After a year caring for patients at the heart of Brazil’s Zika epidemic, pediatric neurologist Vanessa van der Linden has seen some of the worst cases.
She was one of the first researchers to link Zika virus to microcephaly, a now well-known birth defect marked by a small, misshapen head and, sometimes, a forehead that slopes backward. Babies with the defect can have other symptoms, too: Van der Linden has seen 24-hour crying bouts, spasms, extreme irritability and difficulty swallowing. But microcephaly is just the tip of the Zika iceberg, she said September 22 at a workshop hosted by the National Institutes of Health in North Bethesda, Md. That’s something public health officials have been warning about for months. Now, scientists have begun to describe a head-to-toe assortment of health problems linked to Zika virus infection in utero; they’re calling it congenital Zika syndrome.
Still, the full scope of the problem, including the threat of more subtle neurologic disorders such as learning disabilities or developmental delays, remains murky, says Peter Hotez, a pediatrician and microbiologist at Baylor College of Medicine in Houston.
“That’s the big unknown: There’s probably a spectrum of illness,” similar to autism, he says. And it could take years for scientists to sort it all out.
It’s a problem that Brazil is facing now, and one that Puerto Rico has just begun grappling with.
As of September 23, the U.S. territory had reported 22,358 confirmed cases of Zika infection. Of these cases, 1,871 are pregnant women. Carmen Zorrilla, an obstetrician-gynecologist at the University of Puerto Rico’s Maternal-Infant Studies Center who has examined some of these women and their babies, emphasizes the importance of following up on all babies exposed to Zika in the womb — even those without apparent birth defects. “Even if they are born normal,” she said, “it doesn’t mean they’ll be OK.”
Insidious problems At the workshop, Zorrilla described the case of one of the first Puerto Rican babies born to a mother diagnosed with Zika. The baby didn’t have microcephaly, but she did have another unusual problem: She couldn’t open her eyes. A bad case of conjunctivitis (pinkeye) left her needing help opening her eyelids every morning — even 27 days after birth. Zorrilla can’t say for sure whether the problem was related to Zika, but “it really concerned me,” she said. “This is the first baby I’ve seen with conjunctivitis that lasted for so long.”
The case may be another clue that Zika’s assaults on the body are widespread. And Zorrilla can expect to see more cases soon. Ultrasound examinations of 228 women in Puerto Rico with confirmed Zika infection have spotted brain abnormalities in 13 fetuses, including one with microcephaly.
Another observation could hint at problems yet to come: Most of the Zika-exposed fetuses tended to have slightly smaller heads than average, although “still within the normal limits,” Zorrilla said. But measurements of leg bones and stomach size indicate that the rest of the body is growing normally. Implications remain unclear, but the findings — preliminary results from Alberto de la Vega, also an obstetrician-gynecologist at the University of Puerto Rico — are the latest in a litany of anomalies linked to Zika.
Long-term problems aren’t unusual in babies infected with a different kind of virus that causes microcephaly. Like Zika, cytomegalovirus can infect babies in the womb. Most CMV-infected babies don’t have any obvious symptoms, but asymptomatic kids may have problems as they grow, including intellectual disabilities, hearing loss or cerebral palsy, researchers suggested in the October Brain and Development.
Beyond microcephaly, scientists have recently described other symptoms linked to Zika infection. In some babies, for example, Zika seems to damage hearing. Of 70 Zika-exposed infants born with microcephaly, 10 percent had some hearing loss, researchers noted in a Sept. 2 report published by the U.S. Centers for Disease Control and Prevention. Zika can leave a mark on the eyes, too. More than a third of 29 babies with microcephaly had some sort of eye oddity, including mottled pigmenting and withered tissue, researchers reported in May in JAMA Ophthalmology.
Van der Linden has also observed a link between Zika and a deformity called arthrogryposis, where a child’s joints can be stuck in contorted positions — even in babies without microcephaly. The condition might stem from problems with infected babies’ motor neurons, the nerve cells that relay messages from the brain to the muscles, van der Linden and colleagues suggested August 9 in BMJ.
She has even seen babies born with normal head circumferences who later develop microcephaly or other brain defects. One mother, she says, came in five months after giving birth because she thought her baby wasn’t developing normally. Like children with congenital Zika syndrome, the baby’s head scans revealed “the same pattern of brain damage,” van der Linden says. This pattern includes a malformed cerebral cortex, the wrinkled outer layer of the brain, and calcifications, strange lumps of calcium deposited within the tissue.
Infiltrating the brain Scientists still don’t know exactly how Zika damages the brain, but they have some ideas.
One recent report found that the virus can infiltrate and kill both neuroepithelial stem cells, which give rise to all sorts of brain cells, and radial glial cells, which can generate newborn neurons and help guide them to their proper place in the brain.
Zika also hinders these cells’ ability to split into new cells, Yale University neuroscientist Marco Onorati and colleagues reported September 6 in Cell Reports. Stem cells at work in the fetal brain eventually give rise to structures responsible for thought and memory and learning, raising concerns of a cascade of problems down the road. “This is a virus that blocks the development of the fetal brain,” Hotez says. “That’s about the worst thing you can possibly imagine.”
And fetuses might not be the only ones at risk, he points out. “Kids in the first years of life also have growing, developing brains,” he says. “What if they get infected with Zika?”
It’s not an easy question to answer. But another disease could offer clues.
