The new approach to manipulating light, conducted by a group from France's Université de Nice-Sophia Antipolis and China's Xiamen University, uses little power, does not require an external electrical field, and operates at room temperature, making it more practical than many other slow light experiments. Putting the brakes on light can help scientists compare the characteristics of different light pulses more easily, which in turn can help them build highly sensitive instruments to measure extremely slow speeds and small movements, says Umberto Bortolozzo, one of the authors on the Optics Express paper. In a second paper, also published today and appearing in OSA's journal Optics Letters, Bortolozzo and colleagues from the Université de Nice-Sophia Antipolis and the University of Rochester describe an instrument that uses slow light to measure speeds less than one trillionth of a meter per second.

Scientists have known for a long time that a wave packet of light becomes more sluggish when it travels through matter, but the magnitude of this slow-down in typical materials such as glass or water is less than a factor of two. "The question is: can we do something to the matter in order to make light slow down much more considerably?" says Bortolozzo.

The key to achieving a significant drop-off in speed is to take advantage of the fact that when light travels as a pulse it is really a collection of waves, each having a slightly different frequency, says Bortolozzo. However, all the waves in the pulse must travel together. Scientists can design materials to be like obstacles courses that "trip up" some of the waves more than others. In order to exit the material together, the pulse must wait until it can reconstitute itself.

Other research groups have manipulated the properties of atomic vapors or crystal lattices to significantly slow light and, under certain circumstances, to temporarily "stop" it inside the medium. Bortolozzo's team instead used a liquid crystal similar to the materials used in LCD television and computer displays that could operate in a simple setup, does not require external voltages or magnetic fields, and works at room temperature and with very low optical power. They added a chemical component that twisted the liquid crystal molecules into a helical shape and then added dye molecules that nestled in the helical structures. The dye molecules change their shape when irradiated by light, altering the optical properties of the material and hence changing the relative velocities of the different wave components of the light pulse as it travelled through. In addition, the helical structure of the liquid crystal matrix ensures a long lifetime of the shape-shifted dyes, which makes it possible to "store" a light pulse in the medium and later release it on demand.

Although one of the ultimate goals of slow light research is to find a way to slow and store light pulses for optical communications, the long length of the light pulses used by Bortolozzo's team make such an application impractical. However, Bortolozzo says the team's technique is well suited to sensing and interferometry applications. In the Optics Letters,paper Bortolozzo and colleagues demonstrate how slow light can be used to build a highly sensitive instrument that works on a principle similar to the concept behind a police officer's radar gun. Radar guns catch speeders by detecting a shift in the frequency of radio waves (called a Doppler shift) that can be used to determine a car's velocity. Bortolozzo's team used slow light to detect a very slight Doppler shift in a pair of light beams.

The approach "allows us to measure extremely low speeds in only one second of measurement time," explains Bortolozzo. He says a next step will be for the team to test their dye and liquid crystal slow light approach in similar phase sensing applications. The team will also endeavor to extend the work to other molecular arrangements and different types of dye. "Realizing slow and stopped light in these media is very exciting both for the fundamental research that discovers such new effects in soft matter systems, and for the new possibilities that these investigations could open in the fields of remote sensing and optical storage," says Bortolozzo. Papers:

Tsar Bomba is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. Its October 30, 1961 test remains the most powerful artificial explosion in human history. It was also referred to as Kuz'kina Mat' ,referring to Nikita Khrushchev's promise to show the United States a "Kuz'kina Mat'" at the 1960 United Nations General Assembly.

The famous Russian idiom, which has been problematic for translators, literally meaning “to show somebody Kuzka's mother”, equates roughly with the English “We’ll show you!” Developed by the Soviet Union, the bomb had the yield of 50 to 58 megatons of TNT (210 to 240 PJ). Only one bomb of this type was ever officially built and it was tested on October 30, 1961, in the Novaya Zemlya archipelago, atSukhoy Nos.

