ScienceWeek

SCIENCEWEEK

August 25, 2007

Vol. 11 - Number 32

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Do not undertake a scientific career in quest of fame or money. There are easier and better ways to reach them. Undertake it only if nothing else will satisfy you; for nothing else is probably what you will receive. Your reward will be the widening of the horizon as you climb. And if you achieve that reward you will ask no other.

-- Cecilia Payne-Gaposchkin (1900-1979)

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Contents (full text below):

1. Economics: Money Illusion and the Market

2. Neuroscience: The Threatened Brain

3. Geochemistry: The Oldest Fossil or Just Another Rock?

4. Social Science: Sacred Barriers to Conflict Resolution

5. Quantum Physics: On Photons and Waves

6. Materials science: On Complex System Self-Assembly

7. Statistics: Fallacies in Gender-Difference Analysis

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1.

Science 24 August 2007: Vol. 317. no. 5841, pp. 1042 - 1043 DOI: 10.1126/science.1143917

Economics: Money Illusion and the Market

Jean-Robert Tyran

Imagine a consumer who discovers to his surprise that the money in his bank account and his salary have doubled overnight. Now suppose that all prices have also doubled overnight. Will this consumer be happy about being awash with money? Will he feel richer today and buy more or different goods than he did yesterday? Not according to standard economic theory. After all, he has to work the same number of minutes to buy, say, a loaf of bread, and can therefore afford to buy exactly the same set of goods as he did yesterday. In short, the boost in purely "nominal" terms (which inflates all monetary values by the same factor) should not affect behavior because nothing has changed in "real" terms (i.e. when taking this inflation properly into account).

This is the textbook example that economists use to explain the standard assumption that economic agents are free from money illusion, i.e., that they think about economic transactions exclusively in real terms. But now imagine a situation in which all prices increase by 3.1% and nominal wages increase by, for example, 2.3% over 1 year. Do people behave the same way in this situation as in the effectively equivalent case when their nominal wages fall by about 0.8% at constant prices? Or do some people perceive these two situations differently because of different nominal representations?

Despite increasing evidence that thinking in nominal terms is common and that purely nominal changes can affect individual choices (1, 2), economists have only started to understand when and how money illusion affects market outcomes. Economists often claim that learning and market forces eliminate distortions from money illusion at the market level if irrational agents are swiftly selected out of the market (e.g., because they go bankrupt) or if rational agents can effectively take advantage of irrational behavior. Yet, recent evidence, from both the experimental laboratory and the field, suggests that money illusion can affect market outcomes.

An intriguing example comes from the housing market. Housing prices have reached unprecedented heights in recent years in several countries. Sharp run-ups followed by busts are a common feature of housing prices. Recently, Brunnermeier and Julliard proposed that a particular type of money illusion, which results from confusing nominal and real interest rates, could explain such "housing frenzies" (3). They found that falling nominal interest rates and inflation increased housing prices, and vice versa, even when controlling for other factors that affect real housing prices such as construction costs, housing quality, property taxes, demographics, and general economic conditions.

The reasoning for this result is as follows. When inflation is low, monthly nominal interest payments on mortgages are low compared to the rent on a similar house. Because houses seem cheap, illusion-prone investors entering the market tend to buy rather than rent and cause an upward pressure on housing prices when inflation declines. However, decreasing inflation not only reduces entrants' current payments on the mortgage but also increases the real cost of future mortgage payments. Investors who base their decisions on the salient low nominal mortgage payments, but ignore the less-visible effect of inflation on the future real mortgage cost, are prone to an illusion. In a sense, these investors act like a person who thinks that a car is cheaper if the down-payment is spread over 4 years rather than 2 years because the monthly payments are lower. Some researchers have suggested that a similar relationship between inflation and real asset prices exists in the stock market, and have proposed money illusion as a cause (4, 5).

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2.

