Manipulating memory with light: Scientists erase specific memories in mice

Manipulating memory with light: Scientists erase specific memories in mice

  8:13:00 PM    Science Lover

---

Just look into the light: not quite, but researchers at the UC Davis Center for Neuroscience and Department of Psychology have used light to erase specific memories in mice, and proved a basic theory of how different parts of the brain work together to retrieve episodic memories.

During memory retrieval, cells in the hippocampus
connect to cells in the brain cortex.

Credit: Photo illustration by Kazumasa Tanaka and 
Brian Wiltgen/UC Davis

Optogenetics, pioneered by Karl Diesseroth at Stanford University, is a new technique for manipulating and studying nerve cells using light. The techniques of optogenetics are rapidly becoming the standard method for investigating brain function.

Kazumasa Tanaka, Brian Wiltgen and colleagues at UC Davis applied the technique to test a long-standing idea about memory retrieval. For about 40 years, Wiltgen said, neuroscientists have theorized that retrieving episodic memories -- memories about specific places and events -- involves coordinated activity between the cerebral cortex and the hippocampus, a small structure deep in the brain.

"The theory is that learning involves processing in the cortex, and the hippocampus reproduces this pattern of activity during retrieval, allowing you to re-experience the event," Wiltgen said. If the hippocampus is damaged, patients can lose decades of memories.

But this model has been difficult to test directly, until the arrival of optogenetics.

Wiltgen and Tanaka used mice genetically modified so that when nerve cells are activated, they both fluoresce green and express a protein that allows the cells to be switched off by light. They were therefore able both to follow exactly which nerve cells in the cortex and hippocampus were activated in learning and memory retrieval, and switch them off with light directed through a fiber-optic cable.

They trained the mice by placing them in a cage where they got a mild electric shock. Normally, mice placed in a new environment will nose around and explore. But when placed in a cage where they have previously received a shock, they freeze in place in a "fear response."

Tanaka and Wiltgen first showed that they could label the cells involved in learning and demonstrate that they were reactivated during memory recall. Then they were able to switch off the specific nerve cells in the hippocampus, and show that the mice lost their memories of the unpleasant event. They were also able to show that turning off other cells in the hippocampus did not affect retrieval of that memory, and to follow fibers from the hippocampus to specific cells in the cortex.

"The cortex can't do it alone, it needs input from the hippocampus," Wiltgen said. "This has been a fundamental assumption in our field for a long time and Kazu’s data provides the first direct evidence that it is true."

They could also see how the specific cells in the cortex were connected to the amygdala, a structure in the brain that is involved in emotion and in generating the freezing response.

Co-authors are Aleksandr Pevzner, Anahita B. Hamidi, Yuki Nakazawa and Jalina Graham, all at the Center for Neuroscience. The work was funded by grants from the Whitehall Foundation, McKnight Foundation, Nakajima Foundation and the National Science Foundation.

Story Source:
The above story is based on materials provided by University of California - Davis. Note: Materials may be edited for content and length.

Journal Reference:
Kazumasa Z. Tanaka, Aleksandr Pevzner, Anahita B. Hamidi, Yuki Nakazawa, Jalina Graham, Brian J. Wiltgen. Cortical Representations Are Reinstated by the Hippocampus during Memory Retrieval. Neuron, 2014 DOI: 10.1016/j.neuron.2014.09.037

Read More

Incredibly light, strong materials recover original shape after being smashed

Incredibly light, strong materials recover original shape after being smashed

  4:10:00 PM    Science Lover

---

Materials scientists have developed a method for creating new structural materials by taking advantage of the unusual properties that solids can have at the nanometer scale. They have used the method to produce a ceramic (e.g., a piece of chalk or a brick) that contains about 99.9 percent air yet is incredibly strong and can recover its original shape after being smashed by more than 50 percent.

This sequence shows how the Greer Lab's three-dimensional,
ceramic nanolattices can recover after being compressed by
more than 50 percent. Clockwise, from left to right, an alumina
nanolattice before compression, during compression, fully
compressed, and recovered following compression.