The remaining bomb casings are located at the Russian Atomic Weapon Museum, Sarov (Arzamas-16), and the Museum of Nuclear Weapons, All-Russian Research Institute of Technical Physics, Snezhinsk (Chelyabinsk-70). Neither of these casings has the same antenna configuration as the device that was tested.

Many names are attributed to the Tsar Bomba in the literature: Project 7000; product code 202 ;article designations RDS-220 , RDS-202, RN202 (PH202), AN602 (AH602); codename Vanya; nicknames Big Ivan, Tsar Bomba, Kuz'kina Mat'.

 The term "Tsar Bomba" was coined in an analogy with two other massive Russian objects: the Tsar Kolokol (Tsar Bell) and the Tsar Pushka (Tsar Cannon). The CIA denoted the test as "JOE 111".

Researchers at the University of Rochester have measured for the first time light emitted by photoluminescence from a nano diamond levitating in free space. In a paper published this week in Optics Letters, they describe how they used a laser to trap nano diamonds in space, and -- using another laser -- caused the diamonds to emit light at given frequencies.

The experiment, led by Nick Vamivakas, an assistant professor of optics, demonstrates that it is possible to levitate diamonds as small as 100 nanometers (approximately one-thousandth the diameter of a human hair) in free space, by using a technique known as laser trapping.

"Now that we have shown we can levitate nanodiamonds and measure photoluminescence from defects inside the diamonds, we can start considering systems that could have applications in the field of quantum information and computing," said Vamivakas. He said an example of such a system would be an optomechanical resonator.

Vamivakas explained that optomechanical resonators are structures in which the vibrations of the system, in this case the trapped nanodiamond, can be controlled by light. "We are yet to explore this, but in theory we could encode information in the vibrations of the diamonds and extract it using the light they emit."

Possible avenues of interest in the long-term with these nano-optomechanical resonators include the creation of what are known as Schrödinger Cat states (macroscopic, or large-scale, systems that are in two quantum states at once). These resonators could also be used as extremely sensitive sensors of forces -- for example, to measure tiny displacements in the positions of metal plates or mirrors in configurations used in microchips and understand friction better on the nanoscale.

"Levitating particles such as these could have advantages over other optomechanical oscillators that exist, as they are not attached to any large structures," Vamivakas explained. "This would mean they are easier to keep cool and it is expected that fragile quantum coherence, essential for these systems to work, will last sufficiently long for experiments to be performed."

The future experiments that Vamivakas and his team are planning build on previous work at Rochester by Lukas Novotny, a co-author of the paper and now at ETH in Zurich, Switzerland. Novotny and his group showed previously that by tweaking the trapping laser's properties, a particle can be pushed towards its quantum ground state. By linking the laser cooling of the crystal resonator with the spin of the internal defect it should be possible to monitor the changes in spin configuration of the internal defect -- these changes are called Bohr spin quantum jumps -- via the mechanical resonator's vibrations. Vamivakas explained that experiments like this would expand what we know about the classical-quantum boundary and address fundamental physics questions.

The light emitted by the nanodiamonds is due to photoluminescence. The defects inside the nanodiamonds absorb photons from the second laser -- not the one that is trapping the diamonds -- which excites the system and changes the spin. The system then relaxes and other photons are emitted. This process is also known as optical pumping.

The defects come about because of nitrogen vacancies, which occur when one or more of the carbon atoms in diamond is replaced by a nitrogen atom. The chemical structure is such that at the nitrogen site it is possible to excite electrons, using a laser, between different available energy levels. Previous experiments have shown that these nitrogen vacancy centers in diamonds are good, stable sources of single photons, which is why the researchers were keen to levitate these particles.

Using lasers to trap ions, atoms and more recently larger particles is a well-established field of physics. Nanodiamonds, however, had never been levitated. To position these 100 nanometers diamonds in the correct spot an aerosol containing dissolved nanodiamonds sprays into a chamber about 10 inches in diameter, where the laser's focus point is located. The diamonds are attracted to this focus point and when they drift into this spot they are trapped by the laser. Graduate student Levi Neukirch explains that sometimes "it takes a couple of squirts and in a few minutes we have a trapped nanodiamond; other times I can be here for half an hour before any diamond gets caught. Once a diamond wanders into the trap we can hold it for hours."