Science 24 August 2007: Vol. 317. no. 5841, pp. 1043 - 1044 DOI: 10.1126/science.1147797

Neuroscience: The Threatened Brain

Stephen Maren

The world is a dangerous place. Every day we face a variety of threats, from careening automobiles to stock market downturns. Arguably, one of the most important functions of the brain and nervous system is to evaluate threats in the environment and then coordinate appropriate behavioral responses to avoid or mitigate harm.

Imminent threats and remote threats produce different behavioral responses, and many animal studies suggest that the brain systems that organize defensive behaviors differ accordingly (1). On page 1079 of this issue, Mobbs and colleagues make an important advance by showing that different neural circuits in the human brain are engaged by distal and proximal threats, and that activation of these brain areas correlates with the subjective experience of fear elicited by the threat (2). By pinpointing these specific brain circuits, we may gain a better understanding of the neural mechanisms underlying pathological fear, such as chronic anxiety and panic disorders.

To assess responses to threat in humans, Mobbs and colleagues developed a computerized virtual maze in which subjects are chased and potentially captured by an "intelligent" predator. During the task, which was conducted during high-resolution functional magnetic resonance imaging (fMRI) of cerebral blood flow (which reflects neuronal activity), subjects manipulated a keyboard in an attempt to evade the predator. Although the virtual predator appeared quite innocuous (it was a small red circle), it could cause pain (low- or high-intensity electric shock to the hand) if escape was unsuccessful. Brain activation in response to the predatory threat was assessed relative to yoked trials in which subjects mimicked the trajectories of former chases, but without a predator or the threat of an electric shock. Before each trial, subjects were warned of the contingency (low, high, or no shock). Hence, neural responses evoked by the anticipation of pain could be assessed at various levels of threat imminence not only before the chase, but also during the chase when the predator was either distant from or close to the subject.

How does brain activity vary as a function of the proximity of a virtual predator and the severity of pain it inflicts? When subjects were warned that the chase was set to commence, blood oxygenation level-dependent (BOLD) responses (as determined by fMRI) increased in frontal cortical regions, including the anterior cingulate cortex, orbitofrontal cortex, and ventromedial prefrontal cortex. This may reflect threat detection and subsequent action planning to navigate the forthcoming chase. Once the chase commenced (independent of high- or low-shock trials), BOLD signals increased in the cerebellum and periaqueductal gray. Activation of the latter region is notable, as it is implicated in organizing defensive responses in animals to natural and artificial predators (3, 4). Surprisingly, this phase of the session was associated with decreased activity in the amygdala and ventromedial prefrontal cortex. The decrease in amygdala activity is not expected, insofar as cues that predict threat and unpredictable threats activate the amygdala (5, 6).

However, activity in these brain regions varied considerably according to the proximity of the virtual predator and the shock magnitude associated with the predator on a given trial (see the figure). When the predator was remote, blood flow increased in the ventromedial prefrontal cortex and lateral amygdala. This effect was more robust when the predator predicted a mild shock. In contrast, close proximity of a predator shifted the BOLD signal from these areas to the central amygdala and periaqueductal gray, and this was most pronounced when the predator predicted an intense shock. Hence, the prefrontal cortex and lateral amygdala were strongly activated when the level of threat was low, and this activation shifted to the central amygdala and periaqueductal gray when the threat level was high.

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3.

Science 24 August 2007: Vol. 317. no. 5841, pp. 1046 - 1047 DOI: 10.1126/science.1146923

Geochemistry: The Oldest Fossil or Just Another Rock?

John M. Eiler

The history of the past 542 million years of life on Earth can be read from shells, bones, teeth, and leaf casts preserved in the geological record. For the preceding 4 billion years, more subtle clues, such as remnants of microbial cells, biomolecules, and the impressions left by soft-bodied organisms, may be preserved in sedimentary rocks. But in sediments deposited in the first billion years of Earth history, these traces have been destroyed by metamorphism (recrystallization without melting, often accompanied by reaction and chemical exchange). Here, the only widely recognized evidence for life comes from measurements of carbon isotopes in kerogen and graphite (1). Because metabolic carbon fixation discriminates against 13C, the 13C/12C ratio in biogenic carbon is ~3% lower than in inorganic carbon. This signature can be preserved through metamorphic processes that destroy microfossils and biomolecules.