Credit: Lucas Meza/Caltech

Imagine a balloon that could float without using any lighter-than-air gas. Instead, it could simply have all of its air sucked out while maintaining its filled shape. Such a vacuum balloon, which could help ease the world's current shortage of helium, can only be made if a new material existed that was strong enough to sustain the pressure generated by forcing out all that air while still being lightweight and flexible. 

Caltech materials scientist Julia Greer and her colleagues are on the path to developing such a material and many others that possess unheard-of combinations of properties. For example, they might create a material that is thermally insulating but also extremely lightweight, or one that is simultaneously strong, lightweight, and nonbreakable -- properties that are generally thought to be mutually exclusive.

Greer's team has developed a method for constructing new structural materials by taking advantage of the unusual properties that solids can have at the nanometer scale, where features are measured in billionths of meters. In a paper published in the September 12 issue of the journal Science, the Caltech researchers explain how they used the method to produce a ceramic (e.g., a piece of chalk or a brick) that contains about 99.9 percent air yet is incredibly strong, and that can recover its original shape after being smashed by more than 50 percent.

"Ceramics have always been thought to be heavy and brittle," says Greer, a professor of materials science and mechanics in the Division of Engineering and Applied Science at Caltech. "We're showing that in fact, they don't have to be either. This very clearly demonstrates that if you use the concept of the nanoscale to create structures and then use those nanostructures like LEGO to construct larger materials, you can obtain nearly any set of properties you want. You can create materials by design."

The researchers use a direct laser writing method called two-photon lithography to "write" a three-dimensional pattern in a polymer by allowing a laser beam to crosslink and harden the polymer wherever it is focused. The parts of the polymer that were exposed to the laser remain intact while the rest is dissolved away, revealing a three-dimensional scaffold. That structure can then be coated with a thin layer of just about any kind of material -- a metal, an alloy, a glass, a semiconductor, etc. Then the researchers use another method to etch out the polymer from within the structure, leaving a hollow architecture.

The applications of this technique are practically limitless, Greer says. Since pretty much any material can be deposited on the scaffolds, the method could be particularly useful for applications in optics, energy efficiency, and biomedicine. For example, it could be used to reproduce complex structures such as bone, producing a scaffold out of biocompatible materials on which cells could proliferate.

In the latest work, Greer and her students used the technique to produce what they call three-dimensional nanolattices that are formed by a repeating nanoscale pattern. After the patterning step, they coated the polymer scaffold with a ceramic called alumina (i.e., aluminum oxide), producing hollow-tube alumina structures with walls ranging in thickness from 5 to 60 nanometers and tubes from 450 to 1,380 nanometers in diameter.

Greer's team next wanted to test the mechanical properties of the various nanolattices they created. Using two different devices for poking and prodding materials on the nanoscale, they squished, stretched, and otherwise tried to deform the samples to see how they held up.

They found that the alumina structures with a wall thickness of 50 nanometers and a tube diameter of about 1 micron shattered when compressed. That was not surprising given that ceramics, especially those that are porous, are brittle. However, compressing lattices with a lower ratio of wall thickness to tube diameter -- where the wall thickness was only 10 nanometers -- produced a very different result.

"You deform it, and all of a sudden, it springs back," Greer says. "In some cases, we were able to deform these samples by as much as 85 percent, and they could still recover."

To understand why, consider that most brittle materials such as ceramics, silicon, and glass shatter because they are filled with flaws -- imperfections such as small voids and inclusions. The more perfect the material, the less likely you are to find a weak spot where it will fail. Therefore, the researchers hypothesize, when you reduce these structures down to the point where individual walls are only 10 nanometers thick, both the number of flaws and the size of any flaws are kept to a minimum, making the whole structure much less likely to fail.

"One of the benefits of using nanolattices is that you significantly improve the quality of the material because you're using such small dimensions," Greer says. "It's basically as close to an ideal material as you can get, and you get the added benefit of needing only a very small amount of material in making them."

The Greer lab is now aggressively pursuing various ways of scaling up the production of these so-called meta-materials.

Story Source: http://www.sciencedaily.com/releases/2014/09/140911135450.htm

Read More

20 Things You Didn't Know About... Time

20 Things You Didn't Know About... Time

  8:02:00 PM    Science Lover

---

The beginning, the end, and the funny habits of our favorite ticking force.

