Earth’s earliest land-walking vertebrates didn’t paddle about in freshwater lakes or rivers. Instead, these four-footed creatures, which appeared about 375 million years ago, lived in the brackish waters of an estuary or delta, researchers report online May 30 in Nature.
Early tetrapods, such as Ichthyostega and Acanthostega, lived an amphibious existence between land and sea: They had feet, but also gills and tails made for swimming. A new study by paleontologist Jean Goedert of Université Lyon in France and colleagues suggests that the animals also could have tolerated rapid changes in salinity, such as is found in an estuary. The researchers analyzed sulfur and oxygen isotopes — forms of these elements with the same number of protons, but different masses — in 51 fossilized tetrapod bones from locations in what’s now Greenland and China. Compared with freshwater, seawater has a higher ratio of the sulfur-34 isotope relative to sulfur-32. The tetrapod bones tended to show elevated sulfur-34, the researchers report, suggesting that the creatures spent at least some time in seawater. But oxygen isotope analyses of the bones show that freshwater was also present, arguing against a purely salty environment such as an ocean.
The results challenge a long-held view that the earliest tetrapods emerged from freshwaters, such as rivers or lakes. In 1929, the first Ichthyostega fossils were found in a series of red sandstone layers in eastern Greenland that geologists once thought had been deposited in a freshwater environment. But later discoveries of tetrapod fossils found associated with known marine species suggested that the early walkers may have lived in saltier waters than once thought.
An ability to tolerate different salinity environments could have helped tetrapods — a group that includes today’s amphibians, reptiles and mammals — survive a mass extinction of ocean-dwellers that occurred by the end of the Devonian Period about 359 million years ago, the researchers say.
Each year, finding and extracting oil and gas for energy produces hundreds of billions of gallons of wastewater in the United States. When recycled and spread on roads, the wastewater can leak its contaminants, including salt, radioactive elements and chemicals that interfere with hormones, into groundwater and surface water, researchers report May 30 in Environmental Science and Technology.
Currently, 13 states permit this wastewater to be used on streets for road maintenance, as a cheap deicing fluid or to keep down dust on unpaved roads. It’s a particularly common practice in rural communities with low budgets for keeping roads in shape. Spills from oil and gas wastewater treatment plants have sparked concern about contaminants such as radium (which naturally occurs in oil and natural gas deposits) that could affect human and environmental health. But the water’s use on roads might be a bigger problem, the study shows. For example, in Pennsylvania, the amount of radium that leached from wastewater spread on roads from 2008 to 2014 is about four times as high as what was discharged from wastewater treatment facilities during the same period, the researchers calculated using existing data. And it was about 200 times as high as the amount leached during wastewater spills.
The new research could lead to policy interventions, such as requiring the wastewater to be tested for radium before being used on roads. And it also suggests a need for affordable deicing alternatives, the team suggests.
Conservationists are stuck in a catch-22: In trying to save some species, the would-be protectors may be giving the animals an evolutionary disadvantage. A new study describes how efforts to protect the endangered northern quoll, a spotted, kitten-sized marsupial native to Australia, by placing a population on a threat-free island may have actually undermined a key survival instinct.
After 13 generations — just 13 years — in isolation, the northern quolls (Dasyurus hallucatus) had lost their fear response to native predators, researchers report June 5 in Biology Letters. “Evolution can happen very rapidly” for animals with fast breeding times, says evolutionary biologist Rick Shine of the University of Sydney, who was not involved in the study.
Separating endangered species from predators is a common conservation technique, sometimes taking place in captive-breeding programs in zoos or fenced enclosures or on isolated islands. The approach allows a species to build up its population before eventually being reintroduced to the wild.
Populations of northern quolls have been drastically reduced in recent decades by invasive poisonous cane toads (SN Online: 2/3/14). In 2003, the Australian Northern Territory Government tried to preserve the quolls in part by moving 45 of them to toad-free Astell Island, off mainland Australia’s northern coast. In 2016, biologist Christopher Jolly of the University of Melbourne and colleagues tried to reintroduce some quolls from Astell to the mainland. But the effort was quickly halted after dingoes and feral cats killed many of the new arrivals ( SN Online: 2/11/15 ). In trying to figure out what happened, the researchers tested the fear responses of four populations of quolls: wild mainland quolls, island-born quolls and offspring from both groups. Quolls from each group were given boxes of mealworms; some had no scent and some were tainted with the scent of either feral cats or dingoes. While the wild quolls shied away from the predator-scented worms, the island quolls slurped the worms down. The quoll babies in each group showed the same behavior as the adults, suggesting the lost fear response was not learned but had evolved over 13 generations.
