Because he didn’t have to correct course, monkey G’s strategy was faster, so what advantage was it to monkey H to jump the gun? In the minority of trials where no obstacle appeared, monkey H approached the target more accurately than monkey G. Maybe monkey H is just cognitively adapted to a Whac-A-Mole world. And monkey G, when caught without a plan, was at a disadvantage.

Working with the monkeys, the scientists had been aware that they had very different personalities, but they had no idea this difference would show up in their neural recordings.

“That’s what makes this really interesting,” Moran says.

New research suggests that many men with prostate cancer do not need immediate treatment, especially if they have low PSA scores or low-risk tumors that are unlikely to grow and spread.

The multi-center study, published July 18 in the New England Journal of Medicine, compared prostate cancer surgery soon after diagnosis to observation in men with early-stage prostate tumors detected by PSA screening. Overall, most men did not benefit from surgery – it did not reduce the likelihood they would die from prostate cancer or other causes.

But the findings indicate that surgery did reduce mortality in two groups of men – those with relatively high PSA levels (greater than 10 ng/mL) and potentially those with higher-risk, more aggressive tumors. 

Andriole

Less than 10 percent of men in the study were in their 40s and 50s, too few to determine whether surgery would lower their mortality. But Andriole says if more of these men had been included in the study and followed for many more years, the data may have shown whether they  benefitted from early treatment with surgery.

The study’s findings support the results of the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial, which to date has shown that most cancers detected by repeated PSA screening are low risk and that annual prostate cancer screening does not reduce mortality. Andriole is leading that study and is chairman of the PLCO’s prostate cancer committee.

“The findings of these two studies should be reassuring to men with low-risk prostate cancer,” says Andriole, who also is the Robert K. Royce Distinguished Professor of Urologic Surgery. “PSA screening commonly results in the discovery of cancers that are generally not a threat to life. This ‘over diagnosis’ of non-lethal cancers is concerning in and of itself and becomes especially problematic if men with such low-risk cancers are ‘over treated’ since they are unlikely to benefit from the treatment and may experience side effects like incontinence and impotence.”

The results of both the PLCO study and the current study, called Prostate cancer Intervention Versus Observation Trial (PIVOT), were among those considered by the U.S. Preventative Services Task Force, which recently gave PSA screening a Grade D recommendation and generally discouraged its use.

The PIVOT study, led by Timothy J. Wilt, MD, at the Minneapolis Veterans Administration Health Care System, enrolled patients beginning in 1994, at the dawn of the PSA screening era. At that time, the blood test was more likely to find larger, more aggressive tumors because most men were not routinely getting annual PSA screening tests.

Indeed, only 40 percent of men in the PIVOT study had low-risk prostate tumors, defined as a PSA level of less than 10 ng/mL or a Gleason score of less than 7. In more recent years, up to two-thirds of prostate cancers detected by PSA tests are considered low-risk and not likely to cause harm, yet most of these men have receive early treatment with surgery or radiation therapy.

Instead of treatment early on, Andriole says many men with low-risk prostate cancer detected by PSA screening initially can be managed with “active surveillance.” This involves periodic PSA tests and biopsies to monitor tumor growth.

“Active surveillance is apt to be better than observation or immediate treatment in most low-risk patients,” says Andriole, who follows several hundred patients at Washington University who have opted for close monitoring rather than treatment soon after their diagnosis. “We watch the PSA very closely and biopsy men periodically, so if a tumor starts growing or becomes more aggressive, we can still successfully treat it.” 

Thomas Wheeler, MD, at the Baylor College of Medicine in Houston, is the study's senior author.

The research is supported by the Department of Veterans Affairs Cooperative Studies Program, the National Cancer Institute and the Agency for Healthcare Research and Quality.

Washington University School of Medicine’s 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children’s hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked sixth in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children’s hospitals, the School of Medicine is linked to BJC HealthCare.

White House photo by chuck kennedy

President Barack Obama and Prime Minister Singh of India walk toward the East Room Nov. 24, 2009. It was during this state visit that they signed a memorandum of understanding to work jointly to accelerate development and deployment of clean energy technologies, to invest in clean energy projects in India and to take significant actions to mitigate greenhouse gas emissions. The leaders also launched an Indo-U.S. Clean Energy and Deployment Initiative that includes a joint research center operating in both the United States and India to foster innovation and joint efforts to accelerate deployment of clean energy technologies.

In The Best Exotic Marigold Hotel, there is a moment where the only landline phone in the dilapidated hotel in Jaipur, India, starts ringing after a silence of many years. 

