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 1 
 on: Today at 09:10 AM 
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 SPIEGEL ONLINE
09/02/2015 03:05 PM

Our Solar System: You Are Now Leaving Earth

By Christoph Seidler and Anne Martin  (Videos) .. Click here to watch all these incredible videos with the original article: http://www.spiegel.de/international/world/a-1045692.html

With eight planets, five dwarf planets, at least 146 moons, more than half a million known asteroids and about 4,000 comets, the solar system is more crowded than you might think. Come join us on our cosmic voyage. And don't forget to turn on the Sound.

    "The solar system is an insignificant bunch of dust. It also happens to be where we live." (Gene Shoemaker)

Our solar system is four-and-a-half billion years old. Science is only gradually gaining insights into its endless expanse. NASA's New Horizons spacecraft recently paid a visit to Pluto. For the first time since its discovery 85 years ago, mankind now knows what the planet looks like. This tour through the solar system takes you to Pluto and beyond.

Our journey starts at the sun, which makes up 99.8 percent of the mass of our solar system. The sun's gravitational force ensured that the planets, including Earth, were able to form.

By Milky Way standards, the sun is a perfectly normal, average star. With surface temperatures of about 5,000 degrees Celsius (9,032 degrees Fahrenheit), and up to 15 million degrees Celsius at its core, the sun derives its energy from the process of nuclear fusion. Hydrogen atoms melt into helium, fueling the solar fire.

The good news is that this will continue for about another 5 to 6 billion years. The bad news is that at the end of this period, the sun could expand to the point that it will swallow Earth.

From the hottest place in the solar system, we now go to somewhat cooler realms. The first stop is a planet of extremes.

With temperatures ranging from minus 180 to plus 430 degrees Celsius, Mercury has the largest temperature fluctuations of all planets as a result of its proximity to the sun. The side that happens to be facing the sun heats up while the other side cools off. Did you bring your long johns? They might come in handy now.

Mercury's surface, with its many craters, resembles the surface of Earth's moon. There is tons of water ice in craters on the planet's poles.

Given its proximity to the sun, Mercury has seen relatively few visits by spacecraft to date. In 1974 and 1975, the US spacecraft Mariner 10 flew past Mercury three times and once even came within 320 kilometers (199 miles) of its surface. In March 2011, Messenger became the first spacecraft to orbit the planet. It was then deliberately crashed into Mercury in April 2015.

From Mercury, we continue to our cosmic neighbor, a true beauty, but one that packs a punch.

Next to the moon, Venus is the brightest object in the terrestrial night sky. As far as size goes, Venus is pretty similar to Earth. Other than that, they have little in common -- in fact, this place is the opposite of cozy.

The planet's dense atmosphere wouldn't be much fun for human beings. It consists of 96 percent carbon dioxide, with air pressure that is 90 times as high as on Earth's surface. If you were hoping to travel in comfort here, we hope you brought a diving bell along. Your equipment should also be good enough to withstand the pressure.

The average ground temperature on Venus is 462 degrees Celsius. At those temperatures, metals like lead become liquid. Sulfuric acid rain and volcanic activity also help make Venus a pretty unpleasant place.

The US Mariner 2 spacecraft completed the first successful Venus flyby in December 1962, at an altitude of 35,000 meters (114,830 feet). The Soviets achieved the first hard landing with Venera 2 in March 1966, but it was unable to collect and send data back to Earth. Venera 7 achieved this in August 1970, for an impressive 23 minutes. Remember, it's hot up there, so maybe it's a good idea to keep your distance from Venus. Since April 2006, the European Venus Express spacecraft has been transmitting data from its orbit around the planet.

So-called Aten asteroids, of which more than 900 are known, can be found on the route toward Earth. In principle, some of them could even cross Earth's orbit and pose a threat to the planet. But there is currently no evidence that any specific asteroid is about to crash into Earth anytime soon.

Astronaut Thomas Reiter Peers at Earth from Space:

The most recognizable feature of Earth from space is its blue color. Oceans cover about 70 percent of its surface. With an average depth of 3,500 meters, many parts of our oceans remain as unexplored as space.

When it comes to land surface, human beings are of course deeply familiar with their home planet. This applies to the 7.2 billion people who explore their world on the ground every day, the three to six residents of the International Space Station and countless earth observation satellites, which keep a constant eye on all signs of life.

Before we go from Earth to the next planet, let's take a little detour to our neighbor.

Thomas Reiter Looks Skyward to the Moon

So far, the moon is the only celestial body in space on which humans have landed. Of course, it's also the one we are most familiar with, given its visibility in the night sky. Although some of the craters on its surface can be seen with the naked eye, the moon's largest, at its south pole, is not visible from Earth.

The first spacecraft to fly past the moon was the Soviet Union's Lunik 1, in January 1959. Its successor, Lunik 2, made a landing in the same year, but it was a hard landing. The Soviets accomplished the first soft landing with the Luna 9 spacecraft in February 1966.

More than three years later, in July 1969, two human beings landed on the moon for the first time, as part of NASA's Apollo 11 mission. A total of 12 people -- all men, and all Americans -- have set foot on the moon. But that happened more than 40 years ago. Johann-Dietrich Wörner, head of the European Space Agency (ESA), is currently campaigning for an international, manned moon base. Let's see where that leads.

    "Don't tell me that man doesn't belong out there. Man belongs wherever he wants to go -- and he'll do plenty well when he gets there." (Wernher von Braun, the famous German-American aerospace engineer who designed the Saturn V launch vehicle that propelled the Apollo spacecraft to the moon.)

Better shake off that dust! The nearest dry cleaner is a long, long way away. On the way to Mars, our flight passes the so-called Apollo asteroids, of which more than 7,000 are known. Some of them could cross Earth's orbit, but there is currently no indication of an impending collision. Let's get a move on it. There's nothing to see here.

When Will Men be able to travel to Mars?

Mars is the second-smallest planet in the solar system after Mercury. Because a significant portion of its surface is covered with dusty iron oxide, it is known as the Red Planet. Although its atmosphere is very thin, there are still storms on Mars. It's also pretty chilly there, with temperatures ranging from minus 153 to plus 20 degrees Celsius, depending on the place and time. Although Mars seems cold and barren today, it used to be a lot more pleasant, and there was even liquid water on the planet.

There is two-thirds less gravity on Mars than on Earth. Even with a bulky space suit on, you could still jump three times higher than you could at home. If your old gym teacher could only see!

The Olympus Mons on Mars is the tallest volcano in the solar system. The mountain, known as a shield volcano, is about 25 kilometers high, or almost three times as high as Earth's Mount Everest. The Red Planet also has the deepest canyons in the solar system. The Valles Marineris, for example, is steep and runs up to seven kilometers deep.

Mars is a popular destination for research spacecraft from Earth. The Soviet Union achieved the first flyby in June 1963, with Mars 1. In July 1965, the US' Mariner 4 spacecraft delivered the first images of Mars, from a distance of about 10,000 kilometers. The Soviets accomplished the first successful landing in December 1971, with their Mars 3 craft. In December 2003, the Europeans made a hard landing on Mars with the Beagle 2. Meanwhile, the Mars Express has been in orbit since December 2003, together with four other active spacecraft.

NASA currently has two robotic vehicles on Mars, Opportunity and Curiosity. The agency is officially pursuing a plan to accomplish a manned Mars landing, sometime after 2030. Some astronauts are keen to make the trip, including Alexander Gerst of Germany.

On the way to the edge of the solar system, our route now passes through the asteroid belt. It contains half a million known asteroids, and more are constantly being added to the list. These rocks of various sizes are remnants from the early days of the solar system. Rapidly growing Jupiter once ensured that they could not come together to form a planet. This is one reason asteroids are so interesting to scientists -- as a sort of cosmic time capsule.