The study’s findings may have implications for other animals as well, as Australia grapples with how to conserve an increasing number of threatened and endangered species. “For many of Australia’s mammals, the future is fenced,” says Alexandra Carthey, an ecologist at Macquarie University in Sydney who was not involved in the study.
There may be a few other solutions. Quolls could possibly be trained to avoid the cane toad, and then wouldn’t need to be taken from their native habitat, according to a study by Jolly and colleagues published last October in Austral Ecology. Or, a small number of predators could be added to the isolation locations — not enough to threaten the quolls’ proliferation, but enough to put the fear back into them.
NASA’s Curiosity rover has found evidence that methane in Mars’ thin atmosphere varies during the year. Higher concentrations appear in late summer and early autumn in the northern hemisphere and lower concentrations in the winter and spring, researchers report in the June 8 Science.
What’s more, Curiosity also spotted organic molecules previously unseen on Mars preserved in mudstone, some of the same researchers report in another study in the same issue of Science. Although neither methane nor organics alone are signs of life, the implications for astrobiology are “potentially huge,” says planetary scientist Michael Mumma of NASA’s Goddard Space Flight Center in Greenbelt, Md., who was not involved in the studies. In 2004, Mumma and colleagues reported the first observation of huge plumes of methane spewing into Mars’ atmosphere (SN: 2/14/09, p. 10). These plumes, detected with Earth-based telescopes, had methane concentrations as high as 45 parts per billion.
That finding was exciting, because methane doesn’t last long in the Martian atmosphere before ultraviolet radiation from the sun destroys it. Something must have been creating or releasing the gas as astronomers watched. On Earth, most methane is produced by living creatures, so the plumes raised hopes that Mars supports life.
When Curiosity landed on the Red Planet in 2012, however, the rover initially found no methane to speak of (SN: 10/19/13, p. 7). “A lot of people were disappointed and upset,” says Christopher Webster, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and a coauthor of the new methane study. But in 2014, after more searching, the Curiosity team found traces of methane, though much less than what was expected based on the earlier results (SN: 1/10/15, p. 11). Now after two full Martian years (five Earth years) of observing, the team reports that the annual average concentration of methane in Mars’ atmosphere is 0.41 ppb. But methane levels seem to rise and fall with the seasons, ranging from 0.24 ppb in winter to 0.65 ppb in summer. The researchers also saw relatively large methane spikes, up to about 7 ppb, at apparently random intervals. Slow seepage from an underground reservoir could explain both the seasonal cycle and the spikes, Webster says. Surface rocks could mostly hold on to the methane in winter and release it when warmed by the summer sun. Occasionally, something in the rocks could break loose, releasing larger spurts. Similar scenarios are found on Earth.
Scientists can’t say what produced the stored methane in the first place. “The existence and behavior of methane on Mars remains puzzling,” Webster says. “While we think it likely that it’s produced abiologically [by a geologic process], we cannot rule out the possibility of a biological or microbial source.”
Though lower, the concentrations of methane in the spikes that Curiosity sees are still consistent with the huge plumes seen from Earth, Mumma says, if Curiosity is located at the edge of a plume. But he’s not sure if a seasonal cycle is the only explanation for the data. A flat, constant methane level could fit within the errors of the measurements, too, he argues.
Webster disagrees. “Even to the untrained eye,” he says of the results, “there is a clear, repeatable rise in the summertime…. The seasonal cycle is real.”
In the other new paper, astrobiologist Jennifer Eigenbrode of NASA Goddard and colleagues analyzed samples collected from 3.5-billion-year-old mudstone that was once part of an ancient lake and found chemical evidence that plenty of organic molecules had been preserved in the lake bed.
In 2014, Curiosity had detected organic molecules in rocks from one location in Gale crater. The new finding, from samples drilled at the base of a mountain in the crater’s center, shows signs of larger and more complex organic molecules than had been seen before, including some that are similar to coal and black shale found on Earth.
“There were a lot of people who didn’t think we were going to find organic matter using the drill on the Curiosity rover, because it only goes down five centimeters,” Eigenbrode says. The Martian surface is bombarded with radiation that can break up organic molecules. The fact that organics survive on the surface means digging deeper may yield even more.
The European Space Agency’s ExoMars rover, slated to launch in 2020, will drill two meters into the surface. “This opens up the prospect that [the rover] might find better preserved organic material, and maybe find biosignatures” of life, Eigenbrode says.
Curiosity isn’t done drilling yet, though. The rover’s drill broke in 2016. But engineers successfully hacked the drill, which dug out a sample on May 20.
Newly identified nerve cells deep in the brains of mice compel them to eat. Similar cells exist in people, too, and may ultimately represent a new way to target eating disorders and obesity.