Sunny, the hotel’s owner, frantically digs through accumulated clutter in the hotel office trying to locate the phone before it stops ringing. Ironically he is hampered in his search by the cell phone conversation that is also demanding his attention.

The scene epitomizes a phenomenon called leapfrogging that holds great promise for sustainable development.

The idea is that developing countries can leapfrog developed ones by skipping older, more expensive technologies, such as telephone networks, and moving directly to newer less expensive technologies, such as cell phones.

According to Pratim Biswas, PhD, chair of the Department of Energy, Environmental & Chemical Engineering in the School of Engineering & Applied Science at Washington University in St. Louis and director of the McDonnell Academy Global Energy and Environmental Partnership (MAGEEP), the idea behind a recently announced U.S.-India consortium in solar energy is that India might be able to leapfrog energy production technology, moving directly to solar in areas of the country that have never been electrified.

WUSTL and its McDonnell Academy partner the Indian Institute of Technology, Bombay (IIT-Bombay), together with corporate partners, such as the St. Louis-based solar company MEMC Electronic Materials, Inc. (MEMC), will play key roles in the effort to define and invent solar technologies that might make this leap possible. 

WUSTL’s contribution

Biswas foresees a three-pronged research effort at WUSTL to advance the institute’s goals, an effort he will lead together with Robert Blankenship, Cynthia Lo, P. Ramachandran and Venkat Subramanian.

One effort will build on the work done at WUSTL’s Photosynthetic Antenna Research Center (PARC) since its establishment in 2009. PARC scientists study the elegantly arranged proteins plants use to harvest light and funnel the light to reaction centers. The fundamental knowledge gained in this intensive effort to understand how nature harvests light will guide the effort to improve next-generation solar technology.

The second goal is to develop processes for the production of solar cells that are lower cost and scalable, probably by switching to a material such as titanium dioxide (TiO2) that is easier and cheaper to process than silicon.

In its pristine state, titanium dioxide absorbs only ultraviolet light, but combined with dyes, quantum dots, or nanowires, it can be used to make solar cells that absorb light at a wide range of wavelengths. These “dye-sensitized” metal-oxide solar cells are not yet as efficient as silicon solar cells, but they cost much less to make and process.

The third goal, says Biswas, is to find a way to store excess solar energy for use at night or when the sky is overcast. To be truly practical, the electricity generating solar cells must be integrated with batteries to create a “solar system in a box.” 

Biswas remarks that the practical, deployable solar systems might include batteries that are traveling down the value chain. Batteries that can no longer hold enough of a charge to power an electric car in the U.S. could be integrated with photovoltaic systems used in buildings, or shipped to India for off-grid applications.

For example, reused batteries might provide energy for the cell towers India needs to power cell phone transmissions. Most cell towers are powered today by diesel generators, which are expensive to operate.

Why India? 

India has 960 million cell phone subscribers and very few landline telephones, having skipped that step in the development of telephony. Technology leaders believe a similar leapfrog may be possible in energy technology.

Biswas is optimistic about the prospects for an energy leapfrog in India, perhaps because he witnessed the telephony leapfrog personally. 

When he was growing up in India, it took a long time to get a landline connection. Today, the country has completely bypassed that system and most Indians own a cell phone instead. There are roughly 960 million cell phones in use in India, compared with about 330 million in the U.S.

According to Biswas the introduction of the cell phone has led to the social transformation of rural India over the past 15 years. Pre-cell phone India’s poor farmers were often forced to take any price they were offered for their crops. With cellphones, they now can bid up the price and start to keep part of the profit for themselves rather than passing it to a middleman.

“There are exciting opportunities to explore alternative energy futures in places like India,” Biswas says. “Distributed energy production makes more sense in a country not bound by existing grids, which run into stability problems if production is intermittent. In fact, some parts of India do not even have a grid!

“Although it is clear that the world’s energy needs can only be met by relying on a mix of energy sources,” he continues, “solar energy, coupled with energy storage options, will be one of them. 

“The collaboration with India gives us the chance to explore solar’s potential in a setting where its characteristics are better matched to needs and market demand. Some of the technology that develops in this encouraging environment might then transfer back to us,” he says.

“Working with collaborators such as the IIT-Bombay, the Indian Institute of Science, Bangalore, and corporations such as MEMC, researchers at Washington University in St. Louis hope to make a difference in our energy future,” Biswas says.

When it comes to intelligence, what factors distinguish the brains of exceptionally smart humans from those of average humans?