Asteroids are constantly colliding with each other or -- if they are thrown out of their orbits -- with planets. Asteroids have collided with Earth before, sometimes with dramatic consequences. We don't have to worry about an asteroid entering a collision course with Earth in the near future, but sooner or later it will happen again - an eventuality we are still poorly equipped to deal with. NASA is thinking about a manned asteroid mission. But so far only thinking about it.

There is a very special dwarf planet orbiting within the asteroid belt.

The especially fascinating features of the dwarf planet Ceres are its white spots, the origins of which still remain a mystery.

The goal of NASA's Dawn spacecraft is to unlock Ceres' secrets. It has been orbiting Ceres since March 2015 and has already sent back large numbers of images.

The European Space Agency's Rosetta spacecraft has been orbiting the comet 67P/ Churyumov-Gerasimenko since August 2014. Like asteroids, comets are also leftovers from the early days of the solar system. The comet, affectionately known as Churi, which Rosetta and its small Philae landing robot are studying, is only one of 4,000 known comets. Never before has mankind learned as much about this type of object.

We are now about to enter the region of the so-called gas planets. The biggest one is the next station on our journey through the solar system.

Jupiter is the giant of the solar system -- larger and with a greater mass than all of its relatives, making up 70 percent of the combined mass of all planets in the solar system. It presumably has a solid core, and it is surrounded by giant layers of gas, consisting mainly of hydrogen and helium. Unimaginably powerful storms rage within those layers. The layers are also responsible for Jupiter's rings. Another known feature of Jupiter is the Great Red Spot, a storm system larger than Earth.

At the end of 1973, NASA's Pioneer 10 became the first spacecraft to fly past Jupiter, transmitting data back to Earth from an altitude of 130,000 kilometers. In December 1995, the NASA Galileo spacecraft dropped a probe into Jupiter's atmosphere, where it burned up in 2003. NASA's Juno probe is currently en route to Jupiter, where it is expected to arrive in just under a year.

In addition to the planet itself, Jupiter's moons, of which there are at least 50 (more than any other planet), are also of interest to scientists. For instance, they believe that there is an ocean of water under thick ice on giant Ganymede, which is larger than Mercury.

The Jupiter moon Europa, a veritable flying snowball, is also fascinating to scientists, who speculate that simple life forms may exist there as well. The conditions for life there are not bad, prompting repeated discussion about a possible Europa landing mission. In 2022, ESA plans to launch its spacecraft Juice, with which it hopes to at least conduct a flyby of the Jupiter moon.

    "Can we actually "know" the universe? My God, it's hard enough to find your way around in Chinatown." (Woody Allen)

The next gas giant is Saturn, the second-largest planet. Its rings, the planet's most salient feature, are made up of water ice and rock. What most people probably don't know is that there are more than 100,000 individual rings, some with a diameter of almost a million kilometers.

As on Jupiter, there are storms raging on Saturn of almost unimaginable dimensions. They spin through the atmosphere for months, generating giant bolts of lightning 10,000 times stronger than those found on Earth. And like Jupiter, Saturn appears to have a solid core.

Mankind has known what Saturn looks like up close since September 1979, when the Americans successfully completed the first flyby, at a distance of 22,000 kilometers, with Pioneer 11. The Cassini spacecraft has been orbiting Saturn since July 2004 and is still transmitting data today.

Scientists are also interested in Saturn's moons, the biggest of which, Titan -- like Jupiter's moon Ganymede -- has a larger diameter than Mercury. In January 2005, ESA's Huygens lander managed to gather data for 70 minutes on the moon's surface, which is usually concealed by a thick atmosphere. Titan also has giant hydrocarbon seas. It's a fascinating but uncomfortable world.

The next stop is Uranus, also a gas planet. It has a bluish-green shimmer, because methane gas in its atmosphere swallows some of the incoming sunlight. The reflected remaining light creates the planet's characteristic Color.

No one has ever seen Uranus's small core beneath its atmosphere. The gas planet has a uniquely tilted rotational axis, probably the result of a collision long ago. It's also pretty cold there, so let's keep going!

So far only the US' Voyager 2 spacecraft has flown past Uranus, coming within 71,000 kilometers of the planet in January 1986. Another mission is unlikely to take place within the next two decades.

The icy planet Neptune is even farther out in the solar system. This planet also has a dense, gaseous atmosphere, in which storms churn at speeds of more than 2,000 kilometers per hour.

There are seasons in Neptune's atmosphere, but they last 40 years.

Voyager 2 has also been the only visitor from Earth to Neptune to date. In August 1989, the spacecraft approached the planet's north pole at a distance of about 5,000 kilometers, only to continue flying farther out into space.

Neptune's Triton moon is considered the coldest place in the solar system visited to date. Temperatures as low as minus 2,235 degrees Celsius have been measured on Triton, where ice geysers spew nitrogen.

In the past, we would have been flying on to the next planet. But according to a vote by the International Astronomical Union, Pluto is no longer considered a planet. Pluto, now classified as a dwarf planet, is probably the best known object in the so-called Kuiper belt.

Given Pluto's location far out in the solar system, light from the sun is very weak on the dwarf planet. It takes more than four-and-a-half hours to reach it, which is how long the trip would take if one were to fly there at the speed of light.

Pluto isn't at the end of the solar system by a long shot, but man still knows very little about the darkness beyond. Scientists cannot rule out the possibility that yet another, still unknown planet is orbiting the sun beyond Pluto.

Astronomers know even less about a structure called the Oort Cloud. They believe it contains an unimaginably large number of objects made of rock and ice, left behind when the solar system was created. No one has actually observed the cloud, but many believe it exists, as a sort of garbage dump of the solar system. Gravitational effects occasionally propel objects from the Oort Cloud into the inner solar system, where they become long-period comets.

The edge of the Oort Cloud could be 1.6 light-years away from Earth, or almost half the distance to the nearest star, Proxima Centauri. It is significantly smaller than the sun and has only an eighth of its mass. Traveling at the speed of light, it would take more than four years to reach Proxima Centauri. Put differently, if the distance between the sun and Earth were only one meter, Proxima Centauri would be about 270 kilometers away. But we'll save this part of the trip for another journey.

    "Today's science fiction is tomorrow's science fact." (Science fiction writer Arthur C. Clarke)

Note: The numbers used in the article on individual celestial bodies were obtained from solarsystem.nasa.gov. Moons whose existence has not yet been confirmed were not taken into account. The distances quoted for the approach videos are based on the shortest distances from the sun .

Author: Christoph Seidler. Videos: Anne Martin. Editor: Holger Dambeck. Research and fact-checking: Almut Cieschinger, Maximilian Schäfer. Copyediting: Sarah Omar. Design: Hanz Sayami. Coordination: Jule Lutteroth. Translation: Christopher Sultan.

 2 
 on: Today at 07:18 AM 
Started by Steve - Last post by Rad
Court rules Ecuadoran villagers can pursue Chevron in Canada

Agence France-Presse
04 Sep 2015 at 15:34 ET                   

Ecuadoran villagers can seek to enforce in Canada a multi-billion-dollar Ecuadoran judgment against US oil giant Chevron (Swiss: CVX.SW – news) on pollution in the Amazon rainforest, the country’s top court said Friday.

However, the decision only establishes jurisdiction and does not settle the claim itself.

Chevron’s Canadian subsidiary dismissed the ruling, calling the Ecuadoran judgment fraudulent and unenforceable.

In Canada and in parallel legal fights in the United States and Brazil, the indigenous people of Ecuador’s Lago Agrio region have sought to collect compensation for the mass dumping of oilfield waste between the 1970s and 1990s, after an Ecuadoran court ordered Chevron to pay $9.5 billion in damages.