1  “Time is an illusion. Lunchtime doubly so,” joked Douglas Adams in The Hitchhiker’s Guide to the Galaxy. Scientists aren’t laughing, though. Some speculative new physics theories suggest that time emerges from a more fundamental—and timeless—reality.

2  Try explaining that when you get to work late. The average U.S. city commuter loses 38 hours a year to traffic delays.

3  Wonder why you have to set your clock ahead in March?Daylight Saving Time began as a joke by Benjamin Franklin, who proposed waking people earlier on bright summer mornings so they might work more during the day and thus save candles. It was introduced in the U.K. in 1917 and then spread around the world.

4  Green days. The Department of Energy estimates that electricity demand drops by 0.5 percent during Daylight Saving Time, saving the equivalent of nearly 3 million barrels of oil.

5  By observing how quickly bank tellers made change, pedestrians walked, and postal clerks spoke, psychologists determined that the three fastest-paced U.S. cities are Boston, Buffalo, and New York.

6  The three slowest? Shreveport, Sacramento, and L.A.

7  One second used to be defined as 1/86,400 the length of a day. However, Earth’s rotation isn’t perfectly reliable. Tidal friction from the sun and moon slows our planet and increases the length of a day by 3 milli­seconds per century.

8  This means that in the time of the dinosaurs, the day was just 23 hours long.

9  Weather also changes the day. During El Niño events, strong winds can slow Earth’s rotation by a fraction of a milli­second every 24 hours.

10  Modern technology can do better. In 1972 a network of atomic clocks in more than 50 countries was made the final authority on time, so accurate that it takes 31.7 million years to lose about one second.

11  To keep this time in sync with Earth’s slowing rotation, a “leap second” must be added every few years, most recently this past New Year’s Eve.

12  The world’s most accurate clock, at the National Institute of Standards and Technology in Colorado, measures vibrations of a single atom of mercury. In a billion years it will not lose one second.

13  Until the 1800s, every village lived in its own little time zone, with clocks synchronized to the local solar noon.

14  This caused havoc with the advent of trains and timetables. For a while watches were made that could tell both local time and “railway time.”

15  On November 18, 1883, American railway companies forced the national adoption of standardized time zones.

16  Thinking about how railway time required clocks in different places to be synchronized may have inspired Einstein to develop his theory of relativity, which unifies space and time.

17  Einstein showed that gravity makes time run more slowly. Thus airplane passengers, flying where Earth’s pull is weaker, age a few extra nano­seconds each flight.

18  According to quantum theory, the shortest moment of time that can exist is known as Planck time, or 0.0000000000000000000000000000000000000000001 second.

19  Time has not been around forever. Most scientists believe it was created along with the rest of the universe in the Big Bang, 13.7 billion years ago.

20  There may be an end of time. Three Spanish scientists posit that the observed acceleration of the expanding cosmos is an illusion caused by the slowing of time. According to their math, time may eventually stop, at which point everything will come to a standstill.

Read More

Engineers build world's smallest, fastest nanomotor: Can fit inside a single cell

Engineers build world's smallest, fastest nanomotor: Can fit inside a single cell

  7:47:00 PM    Science Lover

---

Researchers at the Cockrell School of Engineering at The University of Texas at Austin have built the smallest, fastest and longest-running tiny synthetic motor to date. The team's nanomotor is an important step toward developing miniature machines that could one day move through the body to administer insulin for diabetics when needed, or target and treat cancer cells without harming good cells.

Simple nanomotor. Credit: Image courtesy of University of Texas at Austin

With the goal of powering these yet-to-be invented devices, UT Austin engineers focused on building a reliable, ultra-high-speed nanomotor that can convert electrical energy into mechanical motion on a scale 500 times smaller than a grain of salt.

Mechanical engineering assistant professor Donglei "Emma" Fan led a team of researchers in the successful design, assembly and testing of a high-performing nanomotor in a nonbiological setting. The team's three-part nanomotor can rapidly mix and pump biochemicals and move through liquids, which is important for future applications. The team's study was published in a recent issue of Nature Communications.

Fan and her team are the first to achieve the extremely difficult goal of designing a nanomotor with large driving power.