Malaria, for example, can cause severe neurological problems. In children, a condition called cerebral malaria may be linked to mental health disorders such as attention-deficit/hyperactivity disorder, antisocial behavior and depression, researchers reported in March in Malaria Journal.
Researchers will also need to watch out for long-term troubles in Zika-exposed babies born with no obvious symptoms, says the CDC’s Sonja Rasmussen. “We don’t want to make families too scared,” she says. “But we do recognize the possibility of later-on seizures or developmental delay.”
Since most people don’t show signs of Zika infection, pinpointing the total number of pregnant women (and babies) exposed to the virus may be impossible.
In the Americas, at least, the number is probably enormous. Tens of thousands of children may eventually suffer some sort of neurologic or psychiatric illness triggered by Zika, Hotez predicted in a paper published in JAMA Pediatrics in August.
Van der Linden can’t say whether the babies she has seen have learning disabilities or psychiatric illnesses, or other more subtle cognitive problems — most of her patients are between 9 months and 1 year old.
But she plans to follow these patients, and the babies who appeared normal at birth, for years. “We need time to better understand the disease,” she says.
Hotez agrees: “It’s going to take a generation of pediatric neurologists and infectious disease experts to figure this out.”
Figuring out the nuts and bolts of the cell’s recycling machinery has earned the 2016 Nobel Prize in physiology or medicine. Cell biologist Yoshinori Ohsumi of the Tokyo Institute of Technology has received the prize for his work on autophagy, a method for breaking down and recycling large pieces of cellular junk, such as clusters of damaged proteins or worn-out organelles.
Keeping this recycling machinery in good working condition is crucial for cells’ health (SN: 3/26/11, p. 18). Not enough recycling can cause cellular trash to build up and lead to neurological diseases such as Alzheimer’s and Parkinson’s. Too much recycling, on the other hand, has been linked to cancer. “It’s so exciting that Ohsumi has received the Nobel Prize, which he no question deserved,” says biologist Jennifer Lippincott-Schwartz of Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Va. “He set the framework for an entire new field in cell biology.”
Ohsumi‘s discoveries helped reveal the mechanism and significance of a fundamental physiological process, biologist Maria Masucci of the Karolinska Institute in Sweden said in a news briefing October 3. “There is growing hope that this knowledge will lead to the development of new strategies for the treatment of many human diseases.”
Scientists got their first glimpse of autophagy in the 1960s, not long after the discovery of the lysosome, a pouch within cells that acts as a garbage disposal, grinding fats and proteins and sugars into their basic building blocks. (That discovery won Belgian scientist Christian de Duve a share of the Nobel Prize in 1974.) Researchers had observed lysosomes stuffed with big chunks of cellular material — like the bulk waste of the cellular world — as well as another, mysterious pouch that carried the waste to the lysosome.
Somehow, the cell had devised a way to consume large parts of itself. De Duve dubbed the process autophagy, from the Greek words for “self” and “to eat.” But over the next 30 years, little more became known about the process. “The machinery was unknown, and how the system was working was unknown, and whether or not it was involved in disease was also unknown,” said physiologist Juleen Zierath, also of the Karolinska Institute, in an interview after the prize’s announcement.
That all changed in the 1990s when Ohsumi decided to study autophagy in a single-celled organism called baker’s yeast, microbes known for making bread rise. The process was tricky to catch in action, partly because it happened so fast. So Ohsumi bred special strains of yeast that couldn’t break down proteins in their cellular garbage disposals (called vacuoles in yeast).
“He reasoned that if he could stop the degradation process, he could see an accumulation of the autophagy machinery in these cells,” Zierath said.
And that’s just what Ohsumi saw. When he starved the yeast cells, the “self-eating” machinery kicked into gear (presumably to scrounge up food for the cells). But because the garbage disposals were defective, the machinery piled up in the vacuoles, which swelled like balloons stuffed with sand. Ohsumi could see the bulging, packed bags clearly under a light microscope. He published the work in a 1992 paper in the Journal of Cell Biology. Finding the autophagy machinery let Ohsumi study it in detail. A year later, he discovered as many as 15 genes needed for the machinery to work. In the following years, Ohsumi and other scientists examined the proteins encoded by these genes and began to figure out how the components of the “bulk waste” bag, or autophagosome, came together, and then fused with the lysosome.
The work revealed something new about the cell’s garbage centers, Zierath said. “Before Ohsumi came on the scene, people understood that the waste dump was in the cell,” she said. “But what he showed was that it wasn’t a waste dump. It was a recycling plant.”
Later, Ohsumi and his colleagues studied autophagy in mammalian cells and realized that the process played a key maintenance role in all kinds of cells, breaking down materials for reuse. Ohsumi “found a pathway that has its counterparts in all cells that have a nucleus,” says 2013 Nobel laureate Randy Schekman, a cell biologist at the University of California, Berkeley. “Virtually every corner of the cell is touched by the autophagic process.”
Since Ohsumi’s discoveries, research on autophagy has exploded, says Lippincott-Schwartz. “It’s an amazing system that every year becomes more and more fascinating.”
Ohsumi, 71, remains an active researcher today. He received the call from the Nobel committee at his lab in Japan. The prize includes an award of 8 million Swedish kronor (equivalent to about $934,000). About his work, he said: “It was lucky. Yeast was a very good system, and autophagy was a very good topic.”