The environmental destruction was allegedly committed by Texaco, which Chevron bought in 2001.

The villagers had asked the Ontario Superior Court to force Chevron to hand over Can$12 billion (US$11.3 billion) in Canadian assets held by subsidiaries.

The court turned them down, but they won on appeal.

The oil company has refused to pay, alleging fraud and bribery was used to obtain the ruling in Ecuador and maintains that its Canadian subsidiaries are wholly independent and have nothing to do with the case.

In March 2014, a US court ruled that the Ecuadoran judgment was the product of “fraud and racketeering” and was unenforceable in the United States.

In its decision Friday, the Canadian Supreme Court said “Chevron Canada has a physical office in Ontario, where it was served. Its business activities at this office are sustained; it has representatives who provide services to customers in the province. Canadian courts have found that jurisdiction exists in such circumstances.”

“In an enforcement process like this for the collection of a debt against a third party, assets in the jurisdiction through the carrying on of business activities are undoubtedly tied to the subject matter of the claim,” it said.

But it added that “a finding of jurisdiction does nothing more than afford the plaintiffs the opportunity to seek recognition and enforcement of the Ecuadoran judgment.”

Thousands of villagers in the polluted area say they were sickened and that many have cancer from the contamination of their water supply from oil spillage.

Chevron contends that Texaco paid all of the required clean-up costs before leaving the country in the 1990s.

In a statement, its Canadian subsidiary said the latest ruling “has no bearing on the legitimacy or enforceability of the fraudulent Ecuadoran judgment.”

“The facts remain, as Chevron Corp. established in the United States, that the Ecuadoran judgment is the product of fraud and other misconduct, and is therefore illegitimate and unenforceable,” it said.

 3 
 on: Today at 05:43 AM 
Started by Steve - Last post by Rad
Climate stalemate prompts call for world leaders to intervene

Act now to remove roadblocks and lay the groundwork for Paris climate deal, say experts including Kofi Anan as Bonn talks stumble

Fiona Harvey, environment correspondent
Friday 4 September 2015 16.33 BST
Guardian

World leaders must step into the ongoing UN climate change negotiations, to remove roadblocks and ensure their negotiating teams can lay the groundwork for an agreement at landmark talk in December, an influential group of former leaders has urged.

The Elders - a group including former UN secretary general Kofi Annan, Graca Machel, the Mozambican politician and widow of Nelson Mandela, and Mary Robinson, formerly president of Ireland and a UN high commissioner – made their call on Friday, as the latest round of pre-Paris negotiations ended with many key issues left open. That stalemate leaves only five official negotiating days left before the Paris climate conference, at which governments are supposed to forge a new global climate change agreement to take effect from 2020.


 4 
 on: Today at 05:41 AM 
Started by Rad - Last post by Rad
How long until America's newest baby panda is actually cute?

Guardian
9/5/2015

Two baby giant pandas were born at the Smithsonian’s National Zoo on 22 August. But the death of one days later has pushed the nation’s attention onto the remaining twin.

The giant panda at the zoo will eventually be adorable, but right now it’s hairless and pink and generally not that cute. It takes some time for baby pandas to sprout their beautiful white and black coats

Click to view all: http://www.theguardian.com/world/ng-interactive/2015/sep/05/baby-panda-mei-xiang-national-zoo-cute

 5 
 on: Today at 05:38 AM 
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Indian government takes major step to save vultures

Almost a decade after banning the veterinary drug diclofenac, the Indian government has banned large vials of the drug meant for human use

Janaki Lenin
Saturday 5 September 2015 05.59 BST
Guardian

The government of India’s Ministry of Health and Family Welfare finally issued a directive banning multi-dose vials of the non-steroidal pain-killer diclofenac in the last week of August.

For a decade, numbers of three species of vultures had been in a precipitous decline throughout the subcontinent. Millions of white-backed vultures shrank in number by 99.9% reduced to a mere 11,000 by the early 2000s. Populations of two other species – long-billed vulture and slender-billed vulture – dropped by 97%. All three are listed as critically endangered in the IUCN’s Red List.

After extensive studies, scientists identified diclofenac as the culprit. The cheap painkiller was commonly used by veterinarians to treat minor ailments in livestock, but is toxic to vultures, causing fatal gout or renal failure. When sick cattle, treated with diclofenac, died, their carcasses were disposed in the open as was the age-old practice. Hundreds of vultures stripped the meat within minutes, and died within a month.

In 2006, the government banned the formulation, manufacture, and import of veterinary diclofenac. Meloxicam was promoted as a substitute anti-inflammatory drug.

The Royal Society for Protection of Birds conducted a survey for nearly three years in 11 Indian states after the ban. It found diclofenac being sold in more than a third of the pharmacies, but 70% of them had switched to meloxicam.

Vulture populations stabilised, but more action was needed. The birds continued to die, even if not in such great numbers as before.

Meloxicam was much more expensive. It didn’t find favour with veterinarians who said it wasn’t as effective as diclofenac. Instead, large 30 ml vials of diclofenac meant for humans were diverted for veterinary use. Large animals like cattle need only 10 to 15 ml.

Even though Boehringer-Ingelheim, the company that developed meloxicam, no longer held the patent, it offered its expertise to Indian manufacturers to produce better formulations. More than 30 companies then began producing the drug. It became cheaper and more acceptable to veterinarians.

Now that the government has banned these multi-dose vials, only 3 ml vials will be available. Sourcing five small ampoules for one cow will not be cheap.

The ban is likely to put a stop to vultures’ access to diclofenac. But bird conservationists say other similar drugs like nimesulide, fatal to vultures, are still being used. They want all veterinary painkillers to be tested for toxicity in vultures.

Asad Rahmani, senior scientific advisor to the Bombay Natural History Society, says, “We’ll see how the ban is being implemented. Based on the results, we’ll decide what more needs to be done.”

 6 
 on: Today at 05:36 AM 
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Angry apes that attacked drone used ‘forward-planning’ – video

Guardian
9/55/2015

Animal experts have concluded that an ape attack on a drone at Royal Burgers’ zoo in the Netherlands was ‘pre-planned’ and utilized a high level of ingenuity. The footage, shot in April, shows a group of chimpanzees observing the drone, gathering sticks and then climbing a scaffold to target it. A female ape called Tushi eventually downs the drone, and a group of apes then inspect it

Click to watch:<iframe src="https://embed.theguardian.com/embed/video/world/video/2015/sep/04/apes-drone-attack-zoo-video" width="560" height="315" frameborder="0" allowfullscreen></iframe>

 7 
 on: Today at 05:32 AM 
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Russian town besieged by hungry bears

Shortages of nuts and berries have driven animals into towns to search for food, roaming the streets and scaring residents

Alec Luhn in Moscow
Friday 4 September 2015 16.33 BST
Guardian

Dozens of hungry bears have besieged a small town in Russia’s far east, roaming the streets and attacking residents.

In the past month, more than 30 bears have entered inhabited areas in Russia’s Primorsky region, located between China, North Korea and the Sea of Japan. Local authorities have had to shoot at least two animals.

Luchegorsk, a town of 21,000 on the river Kontrovod near the Chinese border, has been particularly affected. Two large bears – a brown bear and a Himalayan bear – are now “ruling over” Luchegorsk, wandering the streets and scaring local people, the Primorskaya newspaper reported. Asian black bears have also been seen, and a further three dozen bears are circling the town, according to other reports.

Local people say they are afraid to leave their homes and that the streets are filled with the sounds of sirens and loudspeakers telling citizens not to go outside for their own safety, VladNews reported. In one case, bears reportedly ransacked bee hives kept by locals. Kindergartens have kept children inside.