As science has long suspected, overall brain size matters somewhat, accounting for about 6.7 percent of individual variation in intelligence. More recent research has pinpointed the brain's lateral prefrontal cortex, a region just behind the temple, as a critical hub for high-level mental processing, with activity levels there predicting another 5 percent of variation in individual intelligence.

Now, new research from Washington University in St. Louis suggests that another 10 percent of individual differences in intelligence can be explained by the strength of neural pathways connecting the left lateral prefrontal cortex to the rest of the brain.

Published in the Journal of Neuroscience, the findings establish "global brain connectivity" as a new approach for understanding human intelligence.

Michael W. Cole

Todd Braver

Zuum, a free iPad app, estimates disease risk and offers users a customized plan for living healthier lives.

Health-care professionals have developed a free iPad app that estimates a user's disease risk and offers a customized plan for living a healthier life.

“We wanted to get the word out about easy changes in behavior that might help people prevent certain diseases,” says Graham Colditz, MD, PhD, an internationally recognized disease prevention expert at the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine in St. Louis.

Called Zuum, the app quickly estimates a person’s risk of heart disease, diabetes, stroke and different cancers, including lung, colon, breast and prostate. Zuum then provides tailor-made tips to prevent these illnesses and boost overall health. For example, the app shows users how diet, TV viewing habits and other factors could affect future health.

Zuum is available on iTunes at http://itunes.apple.com/us/app/id521273376.

“We've taken three decades of research and turned it into Zuum, a free app that provides personalized health advice at your fingertips,” Colditz says.

Zuum’s features include:

• A quick, easy health questionnaire.

• Risk estimates for heart disease, stroke, diabetes, lung cancer, colon cancer, breast cancer (for women) and prostate cancer (for men).

• A list of specific factors that increase or decrease the risk of each disease and how healthy lifestyle changes could affect future risk.

• Personalized tips for lowering disease risk and boosting health.

• Tailored messages delivered regularly to the app’s inbox, which encourage ongoing healthy behavior change.

Dart says user security and promoting a healthy lifestyle were equally important when it came to the app’s design.

“The privacy and confidentiality of Zuum users is key,” he says. “Data are stored on secure servers and sent through an encrypted link, and unlike many other risk assessment tools, we never sell or share user information. Our only goal is to provide important tips that can help people live the healthiest life possible.”

Colditz stresses that Zuum is not intended to replace a physician’s advice or regular medical checkups. Zuum can’t predict if an individual will develop a particular disease, and it doesn’t guarantee good health. But the personalized advice it offers may help reduce risk and provide a blueprint for a better quality of life.

“We want to make it easy for people to be health-conscious,” Colditz says. “With Zuum, anyone can make healthier choices.”

For more information about Zuum, visit http://zuum.wustl.edu, or follow the app’s Twitter account at http://twitter.com/Zuum_Health.

The Siteman Cancer Center is the only NCI-designated Comprehensive Cancer Center within a 240-mile radius of St. Louis. Siteman Cancer Center comprises the cancer research and treatment programs of Barnes-Jewish Hospital and Washington University School of Medicine.

The Department of Energy (DOE) announced Aug. 2 that a team of engineers at Washington University in St. Louis will receive $2 million to design a battery management system for lithium-ion batteries that will guarantee their longevity, safety and performance. This is a particularly challenging project because the electrochemical reactions inside the battery are not easily captured in mathematical form.

The project is one of 12 that won funding from the DOE’s Advanced Research Projects Agency-Energy (ARPA-E) under the new AMPED program that focuses on innovations in battery management and storage to advance electric vehicle technologies and to help improve the efficiency and reliability of the electrical grid.

“This latest round of ARPA-E projects seek to address the remaining challenges in energy storage technologies, which could revolutionize the way Americans store and use energy in electric vehicles, the grid and beyond, while also potentially improving the access to energy for the U.S. military at forward operating bases in remote areas,” says Secretary of Energy Steven Chu.

“These cutting-edge projects could transform our energy infrastructure, dramatically reduce our reliance on imported oil and increase American energy security,” Chu says.

“This initiative is part of a broader effort to strengthen the university’s expertise in energy-related technologies,” says Pratim Biswas, PhD, chair of the Department of Energy, Environmental & Chemical Engineering in the School of Engineering & Applied Science. 

“While this grant targets car batteries,” he says, “the technology is also directly applicable to intermittent sources of energy such as solar that produce energy that may need to be buffered rather than plugged directly into electrical grid.”

The department also recently won a large grant in solar technology and plans to launch an effort called Solar Energy and Energy Storage, or SEES.

The AMPED award goes to the Modeling, Analysis and Process-control Laboratory for Electrochemical systems (MAPLE) in the Department of Energy, Environmental & Chemical Engineering, led by Venkat Subramanian, PhD, associate professor.

