Brain's hippocampus can organize memories for events as well as places 06-09

People organize memories in photo albums, journals or calendars, but how does the brain first put
events in order? Though a great deal of work has been done on how the brain encodes memory for locations, leading to the discovery of 'place cells' in the hippocampus, we still have relatively little understanding of how personally experienced, or episodic, memories are represented by neurons.

Now, researchers at Japan's RIKEN Brain Science Institute have found that the hippocampus can generalize, putting not just places but also events into sequence by changing the neural code in the rat brain. These 'event cells' discovered by the researchers may be a bridge linking information about the world with subsequent decision-making.

Neurons have two main ways they can signal to each other: by changing the timing or the frequency of their firing. In this study, Shigeyoshi Fujisawa and colleagues looked at how these two parameters changed while rats did a decision-making task based on certain combinations of smells and sounds. Using non-spatial stimuli presented in sequence was crucial to demonstrating that cells in the hippocampus also represent events, not just places. The study was published in the journal Neuron on June 8.

The research team recorded the combined activity of a large number of neurons in central hippocampal area CA1 while rats were engaged in choosing different sound-odor combinations to get a water reward. Many cells displayed elevated activity in response to one or both stimuli—often with a strong preference for one odor or sound versus the other—and retained this activation through the 'decision' phase, indicating that the inputs were being integrated by the brain and retained in a specific order to facilitate a subsequent choice.

The hippocampus is known to have a 'refresh rate' of around 8 Hz—the theta cycle— which guides how often neurons update their activity, a phenomenon called theta-cycle phase precession. The researchers were particularly interested in how this cyclic organization of information is modified by inputs, like a smell event followed by a sound event followed by a decision. Among the neurons that were responsive to smells, the theta phase precession occurred only for 'preferred' odors, followed by a locking of their activity to the theta cycle. This occurred for about 90 per cent of smell-sensitive cells, and was true for an equally high proportion of choice-sensitive cells.

On a more global scale, assemblies of hippocampal neurons can also form theta sequences, coordinated sequential activation patterns representing past, present and future locations during animal navigation. The authors investigated whether theta sequences were also formed by this cue-combination task. Such sequences were indeed present, and it was possible to 'decode' whether neural spikes at different phases of the theta cycle represented real-time inputs—the moments when the smell or sound event happened—or future periods—the decision-making moment. "Spikes that were locked to different phases of the cycle could even tell us if the rat had made a correct, rewarded choice or chosen the wrong cue combination," said Fujisawa.

Finally, the conditions of the experiment were reversed: the previously rewarding sound-odor combination became incorrect and vice-versa. Rats learned the new relationship after a few days, and their brain cell activity adapted too, exhibiting the phase precession and locking observed before the switch. "This neural reorganization reflects the sequence of the events and can be flexibly remapped," commented Fujisawa. "Cells that encode specific cues, combinations or choices can collectively represent an entire sequence of events when they become temporally organized with the hippocampal theta phase." The researchers surmise that the function of the hippocampus is to organize networks of relational elements, whether these are locations or events, as a mechanism underlying both episodic and spatial memory.

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Seven Ways To Sharpen Your Memory 03-26

Seven Ways To Sharpen Your Memory

We often talk about our ability to remember in terms of its being good or bad: “I have a mind like a sieve,” “He has a photographic memory,” “She works hard, but she just can’t retain what she's learned."

What we fail to recognize is that the way we use our memory has a lot to do with how effectively it operates. Here, seven strategies from cognitive science and psychology that will allow us to remember better.

1. Be conscious of the limits of your working memory—the mental holding area that contains the facts and concepts you're thinking about at any one time. We can hang onto only about four facts or ideas at a time in working memory, but we can pack more information into those four slots by engaging in chunking: linking multiple pieces of information into a few meaningful groups.

2. We all remember from school that cramming the night before a test doesn't work too well, but many of us use the same approach in our working lives, hurriedly reviewing what we need to know on the way to a meeting or presentation. It's much more effective to expose yourself to the information in brief sessions spaced out over time. One easy way to do this is to use your email program to send yourself a weekly or biweekly message containing the material you need to review.

3. Despite its many proponents, there's little scientific evidence to support the idea that we have distinctive learning styles (visual, auditory, and so on). However, we do all learn and remember best when information is presented in multiple modalities—when we hear it, see it, act it out, and so on. If there's something you need to remember, try to absorb it through several senses: read the material out loud, watch a video lecture on YouTube.

4. Sleep is key to memory: it's during slumber that we consolidate and make permanent the knowledge we've gathered during the day. After you've been exposed to a lot of information (for example, when you've spent the day at a conference), make sure you get a good night's sleep. You can also try reviewing important information just before you go to bed at night—or following a study session with a daytime nap!

5. We often conceive of memory as something like a storage tank, and a test as a kind of dipstick that measures how much information we’ve put in there. But that’s not actually how the brain works. Every time we pull up a memory, we make it stronger and more lasting—so quizzing yourself doesn’t just measure what you know, it changes what you know. Put away your notes and try to recall the material from memory.

6. We remember new knowledge better when it connects to what we already know. Before heading into a situation in which you'll be absorbing a lot of new information, "activate" your prior knowledge by reflecting on what you currently understand of the topic, maybe jotting down a few notes. You'll be priming your mind to grab and hold onto the new material.

7. The "generation effect" is the term psychologists use to describe the following phenomenon: we remember material better when we've generated it ourselves. Rather than reading or repeating someone else's formulation, put the information to be learned into your own words: explain it to yourself, or talk about it to someone else. Research also shows that teaching someone else helps the teacher to remember the material better.

So the next time you complain about your "bad memory," remember that its only flaw may lie in the way you're using it.