With all its dimensions under 1 micrometer in size, the nanomotor could fit inside a human cell and is capable of rotating for 15 continuous hours at a speed of 18,000 RPMs, the speed of a motor in a jet airplane engine. Comparable nanomotors run significantly more slowly, from 14 RPMs to 500 RPMs, and have only rotated for a few seconds up to a few minutes.

Looking forward, nanomotors could advance the field of nanoelectromechanical systems (NEMS), an area focused on developing miniature machines that are more energy efficient and less expensive to produce. In the near future, the Cockrell School researchers believe their nanomotors could provide a new approach to controlled biochemical drug delivery to live cells.

To test its ability to release drugs, the researchers coated the nanomotor's surface with biochemicals and initiated spinning. They found that the faster the nanomotor rotated, the faster it released the drugs.

"We were able to establish and control the molecule release rate by mechanical rotation, which means our nanomotor is the first of its kind for controlling the release of drugs from the surface of nanoparticles," Fan said. "We believe it will help advance the study of drug delivery and cell-to-cell communications."

The researchers address two major issues for nanomotors so far: assembly and controls. The team built and operated the nanomotor using a patent-pending technique that Fan invented while studying at Johns Hopkins University. The technique relies on AC and DC electric fields to assemble the nanomotor's parts one by one.

In experiments, the researchers used the technique to turn the nanomotors on and off and propel the rotation either clockwise or counterclockwise. The researchers found that they could position the nanomotors in a pattern and move them in a synchronized fashion, which makes them more powerful and gives them more flexibility.

Fan and her team plan to develop new mechanical controls and chemical sensing that can be integrated into nanoelectromechanical devices. But first they plan to test their nanomotors near a live cell, which will allow Fan to measure how they deliver molecules in a controlled fashion.

Video: 

Read More

Sugar-powered biobattery has 10 times the energy storage of lithium: Your smartphone might soon run on enzymes

Sugar-powered biobattery has 10 times the energy storage of lithium: Your smartphone might soon run on enzymes

  7:33:00 PM    Science Lover

---

As you probably know, from sucking down cans of Coke and masticating on candy, sugar — glucose, fructose, sucrose, dextrose — is an excellent source of energy. Biologically speaking, sugar molecules are energy-dense, easy to transport, and cheap to digest. There is a reason why almost every living cell on Earth generates its energy (ATP) from glucose. Now, researchers at Virginia Tech have successfully created a sugar-powered fuel cell that has an energy storage density of 596 amp-hours per kilo — or “one order of magnitude” higher than lithium-ion batteries. This fuel cell is refillable with a solution of maltodextrin, and its only by products are electricity and water. The chief researcher, Y.H. Percival Zhang, says the tech could be commercialized in as soon as three years.

Now, it’s not exactly news that sugar is an excellent energy source. As a culture we’ve probably known about it since before we were Homo sapiens. The problem is, unless you’re a living organism or some kind of incendiary device, extracting that energy is difficult. In nature, an enzymatic pathway is used — a production line of tailor-made enzymes that meddle with the glucose molecules until they become ATP. Because it’s easy enough to produce enzymes in large quantities, researchers have tried to create fuel cells that use artificial “metabolism” to break down glucose into electricity (biobatteries), but it has historically proven very hard to find the right pathway for maximum efficiency and to keep the enzymes in the right place over a long period of time.

A diagram of the enzymatic fuel cell. The little Pac-Man things are enzymes.

Now, however, Zhang and friends at Virginia Tech appear to have built a high-density fuel cell that uses an enzymatic pathway to create a lot of electricity from glucose. There doesn’t seem to be much information on how stable this biobattery is over multiple refills, but if Zhang thinks it could be commercialized in three years, that’s a very good sign. Curiously, the research paper says that the enzymes are non-immobilized — meaning Zhang found a certain battery chemistry that doesn’t require the enzymes to be kept in place… or, alternatively, that it will only work for a very short time.