The Rochester researchers collaborated on this paper with Lukas Novotny, formerly at the University of Rochester and now at ETH Zurich, Switzerland, and with Jan Gieseler and Romain Quidant, at ICFO in Barcelona, Spain.

The researchers acknowledge the support from the University of Rochester, the European Community's Seventh Framework Program, Fundació privada CELLEX and from the U.S. Department of Energy.

India on Saturday took a major leap towards completing its nuclear triad – the ability to launch strategic weapons from land, air and sea with the miniature reactor on board the country’s first indigenous nuclear-powered submarine “attaining criticality”. It means the reactor is in stable configuration producing constant power.

The 6,000 tonne Arihant, which means destroyer of enemies, will head for sea trials later this year. The submarine will kick off deterrent patrols, armed with nuclear warheads, in early 2014.The submarine will complete the sea-leg of India’s nuclear triad, giving it enduring nuclear strike and counter-strike capabilities.
It will be equipped with the K-15 missile, a closely guarded DRDO secret, capable of delivering a nuclear warhead up to 750 km away.

India already has the capability to carry out nuclear strikes with fighter planes and land-launched missiles. The Agni series of ballistic missiles and fighters planes such as Sukhoi-30MKIs and French-origin Mirage-2000s can deliver nuclear warheads. The Rafale fighters being acquired from France are also nuclear capable.India has 90-110 nuclear warheads, compared to 250 in the Chinese arsenal.

The United States, Russia, the UK, France and China are the only countries that can deliver nuclear warheads from a submarine.Experts say India’s submarine fleet should have at least 5 nuclear-powered ballistic missile submarines.Two more nuclear-powered submarines are in the works to reinforce India’s strategic deterrent force at sea.The INS Chakra, leased from Russia in January 2012, cannot deliver nuclear warheads in its current configuration. It only carries torpedoes, land-attack cruise missiles and anti-ship missiles.

A Maya pyramid beautifully decorated with a rare polychrome-painted stucco frieze was unearthed in July 2013 at the site of Holmul, a Classic Maya city in northeastern Peten region of Guatemala. The find came as archaeologist Francisco Estrada-Belli's team excavated in a tunnel left open by looters. The stucco relief stands along the exterior of a multi-roomed rectangular building, measuring 8m in length and 2m in height. Much of the building still remains encased under the rubble of a later 20m-high structure. The carving is painted in red, with details in blue, green and yellow.

"This is a unique find. It is a beautiful work of art and it tells us so much about the function and meaning of the building, which was what we were looking for," says Estrada-Belli. The carving depicts human figures in a mythological setting, suggesting these may be deified rulers. The team had hoped to find clues to the function of this building, since the unearthing of an undisturbed tomb last year. The burial contained an individual accompanied by 28 ceramic vessels and a wooden funerary mask.

An inscription below the figures tells us that this edifice was commissioned by the ruler of Naranjo, a powerful kingdom to the south of Holmul. In the dedication, king "Ajwosaj Chan K'inich" claims to have restored the local ruling line and patron deities. The images and glyphic text on the frieze also provide information about political actors in the Maya Lowlands well beyond this small kingdom. "One of the glyphs describes Ajwosaj as 'vassal of the Kanul king,' suggesting a much wider network of influences was being felt at Holmul. When this building was erected, Kanul kings were already on their way to controlling much of the lowlands, except Tikal of course," added Estrada-Belli.

The text places the building in the decade of the 590s, according to Alex Tokovinine, a Harvard University Maya epigrapher associated with the project. who has deciphered the text. "Ajwosaj was one of the greatest rulers of Naranjo. The new inscription provides the first glimpse of the remarkable extent of Ajwosaj's political and religious authority. It also reveals how a new order was literally imprinted on a broader landscape of local gods and ancestors," says Tokovinine.