Still, he added in an interview with a Nobel representative, “we have so many questions. Even now we have more questions than when I started.”
A satellite of Saturn joins the club of moons with possible oceans. A subsurface sea of water might hide beneath the icy crust of Dione, one of Saturn’s moons, researchers report online October 9 in Geophysical Research Letters. That puts Dione in good company alongside Enceladus (another moon of Saturn) and several moons of Jupiter, as well as possibly Pluto (SN Online: 9/23/16).
Dione’s ocean is about 100 kilometers below the surface and roughly 65 kilometers deep, Mikael Beuthe, a planetary scientist at the Royal Observatory of Belgium in Brussels, and colleagues report. They inferred the ocean’s presence from measurements of Dione’s gravity made by the Cassini spacecraft.
When babies are ready for solid foods, the meal usually arrives on a spoon. Parents scoop up pureed carrots, liquefied banana or soupy rice cereal and deliver it straight to their baby’s mouth (or forehead). But a different way of introducing solids is gaining ground. Called baby-led weaning, the approach is based on letting the baby feed herself whole foods such as a soft pear or a spear of cooked broccoli — no spoon required.
Advocates say that by having control over what goes in their mouths, babies learn to regulate their food intake, refine motor skills and perhaps even become more adventurous eaters. But critics fret that inexperienced eaters may be more likely to choke on solid foods that they feed themselves. A new study of about 200 Australian babies has some reassuring news: Provided that certain risky foods were avoided, babies who fed themselves solid foods were no more likely to choke than spoon-fed babies.
Half of the babies started solid food the traditional way, with parents spoon-feeding them purees and other mushy foods. The other half were given solid foods on their trays and encouraged to feed themselves. Parents were told that babies ought to be sitting up and in the presence of a caregiver while eating. And parents also received a list of risky foods to avoid: hard crackers, diced or hard meat, raw vegetables and popcorn made the list. (A general rule of thumb for checking whether the food is safe: If you can squish the food against the roof of your mouth, then it’s probably OK for your baby to try.)
Spoon-fed babies choked just as much as babies who fed themselves, the researchers report in the September Pediatrics. At 6 months of age, about 22 percent of spoon-fed babies had choked at least once. In the baby-led weaning group, about 18 percent of babies had choked at least once. Choking rates between the two groups were on par as the babies grew older.
There’s an important distinction here between gagging and true choking. Gagging is common among babies as their mouths learn to handle new textures and flavors. The throat slams shut and the mouth tries to get the offending food out. A gagging baby may have watery eyes, push his tongue out of his mouth and make retching movements. He may even puke. This can be hard for parents to watch, but gagging isn’t dangerous.
True choking is. This is when the airway becomes partially or fully blocked. The baby may cough or sputter in an attempt to dislodge the food. He may make a raspy, squeaky whisper as he tries to communicate distress. Or he may go silent. It’s always good to be up on infant CPR, particularly if you’ve got a new eater.
The babies who fed themselves seemed to quickly hone their skills. Initially, self-feeding babies gagged more often than spoon-fed babies at 6 months of age. But by 8 months old, self-feeders had become experts, gagging less than spoon-fed babies. Although the news seems good for parents who want to try baby-led weaning, the research also turned up something concerning: Lots of babies were given risky foods, regardless of feeding style. At seven months of age, just over half of babies were given something from the no-feed list. By 12 months, almost all the babies had been given riskier foods that can lead to choking. Hard crackers, meat and whole grapes topped the list.
The results suggest that whether you feed your baby or you let your baby feed herself, it’s still important to pay attention to the type of food that’s going into her cute little mouth.
Scientists have lost their latest round of hide-and-seek with dark matter, but they’re not out of the game.
Despite overwhelming evidence that an exotic form of matter lurks unseen in the cosmos, decades of searches have failed to definitively detect a single particle of dark matter. While some scientists continue down the road of increasingly larger detectors designed to catch the particles, others are beginning to consider a broader landscape of possibilities for what dark matter might be.
“We’ve been looking where our best guess told us to look for all these years, and we’re starting to wonder if we maybe guessed wrong,” says theoretical astrophysicist Dan Hooper of Fermilab in Batavia, Ill. “People are just opening their minds to a wider range of options.”
Dark matter permeates the cosmos: The material keeps galaxies from flying apart and has left its imprints in the oldest light in the universe, the cosmic microwave background, which dates back to just 380,000 years after the Big Bang. Indirect evidence from dark matter’s gravitational influences shows that it makes up the bulk of the mass in the universe. But scientists can’t pin down what dark matter is without detecting it directly. In new results published in August and September, three teams of scientists have come up empty-handed, finding no hints of dark matter. The trio of experiments searched for one particular variety of dark matter — hypothetical particles known as WIMPs, or weakly interacting massive particles, with a range of possible masses that starts at several times that of a proton. WIMPs, despite their name, are dark matter bigwigs — they have long been the favorite explanation for the universe’s missing mass. WIMPs are thought to interact with normal matter only via the weak nuclear force and gravity.
Part of WIMPs’ appeal comes from a prominent but unverified theory, supersymmetry, which independently predicts such particles. Supersymmetry posits that each known elementary particle has a heavier partner; the lightest partner particle could be a dark matter WIMP. But evidence for supersymmetry hasn’t materialized in particle collisions at the Large Hadron Collider in Geneva, so supersymmetry’s favored status is eroding (SN: 10/1/16, p. 12). Supersymmetry arguments for WIMPs are thus becoming shakier — especially since WIMPs aren’t showing up in detectors.