These neurons, described in the July 6 Science, are not the first discovered to control appetite. But because of the mysterious brain region where they are found and the potential relevance to people, the mouse results “are worth pursuing,” says neurobiologist and physiologist Sabrina Diano of Yale University School of Medicine. Certain nerve cells in the human brain region called the nucleus tuberalis lateralis, or NTL, are known to malfunction in neurodegenerative diseases such as Huntington’s and Alzheimer’s. But “almost nothing is known about [the region],” says study coauthor Yu Fu of the Singapore Bioimaging Consortium, Agency for Science, Technology and Research. In people, the NTL is a small bump along the bottom edge of the hypothalamus, a brain structure known to regulate eating behavior. But in mice, a similar structure wasn’t thought to exist at all, until Fu and colleagues discovered it by chance. The researchers were studying cells that produce a hormone called somatostatin — a molecular signpost of some NTL cells in people. In mice, that cluster of cells in the hypothalamus seemed to correspond to the human NTL. Not only do these cells exist in mice, but they have a big role in eating behavior. The neurons sprang into action when the mice were hungry, or when the hunger-signaling hormone ghrelin was around, the team found. And when the researchers artificially activated the cells, using either laser light or molecular techniques, the mice ate more and gained weight faster than normal mice. Conversely, when the researchers killed the neurons, the mice didn’t eat as much and gained less weight than mice that still possessed the cells. The results suggest that, in mice, these neurons influence the impulse to eat — and subsequent changes in weight.
More experiments need to be done to study whether the cells behave similarly in people, Diano cautions.
Both Alzheimer’s and Huntington’s have been tied to metabolic problems and changes in appetite. The demise of appetite-controlling cells in the NTL might help explain why.
If NTL cells do control appetite in humans, that brain region wouldn’t be working alone. Far from it. Neighboring nerve cells in and around the hypothalamus are also known to play big roles in prodding the body to eat when food is available (SN Online: 5/25/17). “Our bodies were built to make sure we will eat whenever we have the chance,” Fu says.
For many people, high-calorie foods are now easy to come by. “When suddenly we are faced with food abundance, our bodies simply can’t cope with it,” Fu says. The result can be metabolic disorders, such as obesity. Tweaking the behavior of these appetite-controlling cells, perhaps with drugs, may one day offer a way to treat obesity or eating disorders such as anorexia (SN: 3/7/15, p. 8).
Spiders may lack wings, but they aren’t confined to the ground. Under the right conditions, some spider species will climb to a high point, release silk strands to form a parachute, and float away on the breeze. Buoyed by air currents, they’ve been known to drift kilometers above Earth’s surface, and even to cross oceans to reach new habitats (SN: 2/4/17, p. 12).
Now, new research suggests air isn’t the only force behind this flight, called ballooning. Spiders can sense electrical charges in Earth’s atmosphere, and the forces exerted by these charges might be a cue for them to alight, researchers suggest July 5 in Current Biology. That invisible signal could help explain why spiders’ take-off timing seem a bit, well, flighty. Some days, arachnids balloon en masse; other days, they remain firmly grounded despite similar weather conditions. Spiders with atmospheric aspirations do need a gentle breeze with speeds below around 11 kilometers per hour, past studies have shown. But those speeds alone shouldn’t be strong enough to get some of the larger species of ballooning spiders off the ground, says Erica Morley, a sensory biologist at the University of Bristol in England. So scientists have long wondered if some other force might be involved: Perhaps electrical charges in Earth’s atmosphere push against the silken threads of airborne spiders’ silk streamers to help them stay fanned out in a parachute. These electric charges form an electric field that attracts or repels other charged objects or particles. It varies in strength, becoming stronger around objects such as leaves and branches on trees, and also fluctuating with meteorological conditions. In the first experimental test of whether spiders can sense these electric charges, Morley and Bristol sensory biologist Daniel Robert blocked out naturally occurring electric fields in a lab. They then created an artificial one mimicking what would-be arthropod aerialists would experience, and placed teeny-tiny spiders from the Linyphiidae family into that faux field. Under the electric field, even with no breeze, the spiders perched on the tips of their legs, a ballerina-like behavior that precedes ballooning. When the researchers switched off the artificial electric field, the behavior (which scientists call the “tiptoe stance”) subsided. Tiny hairs on the spiders’ bodies react to both moving air and an electric field’s presence, but differently, Morley found. The hairs stood on end as long as air was blowing on them. But when faced with an electric field, they stood on end most dramatically when the field was switched on and then gradually deflated to their resting position over about 30 seconds.