Man walking his dog attacked by bear: https://www.youtube.com/watch?v=zZ1LeJ8vaUI

There is good reason for the caution: a dashcam recently captured footage of a bear jumping out from beneath a balcony to attack a man in Luchegorsk as he was walking his dog near the entrance to his apartment building. Another man was wounded in a bear attack at the local bus station.

Vladimir Vasilyev, head of the Primorsky region’s animal control department, said the situation in Luchegorsk had “stabilised” thanks to the efforts of police and game wardens.

“Law enforcement officers are using the sirens on their cars to chase away the bears and are shooting in the air to frighten them,” Vasilyev said, adding that some bears had been dispersed with fire hoses. “Two animals have had to be shot since the start of this invasion. They needed to be neutralised because they posed a real threat to humans and were attacking local residents.”

A bear runs away from law enforcement officers: https://www.youtube.com/watch?v=sbV39NPvhFY

Vasilyev was apparently referring to an incident on 24 August when a mother bear and her grown cub roamed the streets of Luchegorsk looking for food. After the cub attacked a man, police and game wardens shot both bears. The man was later taken to hospital.

Other reports put the number of bears killed higher. A game warden told the OTV Primorye channel he had to shoot a bear when it turned on him as he was trying to chase it out of Luchegorsk.

Experts believe the hungry bears have been migrating to the Primorsky region from neighbouring Khabarovsk and China in search of food. The number of bears in Primorsky has also grown in recent years due to fewer hunters, Pavel Fomenko of the World Wildlife Fund told news agency Rosbalt. Poor yields this year of Manchurian walnuts, acorns, pine nuts and berries across all these areas have deprived the bears of their main sources of food to fatten up for winter hibernation, sending them into towns in looking to eat.

Bear attacks have long been a problem in Russia in years when their food supplies run low. In the most extreme case, 270 bears were reportedly killed in four villages in Irkutsk province in 1968.

A heatwave last summer coincided with a rash of bear attacks in Russia’s far east that left at least three people dead. In 2010, a scorching summer left bears in Siberia so hungry that some began digging up human graves.

The bear invasion is unlikely to subside any time soon. “We predict that failing to find food in the taiga [boreal forest], bears will come to where people live more and more,” Vasilyev said.

 8 
 on: Today at 05:26 AM 
Started by Rad - Last post by Rad
September 4, 2015

NASA: We want to tether a spacecraft to a comet and fly through space

by Chuck Bednar
Red Orbit

NASA is reportedly working on a new spacecraft that borrows a page from Spider-Man’s book, using a harpoon and a long tether to swing from one asteroid or comet to another and using the kinetic energy of those objects to enter orbit and complete landing maneuvers.

The project, known as Comet Hitchhiker, is being funded through the US space agency’s NIAC (NASA Innovative Advanced Concepts) program and would use its harpoon to secure a foothold on a comet or asteroid. Once it is attached, it would release some of its tether while applying the brake in order to capture kinetic energy from its target, according to Space.com.

Next, the Comet Hitchhiker would land by reeling in the line, which would be approximately 62 miles to 620 miles (100 to 1,000 kilometers) long. Using the harvested kinetic energy to quickly collect the tether would propel the probe away from the object and towards its next target. Most importantly, this would enable the spacecraft to travel without using propellant.

In a statement, Masahiro Ono, principal investigator of the project from NASA's Jet Propulsion Laboratory in Pasadena, California, explained that, “This kind of hitchhiking could be used for multiple targets in the main asteroid belt or the Kuiper Belt, even five to 10 in a single mission.”

Comet-catching concept similar to reeling in a fish

The technique, the agency explained, is similar to fishing: Once you get a bite from a big fish, you initially release some of the fishing line with moderate tension instead of keeping it tight. Provided you have enough line, the boat you are on will ultimately catch up with the fish.

Similarly, once the Comet Hitchhiker hooks its “fish” and matches velocity to that asteroid or comet, it lands by reeling in its tether and descending gently. Once its ready to move on, it uses its harvested energy to quickly retrieve its tether, which accelerates it away from the object it is currently on. This technique could help it reach distant objects fairly quickly, Ono said.

In fact, the research team calculated that using zylon and kevlar, the spacecraft would be capable of executing a velocity change of nearly one mile per hour (1.5 kilometers per hour), which Ono explained is “like going from Los Angeles to San Francisco in under seven minutes.” A 6.2 mile per second (10 km per second) speed is possible, but would require advanced materials such as a carbon nanotube tether and a diamond harpoon, the Comet Hitchhiker team noted.

Of course, as Space.com pointed out, this is all merely speculation at this point. The project is in Phase I NIAC study at this point, having received a grant of about $100,000 to begin initial work over a nine-month period. The next steps for the Comet Hitchhiker team, NASA said, are to run additional simulations and attempt to cast a mini-harpoon at a simulated comet or asteroid.

 9 
 on: Today at 05:25 AM 
Started by Rad - Last post by Rad
September 4, 2015

Aside from being hunted by MN dentists: Why are there less lions?

by Chuck Bednar
Red Orbit

Curious as to why there weren’t more lions and other predators at dozens of wildlife parks in eastern and southern Africa, McGill University PhD student Ian Hatton set out to discover the reasons behind this phenomenon – and came up with some rather startling revelations.

The lack of predators, Hatton and his colleagues learned, had nothing to do with human hunters, and prey was bountiful enough to be able to support a larger lion population. In reality, the team found that even as the quantity of prey increased significantly, the amount of food produced for predators failed to keep pace, causing their populations to only increase slightly.

The discovery suggests that ecosystems possess a previously unrecognized level of structure and function, the study authors explained in a statement. Furthermore, while biologists already knew that regular, mathematical laws governed body functions, this study is the first to suggest that the same types of laws could also exist and govern ecosystems all over the world.

Van Savage, an associate professor of biomathematics at UCLA who was not involved in the study, called the findings “compelling and mysterious... because it is rare to find such strong, systematic patterns in biology, especially at such a large scale as an ecosystem.” The research was published in the September 4 online edition of the journal Science.

Reduced herbivore reproduction rates limits carnivore abundance

In a statement, Hatton explained that the discovery happened by chance during vacations spent at national parks while he was a high school student in Zimbabwe. After beginning his PhD studies at McGill, he returned there to compare communities of African animals in protected ecosystems to investigate the relationship between carnivore numbers and available prey.

He gathered as much animal census data as possible, and when he and his fellow investigators started analyzing the numbers, they found a regular but unexpected pattern: in each park, there appeared to be a consistent but complex predator to prey relationship, and that surprisingly, the number of predators did not directly correspond to the size of the herbivore populations.

Previously, Hatton said, “the assumption has been that when there is a lot more prey, you'd expect correspondingly more predators.” However, as he looked at their figures, he discovered that the ratio of predators to their prey was “greatly reduced” in the lushest ecosystems all over the world, and that the increased crowding resulted in a reduced rate of reproduction amongst prey species, which in turn limited the abundance of their predators.

“These results are striking because they indicate that the quantity of harvestable predators, for example, commercial fisheries that feed on marine prey, increase little despite large increases in prey,” Dr. Just Cebrian, a professor in marine sciences at the University of South Alabama and a senior marine scientist at Dauphin Island Sea Lab said in a statement emailed to redOrbit.

“Clearly more productive ecosystems are inefficient when it comes to transferring energy up the food chain,” he continued, adding that the authors of the paper “generalize this for all ecosystems on Earth and quantify the inefficient rate at which energy is transferred up the food chain.”

