Category Archives: Scientific American


Health Benefits of Bike Sharing Depend on Age, Gender

In the middle of the evening rush hour last November 29 more than 1,000 London cyclists staged a “die-in” to protest the traffic deaths of fellow riders and to demand more investment in bike-friendly roads. London’s streets may have grown friendlier to cyclists since the 2010 introduction of its Barclays Cycle Hire bike-sharing system but according to those at the protest, London is still too dangerous. The hundreds of cities that have launched bicycle-sharing systems in the last decade offer similar reasons for doing it: Bicycling reduces car traffic and pollution in city centers and is healthy exercise. But although all road-users benefit from less-crowded streets, a recent study suggests that the health benefits of bike-sharing programs depend on who is doing the riding.London’s bike-sharing program had registered 191,702 users at last count. Public health researcher James Woodcock at the University of Cambridge in England and his colleagues imagined, and calculated, how those riders lives might have been different had they not used the bikes. They examined data from 2.1 million hours of use between April 2011 and March 2012 and compared the health impact of those 2.1 million hours with the alternatives: more walking, public transit use or driving. To their surprise, the team reports in the February 13 BMJ (British Medical Journal), the switch to cycling may not have been helpful for young women. The health benefits also seem to differ by age, with older riders of both genders gaining more benefits than younger ones.

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Train of Thought Derailed: How an Accident Can Affect Your Brain

My cousin Guillermo Cassinello Toscano was on the train that derailed in Santiago de Compostela, Spain, last week when it went around a bend at twice the speed limit. Cassinello heard a loud vibration and then a powerful bump and then found himself surrounded by bloody bodies in wagon number nine. Shaking, he escaped the wreckage through either a door or a hole in the train—he cannot recall—then sat amid the smoke and debris next to the track and began to cry. Seventy-nine passengers died.

Cassinello doesn’t remember everything that happened to him. The same mechanisms that kept his brain sharp enough to escape immediate danger may also make it harder for him both to recall the accident, and to put the trauma behind him. “The normal thing is that the person doesn’t remember the moment of the accident or right after,” says clinical psychologist Javier Rodriguez Escobar of trauma therapy team Grupo Isis in Seville, who helped treat and study victims of the 2004 Madrid train bombings. That’s because the mind and the body enter a more alert but also more stressed state, with trade-offs that can save your life, but harm your mind’s memory-making abilities.

As the train fell over, several changes would have swept through Cassinello’s body. His adrenal glands, near his kidneys, would have released adrenaline (also known as epinephrine) into his bloodstream. The adrenaline would have directed blood to the powerful muscles of his arms and legs, where it would help him escape the wreckage faster. The hormone would have raised his heart and breathing rates. It also would have stimulated his vagus nerve, which runs from his spine to his brain. Although adrenaline cannot cross the blood–brain barrier, the vagus can promote noradrenaline production in the brain. That hormone activates the amygdala, which helps form memories.

Just the right amount of noradrenaline, researchers have found, can boost memory storage; too much can destroy it. Figuring out the balance could allow researchers to harness the hormone. Neuroscientist Christa McIntyre at the University of Texas at Dallas and colleagues have been studying how the chemical shapes memory-making in rats (her team is planning a human trial). When the team stimulated rats’ vagus nerves the animals’ memories improved. McIntyre has to keep the dose low, however, because other experiments have shown that too much noradrenaline appears to impede memory-making. Researchers are still trying to determine whether the excess noradrenaline directly causes the memory lapses or if the hormone is associated with high stress levels that cause some other chemical system to interfere. “That’s the part we don’t really understand: if there’s too much [noradrenaline] or if there’s another system that kicks in and puts a brake on it,” McIntyre says.

Cassinello’s memory lapses may be due to a noradrenaline overflow. But there may be other explanations for the gaps in his memory. His brain may have narrowed his attention at the time of the crash to only those things that matter for survival, such as escaping the train, leading him to ignore things that do not, such as whether the path out of the train passed through a door or a hole. Researchers have shown that humans report selective hearing during stressful events and that stressed people pay attention to different things than do unstressed people (pdf).