The study links the pre-ballooning tiptoeing behavior to the presence of an electric field, but actually taking off might require something more, suggests Moonsung Cho, an aerodynamics researcher at the Technical University of Berlin who wasn’t involved in the study. While some spiders in the study did incidentally float away, that liftoff behavior wasn’t actually measured.
And responding to electric fields probably isn’t the full story when it comes take-off timing: A different genus of spider, Xysticus, or ground crab spiders, appears to sense wind speed with its legs before going aloft, wiggling one spindly appendage around to sense moving air and determine whether wind conditions are favorable for lift-off, Cho’s team reported June 14 in PLOS Biology.
Neuroscientist Barbara Bendlin studies the brain as Alzheimer’s disease develops. When she goes home, she tries to leave her work in the lab. But one recent research project has crossed into her personal life: She now takes sleep much more seriously.
Bendlin works at the University of Wisconsin–Madison, home to the Wisconsin Registry for Alzheimer’s Prevention, a study of more than 1,500 people who were ages 40 to 65 when they signed up. Members of the registry did not have symptoms of dementia when they volunteered, but more than 70 percent had a family history of Alzheimer’s disease.
Since 2001, participants have been tested regularly for memory loss and other signs of the disease, such as the presence of amyloid-beta, a protein fragment that can clump into sticky plaques in the brain. Those plaques are a hallmark of Alzheimer’s, the most common form of dementia.
Each person also fills out lengthy questionnaires about their lives in the hopes that one day the information will offer clues to the disease. Among the inquiries: How tired are you? Some answers to the sleep questions have been eye-opening. Bendlin and her colleagues identified 98 people from the registry who recorded their sleep quality and had brain scans. Those who slept badly — measured by such things as being tired during the day — tended to have more A-beta plaques visible on brain imaging, the researchers reported in 2015 in Neurobiology of Aging.
In a different subgroup of 101 people willing to have a spinal tap, poor sleep was associated with biological markers of Alzheimer’s in the spinal fluid, Bendlin’s team reported last year in Neurology. The markers included some related to A-beta plaques, as well as inflammation and the protein tau, which appears in higher levels in the brains of people with Alzheimer’s.
Bendlin’s studies are part of a modest but growing body of research suggesting that a sleep-deprived brain might be more vulnerable to Alzheimer’s disease. In animal studies, levels of plaque-forming A-beta plummet during sleep. Other research suggests that a snoozing brain runs the “clean cycle” to remove the day’s metabolic debris — notably A-beta — an action that might protect against the disease. Even one sleepless night appears to leave behind an excess of the troublesome protein fragment (SN Online: 7/10/17).
But while the new research is compelling, plenty of gaps remain. There’s not enough evidence yet to know the degree to which sleep might make a difference in the disease, and study results are not consistent.
A 2017 analysis combined results of 27 studies that looked at the relationship between sleep and cognitive problems, including Alzheimer’s. Overall, poor sleepers appeared to have about a 68 percent higher risk of these disorders than those who were rested, researchers reported last year in Sleep. That said, most studies have a chicken-and-egg problem. Alzheimer’s is known to cause difficulty sleeping. If Alzheimer’s both affects sleep and is affected by it, which comes first?
For now, the direction and the strength of the cause-and-effect arrow remain unclear. But approximately one-third of U.S. adults are considered sleep deprived (getting less than seven hours of sleep a night) and Alzheimer’s is expected to strike almost 14 million U.S. adults by 2050 (5.7 million have the disease today). The research has the potential to make a big difference. It would be easier to understand sleep deprivation if scientists had a better handle on sleep itself. The brain appears to use sleep to consolidate and process memories (SN: 6/11/16, p. 15) and to catalog thoughts from the day. But that can’t be all. Even the simplest animals need to sleep. Flies and worms sleep.
But mammals appear to be particularly dependent on sleep — even if some, like elephants and giraffes, hardly nod off at all (SN: 4/1/17, p. 10). If rats are forced to stay awake, they die in about a month, sometimes within days.
And the bodies and brains of mice change when they are kept awake, says neurologist David Holtzman of Washington University School of Medicine in St. Louis. In one landmark experiment, Holtzman toyed with mice’s sleep right when the animals’ brain would normally begin to clear A-beta. Compared with well-rested mice, sleep-deprived animals developed more than two times as many amyloid plaques over about a month, Holtzman says. He thinks Alzheimer’s disease is a kind of garbage collection problem. As nerve cells, or neurons, take care of business, they tend to leave their trash lying around. They throw away A-beta, which is a leftover remnant of a larger protein that is thought to form connections between neurons in the developing brain, but whose role in adults is still being studied. The body usually clears away A-beta.