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 on: Sep 04, 2015, 11:34 AM 
Started by Gonzalo - Last post by Gonzalo
Conscious and Unconscious Memory Systems

Larry R. Squire and Adam J.O. Dede

4 September 2015 - Published by Cold Spring Harbor Laboratory Press

Abstract:

The idea that memory is not a single mental faculty has a long and interesting history but became a topic of experimental and biologic inquiry only in the mid-20th century. It is now clear that there are different kinds of memory, which are supported by different brain systems. One major distinction can be drawn between working memory and long-term memory. Long-term memory can be separated into declarative (explicit) memory and a collection of nondeclarative (implicit) forms of memory that include habits, skills, priming, and simple forms of conditioning. These memory systems depend variously on the hippocampus and related structures in the parahippocampal gyrus, as well as on the amygdala, the striatum, cerebellum, and the neocortex. This work recounts the discovery of declarative and nondeclarative
memory and then describes the nature of declarative memory, working memory, nondeclarative memory, and the relationship between memory systems.

The idea that memory is not a single faculty has a long history. In his Principles of Psychology, William James (1890) wrote separate chapters on memory and habit. Bergson (1910) similarly distinguished between a kind of memory that represents our past and memory that is not representational but nevertheless allows the effect of the past to persist into the present. One finds other antecedents as well. McDougall (1923) wrote about explicit and implicit recognition memory, and Tolman (1948) proposed
that there is more than one kind of learning. These early proposals were often expressed as a dichotomy involving twoforms of memory. The terminologies differed, but the ideas were similar. Thus, Ryle (1949) distinguished between knowing how and knowing that, and Bruner (1969) identified memory without record and memory with record. Later, the artificial intelligence literature introduced a distinction between
declarative and procedural knowledge (Winograd 1975). Yet constructs founded in philosophy and psychology are often abstract and have an uncertain connection to biology, that is, to how the brain actually stores information. History shows that as biological information becomes available about structure and function, understanding becomes more concrete and less dependent on terminology.

THE DISCOVERY OF DECLARATIVE AND NONDECLARATIVE MEMORY SYSTEMS

Biological and experimental inquiry into these matters began with studies of the noted patient H.M. (Scoville and Milner 1957; Squire 2009). H.M. developed profound memory impairment following a bilateral resection of the medial temporal lobe, which had been performed to relieve severe epilepsy. The resection included much of the hippocampus and the adjacent parahippocampal gyrus (Annese et al. 2014;
Augustinack et al. 2014). H.M.’s memory impairment was disabling and affected all manner of material (scenes, words, faces, etc.), so it was quite unexpected when he proved capable of learning a hand –eye coordination skill (mirror drawing) over a period of 3 days (Milner 1962). He learned rapidly and efficiently but on each test day had no memory of having practiced the task before. This finding showed that memory is not a single entity. Yet, at the time, discussion tended to set aside motor skills as an exception, a less cognitive form of memory. The view was that all of the rest of memory was impaired in H.M. and that the rest of memory is of one piece. There were early suggestions in the animal literature that more than just motor skills were intact after lesions of hippocampus or related structures (Gaffan 1974; Hirsh 1974; O’Keefe and Nadel 1978). However, these proposals differed from each other, and they came at a time
when the findings in experimental animals did not conform well to the findings for human memory and amnesia. In particular, animals with hippocampal lesions often succeeded at tasks that were failed by patients with similar lesions. It gradually became clear that animals and humans can approach the same task with different strategies (and using different brain systems), and also that patients withmedial temporal lobe lesions, like experimental animals with similar lesions, can in fact succeed at a wide range of learning and memory abilities.

First came the finding that memory-impaired patients could acquire, at a normal rate, the perceptual skill of reading mirror-reversed words, despite poor memory for the task and for the words that were read (Cohen and Squire 1980). Thus, perceptual skills, not just motor skills, were intact. This finding was presented in the framework of a brain-based distinction between two major forms of memory that afford either declarative or procedural knowledge.

Declarative knowledge is knowledge available as conscious recollection, and it can be brought to mind as remembered verbal or nonverbal material, such as an idea, sound, image, sensation, odor, or word. Procedural knowledge refers to skill-based information. What is learned is embedded in acquired procedures and is expressed through performance. Subsequently, other forms of experiencedependent
behaviors were found to be distinct from declarative memory. One important phenomenon was priming—the improved ability to detect, produce, or classify an item based on a recent encounter with the same or related item (Tulving and Schacter 1990; Schacter and Buckner 1998). For example, individuals will name objects faster on their second presentation, and independent of whether they recognize the objects as having been presented before. Another important discovery was that the neostriatum (not the medial temporal lobe) is important for the sort of gradual feedback guided learning that results in habit memory
(Mishkin et al. 1984; Packard et al. 1989; Knowlton et al. 1996). Tasks that assess habit learning are often structured so that explicit memorization is not useful (e.g., because the outcome of each trial is determined probabilistically), and individuals must depend more on a gut feeling. After learning, it is more accurate to say that individuals have acquired a disposition to perform in a particular way than to say that they have acquired a fact (i.e., declarative knowledge) about the world.

Given the wide variety of learning and memory phenomena that could eventually be shown in patients (e.g., priming and habit learning as well as simple forms of classical conditioning), the perspective eventually shifted to a framework involving multiple memory systems rather than just two kinds of memory (Fig. 1). Accordingly, the term “nondeclarative” was introduced with the idea that nondeclarative
memory is an umbrella term referring to multiple forms of memory that are not declarative (Squire and Zola-Morgan 1988). Nondeclarative memory includes skills and habits, simple forms of conditioning, priming, and perceptual learning, as well as phylogenetically early forms of behavioral plasticity like habituation and sensitization that are well developed in invertebrates. The various memory systems
can be distinguished in terms of the different kinds of information they process and the principles
by which they operate.

Declarative memory provides a way to represent the external world. It is the kind of memory we typically have in mind when we use the term memory in everyday language. Declarative memory has two major components, semantic memory (facts about the world) and episodic memory (the ability to re-experience a timeand-place-specific event in its original context) (Tulving 1983). The acquisition of episodic memory requires the involvement of brain systems in addition to medial temporal lobe structures, especially the frontal lobes (Tulving 1989; Shimamura et al. 1991). There is some uncertainty around the issue of whether nonhuman animals have the capacity for episodic memory (i.e., the capacity for mental time travel that can return an animal to the scene of an earlier event), and the idea has been difficult to put
to the test (Tulving 2005). For elegant demonstrations of episodic-like memory in nonhuman animals, see Clayton and Dickinson (1998).

Nondeclarativememory is dispositional and is expressed through performance rather than recollection. An important principle is the ability to gradually extract the common elements from a series of separate events. Nondeclarative memory provides for myriad unconscious ways of responding to the world. The unconscious status of nondeclarative memory creates some of the mystery of human experience. Here arise the habits and preferences that are inaccessible to conscious recollection, but they nevertheless are shaped by past events, they influence our current behavior and mental life, and they are a fundamental part of who we are.

Sherry and Schacter (1987) suggested that multiple memory systems evolved because they serve distinct and fundamentally different purposes. For example, the gradual changes that occur in birdsong learning are different from, and have a different function than, the rapid learning that occurs when a bird caches food for later recovery. These memory systems operate in parallel to support and guide behavior. For example, imagine an unpleasant event from early childhood, such as being knocked down by a large dog. Two independent consequences of the event could potentially persist into adulthood as declarative and nondeclarative memories. On the one hand, the individual might have a conscious, declarative memory of the event itself. On the other hand, the individual might have a fear of large dogs, quite independently of whether the event itself is remembered. Note that a fear of dogs would not be experienced as a memory but rather as a part of personality, a preference, or an attitude about the world.

THE NATURE OF DECLARATIVE MEMORY

Studies of patients and experimental animals with medial temporal lobe damage have identified four task requirements that reliably reveal impaired memory: (1) tasks where learning occurs in a single trial or single study episode (Mishkin 1978); (2) tasks where associations between stimuli are learned across space and time (e.g., Higuchi and Miyashita 1996; Fortin  et al. 2002); (3) tasks where the acquired information can be used flexibly (e.g., Bunsey and Eichenbaum 1996; Smith and Squire 2005); and (4) tasks where learning depends on awareness of what is being learned (Clark and Squire 1998; Smith and Squire 2008).