In 1996, Mojzsis et al. reported the oldest indications of life on Earth to date (2) in a rock collected from a patch of intensely folded and metamorphosed quartz-rich rocks on Akilia, a tiny, barren island off the southwest coast of Greenland. The authors suggested that these quartz-rich rocks are banded iron formations (a type of iron-rich marine sediment) deposited more than 3860 million years ago, and that at least one of them contains 13C-poor graphite derived from organic matter. Rocks nearly this old from elsewhere also contain 13C-depleted carbon (1).

The graphitic, quartz-rich rocks on Akilia have been widely discussed and intensely scrutinized. Much of this scrutiny has been critical and has eroded confidence in the original finding (3-11). But this year, the authors of the original study have punched back in a pair of papers (12, 13) that address the critics' most serious charges.

The ages of old, metamorphosed sediments can be constrained through isotope dating of igneous rocks that cut through, or contain inclusions of, those sediments. The originally reported age of the Akilia quartz-rich rocks [(2) and references therein] was based on the isotopic age of the mineral zircon in such a cross-cutting granitoid (an igneous rock rich in quartz and feldspar). But these zircons could be minerals from an unknown older rock that were entrained in the igneous rock while it was still liquid (3). It has also been suggested that the intense deformation undergone by nearly all Akilia island rocks prevents confident identification of places where granitoids cross-cut older volcanic or sedimentary rocks (4).

Manning et al. (12) refute the first criticism by showing that the trace-element contents of the suspect zircons (redated at 3820 to 3840 million years ago) are consistent with them having crystallized from their host rocks; thus, at least some granitoids on Akilia very likely are as old as originally claimed. The authors also strive to address the second critique, but against long odds: No crosscutting relations between granitoids and the quartz-rich rocks have been observed. In some places, granitoids to cross-cut volcanic strata that are part of the same original set of strata as the quartz-rich rocks, providing a minimum age for the whole stratigraphic section. However, even these cross-cutting relations are partially obscured or otherwise ambiguous. Barring discovery of further cross-cutting relations, it is difficult to foresee how this part of the debate can be more definitively resolved.

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4.

Science 24 August 2007: Vol. 317. no. 5841, pp. 1039 - 1040 DOI: 10.1126/science.1144241

Social Science: Sacred Barriers to Conflict Resolution

Scott Atran, Robert Axelrod, Richard Davis

Efforts to resolve political conflicts or to counter political violence often assume that adversaries make rational choices (1). Ever since the end of the Second World War, "rational actor" models have dominated strategic thinking at all levels of government policy (2) and military planning (3). In the confrontations between nation states, and especially during the Cold War, these models were arguably useful in anticipating an array of challenges and in stabilizing world peace enough to prevent nuclear war. Now, however, we are witnessing "devoted actors" such as suicide terrorists (4), who are willing to make extreme sacrifices that are independent of, or all out of proportion to, likely prospects of success. Nowhere is this issue more pressing than in the Israeli-Palestinian dispute (5). The reality of extreme behaviors and intractability of political conflicts there and discord elsewhere--in the Balkans, Kashmir, Sri Lanka, and beyond--warrant research into the nature and depth of commitment to sacred values.

Sacred values differ from material or instrumental ones by incorporating moral beliefs that drive action in ways dissociated from prospects for success. Across the world, people believe that devotion to core values (such as the welfare of their family and country or their commitment to religion, honor, and justice) is, or ought to be, absolute and inviolable. Such values outweigh other values, particularly economic ones (6).