But sometimes, especially when cheated on sleep, the brain doesn’t get the chance to mop up all the A-beta that the neurons produce, according to a developing consensus. A-beta starts to collect in the small seams between cells of the brain, like litter in the gutter. If A-beta piles up too much, it can accumulate into plaques that are thought to eventually lead to other problems such as inflammation and the buildup of tau, which appears to destroy neurons and lead to Alzheimer’s disease.
About a decade ago, Holtzman wanted to know if levels of A-beta in the fluid that bathes neurons fluctuated as mice ate, exercised, slept and otherwise did what mice do. It seemed like a run-of-the-mill question. To Holtzman’s surprise, time of day mattered — a lot. A-beta levels were highest when the animals were awake but fell when the mice were sleeping (SN: 10/24/09, p. 11).
“We just stumbled across this,” Holtzman says. Still, it wasn’t clear whether the difference was related to the hour, or to sleep itself. So Holtzman and colleagues designed an experiment in which they used a drug to force mice to stay awake or fall asleep. Sure enough, the A-beta levels in the brain-bathing fluid rose and fell with sleep, regardless of the time on the clock.
A-beta levels in deeply sleeping versus wide-awake mice differed by about 25 percent. That may not sound like a dramatic drop, but over the long term, “it definitely will influence the probability [that A-beta] will aggregate to form amyloid plaques,” Holtzman says.
The study turned conventional thinking on its head: Perhaps Alzheimer’s doesn’t just make it hard to sleep. Perhaps interrupted sleep drives the development of Alzheimer’s itself.
Published in Science in 2009, the paper triggered a flood of research into sleep and Alzheimer’s. While the initial experiment found that the condition worsens the longer animals are awake, research since then has found that the reverse is true, too, at least in flies and mice.
Using fruit flies genetically programmed to mimic the neurological damage of Alzheimer’s disease, a team led by researchers at Washington University School of Medicine reversed the cognitive problems of the disease by simply forcing the flies to sleep (SN: 5/16/15, p. 13).
Researchers from Germany and Israel reported in 2015 in Nature Neuroscience that slow-wave sleep — the deep sleep that occupies the brain most during a long snooze and is thought to be involved in memory storage — was disrupted in mice that had A-beta deposits in their brains. When the mice were given low doses of a sleep-inducing drug, the animals slept more soundly and improved their memory and ability to navigate a water maze.
Gray matters Even with these studies in lab animals indicating that loss of sleep accelerates Alzheimer’s, researchers still hesitate to say the same is true in people. There’s too little data. Human studies are harder and more complicated to do. One big hurdle: The brain changes in humans that lead to Alzheimer’s build up over decades. And you can’t do a controlled experiment in people that forces half of the study’s volunteers to endure years of sleep deprivation.
Plus the nagging chicken-and-egg problem is hard to get around, although a study published in June in JAMA Neurology tried. Researchers from the Mayo Clinic in Rochester, Minn., examined the medical records of 283 people older than 70. None had dementia when they enrolled in the Mayo Clinic Study of Aging. At the study’s start, participants answered questions about their sleep quality and received brain scans looking for plaque deposits.
People who reported excessive daytime sleepiness — a telltale sign of fitful sleep — had more plaques in their brains to start with. When checked again about two years later, those same people showed a more rapid accumulation than people who slept soundly.
Other scientists have used brain scans to measure what happens to A-beta in people’s brains after a sleepless night. Researchers from the National Institutes of Health and colleagues completed a study involving 20 healthy people who had a brain scan while rested and then again after they were forced to stay awake for 31 hours.
Nora Volkow, head of the National Institute on Drug Abuse in Bethesda, Md., led the study. She is interested in sleep’s potential connections to dementia because people with drug addiction have massive disruptions of sleep. For the study, the researchers injected people with a compound that latches onto A-beta and makes it visible under a PET scanner.
The sleep-deprived brains showed an increase in A-beta accumulation that was about 5 percent higher in two areas of the brain that are often damaged early in Alzheimer’s: the thalamus and hippocampus. Other regions had lesser buildup.
“I was surprised that it was actually so large,” says study coauthor Ehsan Shokri-Kojori, now at the National Institute on Alcohol Abuse and Alcoholism. “Five percent from one night of sleep deprivation is far from trivial.” And while the brain can likely recover with a good night’s sleep, the question is: What happens when sleep deprivation is a pattern night after night, year after year?
“It does highlight that sleep is indispensable for proper brain function,” Volkow says. “What we have to question is what happens when you are consistently sleep deprived.” The study was published April 24 in the Proceedings of the National Academy of Sciences. As tantalizing as studies like this may seem, there are still inconsistencies that scientists are trying to resolve. Consider a study published in May in Sleep from a team of Swedish and British researchers. They set out to measure levels of A-beta in cerebrospinal fluid and markers of neuron injury in 13 volunteers, sleep deprived and not.