Cassinello’s uncle picked him up from the accident scene and drove him to a hospital for a checkup. Apart from a few minor scratches, he was fine. But Cassinello says he has flashbacks to the disaster. “The images of shattered people in my cabin and outside are in my head,” he says. Flashbacks are a normal part of the stress response. If Cassinello is lucky, the flashbacks will fade within weeks as he learns to suppress the bad memories cued up by triggers such as the sound of a train.

That process is called fear extinction. McIntyre and colleagues want to be able to influence it, so as to better help victims of post-traumatic stress disorder (PTSD). Scientists could activate a trauma victim’s vagus nerve, amplifying the memory-writing process while the patient practiced healthy responses to a fear-inducing stimulus. If the process works, it could speed up recovery. Other researchers are working on drug-enhanced fear extinction using chemicals such as zeta inhibitory peptide (ZIP) or D-cycloserine. Another approach, called fear reversal, aims to provoke fear-inducing memories into a malleable state, such as all memories enter when we access them, and then changing them with the help of a different drug, propranolol, which interferes with protein formation, or even with precisely timed talk therapy aimed at blocking the reconsolidation of bad memories.

One thing that is almost certain is that his memories of the event will change with time. Studies after the September 11, 2001, attacks on the World Trade Center found that New Yorkers’ reports of their experience of the attack changed over the years.

For now, survivors of traumatic experiences such as Cassinello can lean on the trauma therapists who rushed to Santiago after the crash. Some 70 to 80 percent of car accident survivors get away without PTSD, McIntyre reckons. As Rodriguez points out, however, most of those therapists are volunteers in town for a few days. It may take a few weeks or even months of therapy for patients to get past the worst of their experiences.

Read the rest of this story where it first appeared, in Scientific American: [html] [pdf]
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Spanish High-Speed Train Crash Offers Safety-System Lessons

The driver of the high-speed train that derailed July 25 at a sharp curve in Santiago de Compostela, Spain, killing at least 80 passengers and injuring 130 more, told controllers he took the curve at around 190 kilometers per hour, despite an 80 kph speed limit. He survived the crash and is now under investigation by local authorities. Even if the driver turns out to have been responsible for speeding, rail passengers might wonder what else had to fail in the safety system to allow one man’s error to harm so many people.

The crash is the first fatal accident of a high-speed train in Spain, which launched its high-speed network in 1992 and now serves around 100,000 passengers a day. Authorities have not yet assigned it a cause, but it may turn out to be an anomaly. “The most common [reasons for a derailment are] problems with the track or rail and equipment,” says mechanical engineer George Bibel at the University of North Dakota, author of Train Wreck: The Forensic of Rail Disasters. Whereas train accidents from Connecticut to France have made news lately, derailments are a declining threat, at least in the U.S., where they dropped about 90 percent from 1976 to 2011.

The decline has resulted in part from improved monitoring of aging infrastructure such as rails, wheels and bearings, Bibel says. Spanish media reported that the tracks on which this train was running were not designed for the fastest class of high-speed trains. The implication is that the tracks may somehow have contributed to the accident. Lower-grade tracks do vibrate more and wear down faster. And using the same tracks for multiple types of trains, such as high-speed, longer local passenger trains, or even freight, may also promote uneven metal fatigue. Changing temperatures or wet tracks can combine with worn-down train wheels or uneven loading of a train to promote a derailment. Yet things as basic as regular inspections of hot spots with an infrared sensor or of metal fatigue with an ultrasound sensor can alert rail operators to aging infrastructure.

Higher-tech control systems are also emerging. Both the U.S. and Europe are adopting semi-automated braking systems designed to take over from speeding drivers. The track at the accident site, which was very close to the station, used older-generation signaling technology called ASFA, which alerts the driver to upcoming speed restrictions but cannot override his or her control. The Madrid-Barcelona high-speed train line, in contrast, uses the Level 2 European Rail Traffic Management System (ERTMS), which can override the driver. The train drivers union announced that the tragedy “could have been avoided” if ERTMS had been installed on that stretch of track. Even if that is true, Spain already has one of the highest  ERTMS deployments in Europe. In the U.S., rail authorities have warned that they are unlikely to complete a legislated upgrade to similar technology in time for the 2015 deadline.