To say that sacred values are protected from trade-offs with economic values does not mean that they are immune from all material considerations. Devotion to some core values, such as children's well-being (7) or the good of the community (8), or even to a sense of fairness (9), may represent universal responses to long-term evolutionary strategies that go beyond short-term individual calculations of self-interest, yet advance individual interests in the aggregate and long run. Other such values are clearly specific to particular societies and historical contingencies, such as the sacred status of cows in Hindu culture or the sacred status of Jerusalem in Judaism, Christianity, and Islam. Sometimes, as with cows (10) or forests (11), the sacred may represent accumulated material wisdom of generations in resisting individual urges to gain an immediate advantage of meat or firewood for the long-term benefits of renewable sources of energy and sustenance. Political leaders often appeal to sacred values as a way of reducing "transaction costs" (12) in mobilizing their constituents to action and as a least-cost method of enforcing their policy goals (13).

Matters of principle or "sacred honor," when enforced to a degree far out of proportion to any individual or immediate material payoff, are often seen as defining "who we are." After the end of the Vietnam War, successive U.S. administrations resisted Hanoi's efforts at reconciliation until Hanoi accounted for the fate of U.S. soldiers missing in action (14). Granted, the issue was initially entwined with rational considerations of balance of power at the policy-making level: The United States did not want to get too close to Hanoi and so annoy Beijing (a more powerful strategic ally against the Soviet Union). But popular support for the administration's position, especially among veterans, was a heartfelt concern for "our boys," regardless of numbers or economic consequences.

The "who we are" aspect is often hard for members of different cultures to understand; however, understanding and acknowledging others' values may help to avoid or to resolve the hardest of conflicts. For example, at the peaceful implementation of the occupation of Japan in 1945, the American government realized that preserving, and even signaling respect for, the emperor might lessen the likelihood that Japanese would fight to the death to save him (15).

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5.

Nature 448, 872-873 (23 August 2007) | doi:10.1038/448872a; Published online 22 August 2007

Quantum Physics: On Photons and Waves

Luis A. Orozco

When measuring photons, it's a case of 'wanted, dead' — catching them alive is not an option. But we can observe how a superposition of many photon waves progressively collapses as it interacts with a beam of atoms.

Earlier this year, a team from the Ecole Normale Supérieure in Paris recorded jumps of light heralding the birth and death of a photon trapped in a cavity1. As they describe in this issue (Guerlin et al., page 889)2, the same researchers have now performed a similar, more complex trick — recording exactly how a coherent state of many photons collapses as it is measured.

A measurement process differs fundamentally between the classical and quantum worlds. In the classical realm, there is no explicit limitation on a measurement's accuracy. In the quantum domain, by contrast, accuracy is constrained by the Heisenberg uncertainty principle: a measurement will produce a definite result, but one whose value is distributed according to the laws of probability. What is more, the measured object will itself be fundamentally altered by the measurement. Thus, the clicking sound produced when a photon is caught by a detector says two things: yes, a particle was detected; but sorry, the way you detected it killed it, and its energy was converted into an electric pulse.

But the quantum world has more subtle states to investigate than a single photon. Photons, or the probabilistic wavefunctions associated with them, can add together, or superpose. If they superpose coherently (in phase), their combined wavefunction begins to look like a classical wave. This coherent electromagnetic field is the complex beast whose collapse was monitored by Guerlin et al.2.

But how did they achieve this feat, given the difficulties of measuring a quantum object without instantly destroying it? The authors' 'quantum non-demolition measurements' in a cavity quantum-electrodynamical (QED) system required profound understanding of quantum mechanics, continuous theoretical elucidation of subtle details of cavity QED, and unprecedented dedication in realizing a simple theoretical model in the laboratory. This model3 first required the development of a pair of superconducting mirrors for the walls of the cavity whose losses are low enough that light remains captured between them for the length of time it would take the light to circle Earth at the Equator.

The second pivotal ingredient is individual rubidium atoms in a 'Rydberg' state in which one electron is highly excited. These atoms are like little planetary systems, with the excited electrons on a distant orbit around a remote atomic nucleus. They can oscillate between two different excited states, and the regularity of this oscillation makes them excellent timekeepers. The frequency of that oscillation is easily disturbed in the presence of light — to the extent that it can be used to detect the presence of a single photon non-destructively1.