The first measurements took place after five nights of sound sleep. Then participants were cut back to four hours of sleep a night, for five nights. Four participants even lasted eight days with only four hours of nightly sleep. After good sleep versus very little, the measurements did not show the expected differences.
“That was surprising,” says Henrik Zetterberg of the University Gothenburg in Sweden. Given the previous studies, including his own, “I would have expected a change.”
He notes, however, that the study participants were all healthy people in their 20s and 30s. Their youthful brains might cope with sleep deprivation more readily than those in middle age and older. But that’s just a hypothesis. “It shows why we have to do further research,” he says.
Rinse cycle Questions could be better answered if scientists could find a mechanism to explain how sleepless nights might exacerbate Alzheimer’s. In 2013, scientists revealed an important clue.
The lymphatic system flows through the body’s tissues to pick up waste and carry it away. All lymphatic vessels run to the liver, the body’s recycling plant for used proteins from each organ’s operation. But the lymphatic system doesn’t reach the brain.
“I found it weird because the brain is our most precious organ — why should it be the only organ that recycles its own proteins?” asks Maiken Nedergaard, a neuroscientist at the University of Rochester in New York. Maybe, she thought, the brain has “a hidden lymphatic system.”
Nedergaard and colleagues decided to measure cerebrospinal fluid throughout the brain. When mice were awake, there appeared to be little circulation of fluid in the brain. Then the team examined sleeping mice. “You take mice and train them to be quiet under a microscope,” Nedergaard says. “The mice after a couple of days feel very calm. Especially if you do it during the daytime when they are supposed to be sleeping, and they are warm and you give them sugar water. They’re not afraid.” Slumbering stream Flow of cerebrospinal fluid in a mouse’s brain is much higher during sleep (left, red) than when the animal is awake (right, green).
The day of the experiment, the scientists made a hole in the mice’s skulls, placed a cover over it and injected a dye to measure cerebrospinal fluid in the brain. During sleep, the spaces between the brain cells widened by about 60 percent and allowed more fluid to wash through, taking the metabolic debris, including A-beta, with it.
“It’s like the dishwasher turned on,” Nedergaard says. She named this phenomenon the “glymphatic system” because it appears to be controlled by glial cells, brain cells that help insulate neurons and perform much of the brain’s routine maintenance work (SN: 8/22/15, p. 18).
Similar observations of cerebrospinal fluid circulation have been carried out in people, but with less invasive ways of measuring. In one, researchers from Oslo University Hospital, Rikshospitalet compared 15 patients who had a condition called normal pressure hydrocephalus, a kind of dementia caused by buildup of cerebrospinal fluid in the cavities of the brain, with eight people who didn’t have the condition.
The researchers used a tracer for cerebrospinal fluid and magnetic resonance imaging to measure the flow over 24 hours. Immediately after a night’s sleep, cerebrospinal fluid had drained in healthy people but lingered in the patients with dementia, the researchers reported in Brain in 2017. Don’t snooze, you lose? The central question — the one that doctors really want to answer — is whether better sleep could treat or even prevent Alzheimer’s. To try to figure this out, Bendlin and her Wisconsin colleagues are now studying people with sleep apnea. People with that condition stop breathing during the night, which wakes them up and makes for a lousy night’s sleep. A machine called a CPAP, short for continuous positive airway pressure, treats the condition.
“Once people start treatment, what might we see in the brain? Is there a beneficial effect of CPAP on markers of Alzheimer’s?” Bendlin wonders. “I think that’s a big question because the implications are so large.”
A study reported in Neurology in 2015 offers a reason to think CPAP might help. Using data from almost 2,500 people in the Alzheimer’s Disease Neuroimaging Initiative, researchers at the New York University School of Medicine found that people with sleep disorders like obstructive sleep apnea showed signs of mild cognitive problems and Alzheimer’s disease at younger ages than those who did not. But for those who used CPAP, onset of mild cognitive problems was delayed.
“If we find out that sleep problems contribute to brain amyloid — what that really says is there may be a window to intervene,” Bendlin says. And the solution — more attention to sleep — is one prescription with no side effects.
A new computer program works smarter, not harder, to solve problems faster than its predecessors.
The algorithm is designed to find the best solution to a given problem among all possible options. Whereas other computer programs winnow down the possibilities one at a time, the new program — presented July 12 at the International Conference on Machine Learning in Stockholm — rules out many choices at once.