Scientists typically search for WIMPs by looking for interactions with normal matter inside a detector. Several current experiments use tanks of liquefied xenon, an element found in trace amounts in Earth’s atmosphere, in hopes of detecting the tiny amounts of light and electric charge that would be released when a WIMP strikes a xenon nucleus and causes it to recoil.
The three xenon experiments are the Large Underground Xenon, or LUX, experiment, located in the Sanford Underground Research Facility in Lead, S.D.; the PandaX-II experiment, located in China’s JinPing underground laboratory in Sichuan; and the XENON100 experiment, located in the Gran Sasso National Laboratory in Italy. Teams of scientists at the three locations each reported no signs of dark matter particles. The experiments are most sensitive to particles with masses around 40 or 50 times that of a proton. Scientists can’t completely rule out WIMPs of these masses, but the interactions would have to be exceedingly rare. In initial searches, proponents of WIMPs expected that the particles would be easy to find. “It was thought to be like, ‘OK, we’ll run the detector for five minutes, discover dark matter, and we’re all done,’” says physicist Matthew Szydagis of the University at Albany in New York, a member of LUX. That has turned into decades of hard work. As WIMPs keep failing to turn up, some scientists are beginning to become less enamored with the particles and are considering other possibilities more closely.
One alternative dark matter contender now attracting more attention is the axion. This particle was originally proposed decades ago as part of the solution to a particle physics quandary known as the strong CP problem — the question of why the strong nuclear force, which holds particles together inside the nucleus, treats matter and antimatter equally. If dark matter consists of axions, the particle could therefore solve two problems at once.
Axions are small fry as dark matter goes — they can be as tiny as a millionth of a billionth the mass of a WIMP. The particles interact so feebly that they are extremely difficult to detect. If axions are dark matter, “you’re sitting in an enormous, dense sea of axions and you don’t even notice them,” says physicist Leslie Rosenberg of the University of Washington in Seattle, the leader of the Axion Dark Matter eXperiment. After a recent upgrade to the experiment, ADMX scientists are searching for dark matter axions using a magnetic field and special equipment to coax the particles to convert into photons, which can then be detected. Although WIMPs and axions remain the front-runners, scientists are beginning to move beyond these two possibilities. In between the featherweight axions and hulking WIMPs lies a broad range of masses that hasn’t been well explored. Scientists’ favorite theories don’t predict dark matter particles with such intermediate masses, says theoretical physicist Kathryn Zurek of Lawrence Berkeley National Laboratory in California, but that doesn’t mean that dark matter couldn’t be found there. Zurek advocates a diverse search over a broad range of masses, instead of focusing on one particular theory. “Dark matter direct detection is not one-size-fits-all,” she says. In two papers published in Physical Review Letters on January 7 and September 14, Zurek and colleagues proposed using superconductors — materials that allow electricity to flow without resistance — and superfluids, which allow fluids to flow without friction, to detect light dark matter particles. “We are trying to broaden as much as possible the tools to search for dark matter,” says Zurek. Likewise, scientists with the upcoming Super Cryogenic Dark Matter Search SNOLAB experiment, to be located in an underground lab in Sudbury, Canada, will use detectors made of germanium and silicon to search for dark matter with smaller masses than the xenon experiments can.
Scientists have not given up on xenon WIMP experiments. Soon some of those experiments will be scaling up — going from hundreds of kilograms of liquid xenon to tons — to improve their chances of catching a dark matter particle on the fly. The next version of XENON100, the XENON1T experiment (pronounced “XENON one ton”) is nearly ready to begin taking data. LUX’s next generation experiment, known as LUX-ZEPLIN or LZ, is scheduled to begin in 2020. PandaX-II scientists are also planning a sequel. Physicists are still optimistic that these detectors will finally find the elusive particles. “Maybe we will have some opportunity to see something nobody has seen,” says Xiangdong Ji of Shanghai Jiao Tong University, the leader of PandaX-II. “That’s what’s so exciting.”
In the sea of nondetections of dark matter, there is one glaring exception. For years, scientists with the DAMA/LIBRA experiment at Gran Sasso have claimed to see signs of dark matter, using crystals of sodium iodide. But other experiments have found no signs of DAMA’s dark matter. Many scientists believe that DAMA has been debunked. “I don’t know what generates the weird signal that DAMA sees,” says Hooper. “That being said, I don’t think it’s likely that it’s dark matter.”
But other experiments have not used the same technology as DAMA, says theoretical astrophysicist Katherine Freese of the University of Michigan in Ann Arbor. “There is no alternative explanation that anybody can think of, so that is why it is actually still very interesting.” Three upcoming experiments should soon close the door on the mystery, by searching for dark matter using sodium iodide, as DAMA does: the ANAIS experiment in the Canfranc Underground Laboratory in Spain, the COSINE-100 experiment at YangYang Underground Laboratory in South Korea, and the SABRE experiment, planned for the Stawell Underground Physics Laboratory in Australia.