Declarative memory (sometimes termed explicit memory) is well adapted for the rapid learning of specific events. Declarative memory allows remembered material to be compared and contrasted. The stored representations are flexible, accessible to awareness, and can guide performance in multiple different contexts. The key structures that support declarative memory are the hippocampus and the adjacent
entorhinal, perirhinal, and parahippocampal cortices, which make up much of the parahippocampal gyrus (Fig. 2) (Squire and Zola-Morgan 1991). These structures are organized hierarchically, and their anatomy suggests how the structures might contribute differently to the formation of declarative memory, for example, in the encoding of objects ( perirhinal cortex) or scenes ( parahippocampal cortex) and in the
forming of associations between them (hippocampus) (Squire et al. 2004; Davachi 2006; Staresina et al. 2011).

Structures in the diencephalic midline (mammillary nuclei, medial dorsal nucleus, anterior thalamic nuclei, together with the internal medullary lamina and the mammillothalamic tract) are also important for declarative memory. Damage to these structures causes the same core deficit as damage to the medial temporal lobe, probably because these nuclei and tracts are anatomically related to the medial temporal
lobe (see Markowitsch 1988; Victor et al. 1989; Harding et al. 2000; Squire and Wixted 2011).

Discussion continues about the nature of declarative memory and about when exactly the hippocampus (and related structures) is involved in learning and memory. One proposal is that, whereas conscious recollection depends on the hippocampus as described above, the hippocampus is also important for unconscious memory under some circumstances (Henke 2010; Hannula and Greene 2012; Shohamy and Turk-Browne 2013). One way to explore this issue has been to record eye movements while volunteers are making behavioral memory judgments. In some situations (e.g., when a change has occurred in the layout of a scene), the eyes do not reveal signs of memory (by moving to the changed location) unless participants are aware of where the change occurred (Smith et al. 2008). Furthermore, these eye movement effects require the integrity of the hippocampus. Nevertheless, in other situations, eye movements can signal which item is correct, and correlate with hippocampal activity, even when behavioral memory judgments are incorrect and participants are therefore thought to be unaware
(Hannula and Ranganath 2009). Such a finding could mean that eye movements (and hippocampal activity) can index unaware memory. Yet, it is also true that awareness is (presumably) continuous, and a low amount of awareness is not the same as a complete lack of awareness (Kumaran and Wagner 2009). Just as recognition memory can succeed when free recall fails, eye movements might reveal signs of aware memory when recognition fails. It would be instructive in this circumstance to obtain confidence ratings in association with memory judgments and ask whether there is any detectable awareness of which items are correct.

Other work has implicated medial temporal lobe structures in the unaware learning of sequences and other tasks with complex contingencies (Chun and Phelps 1999; Rose et al. 2002; Schendan et al. 2003). This idea is often based on functional magnetic resonance imaging (fMRI) evidence of medial temporal lobe
activity during unaware learning. Strategic factors (e.g., explicit attempts to memorize) may explain some of these effects (Westerberg et al. 2011), together with the possibility that awareness may not be entirely absent (Poldrack and Rodriguez 2003). In addition, considering that fMRI data cannot establish a necessary role for a particular structure, it will be useful to supplement fMRI datawith evidence that patients with
hippocampal lesions are impaired at the same tasks that afford unaware learning. Interestingly, for some of these tasks, hippocampal patients were not impaired (Reber and Squire 1994; Manns and Squire 2001), but impairment has been reported in patients when the damage was undescribed or extended beyond the hippocampus (Chun and Phelps 1999). Studies that combine fMRI, patient data, and rigorous measures of awareness will be useful in pursuing this interesting issue.

WORKING MEMORY

Working memory refers to the capacity to maintain a limited amount of information in mind, which can then support various cognitive abilities, including learning and reasoning (Baddeley 2003). Within cognitive neuroscience, the term “working memory” has largely replaced the less precise term “short-term memory.” (Note that the term “short-term memory” remains useful in cellular neuroscience where it has a different and distinct meaning [Kandel et al. 2014].) Historically, working memory has been considered
to be distinct from long-term memory and independent of the medial temporal lobe structures that support the formation of long-term memory (Drachman and Arbit 1966; Atkinson and Shiffrin 1968; Baddeley and Warrington 1970; Milner 1972). Long-term memory is needed when the capacity of working memory is exceeded or whenworkingmemory is disrupted by diverting attention to different material.

Uncertainty can arise when determining in any particular case, whether performance depends on working memory or whether so much information needs to be kept in mind that working memory capacity is exceeded and performance must rely on long-term memory. What is the situation when patients fail at tasks with short retention intervals, or no retention interval (Hannula et al. 2006; Olson et al. 2006;
Warren et al. 2011, 2012; Yee et al. 2014)? Are these long-term memory tasks or, as has been suggested, do such findings show that working memory sometimes depends on the medial temporal lobe (Ranganath and Blumenfeld 2005; Graham et al. 2010). It is important to note that working memory cannot be defined
in terms of any particular retention interval (Jeneson and Squire 2012). Even when the retention interval is measured in seconds, working memory capacity can be exceeded such that performance must depend, in part, on long-term memory (e.g., immediately after presentation of a list of 10 words).

Findings from a scene-location task illustrate the problem. The task involved scenes containing a number of different objects. On each trial, a scene was presented together with a question (e.g., is the plant on the table?). A few seconds later, the same scene was presented again but now the object queried about might or might not appear in a different location. In this condition, patients with hippocampal lesions were accurate at detecting whether or not the object had moved (Jeneson et al. 2011). However, when attention was drawn to four different objects, any one of which might move, patients were impaired (Yee et al. 2014). It is likely that the impairment in the second condition occurred because working memory capacity was exceeded. Visual working memory capacity is quite limited and, typically, even healthy young adults can maintain only three to four simple visual objects in working memory (Cowan 2001; Fukuda et al. 2010).

In any case, there are ways to distinguish working memory and long-term memory (Shrager et al. 2008; Jeneson et al. 2010). For example, one can vary the number of items or associations to be remembered and ask whether patients show a sharp discontinuity in performance as the number of items increases and
working memory capacity is exceeded. In one study (Jeneson et al. 2010), patients with hippocampal lesions or large medial temporal lobe lesions saw different numbers of objects (1 to 7) on a tabletop and then immediately tried to reproduce the array on an adjacent table. Performance was intact when only a few object locations needed to be remembered. However, there was an abrupt discontinuity in performance
with larger numbers of object locations. One patient (who had large medial temporal lobe lesions similar to H.M.) learned one-, two-, or three-object locations as quickly as did controls, never needing more than one or two trials to succeed. Yet when four-object locations needed to be remembered, he did not succeed even after 10 trials with the same array.

These findings indicate that the ability to maintain small numbers of object –place associations in memory is intact after medial temporal lobe lesions. An impairment was evident only when a capacity limit was reached, at which point performance needed to depend on long-term memory. A similar conclusion was reached in studies of a single patient with restricted hippocampal lesions. Performance was fully intact
on an extensive working memory battery, including tasks of relational (associative) memory (Baddeley et al. 2010, 2011).