“I want to give credit to my doctoral students,” Subramanian says. “Without their efforts, we wouldn’t have been able to submit a proposal. The solicitation came and we had two weeks to respond after the team was formed, and then we got a review and we had to respond over the weekend.”

In addition to Subramanian, the team includes doctoral students Venkatasailanathan Ramadesigan, Paul Northrop, Sumitava De, Bharatkumar Suthar and Matthew Lawder.

Lithium-ion batteries

Lithium-ion batteries are what are called secondary cells, because the electrochemical reactions that create a current are reversible and the battery can be recharged. The more familiar primary cells, in contrast are used once and thrown away.

The lithium is stored in metallic (uncharged) form inside the particles of a graphite electrode, explains Subramanian. During discharge the lithium comes to the electrode’s surface, where it is ionized, creating a current that travels to the cathode. At the cathode, typically a lithium-based alloy, the ions are neutralized and enter electrode particles as metallic lithium.

The battery is recharged by forcing a current to flow in the opposite direction, moving the lithium back into the anode.

Lithium-ion batteries hold great promise for applications such as electric vehicles because they have high energy density (energy stored per unit volume) and lose charge very slowly when not in use.

No battery is perfect and lithium-ion batteries, like all batteries, have drawbacks. If the batteries are charged too fast, they can heat up and may explode. To avoid catastrophic failure, manufacturers overdesign the batteries and use only part of their energy capacity per cycle, Subramanian says.

“The goal of the AMPED program is to push the current technology to 100-percent efficiency, while making sure battery lifetime is not compromised,” Subramanian says. This would ultimately reduce the weight of the car and improve its energy efficiency.

Revving up the models

“If you can predict what will happen inside the battery, you can push the battery to do more per cycle,” Subramanian says. “Currently, empirical (experience-based) models that have no predictive capability are used to manage the batteries. This is why manufacturers over-stack the material; they have no idea what’s happening inside.”

There are physics-based models of lithium-ion batteries, but they are computationally intensive and can’t be solved in real time by the usual methods.

This is where the MAPLE lab comes in. The engineers plan to use a class of simulation techniques called spectral methods aided by mathematical analysis to solve a physics-based model’s differential equations. Spectral methods should allow them to cut down on the model’s computational demands so that it runs faster.

The Battery Management System MAPLE lab develops will keep the battery operating optimally, enabling maximum utilization of energy at all times.

“In general,” Subramanian says, “people write mathematical models and then plug them into commercial software to solve them. We relish solving the models ourselves to see if we can find more elegant ways to do it. That’s the overarching theme of our work.

“We are also interested in re-examining predictive models of importance for medicine, such as those used in medical imaging, to see if we can solve them faster but with the same accuracy so that they can be used in real-time sensing and control,” he says.

Modeled on the Defense Advanced Projects Agency (DARPA), famous for its daring funding decisions, ARPA-E was launched in 2009 to seek out breakthrough technologies that are too risky for private-sector investment, but have the potential to transform energy technology, form the foundation for entirely new industries, and have large commercial impacts.

A. Leger et al./Icarus

Scientists at Washington University have simulated the atmospheres of hot Earth-like planets, such as CoRoT-7b, shown here in an artist's conception. CoRoT-7b orbits so close to its star that its starward side is an ocean of molten rock. By looking for atmospheres like those generated by the simulations, astronomers should be able to identify Earth-like exoplanets.

In science fiction novels, evil overlords and hostile aliens often threaten to vaporize the Earth. At the beginning of The Hitchhikers Guide to the Galaxy, the officiously bureaucratic aliens called Vogons, authors of the third-worst poetry in the universe, actually follow through on the threat, destroying the Earth to make way for a hyperspatial express route.

“We scientists are not content just to talk about vaporizing the Earth,” says Bruce Fegley, PhD, professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis, tongue firmly in cheek. “We want to understand exactly what it would be like if it happened.”

And, in fact, Fegley and his colleagues Katharina Lodders, PhD, a research professor of earth and planetary sciences who is currently on assignment at the National Science Foundation (NSF), and Laura Schaefer, a graduate student at Harvard University, have vaporized the Earth — if only by simulation, that is, mathematically and inside a computer.

They weren’t just practicing their evil overlord skills. By baking model Earths, they are trying to figure out what astronomers should see when they look at the atmospheres of super-Earths in a bid to learn the planets’ compositions.