Scientists’ efforts could still end up being for naught; dark matter may not be directly detectable at all. “It’s possible that gravity is the only lens with which we can view dark matter,” says Szydagis. Dark matter could interact only via gravity, not via the weak force or any other force. Or it could live in its own “hidden sector” of particles that interact among themselves, but mostly shun normal matter.
Even if no particles are detected anytime soon, most scientists remain convinced that an unseen form of matter exists. No alternative theory can explain all of scientists’ cosmological observations. “The human being is not going to give up for a long, long time to try to search for dark matter, because it’s such a big problem for us,” says Ji.
SALT LAKE CITY — Flying dinosaurs took off from the ground — no leap from the trees required.
Ancient birds and some nonavian dinosaurs used their wings and powerful legs to launch themselves into the air, a new analysis of 51 winged dinos suggests. Paleontologist Michael Habib of the University of Southern California in Los Angeles reported the findings October 26 at the annual meeting of the Society of Vertebrate Paleontology.
“That’s a big deal, because the classic idea was that early birds started out gliding between trees,” says Yale ornithologist Michael Hanson. The origin of flight in birds is a sticky subject, says paleontologist Corwin Sullivan of the Chinese Academy of Sciences in Beijing. “There’s been a long-standing controversy over whether flight evolved from the ground up or the trees down.”
Traditionally, scientists have thought that early birds scrambled up trees to get an altitude assist. The birds would then start their flight with a jump, like a hang glider diving off a cliff. Over time, descendants of those gliding birds would have evolved larger wings and, eventually, the ability to flap. Flapping “means you can push yourself forward on your own power,” Habib said. That’s how modern birds fly.
But in recent years, several lines of evidence have begun to dismantle the trees-down approach to flight evolution. Birds descended from terrestrial animals, for one, not tree dwellers. Habib’s team wondered whether early birds needed an elevation boost from trees at all — perhaps they could take off directly from the ground.
He and colleagues examined 51 fossil specimens from 37 different winged dinosaur genera that lived from 150 million to 70 million years ago, from the Late Jurassic to Late Cretaceous epochs. The sample included both avian and nonavian dinosaurs.
The specimens all had stiff, flightlike feathers on their forelimbs. But not all animals with feathered wings can fly, Habib says. To figure out if his specimens once could, he and colleagues analyzed wing length, body mass and hind limb muscle power, among other fossil features. Dinos that could fly (by flapping their wings) had to have enough leg strength to propel them up and enough wing speed to carry them forward. Just 18 specimens (representing nine of the 37 groups) had the right stuff to get off the ground: every one of the avian specimens in the sample, as well as a few of the nonavian dinos too, including a tiny, four-winged dinosaur called Microraptor.
“Little guys did well,” Habib says. “Anything over four to five kilograms was struggling.”
Whether the early fliers could sustain flight for long distances is a different ball game, Habib says. “But there’s a big difference between flying a little and not flying at all.”
Early flying dinosaurs may have burst off the ground to escape from predators. This bursting behavior could have set the stage for the powered flight systems of modern birds, Habib says. Quick, powerful takeoffs “put a premium on large wings, large flight muscles and really fast wings” — all characteristics of today’s best fliers.
In empty space, quantum particles flit in and out of existence, electromagnetic fields permeate the vacuum, and space itself trembles with gravitational waves. What may seem like nothingness paradoxically teems with activity.
In Void: The Strange Physics of Nothing, physicist and philosopher James Owen Weatherall explores how physicists’ beliefs about nothingness have changed over several revolutionary periods. The void, Weatherall argues, is physics distilled to its bare essence. If physicists can’t agree on the properties of empty space, they won’t be able to explain the physics of planets or particles either. Scientists have argued over nothingness since the early days of physics. Vacant space was unthinkable to Aristotle, and Descartes so abhorred the idea of a vacuum that he posited that an invisible “plenum” suffused the gaps between objects. But Isaac Newton upended this view, arguing that space was just a barren container into which matter is placed.
Since then, physicists have continued to flip-flop on this issue. The discovery in the mid-1800s that light is an electromagnetic wave led scientists to conclude that a vibrating medium, an “ether,” filled space. Just as sound waves vibrate the air, physicists thought there must be some medium for light waves to ripple. Albert Einstein tore down that idea with his special theory of relativity. Since the speed of light was the same for all observers, no matter their relative speeds, he reasoned, light could not be traveling through some absolute, stationary medium. But he later predicted, as part of his general theory of relativity, that space itself can ripple with gravitational waves (SN: 3/5/16, p. 6) — suggesting that the void is not quite empty.
Under the modern view of quantum physics, various fields pervade all of space, and particles are simply excitations, or waves, in these fields. Even in a vacuum, experiments show, fluctuating fields produce a background of transient particles and antiparticles. Does a space pulsating with gravitational waves and bubbling with particles really qualify as empty? It depends on the scientific definition of “nothing,” Weatherall argues, which may not conform to intuition.
Weatherall serves readers a fairly typical buffet of physics theories, dishing up Newtonian mechanics, relativity, quantum mechanics and a small helping of string theory. But he does this through a lens that highlights connections between those theories in a novel way. Weatherall contends, for instance, that differing notions of nothingness between theories of general relativity and quantum mechanics could help explain why scientists are still struggling to unite the two ideas into one theory of quantum gravity.
Exploring the physics of nothing demands quite a bit of wading through the physics of something, and it’s not always clear how the threads Weatherall is following will lead back to the void. When he finally makes these connections, though, they often reveal insights that are missed in the typical focus on things of substance.