The Virginia Tech biobattery uses 13 enzymes, plus air (it’s an air-breathing biobattery), to produce nearly 24 electrons from a single glucose unit. This equates to a power output of 0.8 mW/cm, current density of 6 mA/cm, and energy storage density of 596 Ah/kg. This last figure is impressive, at roughly 10 times the energy density of the lithium-ion batteries in your mobile devices. [Research paper: doi:10.1038/ncomms4026 - "A high-energy-density sugar biobattery based on a synthetic enzymatic pathway"]

If Zhang’s biobatteries pan out, you might soon be recharging your smartphone by pouring in a solution of 15% maltodextrin. That battery would not only be very safe (it produces water and electricity), but very cheap to run and very green. This seems to fit in perfectly with Zhang’s homepage, which talks about how his main goals in life are replacing crude oil with sugar, and feeding the world.

The other area in which biobatteries might be useful is powering implanted devices, such as pacemakers — or, in the future, subcutaneous sensors and computers. Such a biobattery could feed on the glucose in your bloodstream, providing an endless supply of safe electricity for the myriad implants that futuristic technocrats will surely have. 

Read More

Lithium-sulfur batteries last longer with nanomaterial-packed cathode

Lithium-sulfur batteries last longer with nanomaterial-packed cathode

  8:49:00 PM    Science Lover

---

Electric vehicles could travel farther and more renewable energy could be stored with lithium-sulfur batteries that use a unique powdery nanomaterial.

Pacific Northwest National Laboratory developed
a nickel-based metal organic framework, shown here
in an illustration, to hold onto polysulfide molecules
in the cathodes of lithium-sulfur batteries and extend
the batteries' lifespans. The colored spheres in this i
mage represent the 3D material's tiny pores into with
the polysulfides become trapped.
Credit: Pacific Northwest National Laboratory

Researchers added the powder, a kind of nanomaterial called a metal organic framework, to the battery's cathode to capture problematic polysulfides that usually cause lithium-sulfur batteries to fail after a few charges. A paper describing the material and its performance was published online April 4 in the American Chemical Society journal Nano Letters.

"Lithium-sulfur batteries have the potential to power tomorrow's electric vehicles, but they need to last longer after each charge and be able to be repeatedly recharged," said materials chemist Jie Xiao of the Department of Energy's Pacific Northwest National Laboratory. "Our metal organic framework may offer a new way to make that happen."

Today's electric vehicles are typically powered by lithium-ion batteries. But the chemistry of lithium-ion batteries limits how much energy they can store. As a result, electric vehicle drivers are often anxious about how far they can go before needing to charge. One promising solution is the lithium-sulfur battery, which can hold as much as four times more energy per mass than lithium-ion batteries. This would enable electric vehicles to drive farther on a single charge, as well as help store more renewable energy. The down side of lithium-sulfur batteries, however, is they have a much shorter lifespan because they can't currently be charged as many times as lithium-ion batteries.

Energy Storage 101

The reason can be found in how batteries work. Most batteries have two electrodes: one is positively charged and called a cathode, while the second is negative and called an anode. Electricity is generated when electrons flow through a wire that connects the two. To control the electrons, positively charged atoms shuffle from one electrode to the other through another path: the electrolyte solution in which the electrodes sit.

The lithium-sulfur battery's main obstacles are unwanted side reactions that cut the battery's life short. The undesirable action starts on the battery's sulfur-containing cathode, which slowly disintegrates and forms molecules called polysulfides that dissolve into the liquid electrolyte. Some of the sulfur—an essential part of the battery's chemical reactions—never returns to the cathode. As a result, the cathode has less material to keep the reactions going and the battery quickly dies.

New materials for better batteries

Researchers worldwide are trying to improve materials for each battery component to increase the lifespan and mainstream use of lithium-sulfur batteries. For this research, Xiao and her colleagues honed in on the cathode to stop polysulfides from moving through the electrolyte.

Many materials with tiny holes have been examined to physically trap polysulfides inside the cathode. Metal organic frameworks are porous, but the added strength of PNNL's material is its ability to strongly attract the polysulfide molecules.

The framework's positively charged nickel center tightly binds the polysulfide molecules to the cathodes. The result is a coordinate covalent bond that, when combined with the framework's porous structure, causes the polysulfides to stay put.

"The MOF's highly porous structure is a plus that further holds the polysulfide tight and makes it stay within the cathode," said PNNL electrochemist Jianming Zheng.