Super-Earths are planets outside our solar system (exoplanets) that are more massive than Earth, but less massive than Neptune and made of rock instead of gas. Because of the techniques used to find them, most of the detected super-Earths are those that orbit close to their stars — within rock-melting distance.

Their NSF- and NASA-funded research, described in the Aug. 10 issue of The Astrophysical Journal, shows that Earth-like planets as hot as these exoplanets would have atmospheres composed mostly of steam and carbon dioxide, with smaller amounts of other gases that could be used to distinguish one planetary composition from another.

The WUSTL team is collaborating with the research group of Mark Marley, PhD, at the NASA Ames Research Center to convert the gas abundances they have calculated into synthetic spectra the planet hunters can compare to spectra they measure.

Motivated by degeneracy

Under favorable circumstances, planet-hunting techniques allow astronomers not just to find exoplanets but also to measure their average density.

The average density together with theoretical models let the astronomers figure out the bulk chemical composition of gas giants, but in the case of rocky planets, the possible variety of rocky ingredients can often add up several different ways to the same average density.

This is an outcome scientists, who would prefer one answer per question, call degeneracy.

If a planet passes in front of its star so that astronomers can observe the light from the star filtered by the planet’s atmosphere, they can determine the composition of the planet’s atmosphere, which allows them to distinguish about alternative bulk planetary compositions.

“It’s not crazy that astronomers can do this and more people are looking at the atmospheres of these transiting exoplanets,” Fegley says. “Right now, there are eight transiting exoplanets where astronomers have done some atmospheric measurements and more will probably be reported in the near future.

“We modeled the atmospheres of hot super-Earths because that’s what astronomers are finding and we wanted to predict what they should be looking for when they look at the atmospheres to decipher the nature of the planet,” Fegley says.

Two model Earths

Even though the planets are called super-Earths, Fegley says, the term is a reference to their mass and makes no claim about their composition, much less their habitability. But, he says, you start with what you know.

The team ran calculations on two types of pseudo-Earths, one with a composition like that of the Earth’s continental crust and the other, called the BSE (bulk silicate Earth), with a composition like the Earth’s before the continental crust formed, which is the composition of the silicate portion of the primitive Earth before the crust formed.

The difference between the two models, says Fegley, is water. The Earth’s continental crust is dominated by granite, but you need water to make granite. If you don’t have water, you end up with a basaltic crust like Venus. Both crusts are mostly silicon and oxygen, but a basaltic crust is richer in elements such as iron and magnesium.

Fegley is quick to admit the Earth’s continental crust is not a perfect analog for lifeless planets because it has been modified by the presence of life over the past four billion years, which both oxidized the crust and also led to production of vast reservoirs of reduced carbon, for example in the form of coal, natural gas, and oil.

Using thermodynamic equilibrium calculations, the team determined which elements and compounds would be gaseous at these alien temperatures.

“The vapor pressure of the liquid rock increases as you heat it, just as the vapor pressure of water increases as you bring a pot to boil,” Fegley says. “Ultimately this puts all the constituents of the rock into the atmosphere.”

The continental crust melts at about 940 C (1,720 F), Fegley says, and the bulk silicate Earth at roughly 1,730 C (3,145 F). There are also gases released from the rock as it heats up and melts.

Their calculations showed that the atmospheres of both model Earths would be dominated over a wide temperature range by steam (from vaporizing water and hydrated minerals) and carbon dioxide (from vaporizing carbonate rocks).

The major difference between the models is that the BSE atmosphere is more reducing, meaning that it contains gases that would oxidize if oxygen were present. At temperatures below about 730 C (1,346 F) the BSE atmosphere, for example, contains methane and ammonia.

That’s interesting, Fegley says, because methane and ammonia, when sparked by lighting, combine to form amino acids, as they did in the classic Miller-Urey experiment on the origin of life.

At temperatures above about 730 C, sulfur dioxide would enter the atmosphere, Fegley says. “Then the exoplanet’s atmosphere would be like Venus’, but with steam,” Fegley says.

The gas most characteristic of hot rocks, however, is silicon monoxide, which would be found in the atmospheres of both types of planets at temperatures of 1,430 C (2,600 F) or higher.

This leads to amusing possibility that as frontal systems moved through this exotic atmosphere, the silicon monoxide and other rock-forming elements might condense and rain out as pebbles.

Asked whether his team ever cranked the temperature high enough to vaporize the entire Earth, not just the crust and the mantle, Fegley admits that they did.

“You’re left with a big ball of steaming gas that’s knocking you on the head with pebbles and droplets of liquid iron,” he says. “But we didn’t put that into the paper because the exoplanets the astronomers are finding are only partially vaporized,” he says.