SAN DIEGO — A small number of people maintain razor-sharp memories into their 90s, despite having brains chock-full of the plaques and tangles linked to Alzheimer’s disease. Researchers suspect that these people’s brains are somehow impervious to the usual devastation thought to be caused by those plaques and tangles.
Researchers studied the brains of people 90 years old or older who had excellent memories, performing as well as people in their 50s and 60s on some tests. Postmortem brain tissue from eight such people revealed a range of Alzheimer’s features. Two participants had remarkably clean brains with few signs of amyloid-beta plaques and tangles of tau protein. Four participants had middling levels. Surprisingly, the other two samples were packed with plaques and tangles, enough to qualify those people for an Alzheimer’s diagnosis based on their brains. “These people, for all practical purposes, should be demented,” study coauthor Changiz Geula of Northwestern University’s medical school said November 15 in a news briefing at the annual meeting of the Society for Neuroscience.
Further tests revealed that even in the midst of these Alzheimer’s hallmarks, nerve cells survived in people with strong memories. Those people had more healthy-looking nerve cells than people with dementia and similar plaque and tangle levels. The researchers don’t know how these mentally sharp people avoid the ravages thought to be caused by plaques and tangles. “What’s surprising is this segment of people does exist,” Geula says. “We have to find out why.”
The new record-holder for fastest flying animal isn’t a bat out of hell. It’s a bat from Brazil, a new study claims. Brazilian free-tailed bats (Tadarida brasiliensis) can reach ground speeds of 160 kilometers per hour.
It’s unclear why they need that kind of speed to zoom through the night sky, but Brazilian bats appear to flap their wings in a similar fashion to ultrafast birds, an international group of researchers report November 9 in Royal Society Open Science. A sleek body, narrow wings and a wingspan longer than most other bats’ doesn’t hurt either.
Radio transmitters attached to the backs of seven bats allowed the team, led by evolutionary biologist Gary McCracken of the University of Tennessee, Knoxville, to track the flight path and speed of the bats after they emerged from a cave in southwestern Texas. All seven reached almost 100 km/hr when flying horizontally; one bat hit about 160 km/hr.
Until now, common swifts held the record of fastest fliers, soaring at up to 112 km/hr, often with help from wind and gravity. The Brazilian bats, however, reached their higher speeds with no assist. Since bat flight is rarely studied, there may be even faster bats out there, the researchers speculate.
When Christian Agrillo runs number-related experiments in his lab, he wishes his undergraduate subjects good luck. For certain tests, that’s about all he says. Giving instructions to the people would be unfair to the fish.
Agrillo, of the University of Padua in Italy, is finishing up several years of pitting humans against fish in trials of their abilities to compare quantities. He can’t, of course, tell his angelfish or his guppies to choose, say, the larger array of dots. So in recent tests he made the bemused students use trial and error too. “At the end, they start laughing when they find they are compared with fish,” he says. Yet the fish versus humans face-offs are eye-opening comparisons in his search for the deep evolutionary basis of what has blossomed into human mathematics. If it turns out that fish and people share some idiosyncrasies of their number sense (like spidey sense, except focused on quantities rather than danger), those elements might in theory date from a common ancestor more than 400 million years old. Comparisons of animals’ mental powers are “the paleontology of cognition,” Agrillo says.
No one seriously argues that animals other than people have some kind of symbolic numeral system, but nonhuman animals — a lot of them — can manage almost-math without numbers.
“There’s been an explosion of studies,” Agrillo says. Reports of a quantity-related ability come from chickens, horses, dogs, honeybees, spiders, salamanders, guppies, chimps, macaques, bears, lions, carrion crows and many more. And nonverbal number sensing, studies now suggest, allows much fancier operations than just pointing to the computer screen that shows more dots.
News stories on this diversity often nod to the idea that such a broad sweep of numberlike savvy across the animal tree of life could mean that animals all inherited rudiments of quantification smarts from a shared ancestor. Some scientists think that idea is too simple. Instead of inheriting the same mental machinery, animals could have just happened upon similar solutions when confronting the same challenge. (Birds and bats both fly, but their wings arose independently.)
Chasing down those deep origins means figuring out how animals, including humans too young or too rushed, manage quantitative feats without counting. It’s not easy. Putting together what should be a rich and remarkable story of the evolution of nonverbal number sense is just beginning. Who’s (sort of) counting? Symbolic numbers do marvels for humankind, but for millions of years, other animals without full powers to count have managed life-and-death decisions about magnitude (which fruit pile to grab, which fish school to join, whether there are so many wolves that it’s time to run). Counting dog treats For a sense of the issues, consider the old and the new in dog science. Familiar as dogs are, they’re still mostly wet-nosed conundrums when it comes to their number sense.
When food is at stake, dogs can tell more from less, according to a string of laboratory studies over more than a decade. And dogs may be able to spot cheating when people count out treats. Dog owners may not be amazed at such food smarts, but the interesting question is whether dogs solve the problem by paying attention to the actual number of goodies they see, or some other qualities.