During the Early Classic period (A. D. 300-550) the Tikal kings had established new dynasties and far-reaching alliances with kingdoms throughout the Maya Lowlands, perhaps thanks to a connection with Mesoamerica's greatest state, Teotihuacan. Tikal suffered a defeat in the year 562 by the Kanul "Snake" kingdom, which, for the following 180 years, would come to dominate most other Lowland kingdoms. An inscription at Naranjo indicates that Kanul king K'altuun Hix had overseen the accession of Ajwosaj, as early as the year 545.

The relief depicts three human figures wearing elaborate bird headdresses and jade jewels seated cross-legged over the head of a mountain spirit known as a witz ("mountain"). A cartouche on the headdress contains glyphs identifying each individual by name. The central figure's name is the only readable one: OchChan Yopaat, meaning "The Storm God enters the sky. " Two feathered serpents emerge from the mountain spirit below the main character and form an arch with their bodies. Under each of them is a seated figure of an aged god holding a sign that reads "First tamale. " In front of the serpents' mouths are the two additional human figures, also seated on mountain spirit heads.

A band of about 30 incised glyphs adorns the bottom of the frieze. The legible parts mention the actions of Naranjo king Ajwosaj, who put the king's house in order," put Och Chan Yopaat (the central figure in the frieze) in order, and put several local patron gods in order.

The tomb associated with the building was found in a cavity dug into the stairway leading up to the building. The skeleton of an adult male and his ceramic offering were preserved by large limestone slabs that kept the tomb free of debris. His incisor and canine teeth has been drilled and filled with jade beads. The decayed remains of a wooden mask, perhaps originally worn as a pectoral, were found on his chest. With it were two miniature flower-shaped ear spools.

The number of vessels in the tomb as well as their iconography bore clear references to the nine lords of the underworld as well as to the aged sun god of the underworld. There were two sets of nine polychrome-painted bowls decorated with the water lily motif, each made by a different artist. There were also nine red-painted plates and one spouted tripod plate decorated with the image of the god of the underworld emerging from a shell. Because of the unusually high number of vessels and the jade dental decorations, Estrada-Belli believes this individual may have been a member of the ruling class at Holmul; he had planned this year's excavation to search for more clues about the man and the period in which he had lived.

The team hopes to return to the area in 2014 to continue exploring and to preserve this building. This year's investigation was endorsed by Guatemala's Ministry of Culture with funding from Guatemala's PACUNAM foundation and the U. S. -based Alphawood Foundation with additional support from Boston University, National Geographic Society/Waitt Grants Program, and private donors.

Francisco Estrada-Belli

Francisco Estrada-Belli is an Italian-Guatemalan archaeologist affiliated with Boston University and the American Museum of Natural History, who is currently teaching at Tulane University. He received a Ph. D. degree from Boston University in 1998. Since 2000 he has directed the Holmul Archaeological Project, a multi-disciplinary investigation of early Maya culture in Guatemala. He is author of numerous scholarly articles on the Maya including the recent book "The First Maya Civilization. Ritual and Power before the Classic period. "He is a National Geographic explorer, having received 13 research grants from the National Geographic Society, and a Fellow of the Society of Antiquaries of London. He is co-founder of the Maya Archaeology Initiative, a nonprofit for heritage preservation and education in the Maya Biosphere of Guatemala.

For more information, see National Geographic's news story at:

http://news.nationalgeographic.com/news/2013/08/pictures/130807-maya-frieze-discovered-holmul-guatemala-archaeology
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Astronomers using NASA's Hubble Space Telescope have solved a 40-year mystery on the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around our Milky Way galaxy.

The Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way, are at the head of the gaseous stream. Since the stream's discovery by radio telescopes in the early 1970s, astronomers have wondered whether the gas comes from one or both of the satellite galaxies. Now, new Hubble observations reveal that most of the gas was stripped from the Small Magellanic Cloud about 2 billion years ago, and a second region of the stream originated more recently from the Large Magellanic Cloud.