For instance, imagine a computer is assigned to compile movie recommendations based on a particular film. The ideal recommendation list would include suggestions that are both similar to the original flick — say, in the same genre — yet different enough from each other to give the viewer a variety of choice. A traditional recommendation system would pore over an entire movie library to find films that best met those criteria and add films to its roster of recommendations one by one, a relatively slow and tedious process. By contrast, the new program starts by randomly picking a bunch of movies from the library. Among that sample, the system keeps the movies that strike the best balance between relevance to the original film and diversity, and discards the rest. From that smaller pool, the algorithm again chooses films at random and keeps only the best of the bunch. That strategy helps the algorithm build its rec list far faster.
The new algorithm, built by Harvard University computer scientists Yaron Singer and Eric Balkanski, compiled movie suggestions more than 10 times as fast as a standard recommender system. In another trial, it devised optimal routes for cabs in New York City about six times as fast as a conventional automated dispatcher.
This program could also speed up data processing for everything from drug discovery to social media analytics and analyses of genetic data (SN Online: 7/15/15).
Keeping a tight lid on blood pressure isn’t just good for the heart. It may also help the brain.
People given intensive drug treatment for high blood pressure were less likely to develop an early form of memory loss, according to preliminary results from a major clinical trial. This approach reduced the rate of early memory loss, called mild cognitive impairment, by around 19 percent, compared with people who received less aggressive treatment.
And the intensely treated group developed fewer white matter lesions over time, researchers reported July 25 at the Alzheimer’s Association International Conference in Chicago. White matter lesions, which are associated with dementia, are thought to be caused by blood vessel injuries in white matter, the part of the brain that contains nerve fibers. The brain research is part of SPRINT, the Systolic Blood Pressure Intervention Trial involving more than 9,300 participants. Some received intensive treatment aimed at lowering their systolic blood pressure — the pressure on artery walls when the heart beats — below 120 millimeters of mercury; others got standard treatment to bring it below 140.
The trial had already reported that participants who received the intensive treatment dropped their risk of heart attacks and other cardiovascular problems by 25 percent, compared with the standard group (SN Online: 11/9/2015). The results were the basis for revamped blood pressure guidelines, released last year (SN: 12/9/17, p. 13).
Dubbed SPRINT-MIND, the brain research set out to measure whether aggressively controlling blood pressure benefits the brain along with the heart. Observational studies have shown that people with lower blood pressure have a lower risk of developing dementia, says Jeff Williamson, a geriatrician at Wake Forest School of Medicine in Winston-Salem, N.C. Using memory tests, experts assessed the trial participants for probable dementia (people unable to perform daily activities independently), early memory loss (people with some difficulty functioning, but still independent) or no impairment. More than 8,600 of the participants completed an assessment up until June 2018; their average age was about 68 years old.
Fewer people in the intensely treated group had the early memory loss, which is often a precursor to dementia, Williamson says. And fewer had probable dementia as well, although the results were not statistically significant. The trial was ended early, in 2015, due to the compelling cardiovascular benefits, so participants’ blood pressure was medically managed for only two to three years. “That’s an encouraging message,” Williamson says. “It doesn’t take but just a few years to see this effect.”
The SPRINT-MIND trial also looked at white matter lesions. These injuries in the brain are a consequence of aging, but they are also associated with hypertension, says neuroradiologist Ilya Nasrallah of the University of Pennsylvania. Previous work has found that white matter lesions increase the risk of dementia in people ages 60 and older.
About 450 participants had MRI brain scans at the start of the trial and roughly four years later. The volume of white matter lesions increased by 0.28 cubic centimeters over that time in the intensive treatment group, compared with 0.92 cubic centimeters in the standard treatment group. With intense blood pressure treatment, Nasrallah says, “we could slow progression of white matter lesions.”
But there is evidence that the relationship between blood pressure and brain health may change with advancing age, notes cognitive neurologist Zoe Arvanitakis of Rush University Medical Center in Chicago, who was not involved with the trial.
In adults 75 and older, past work has found that low diastolic blood pressure — the pressure on arteries when the heart rests between beats — increases the risk of dementia. The age at which people are at high risk for dementia is older than the average age of those in SPRINT, Arvanitakis says. “We really need to study this question in older persons as well.”
Neurologist and neuroscientist Costantino Iadecola of Weill Cornell Medicine in New York City says that, in general, the study shows that lowering blood pressure closer to 120 has beneficial effects on the brain. The problem is that in midlife, when people are 40 to 60 years old, “there is no question that high blood pressure is bad for you,” but that’s not true for those 80 and above, he says. Older people may need higher blood pressure to get enough blood flow to the brain.
Still, the study “is a piece of good news in an otherwise grim landscape” regarding dementia, Iadecola says, because it suggests “you can make the brain better if you take care of your blood pressure.”