An experiment in England in 2002, for instance, let 11 pet dogs settle down in front of a barrier that researchers then moved so the dogs could get a peek at a row of bowls. One bowl held a Pedigree Chum Trek treat. The barrier went up again, and researchers lowered a second treat into a bowl behind the screen, or sometimes just pretended to. When the barrier dropped again, the dogs overall stared a bit longer if only one treat was visible than if 1 + 1 had indeed equaled 2. Five of the dogs, in an extra test, also stared longer on average after a researcher covertly sneaked an extra treat into a bowl and then lowered the barrier on the unexpected 1 + 1 = 3.
Dogs could in theory recognize funny business by paying attention to the number of treats — or the treats’ “numerosity,” as researchers often call a quantity recognized nonverbally. But, depending on the design of a test, dogs might also get the right answers by judging the total surface area of treats instead of their numerosity. A multitude of other clues — density of objects in a cluster, a cluster’s total perimeter or darkness and so on — would also work. Researchers lump those giveaways under the term “continuous” qualities, because they change in a smooth continuum of increments instead of in the discrete 1, 2, 3.
The continuous qualities present a real staring-at-the-ceiling, heavy-sigh challenge for anyone inventing a numerosity test. By definition, nonverbal tests don’t use symbols such as numbers, so an experimenter has to show something, and those somethings inevitably have qualities that intensify or dwindle as the numerosity does. To at least see whether dogs evaluate total area to choose more food, Krista Macpherson of the University of Western Ontario in Canada devised a task for her rough collie Sedona. The dog had already served as an experimental subject in Macpherson’s earlier test of whether real dogs would try to seek help for their owners in danger, as TV’s trusty Lassie did. Sedona hadn’t tried to seek help for Macpherson (no dog in the test aided its owner), but she had proved amenable to doing lab work, especially for bits of hot dog or cheese.
Sedona was put to work to select whichever of two magnet boards had a greater number of geometric shapes fastened to it. Macpherson varied the dimensions of black triangles, squares and rectangles so that their total surface area wasn’t a reliable clue to the right answer.
The idea came from an experiment involving monkeys that reacted to a computer touch screen. But “I’m all cardboard and tape,“ Macpherson says. Sedona was perfectly happy to look at two magnet boards fastened to cardboard boxes on the ground and then indicate her choice by knocking over a box.
Sedona in the end triumphed at picking the box with more geometric thingies regardless of area, though the project took considerable effort from both woman and beast. The dog worked through more than 700 trials, starting as simply as 0 versus 1 and eventually scoring better than chance scrutinizing bigger magnitudes, such as 6 versus 9, Macpherson and William A. Roberts reported in Learning and Motivation in 2013. (Eight versus nine finally stumped the collie, but more on patterns in accuracy later.) In a 2016 paper in Behavioural Processes, another lab hailed the Sedona research as the “only evidence of dogs’ ability to use numerical information.”
More is better Dogs might have number sense, but when, or how much, they use it is another matter, notes Clive Wynne of Arizona State University in Tempe, a coauthor of that 2016 paper. To see what dogs do in more natural situations, he and Maria Elena Miletto Petrazzini of the University of Padua designed a test offering pets at a doggie daycare a choice of two plates of cut-up treat strips. A mix of breeds considered such options as a few big treat strips versus a smaller total amount of treats cut up into numerous small pieces. The dogs, without Sedona’s arduous training, went for the greater total amount of food, regardless of the number of pieces. Of course they did; it’s food — more is better. Without controls, food tests may not be measuring numerosity at all.
It’s not just edibility that affects whether an animal pays attention to numerosity. Experience with similarity or differences in objects can matter. Rosa Rugani, also at Padua, has pioneered studying number sense in recently hatched chicks, which can learn experimental procedures fast if she gets them motivated. “One of the more fascinating challenges of my job is to come up with ‘games’ the chicks like to play,” she says. Newly hatched chicks can develop a strong social attachment to objects, as if little plastic balls or ragged crosses of colored bars were pals to huddle near in a flock. Taking advantage of this tendency, Rugani let day-old chicks imprint on either two or three objects. Then she watched them choose between two little flocks of novel pals to toddle over to. If the potential buddy-objects in a flock looked identical to each other, the chicks in the test typically just moved near the larger cluster or largest object. But if the buddies in each group had individual quirks, mixing colors, shapes and sizes, the chicks paid attention to numerosity. Those imprinted on three pals were a bit more likely to club with three different kinds of pals; those imprinted on the pairs more often clubbed with the twos.
Some animals can deal with what people would call numerical order, or ordinality. Rats have learned to choose a particular tunnel entrance, such as the fourth or 10th from the end, even when researchers fiddled with distances between entrances. Five-day-old chicks rewarded for pecking at an item in a sequence, the fourth hole or the third jar, still showed a preference for position when researchers lengthened the distances between options or even moved the whole array.
Rhesus monkeys react if researchers violate rules of addition and subtraction, as dogs seemed to do in the Chums experiment. Chicks can track additions and subtractions too, well enough to pick the card hiding the bigger result. The chicks can also go one better. Rugani and colleagues have shown that chicks have some sense of ratios, for example choosing between mixes of red and green dots to match a ratio they learned from such mixes as 18 greens mingling with 9 reds.