A team of astronomers, led by Andrew J. Fox of the Space Telescope Science Institute in Baltimore, Md., and the European Space Agency, determined the source of the gas filament by using Hubble's Cosmic Origins Spectrograph (COS) to measure the amount of heavy elements, such as oxygen and sulfur, at six locations along the Magellanic Stream. COS observed faraway quasars whose emitted light passes through the stream and detected these elements from the way they absorb ultraviolet light. Quasars are the brilliant cores of active galaxies.Fox's team found a low amount of oxygen and sulfur along most of the stream, matching the levels in the Small Magellanic Cloud about 2 billion years ago, when the gaseous ribbon was thought to have been formed.

In a surprising twist, the team discovered a much higher level of sulfur in a region closer to the Magellanic Clouds. "We're finding a consistent amount of heavy elements in the stream until we get very close to the Magellanic Clouds, and then the heavy element levels go up," said Fox. "This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy more recently."This discovery was a wrinkle Fox's team didn't expect, because computer models of the stream predicted that the gas came entirely out of the Small Magellanic Cloud, which has less gravity than its more massive cousin.

"Only Hubble can measure these abundances," Fox explained. "You have to go to space because the absorption lines we need to measure these abundances are all in the ultraviolet, and Earth's atmosphere absorbs ultraviolet light."

Astronomers have debated whether the two Magellanic Clouds are on their first pass near our Milky Way or are bound to it.

"What's interesting is that all the other nearby satellite galaxies of the Milky Way have lost their gas," Fox said. "The Magellanic Clouds have been able to retain their gas and are still forming stars because they're more massive than the other satellites. However, as they're now approaching the Milky Way, they're feeling its gravity more and also encountering its halo of hot gas, which puts pressure on them. That process, together with the gravitational tug-of-war between the Magellanic Clouds, leads to the production of the stream. You're seeing material stripped out of the Clouds as they come in toward the Milky Way."

Ultimately, the gaseous stream may rain down onto the Milky Way's disk, fueling the birth of new stars. This infusion of fresh gas is part of one process that triggers star formation in a galaxy. Astronomers want to know the origin of that wayward gas in order to more fully understand how galaxies make new stars.

"We want to understand how galaxies like the Milky Way strip the gas from small galaxies that fall into them and use that to form new stars," Fox explained. "This seems like it's an episodic process. It's not a smooth process where a slow stream of gas comes in continuously. Instead, once in a while a large gas cloud falls in. We've got a way of testing that here, where two galaxies are coming in. We have shown which of them is producing the gas that ultimately will fall into the Milky Way."

The team reported its results in two papers that appeared in the Aug. 1 issue of The Astrophysical Journal. Fox is the lead author of one paper; the other paper's lead author is Philipp Richter of the University of Potsdam in Germany
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New Century Global Centre is a multipurpose building in the Tianfu New Area of Chengdu, China. The 100 m (330 ft) structure is 500 by 400 m  with 1,700,000 square metres of floor space, making it the world's biggest building measured by floor space.The Boeing Everett Factory in Everett, Washington has the largest volume, and the Aalsmeer Flower Auction Building in Aalsmeer, Netherlands, has the largest footprint

Nearly 4,300,000 sq ft of the building will be devoted to shopping. It will also house offices, conference rooms, a university complex, two commercial centres, hotels, an IMAXcinema, a "Mediterranean village", a pirate ship and skating rink. The centrepiece of the building will be a 5,000 m2 (54,000 sq ft) artificial beach, a giant 150 by 40 m (490 by 130 ft) screen will form the horizon and offer sunrises and sunsets. The building will face the Chengdu Contemporary Arts Centre, designed by award-winning British-Iraqi architect Zaha Hadid.

The main pool will have a stage that extends out over the pool each night for concerts. A stand has been built overlooking the pool with a food court and entrance underneath at the floor level.The new Intercontinental Hotel will feature 1,009 rooms that are spread over 6 x 8 story blocks around the edge of the complex.While parts of the shopping area are open, the main opening is planned for 22 August 2013.                   

