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Mar 08

Engineered Viruses Boost Memory Recall in Mice.

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Reported by John Timmer (Ars Technical), in Wired Science, March 3, 2011.

Memories fade with time, often to the annoyance of those who can’t recall important details. But scientists have now found a way to boost the recall of memories even after they’ve started to fade. Unfortunately, the method involves injecting an engineered virus directly into the brain, so those of us who are bad with names may want to wait a bit for the technique to be refined.

The work was done in rats, and the memories in question are associations between a specific taste — saccharine, for example — and an unpleasant stimulus, caused by injection of a nausea-inducing drug (the approach is called “conditioned taste aversion”). Unless the unpleasant association is reinforced, the memories will slowly fade with time, although the aversion doesn’t disappear entirely during the two-week period that the authors were looking at.

Two years ago, the same authors found that it was possible to radically accelerate this fading. By injecting a chemical that blocked a specific brain enzyme (protein kinase M ζ), the authors caused the rats to act as if they had never experienced the nausea, even if the memory manipulation took place 25 days after the conditioning. Most chemicals that interfere with memories tend to prevent them from being consolidated for long-term storage, but this chemical seemed to work even after the memory was firmly in place.

That’s potentially helpful, since some people have formed negative associations with harmless or even helpful items. Still, for most of us, it would be nice to think that fading memories could be resuscitated. Apparently, they can. The researchers have now done what’s effectively the converse experiment, and increased the activity of protein kinase M ζ. They did this by engineering a virus to express the gene for the kinase, and then infected specific areas of the brain involved in memory. All the infected cells had additional copies of the gene, and thus made more of its product.

The virus had exactly the effect that the authors would presumably have predicted. The virus was injected a week after the rats were given the aversion conditioning, when the memory would already be starting to fade, and the memory tests were done a week after that, yet rats showed a significantly improved retention of their memories. As the authors point out, the engineered virus boosted a memory that was formed before it was even present.

The memory molecule, PKMzeta, overexpressed in rat neurons. Red (left) shows PKMzeta while green (middle) is a fluorescent protein that shows nerve cells have been infected by viruses engineered to boost the memory molecule. Yellow (right) shows both the memory molecule and green fluorescent protein only overexpress at certain locations in the neuron. Weizmann Institute of Science/Science

Actually, you can make that memories, plural. The authors trained rats to avoid both saccharine and salty liquids over the course of three days, and then injected the virus a week after the last training. The memories of both of these trainings were enhanced by the presence of the viral protein kinase M ζ gene.

The authors can’t tell exactly what protein kinase M ζ is doing to increase the recall of memories, and suggest it could be either enhancing the association between taste and the unpleasant experience, or simply enhancing recall in general. Although they don’t mention it, their findings may also be limited to specific classes of memories, like the associations examined here.

That latter point makes the last sentence of the paper a bit over the top, as the authors suggest that a chemical that enhances protein kinase M ζ activity might make for a good treatment for memory disorders like amnesia and age-related decline. Until we have a clearer sense of how many types of memories it works for, that’s a bit premature. Fortunately, there are lots of ways to test the recall abilities of animals, many of which don’t involve negative associations. Hopefully, testing of the virus’ more general impact on memory is already underway.

Image: HIV (green dots), a member of the lentivirus genus. (C. Goldsmith/P. Feorino/E. L. Palmer/W. R. McManus/CDC)

Citation: “Enhancement of Consolidated Long-Term Memory by Overexpression of Protein Kinase Mζ in the Neocortex.” Reut Shema, Sharon Haramati, Shiri Ron, Shoshi Hazvi, Alon Chen,
Todd Charlton Sacktor and Yadin Dudai.
Science, Vol. 331, March 3, 2011. DOI: 10.1126/science.1200215

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Mar 03

Sweat ducts make skin a memristor.

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Reported by Kate McAlpine, in NewScientist, 02 March 2011.

Breakout technology 😮 (Image: Scott Kleinman/Getty)

The missing link of electronics, which evaded discovery until 2008, was at our fingertips the whole time. Ordinary human skin behaves like a memristor, a device that “remembers” the last current it experienced and varies its resistance accordingly.

In 1971 Leon Chua of the University of California, Berkeley, came up with the notion of a resistor with memory. He showed mathematically that this memristor should be a fourth basic circuit element alongside the familiar trio of resistor, capacitor and inductor.

But it wasn’t until 2008 that a team led by Stanley Williams, director of HP’s Information and Quantum Systems lab in Palo Alto, California, finally made one from a speck of titanium dioxide.

Synapses, junctions between neurons in the brain, display electrical behaviour that depends on past activity and are said to behave like memristors. This has raised the prospect of using memristors as the basis of an artificial brain.

Now, by re-examining data from the early 1980s on the electrical conductivity of human skin in response to various voltages, Gorm Johnsen and his colleagues at the University of Oslo in Norway have uncovered a more prosaic example of memristive behaviour in nature.

They found that when a negative electrical potential is applied to skin on various parts of the arm, creating a current, that stretch of skin exhibits a low resistance to a subsequent current flowing through the skin. But if the first potential is positive relative to the skin, then a subsequent potential produces a current that meets with a much higher resistance. In other words, the skin has a memory of previous currents. The finding is due to be published in Physical Review E.

The researchers attribute skin’s memristor behaviour to sweat pores. Sweat contains positively charged ions such as sodium. When skin is exposed to a negative potential, the fluid at the bottom of the sweat pores is drawn upward. Although a thin layer of fluid always coats the inside of the cylindrical pore, this layer thickens as the sweat rises. As sweat is highly conductive, extra fluid rising to the surface increases skin’s surface conductivity and thereby lowers its resistance if a subsequent potential is applied.

The longer skin is exposed to a negative potential, the lower the subsequent resistance, until it maxes out when sweat fills the pore. Conversely, a positive potential pushes the ions back, thinning the layer of sweat lining the pore walls and increasing the skin’s resistance to current.

Whether this behaviour helps skin function isn’t clear but Yuriy Pershin of the University of South Carolina in Columbia, who has studied memristive behaviour in amoebas, describes the skin’s role in processes such as temperature regulation as “primitive intelligence”.

A new understanding of skin’s electrical properties could have implications for medicine. Resistance to alternating current is already used to diagnose skin abnormalities, says Johnsen’s colleague Andrew Lütken.

Williams, meanwhile, is gratified by the interest in memristors. “It is very interesting to me to see the range of the fields that can benefit from application of memristor theory.”

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Mar 02

Are you ready?

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Just visit Kaggle is a platform for data prediction competitions that allows organizations to post their data and have it scrutinized by the world’s best data scientists. See how it works.

Who should host a competition on Kaggle?

Crowdsourcing data modeling is an effective way to build predictive algorithms. There are any number of approaches that can be applied to a data modeling problem, but it is impossible to know at the outset which will be most effective. A consultant or in-house statisitician can try a few, but opening up the problem to a wider audience ensures that organizations reach the frontier of what is possible from a given dataset.

Most data problems can be framed as a competition:

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Who should compete on Kaggle?

Data scientists rarely have access to real-world data. This is frustrating when you consider that many of the world’s organizations have piles of data that they can’t make the most of. Kaggle corrects this mismatch by giving data scientists access to real-world data and problems. Best of all, the burden of collecting, cleaning and structuring the data will have been done by others.

Competitions offer participants the opportunity to:

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