A Mars orbiter has detected a wide lake of liquid water hidden below the planet’s southern ice sheets. There have been much-debated hints of tiny, ephemeral amounts of water on Mars before. But if confirmed, this lake marks the first discovery of a long-lasting cache of the liquid.
“This is potentially a really big deal,” says planetary scientist Briony Horgan of Purdue University in West Lafayette, Ind. “It’s another type of habitat in which life could be living on Mars today.” The lake is about 20 kilometers across, planetary scientist Roberto Orosei of the National Institute of Astrophysics in Bologna, Italy and his colleagues report online July 25 in Science — but the water is buried beneath 1.5 kilometers of solid ice.
Orosei and colleagues spotted the lake by combining more than three years of observations from the European Space Agency’s orbiting Mars Express spacecraft. The craft’s MARSIS instrument, which stands for Mars Advanced Radar for Subsurface and Ionosphere Sounding, aimed radar waves at the planet to probe beneath its surface. As those waves passed through the ice, they bounced off different materials embedded in the glaciers. The brightness of the reflection tells scientists about the material doing the reflecting — liquid water makes a brighter echo than either ice or rock.
Combining 29 radar observations taken from May 2012 to December 2015, MARSIS revealed a bright spot in the ice layers near Mars’ south pole, surrounded by much less reflective areas. Orosei and colleagues considered other explanations for the bright spot, such as radar bouncing off a hypothetical layer of carbon dioxide ice at the top of the sheet, but decided those options either wouldn’t produce the same radar signal or were too contrived to be physically likely.
That left one option: A lake of liquid water. Similar lakes beneath the ice in Antarctica and Greenland have been discovered in the same way (SN: 9/7/13, p. 26).
“On Earth, nobody would have been surprised to conclude that this was water,” Orosei says. “But to demonstrate the same on Mars was much more complicated.”
The lake is probably not pure water — temperatures at the bottom of the ice sheet are around –68° Celsius, and pure water would freeze there, even under the pressure of so much ice. But a lot of salt dissolved in the water could lower the freezing point. Salts of sodium, magnesium and calcium have been found elsewhere on Mars, and may be helping to keep this lake liquid (SN: 4/11/09, p. 12). The pool could also be more mud than water, but that could still be a habitable environment, Horgan says.
Previously, scientists have discovered extensive solid water ice sheets under the Martian dirt (SN Online: 1/11/18). There were also hints that liquid water flowed down cliff walls (SN: 10/31/15, p. 17), but those may turn out to be tiny dry avalanches. The Phoenix lander saw what looked like frozen water droplets at its site near the north pole in 2008, but that water may have been melted by the lander itself (SN Online: 9/9/10).
“If this [lake] is confirmed, it’s a substantial change in our understanding of the present-day habitability of Mars,” says Lisa Pratt, NASA’s planetary protection officer.
Though the newly discovered lake’s depth is unclear, its volume still dwarfs any previous signs of liquid water on Mars, Orosei says. The lake has to be at least 10 centimeters deep for MARSIS to have noticed it. That means it could contain at least 10 billion liters of liquid water.
“That’s big,” Horgan says. “When we’ve talked about water in other places, it’s in dribs and drabs.”
Under-ice lakes on Mars were first suggested in 1987, and the MARSIS team has been searching since Mars Express began orbiting the Red Planet in 2003. It took the team more than a decade to collect enough data to convince themselves the lake was real.
For the first several years of observations, limitations in the spacecraft’s onboard computer forced the team to average hundreds of radar pulses together before sending the data back to Earth. That strategy sometimes cancelled out the lake’s reflections, Orosei says — on some orbits, the bright spot was visible, on others, it wasn’t.
In the early 2010s, the team switched to a new technique that let them store the data and send it back to Earth more slowly. Then in August 2015, months before the end of the observing campaign, the experiment’s principal investigator, Giovanni Picardi of the University of Rome Sapienza, died unexpectedly.
“It was incredibly sad,” Orosei says. “We had all the data, but we had no leadership. The team was in disarray.”
Finally discovering the lake is “a testament to perseverance and longevity,” says planetary scientist Isaac Smith of the Planetary Science Institute, who is based in Lakewood, Colo. “Long after everyone else gave up looking, this team kept looking.”
But there is still room for doubt, says Smith, who works on a different radar experiment on NASA’s Mars Reconnaissance Orbiter that has seen no sign of the lake, even in CT scan–like 3-D views of the poles. It could be that MRO’s radar is scattering off the ice in a different way, or that the wavelengths it uses don’t penetrate as deep into the ice. The MRO team will look again, and will also try to create a 3-D view from the MARSIS data. Having a specific spot to aim for is helpful, he says.
“I expect there will be debate,” Smith says. “They’ve done their homework. This paper is well earned. But we should do some more follow-up.”