In 1935, the United States Congress announced the first Sunday of August as the National Friendship Day and declared it to be a holiday in honor of friends.

Women's Friendship Day is celebrated on the third Sunday of September.

Best Friends Weekend is an occasion established by the Best Friends Animal Society. It is celebrated every year from June 23 - June 25 to honor and protect the rights of animals. The first day of the weekend is called Best Friends' Day.

'D del Amigo' (The Spanish Friend's Day) is a celebration of friendship, held annually on July 20, mainly in Argentina and Uruguay.

Old Friends, New Friends Week is the third week of May.

The whole of February is designated as the International Friendship Month.

In 1997, the United Nations named Winnie - the Pooh, the famous cartoon character as the world's Ambassador of Friendship.

The immortal song "With a Little Help from My Friends" by Beatles, that deals with the theme of friendship, was released in 1967.

Monash University researchers have brought next generation energy storage closer with an engineering first -- a graphene-based device that is compact, yet lasts as long as a conventional battery.Published today in Science, a research team led by Professor Dan Li of the Department of Materials Engineering has developed a completely new strategy to engineer graphene-based supercapacitors (SC), making them viable for widespread use in renewable energy storage, portable electronics and electric vehicles.

SCs are generally made of highly porous carbon impregnated with a liquid electrolyte to transport the electrical charge. Known for their almost indefinite lifespan and the ability to re-charge in seconds, the drawback of existing SCs is their low energy-storage-to-volume ratio -- known as energy density. Low energy density of five to eight Watt-hours per litre, means SCs are unfeasibly large or must be re-charged frequently.Professor Li's team has created an SC with energy density of 60 Watt-hours per litre -- comparable to lead-acid batteries and around 12 times higher than commercially available SCs.

"It has long been a challenge to make SCs smaller, lighter and compact to meet the increasingly demanding needs of many commercial uses," Professor Li said.

Graphene, which is formed when graphite is broken down into layers one atom thick, is very strong, chemically stable and an excellent conductor of electricity.To make their uniquely compact electrode, Professor Li's team exploited an adaptive graphene gel film they had developed previously. They used liquid electrolytes -- generally the conductor in traditional SCs -- to control the spacing between graphene sheets on the sub-nanometre scale. In this way the liquid electrolyte played a dual role: maintaining the minute space between the graphene sheets and conducting electricity.

Unlike in traditional 'hard' porous carbon, where space is wasted with unnecessarily large 'pores', density is maximised without compromising porosity in Professor Li's electrode.To create their material, the research team used a method similar to that used in traditional paper making, meaning the process could be easily and cost-effectively scaled up for industrial use. These macroscopic graphene material that is a step beyond what has been achieved previously. It is almost at the stage of moving from the lab to commercial development.

The phenomenon of false memory has been well-documented: In many court cases, defendants have been found guilty based on testimony from witnesses and victims who were sure of their recollections, but DNA evidence later overturned the conviction.

The cells where memory traces are stored
in the mouse hippocampus.

In a step toward understanding how these faulty memories arise, MIT neuroscientists have shown that they can plant false memories in the brains of mice. They also found that many of the neurological traces of these memories are identical in nature to those of authentic memories.

"Whether it's a false or genuine memory, the brain's neural mechanism underlying the recall of the memory is the same," says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and senior author of a paper describing the findings in the July 25 edition of Science.

The study also provides further evidence that memories are stored in networks of neurons that form memory traces for each experience we have -- a phenomenon that Tonegawa's lab first demonstrated last year.

Neuroscientists have long sought the location of these memory traces, also called engrams. In the pair of studies, Tonegawa and colleagues at MIT's Picower Institute for Learning and Memory showed that they could identify the cells that make up part of an engram for a specific memory and reactivate it using a technology called optogenetics.