And Bibel points out that no automatic braking system can cover every scenario: There’s been technology to stop trains since the 1920s but one of the problems is you can’t stop a speeding passenger train the same as a 150-car heavy freight train.” That hasn’t stopped researchers from trying. The U.S. Department of Transportation is conducting work on algorithms that would develop a dynamic custom braking profile for each individual train based on its load (pdf). That might improve automatic control systems, although the performance would still depend on local track conditions, which may be harder to account for.

The high rate of death and injury in the Santiago accident is also anomalous. Derailments tend to be less harmful than collisions, Bibel says, unless they occur on a mountainside, over water or near something into which the derailed train can collide. That is, unfortunately, what happened at the curve in Santiago. The 10-car train skipped the rails, the locomotive began rolling over, and then the train slammed into a concrete retaining wall (video).

Survivors, such as American Stephen Ward, called themselves lucky, and relative to the dead and injured, they are. Yet all the passengers were unlucky in that several systems failed. The train’s still-unexplained speed, the lack of a sufficiently sophisticated braking system, and the derailment next to a concrete wall all contributed to the deaths and injuries.

But not all system failures—or solutions—are technological. “The problem is that you are setting up people to fail,” says railroad systems engineer Felix Schmid, of the University of Birmingham, in the England. “You have a very-high protected railway connected virtually straight into a less-protected railway.” The shift is similar to a car driver exiting smooth traffic on a highway for the less predictable gridlock of a city center.  “It’s the change from low demand to high demand which is sometimes quite difficult to manage,” he adds.

New York City’s Metropolitan Transit Authority learned to cut open-door accidents (in which doors open mistakenly when trains are not safely parked at a platform) by adopting a Japanese human-factor innovation: requiring drivers to signal by hand when they reached the appropriate platform marker for opening the doors. The requirement ensured drivers were paying attention to the shift from low-demand cruising to the more demanding platform stop. Japan also claims to have carried 9.2 billion passengers on its high-speed trains between 1964 and 2009 without a single fatality. That’s a standard to which Spain and all other high-speed rail operators can aspire.

Bibel is optimistic that derailments such as this week’s shouldn’t discourage future high-speed rail projects: “These kinds of accidents have been happening forever. Thankfully they’re rare.”

First published by Scientific American [html] [pdf]


Faux Fossils

cover_2013-06On its way from flight to fossil, an ancient beetle’s wings lost their color and then their form. Slow-baked and squished by sand, the glittering green wings darkened and turned blue, then indigo, then black.

That tale of an insect’s life, death and fossilization sounds simple enough, but it took paleobiologist Maria McNamara years of painstaking work to piece together. The University of Bristol researcher wanted to know how ancient insects’ warning signals, camouflage and mating displays evolved. Studying ordinary fossils tells only part of the story, since most fossilized insects are black today, probably because they lost their colors while buried underground.

McNamara and her team decided to work backward. They artificially aged modern beetle (shown above) and weevil wings to figure out how fossilization might affect color. They reported their results in Geology in April.

Fossilization is not a gentle process. To simulate it, McNamara left the insect wings in pond water for 18 months, then baked them at temperatures as high as 518 degrees Fahrenheit, hotter than most home ovens, and pressures almost 500 times the atmosphere’s to simulate the crushing and heat that converts mud-trapped debris into subterranean stone fossils. The team found that the process broke up and thinned out the beetles’ reflective shells, changing the wavelength of light that they reflect, from green to blue to black.

More important, they found that the weevils maintained color-producing structures known as photonic crystals, which could mean any fossil without these structures probably never had them. McNamara concludes that photonic crystals must have evolved recently, at least in weevils, because she examined three-million-year-old weevils that lacked them.

Some scientists disagree. Andrew Parker, an entomologist at the Natural History Museum in London, notes that “every fossil goes through a completely different process,” so it will be difficult to generalize lessons from one species or fossil to others. But he finds the idea tantalizing: “We can start to add up a picture and put together scenes of what life would have been like in color.”

First published in Scientific American [html] [pdf]