Nanomaterial is key

Metal organic frameworks—also called MOFs—are crystal-like compounds made of metal clusters connected to organic molecules, or linkers. Together, the clusters and linkers assemble into porous 3-D structures. MOFs can contain a number of different elements. PNNL researchers chose the transition metal nickel as the central element for this particular MOF because of its strong ability to interact with sulfur.

During lab tests, a lithium-sulfur battery with PNNL's MOF cathode maintained 89 percent of its initial power capacity after 100 charge-and discharge cycles. Having shown the effectiveness of their MOF cathode, PNNL researchers now plan to further improve the cathode's mixture of materials so it can hold more energy. The team also needs to develop a larger prototype and test it for longer periods of time to evaluate the cathode's performance for real-world, large-scale applications.

PNNL is also using MOFs in energy-efficient adsorption chillers and to develop new catalysts to speed up chemical reactions.

"MOFs are probably best known for capturing gases such as carbon dioxide," Xiao said. "This study opens up lithium-sulfur batteries as a new and promising field for the nanomaterial."

This research was funded by the Department of Energy's Office of Energy Efficiency and Renewable Energy. Researchers analyzed chemical interactions on the MOF cathode with instruments at EMSL, DOE's Environmental Molecular Sciences Laboratory at PNNL.

In January, a Nature Communications paper by Xiao and some of her PNNL colleagues described another possible solution for lithium-sulfur batteries: developing a hybrid anode that uses a graphite shield to block polysulfides.

Source: http://phys.org/news/2014-04-lithium-sulfur-batteries-longer-nanomaterial-packed-cathode.html

Read More

Aging Successfully Reversed in Mice; Human Trials to Begin Next

Aging Successfully Reversed in Mice; Human Trials to Begin Next

  7:41:00 PM    Science Lover

---

Scientists have successfully reversed the aging process in mice according to a new study just released. Human trials are to begin next, possibly before the year is over. The study was published in the peer reviewed science journal Cell after researchers from both the U.S and Australia made the breakthrough discovery. Lead researcher David Sinclair of the University of New South Wales says he is hopeful that the outcome can be reproduced in human trials. A successful result in people would mean not just a slowing down of aging but a measurable reversal.

The study showed that after administering a certain compound to the mice, muscle degeneration and diseases caused by aging were reversed. Sinclair says the study results exceeded his expectations, explaining:

I’ve been studying aging at the molecular level now for nearly 20 years and I didn’t think I’d see a day when ageing could be reversed. I thought we’d be lucky to slow it down a little bit. The mice had more energy, their muscles were as though they’d be exercising and it was able to mimic the benefits of diet and exercise just within a week. We think that should be able to keep people healthier for longer and keep them from getting diseases of ageing.

The compound the mice ate resulted in their muscles becoming very toned, as if they’d been exercising. Inflammation, a key factor in many disease processes, was drastically reduced. Insulin resistance also declined dramatically and the mice had much more energy overall. Researchers say that what happened to the mice could be compared to a 60 year old person suddenly having the muscle tone and energy of someone in his or her 20s.

What’s more, say the researchers, these stunning results were realized within just one week’s time. The compound raises the level of a naturally occurring substance in the human body called nicotinamide adenine dinucleotide. This substance decreases as people age, although those who follow a healthy diet and get plenty of exercise do not suffer the same level of reduction in the substance as do people who do not exercise. This may explain why people who remain fit into their senior years often enjoy better health than others.

Scientists who participated in the study say that poor communication between mitochondria and the cell nucleus is to blame for the aging process. The compound the researchers have developed cause the cells to be able to “talk” to each other again. They compared the relationship between the nucleus and the mitochondria to a married couple; by the time the couple has been married for 20 years, “communication breaks down” and they don’t talk to each other as much. Just like a marriage, this relationship and communication within it can be repaired, say the researchers.

Aging has successfully been reversed in mice, but Sinclair says he needs to raise more money before he can commit to a date when trials may begin in humans. The results of this initial study in mice are very promising and may pave the way for similar results in humans.

Sources: ABC News , Science Direct , Huffington Post

Read More