Lead authors of the paper are graduate student Steve Ramirez and research scientist Xu Liu. Other authors are technical assistant Pei-Ann Lin, research scientist Junghyup Suh, and postdocs Michele Pignatelli, Roger Redondo and Tomas Ryan.

Seeking the engram

Episodic memories -- memories of experiences -- are made of associations of several elements, including objects, space and time. These associations are encoded by chemical and physical changes in neurons, as well as by modifications to the connections between the neurons.

Where these engrams reside in the brain has been a longstanding question in neuroscience. "Is the information spread out in various parts of the brain, or is there a particular area of the brain in which this type of memory is stored? This has been a very fundamental question," Tonegawa says.

In the 1940s, Canadian neurosurgeon Wilder Penfield suggested that episodic memories are located in the brain's temporal lobe. When Penfield electrically stimulated cells in the temporal lobes of patients who were about to undergo surgery to treat epileptic seizures, the patients reported that specific memories popped into mind. Later studies of the amnesiac patient known as "H.M." confirmed that the temporal lobe, including the area known as the hippocampus, is critical for forming episodic memories.

However, these studies did not prove that engrams are actually stored in the hippocampus, Tonegawa says. To make that case, scientists needed to show that activating specific groups of hippocampal cells is sufficient to produce and recall memories.

To achieve that, Tonegawa's lab turned to optogenetics, a new technology that allows cells to be selectively turned on or off using light.

For this pair of studies, the researchers engineered mouse hippocampal cells to express the gene for channelrhodopsin, a protein that activates neurons when stimulated by light. They also modified the gene so that channelrhodopsin would be produced whenever the c-fos gene, necessary for memory formation, was turned on.

In last year's study, the researchers conditioned these mice to fear a particular chamber by delivering a mild electric shock. As this memory was formed, the c-fos gene was turned on, along with the engineered channelrhodopsin gene. This way, cells encoding the memory trace were "labeled" with light-sensitive proteins.

The next day, when the mice were put in a different chamber they had never seen before, they behaved normally. However, when the researchers delivered a pulse of light to the hippocampus, stimulating the memory cells labeled with channelrhodopsin, the mice froze in fear as the previous day's memory was reactivated.

"Compared to most studies that treat the brain as a black box while trying to access it from the outside in, this is like we are trying to study the brain from the inside out," Liu says. "The technology we developed for this study allows us to fine-dissect and even potentially tinker with the memory process by directly controlling the brain cells."

Incepting false memories

That is exactly what the researchers did in the new study -- exploring whether they could use these reactivated engrams to plant false memories in the mice's brains.

First, the researchers placed the mice in a novel chamber, A, but did not deliver any shocks. As the mice explored this chamber, their memory cells were labeled with channelrhodopsin. The next day, the mice were placed in a second, very different chamber, B. After a while, the mice were given a mild foot shock. At the same instant, the researchers used light to activate the cells encoding the memory of chamber A.

On the third day, the mice were placed back into chamber A, where they now froze in fear, even though they had never been shocked there. A false memory had been incepted: The mice feared the memory of chamber A because when the shock was given in chamber B, they were reliving the memory of being in chamber A.

Moreover, that false memory appeared to compete with a genuine memory of chamber B, the researchers found. These mice also froze when placed in chamber B, but not as much as mice that had received a shock in chamber B without having the chamber A memory activated.

The researchers then showed that immediately after recall of the false memory, levels of neural activity were also elevated in the amygdala, a fear center in the brain that receives memory information from the hippocampus, just as they are when the mice recall a genuine memory.

The MIT team is now planning further studies of how memories can be distorted in the brain.

"Now that we can reactivate and change the contents of memories in the brain, we can begin asking questions that were once the realm of philosophy," Ramirez says. "Are there multiple conditions that lead to the formation of false memories? Can false memories for both pleasurable and aversive events be artificially created? What about false memories for more than just contexts -- false memories for objects, food or other mice? These are the once seemingly sci-fi questions that can now be experimentally tackled in the lab.
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