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Surprising turns in magnetic thin films could lead to better data storage 06-24

Surprising turns in magnetic thin films could lead to better data storage

MIT researchers discover efficient control of magnetism in chiral ferromagnets.

A magnetic phenomenon newly discovered by MIT researchers could lead to much faster, denser and more energy-efficient chips for memory and computation.

The findings, reported in the journal Nature Materials, could reduce the energy needed to store and retrieve one bit of data by a factor of 10,000, says the paper’s senior author, Geoffrey Beach, an assistant professor of materials science and engineering at MIT. The paper’s co-authors are graduate students Satoru Emori and Uwe Bauer, postdoc Sung-Min Ahn, and Eduardo Martinez of the University of Salamanca in Spain.

Beach says that hints of the new phenomenon have been reported for several years, but these had remained unexplained until now. The new results could overcome “a lot of what had seemed like fundamental limitations” in the control and use of magnetic materials, he says, adding: “It’s a whole new approach to the design of magnetic materials.”

It turns out the key to this phenomenon lies not in the magnetic materials themselves, but in what’s next to them: In this case, the team used very thin films of a ferromagnetic material, deposited on a metal base, and with a layer of an oxide material on top — a sort of ferromagnet sandwich. The behavior of the ferromagnetic layer, it turns out, depends on the metal that layer rests upon.

Ferromagnetic materials, including the familiar bar magnets, have a north and a south pole. When such materials are used for data storage, such as on a computer’s hard disk, separate tiny “domains” on their surface can have these poles pointing either up or down, representing ones and zeros. Normally, when a ferromagnetic material is exposed to a current, these domains are pushed along the surface in the same direction as the electron flow.

But previously, in rare cases, the movement was in the opposite direction, puzzling researchers. The MIT team found that when the thin ferromagnetic film was deposited on a slab of platinum, it exhibited this backward flow — which Beach likens to being dragged upwind.

But under circumstances that were identical, except that the film was deposited on the metal tantalum, the magnetic domains flowed in the normal direction — meaning that the key was not in the ferromagnet itself, but in its next-door neighbor. Both platinum and tantalum are nonmagnetic, so they would not ordinarily be expected to affect magnetic behavior.

It turns out that in either case, an unexpected effect alters how magnetic domains switch from one orientation to the other. Normally, when the spin orientation changes from one domain to the other (say, from “up” to “down”), the direction of that change is random. But in these thin-film sandwiches, spin rotations are aligned, consistently either turning clockwise or counterclockwise. The researchers showed that because of this peculiar effect, current can push domains with much more force than in conventional materials, and the direction that the domains move can be engineered simply by selecting the nonmagnetic metal underneath the magnet.

Such asymmetrical behavior is called a chiral effect; the researchers say this is the first demonstration of chiral behavior in magnetic domains.

“There are very few systems in nature that have this preferred way to rotate,” Beach says. Among the few are the molecules that form the basis for life, such as those that assemble into DNA molecules. Additionally, a few magnetic materials have shown this property, “but only in very exotic structures,” he says: at temperatures just slightly above absolute zero, and only in a perfect single crystal.

The new phenomenon, by contrast, is seen “at room temperature and well above room temperature, and in devices that are ideally suited for integration into electronic devices,” Beach says.

In the new ferromagnetic sandwiches, the forces pushing the magnetic domains are 100 times greater than in conventional ferromagnetic storage systems. Since the power needed to move the domains varies with the square of these forces, Beach says, such a system could be 10,000 times more efficient than existing technology.

With that, “all of a sudden these go from just looking interesting to being competitive even with very entrenched technology,” Beach says. And because these structures are compatible with existing manufacturing methods, he predicts, “these things are going to be out there and making a difference very soon.”

Emori, the paper’s lead author, says that there are now several kinds of memory systems, from the ones within a computer’s internal memory to those on hard disks or solid-state USB thumb drives. Theoretically, by harnessing these new effects, he says, “all of these could be satisfied by one material.”

This is “a very important, major advance,” says Robert Buhrman, a professor of engineering and senior vice provost for research at Cornell University. The MIT research, he says, is part of “a very intense effort worldwide to efficiently control the motion of ferromagnetic domain walls in thin-film nanostructures for future very high-performance data-storage and nonvolatile logic operations.”

Buhrman adds, “This work has answered several important questions raised by earlier studies as to how a current pulse can very rapidly move domain walls in a preferred direction.” Besides providing those answers, he says, it “raises new questions for follow-on work.”

“It’s really a whole new class of magnetic materials,” Beach says. “It opens up possibilities that it would have been difficult to even speculate about a couple of years ago.”

The work was supported in part by the National Science Foundation.

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Caffeine improves recognition of positive words 11-09

Caffeine improves recognition of positive words

PLoS | November 8, 2012 | Psychopharmacology / 

Caffeine perks up most coffee-lovers, but a new study shows a small dose of caffeine also increases their speed and accuracy for recognizing words with positive connotation.

The research published November 7 in the open access journal PLOS ONE by Lars Kuchinke and colleagues from Ruhr University, Germany, shows that caffeine enhances the neural processing of positive words, but not those with neutral or negative associations.

Previous research showed that caffeine increases activity in the central nervous system, and normal doses of caffeine improve performance on simple cognitive tasks and behavioral responses.

It is also known that certain memories are enhanced when strong positive or negative emotions are associated with objects, but the link between caffeine consumption and these emotional biases was unknown.

This study demonstrates, for the first time, that consuming 200 mg of caffeine, equivalent to 2-3 cups of coffee, 30 minutes before a task can improve the implicit recognition of positive words, but has no effect on the processing of emotionally neutral or negative words.

The authors suggest that this effect is driven by caffeine’s strong dopaminergic effects in the language-dominant regions of the brain.

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Memory Retention & Forgetting Curve 07-18

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