Spatial tasks like path integration can also be performed normally by patients with medial temporal lobe lesions, as long as the task can be managed within working memory (Shrager et al. 2008; Kim et al. 2013). The findings are different for rats with hippocampal lesions (Kim et al. 2013), either because for the rat the task relies on long-term memory or because the rat hippocampus is needed for some online
spatial computations, as suggested previously (Whitlock et al. 2008).

fMRI findings are relevant to these issues, because medial temporal lobe activity is sometimes found in association with short-delay recognition memory tasks (Ranganath and D’Esposito 2001; Piekema et al. 2006; Toepper et al. 2010). Yet, it is noteworthy that the extent of medial temporal lobe activity in short-delay tasks can be modulated by memory demands. For example, in some studies, the medial temporal
lobe activity that occurred while maintaining information in memory was correlated with subsequent retention of the material being learned (Schon et al. 2004; Ranganath et al. 2005; Nichols et al. 2006). In addition, in a study that required maintaining faces in memory, the connectivity between the hippocampus
and the fusiform face area increased with higher mnemonic load (one face vs. four faces) (Rissman et al. 2008). Concurrently, with higher load, the connectivity decreased between frontal regions traditionally linked to working memory (Goldman-Rakic 1995; Postle 2006) and the fusiform face area. These findings suggest that fMRI activity in the medial temporal lobe reflects processes related to the formation of longterm memory rather than processes related to working memory itself (for review, see Jeneson
and Squire 2012).

NONDECLARATIVE MEMORY

Nondeclarative memory (sometimes termed implicit memory) refers to a collection of abilities that are expressed through performance without requiring conscious memory content. Study of nondeclarative memory began with motor skills and perceptual skills, as described above, but soon included additional abilities as well. The next of these to come under study was the phenomenon of priming. Priming is evident
as improved access to items that have been recently presented or improved access to associates of those items. This improvement is unconscious and is experienced as part of perception, as perceptual fluency, not as an expression of memory. A key finding was that priming effects were intact in memory-impaired patients. For example, patients can perform normally on tests that use word stems as cues for recently presented words (e.g., study BRICK, CRATE; test with BRI___, CRA___). Importantly, performance was intact in patients only when they were instructed to complete each cue to form the first word that comes to mind. With conventional memory instructions (use the cue to help recall a recently presented word), healthy volunteers outperformed the patients (Graf et al. 1984). Priming can occur for material that has no preexisting memory representation (e.g., nonsense letter strings) (Hamann and Squire 1997a) and for material that is related by meaning to recently studied items. Thus, when asked to free associate to a word (e.g., strap), volunteers produced a related word (e.g., belt) more than twice as often when that word (belt) was presented recently (Levy et al. 2004). Importantly, severely amnesic patients showed fully
intact word priming, even while performing at chance levels in parallel memory tests (Hamann and Squire 1997b; Levy et al. 2004). Thus, priming occurs but it does not benefit conscious memory decisions. Indeed, direct measurements showed that priming provides only a weak and unreliable cue for conscious  judgments of familiarity (Conroy et al. 2005).

Priming is presumably advantageous because animals evolved in a world where things that are encountered once are likely to be encountered again. Priming improves the speed and efficiency with which organisms interact with a familiar environment and may influence feature-based attentional processes (Hutchinson and Turk-Browne 2012; Theeuwes 2013). Evoked-potential studies indicate that the electrophysiological signature of priming occurs early and well before the activity that signals conscious recognition of a past event (Paller et al. 2003). In neuroimaging studies, priming is often associated with reduced activity in regions of neocortex relevant to the task (Squire et al. 1992; Schacter et al. 2007). A similar finding (repetition suppression) (Desimone 1996) has been described in nonhuman primates (a
stimulus-specific attenuation in firing rate with repeated presentation of a stimulus), and may underlie the phenomenon of priming (Wiggs and Martin 1998). Models have been proposed to explain how a net reduction in cortical activity could allow for faster perceptual processing (i.e., priming) (Grill-Spector et al.
2006). Some studies have found a correlation between behavioral measures of priming and reduced activity in the prefrontal cortex (Maccotta and Buckner 2004). This result has not been found in ventral temporal cortex for either humans or nonhuman primates (Maccotta and Buckner 2004; McMahon and Olson 2007). Changes in cortex also underlie the related phenomenon of perceptual learning (Gilbert et al. 2009). Perceptual learning refers to gradual improvement in the detection or discrimination of visual stimuli with repeated practice. Changes in cortical circuitry during perceptual learning are detectable as early as primary visual cortex (V1) and may depend in part on structural changes in the long-range horizontal connections formed by V1 pyramidal cells (Gilbert and Li 2012). This circuitry is under the control of bottom-up processes as well as top-down influences related to attention and behavioral context (Gilbert and Li 2013).

Another early example of nondeclarative memory was simple classical conditioning, best illustrated in the literature of delay eyeblink conditioning. In delay conditioning, a neutral conditioned stimulus (CS), such as a tone, is presented just before an unconditioned stimulus (US), such as an airpuff to the eye. The two
stimuli then overlap and coterminate. Critically, delay eyeblink conditioning is intact in amnesia and is acquired independently of awareness (Gabrieli et al. 1995; Clark and Squire 1998). Participants who did not become aware of the relationship between the CS and US (i.e., that the CS predicts the US) learned just as well as volunteers who did become aware (Manns et al. 2001). Indeed, when CS –US association strength was varied (by changing the number of consecutive CS alone or CS –US presentations), the probability of a conditioned response increased with association strength but was inversely related to how much the US was expected (Clark et al. 2001). Largely on the basis of work with rabbits, delay eyeblink conditioning
proved to depend on the cerebellum and associated brain stem circuitry (Thompson and Krupa 1994; Thompson and Steinmetz 2009). Forebrain structures are not necessary for acquisition or retention of classically conditioned eyeblink responses.

Evaluative information, that is, whether a stimulus has positive or negative value, is acquired largely as nondeclarative memory. Biological study of this kind of memory has focused especially on the associative learning of fear (Davis 2006; Adolphs 2013; LeDoux 2014). Its nondeclarative status is illustrated by the fact that, in humans, associative fear learning proceeded normally after hippocampal lesions, even though the CS –US pairings could not be reported (Bechara et al. 1995). The amygdala has a critical role in fear learning, and its function (as well as its connectivity) appears to be conserved widely across species. In human neuroimaging studies, the amygdala was activated not only by fear but by strongly positive emotions as well (Hamann et al. 2002). Thus, the amygdala appears to be critical for associating sensory stimuli with stimulus valence. Ordinarily, animals express fear learning by freezing behavior (immobility). However, in a task where learned fear must instead be expressed by executing an avoidance response (an escape), freezing is maladaptive. In this case, prefrontal cortex inhibits defense behaviors (such as freezing) that are mediated by the amygdala, thereby allowing the animal to escape (Moscarello and
LeDoux 2013). Inhibitory action of the prefrontal cortex on the amygdala (from infralimbic prefrontal cortex in rat or from ventromedial prefrontal cortex in humans) has also been found to occur during the reversal of fear learning (i.e., extinction) (Milad and Quirk 2012). This work has relevance for clinical disorders, such as phobias and posttraumatic stress disorder (Davis 2011).

In addition to these functions, it is important to note that the amygdala also exerts a modulatory
influence on both declarative and nondeclarative memory. This role of the amygdala is the basis for the fact that emotionally arousing events are typically remembered better than emotionally neutral events. The mechanism for this effect is understood and depends on the release of stress hormones from the adrenal
gland, which affects the forebrain via the vagus nerve, the nucleus of the solitary tract, and the locus coeruleus. Ultimately, the effect is mediated by the amygdala through its basolateral nucleus (McGaugh and Roozendaal 2009).