A sense of numerosity itself, regardless of volume or surface area, may not be limited to fancy vertebrate brains. One recently published test takes advantage of overkill among golden orb-web spiders (Nephila clavipes). When they have a crazy run of luck catching insects faster than they can eat them, the spiders wrap each catch in silk and fasten it with a single strand to dangle from the center of the web. Turning this hoarding tendency into a test, Rafael Rodríguez of the University of Wisconsin–Milwaukee tossed bits of mealworms of different sizes into the web as spiders created a dangling treasure trove. Then shooing the spider off the web, he snipped the strands and watched how long the spiders searched for their stolen meals. Losing a greater volume of food inspired more strumming of the web and searching about. But losing four items instead of just one or two increased the search time even more, Rodríguez and his colleagues reported in 2015 in Animal Cognition. It’s not just volume of food in a hoard, they argue. Numerosity has its own effects.
At a glance Nonhuman animals don’t have human language for counting, so researchers studying behavior talk about an “approximate number system” that allows for good-enough estimates of quantities with no real counting. One of the features of this still mysterious system is its declining accuracy in comparing bigger numbers that are very close together, the trend that made Sedona the collie’s struggles as noteworthy as her successes.
As the ratios of the two quantities Sedona had to compare drew closer to 1, she was more prone to make mistakes. Her scores worsened as she moved from 0.11 (comparing 1 to 9), 0.2 (1 to 5) and so on. She never conquered the fiendish 8 versus 9. That same trend, described by what’s called Weber’s law, shows up in humans’ nonverbal approximate number system as well as in those of other animals. When Agrillo tested guppies against humans, both fell behind in accuracy for such difficult comparisons as 6 versus 8. But for small quantities, both fish and people performed well, he and colleagues reported in 2012. People and fish could tell 3 dots from 4 about as reliably as 1 dot from 4. Researchers have long recognized this instant human ease of dealing with very small quantities, calling it subitizing: suddenly just seeing that there are three dots or ducks or daffodils without having to count them. Agrillo suspects the underlying mechanism will prove different from the approximate number systems, though he describes this as a minority view.
The similarity between guppies and people in subitizing skill doesn’t prove it’s a shared inheritance from that ancient common ancestor several hundred million years ago, Agrillo says. Yet the similarity does raise the possibility. Struggling to separate some pure response to numerosity from all the confounding surface areas and other continuous qualities may not even be the most important question, says Lisa Cantrell, now at the University of California, Davis. Human babies, as an example of noncounting animals, might start figuring out the world by relying on these other confounders and grow into their numerical abilities, she and Linda Smith of Indiana University, Bloomington, suggested in 2013. The hypothesized approximate number system might be part of some more general way of perceiving the world, which can draw on multiple clues to get a clearer sense of quantity. Cantrell and Smith called their version of the idea the “signal clarity hypothesis.”
Into their heads Studying behavior alone isn’t enough to trace the inheritance of any part of number savvy, says Andreas Nieder of the University of Tübingen in Germany. “At the behavioral level, it may look as if number estimation follows the same laws, but the underlying neural code could actually look quite different.”
He’s not going as far afield as fish yet, but Nieder and colleagues have looked at how monkey and bird brains handle quantity. The researchers described neurons (nerve cells) in the brains of carrion crows (Corvus corone corone) that function much like those in rhesus macaques.
Research in monkeys over the last 15 years has identified what Nieder calls “number neurons.” They could have multiple functions, but each responds to a specific number of whatevers, be it six crows or six crowbars. Some number neurons respond to sight, some to sound, and amazingly, some to either. The neurons could be responding to increasing total surface area or density or darkness. But researchers have varied one aspect at a time, and used multiple imaging and pharmacological techniques, to argue that as far as strenuous efforts can tell, these neurons detect the actual numerosity.
Individual neurons in parts of a monkey brain have their own preferred number and respond most strongly to it and less so to neighboring numbers. The neurons for three get less excited for two and four, while others light up at four. In 2015, Nieder and colleagues started untangling how monkey neurons handle zero, suggesting the beginnings of an ability to treat “nothing there” as an abstract numerosity of zero.
These neurons lie in notable places: the six-layered neocortex of the parietal and frontal lobes of the brain. That’s territory that primates boast about, a feature of mammalian brain structure credited with allowing human mental capacities to reach such heights. Nonmammalian vertebrates, including birds, don’t have a multilayered neocortex. Yet Nieder and colleagues have, for the first time, detected individual neurons in the bird brain that fire in response to numerosities much as primate number neurons do.
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Neurons for numbers Recordings from four nerve cells in monkeys suggest each cell responds most to a particular number of dots (lines with circles) and the same number of musical tones (squares). The bird versions of number neurons lie in a relatively newfangled area of the avian brain called the nidopallium caudolaterale, or NCL. It didn’t exist as such, nor did the primate’s precious neocortex, in the reptile-ish ancestors that mammals and birds last shared some 300 million years ago. Both the bird NCL and the primate number neuron zones arose from the same tissue, the pallium. In mammals, that ancient pallium morphed into layers of neocortex tissue, in birds the transformation went a different way.
For the number sense tingling through specialized neurons in birds and primates alike, similarity does not strictly mean shared inheritance, Nieder wrote in the June Nature Reviews Neuroscience. The systems of number neurons probably specialized independently.
Finding some brain structures to compare across deep time is a promising step in fathoming the evolution of animal number sense, but it’s just a beginning. There are many questions about how the neurons work, not to mention what’s going on in all those other brains that contemplate quantity. For now, looking across the tree of life at the crazy abundance of number smarts, which may or may not be related but are certainly numerous, the clearest thing to say may be just: Wow.