The gradual trial-and-error learning that leads to the formation of habits was proposed in the 1980s to be supported by the striatum (Mishkin et al. 1984), and habit memory subsequently became an important focus of study (Yin and Knowlton 2006; Graybiel 2008; Liljeholm and O’Doherty 2012). Habit memory is characterized by automatized, repetitive behavior and, unlike declarative memory, is insensitive to changes in reward value (Dickinson 1985). An early demonstration of the distinction between declarative memory and habit memory came from rats with fornix lesions or caudate lesions tested on two ostensibly similar tasks. Rats with fornix lesions, which disrupt hippocampal function, failed when they needed to acquire a flexible behavior but succeeded when they needed to respond repetitively. Rats with caudate lesions showed the opposite pattern (Packard et al. 1989). A similar contrast between declarative memory and habit memory was shown for memory-impaired patients with hippocampal lesions and patients with nigrostriatal damage caused by Parkinson’s disease (Knowlton et al. 1996). In the task, probabilistic
classification, participants gradually learned which of two outcomes (sun or rain) would occur on each trial, given the particular combination of four cues that appeared. One, two, or three cues could appear on any trial, and each cue was independently and probabilistically related to the outcome. Patients with hippocampal lesions learned the task at a normal rate but could not report facts about the task. Parkinson
patients remembered the facts but could not learn the task.

Tasks that can be learned quickly by memorization can also be learned by a trial-and-error, habit-based strategy, albeit much more slowly. In one study, healthy volunteers were able to learn eight separate pairs of “junk objects” within a single session of 40 trials (i.e., choose the correct object in each pair). Two severely amnesic patients with large medial temporal lobe lesions also learned but only gradually, requiring more than 25 test sessions and 1000 trials (Bayley et al. 2005). Unlike declarative memory, which is flexible and can guide behavior in different contexts, the acquired knowledge in this case was rigidly organized. Patient performance collapsed when the task format was altered by asking participants to sort the 16 objects into correct and incorrect groups (a trivial task for controls). In addition, although by the end of training the patients were consistently performing at a high level, at the start of each test day they were never able to describe the task, the instructions, or the objects. Indeed, during testing they expressed surprise that they were performing so well. These findings provide particularly strong evidence for the distinction between declarative (conscious) and nondeclarative (unconscious) memory systems.
Reward-based learning of this kind depends on dopamine neurons in the midbrain (substantia nigra and ventral tegmental area), which project to the striatum and signal the information value of the reward (Schultz 2013). The dorsolateral striatum is crucial for the development of habits in coordination with other brain regions. Neurophysiological studies in mice during skill learning documented that the dorsolateral striatum was increasingly engaged as performance became more automatic and habit-like (Yin et al. 2009). In contrast, the dorsomedial striatum was engaged only early in training. Similarly, in rats learning a conditioned T-maze task, activity gradually increased in the dorsolateral striatum as training progressed, and this activity correlated with performance (Thorn et al. 2010). In the dorsomedial striatum, activity first
increased but then decreased as training progressed. Increased activity in the dorsolateral striatum during the later stages of habit formation occurred together with late-developing activity in infralimbic cortex (Smith and Graybiel 2013). Moreover, disruption of infralimbic cortex during late training prevented habit formation. Thus, these two regions (dorsolateral striatum and infralimbic cortex) appear to work together to support a fully formed habit.

THE RELATIONSHIP BETWEEN MEMORY SYSTEMS

The memory systems of the mammalian brain operate independently and in parallel to support behavior, and how one system or another gains control is a topic of considerable interest (Poldrack and Packard 2003; McDonald and Hong 2013; Packard and Goodman 2013). In some circumstances, memory systems are described as working cooperatively to optimize behavior and in other circumstances are described
as working competitively. However, it is not easy to pin down what should count for or against cooperativity, competition, or independence in any particular case. For example, the fact that the manipulation of one memory system can affect the operation of another has been taken as evidence for competition between systems (Schwabe 2013). Yet, even for systems that are strictly independent, the loss of one system would be expected to affect the operation of another system by affording it more opportunity to control behavior.

Much of the experimental work on the relationship between memory systems has focused on hippocampus-dependent declarative memory and dorsolateral striatum-dependent habit memory. In an illustrative study (Packard and McGaugh 1996), rats were trained in a fourarm, plus-shaped maze to go left, always beginning in the south arm (and with the north arm blocked). In this situation, rats could learn either a place (the left arm) or a response (turn left). To discriminate between these two possibilities, rats were occasionally started in the north arm (with the south arm now blocked). When these north-arm starts were given early in training, rats tended to enter the same arm that had been rewarded. They had learned a place. However, with extended training, rats tended to repeat the learned left-turn response and enter the unrewarded arm. Place learning was abolished early in training by lidocaine infusions into the hippocampus. In this case, rats showed no preference for either arm. Correspondingly, later in training, response learning was abolished by lidocaine infusions into the caudate nucleus. In this case, however, rats showed place responding. In other words, even though behavior later in training was guided by caudatedependent response learning, information remained available about place. When the caudate
nucleus was inactive, the parallel memory system supported by the hippocampus was unmasked.

A similar circumstance has been described in humans performing a virtual navigation task that could be solved by either a spatial or nonspatial (habit-like) strategy (Iaria et al. 2003). At the outset, spatial and nonspatial strategies were adopted equally often, but as training progressed participants tended to shift to a nonspatial strategy. Participants who used the spatial strategy (navigating in relation to landmarks)
showed increased activity in the right hippocampus early in training. Participants using the nonspatial strategy (counting maze arms) showed increased activity in the caudate nucleus, which emerged as training progressed. Several factors increase the tendency to adopt a striatal strategy, including stress (Kim et al. 2001; Schwabe 2013), psychopathology (Wilkins et al. 2013), aging (Konishi et al. 2013), and a history of alcohol and drug use (Bohbot et al. 2013). Prefrontal cortex may also be important in determining which memory system gains control over behavior (McDonald and Hong 2013).

Although many tasks can be acquired by more than one memory system, other tasks strongly favor one system over another. In this circumstance, engaging the less optimal system can interfere with performance. Thus, fornix lesions in rats facilitated acquisition of a caudate-dependent maze habit that required repeated visits to designated arms (Packard et al. 1989). The fornix lesion presumably disrupted
the tendency to use a nonoptimal declarative memory strategy. Similarly, a familiar feature of skill learning in humans is that trying to memorize, and use declarative memory, can disrupt performance.

Neuroimaging studies show that feedback guided learning typically engages the striatum. A task described earlier, probabilistic classification, requires participants to make a guess on each trial based on cues that are only partially reliable. Participants typically begin by trying to memorize the task structure but then turn to the habit-like strategy of accumulating response strength in association with the cues. Correspondingly, fMRI revealed activity in the medial temporal lobe early during learning (Poldrack
and Gabrieli 2001). As learning progressed, activity decreased in the medial temporal lobe, and activity increased in the striatum. Moreover, when the task was modified so as to encourage the use of declarative memory, less activity was observed in the striatum and more activity was observed in the medial temporal lobe.

CONCLUSION


The memory system framework is fundamental to the contemporary study of learning and memory. Within this framework, the various memory systems have distinct purposes and distinct anatomy, and different species can solve the same task using different systems. Interestingly, efforts have been made to account for some findings (e.g., priming or classification learning) with models based on a single system (Zaki et al. 2003; Zaki 2004; Berry et al. 2012). Yet, these accounts have difficulty explaining double dissociations (e.g., Packard et al. 1989; Knowlton et al. 1996), chance performance on tests of declarative memory when priming is intact (Hamann and Squire 1997b), and successful habit learning in the face of expressed
ignorance about the task (Bayley et al. 2005).

One implication of these facts is that the therapeutic targets for various kinds of memory disorders are quite different. For example, for extreme fear-based memories like phobias, one must target the amygdala, for strong habitbased memories like obsessive–compulsive disorders, one must target the striatum, and for severe forgetfulness, as in Alzheimer’s disease, one must target the hippocampus and adjacent structures. The notion of multiple memory systems is now widely accepted and establishes an
important organizing principle across species for investigations of the biology of memory.

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