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6.

Nature 448, 876-877 (23 August 2007) | doi:10.1038/448876a; Published online 22 August 2007

Materials science: On Complex System Self-Assembly

David J. Pine

Take silicon, soak in water, add acid — and stir. This simple new recipe for the self-assembly of complex microstructures belies an involved sequence of hydrophobic, electrostatic and van der Waals interactions.

In folding its proteins and constructing its complex membranes, nature uses self-assembly: bathed in water or another liquid, tiny building-blocks come together by virtue of their shape and interactions. As they report in the journal Small, Onoe et al.1 adapt these natural processes for their own designs. They describe a method for assembling parts just 10 micrometres across into complex, three-dimensional objects, and go on to build up chains of interlocking rings. The research is another step towards the ultimate goal of building electrical or optical circuits, or even microscopic machines, from components at micrometre and smaller scales.

The folding of a protein molecule from a long, linear sequence of linked amino acids is one of nature's more spectacular demonstrations of self-assembly. In a watery environment, certain amino acids along the chain can attract each other by various means — van der Waals attraction, hydrogen bonding or hydrophobic interactions. Others might repel each other through their electrical charges or hydrophilic interactions. Geometrical constraints limit which amino acids along the chain can interact with each other, so which amino acid occupies a given position in the chain is crucial to the final topology and shape of the protein. Geometry thus conspires with attractive and repulsive forces to fold the amino-acid chain into the complex shape that gives a protein its particular function.

Simpler examples of self-assembly also abound. Soap molecules, or 'surfactants', are one. These consist of a water-loving (hydrophilic) head connected to a water-hating (hydrophobic) tail. When placed in water, the hydrophobic tails of different surfactant molecules bunch together to form the core of a sphere, with their hydrophilic heads at the surface. This way, both heads and tails get to live in their desired surroundings. While arranging themselves, the tails often corral a particle of dirt, isolating it so that it can be washed away.

Onoe and colleagues1 exploit the same ideas of self-assembly, except that their building-blocks are not organic molecules, but particles of silicon formed into slightly tapered cylinders 10 microm in diameter at the wider end. This wider base is coated with a layer of hydrophobic molecules, whereas a thin layer of silicon dioxide (SiO2) forms naturally through oxidation of the remaining surfaces in air. When placed in water with a nearly neutral pH of 6.5, the SiO2 surfaces become negatively charged and repel each other when two particles come close. The hydrophobic bases of two cylinders, by contrast, can avoid contact with the water by pairing up flush against each other. And this is exactly what happens when the water is stirred to bring particles close to one another: the hydrophobic surfaces pair up to form barrel-shaped 'dimers' (Fig. 1a).

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7.

Nature 448, 849 (23 August 2007) | doi:10.1038/448849a; Published online 22 August 2007

Statistics: Fallacies in Gender-Difference Analysis

Claire Ainsworth

Unsound analyses are common in gender genetics papers.

Most claims that men and women are affected differently by disease-associated gene variations are poorly founded. A team of researchers has found that the data supporting such claims are often poorly analysed statistically or come from studies that were not adequately designed to show these links.

"The abysmal standard of statistical analysis in much of genetic epidemiology is little short of scandalous," says David Balding, professor of statistical genetics at Imperial College London, UK, who was not involved in the study. "This paper reveals an entire industry of prominently reported results that are largely unjustified and probably mostly false."

John Ioannidis and his colleagues at the University of Ioannina School of Medicine in Greece evaluated 432 claims in 77 research papers (N. Patsopoulos et al. J. Am. Med. Assoc. 298, 880–893; 2007). The team applied a set of criteria to determine whether the papers' authors had performed the correct analysis, such as comparing like with like, and had taken steps to show that the association was not due to chance. Worryingly, only 12.7% of claims satisfied these criteria. "There is quite a gap between what should have been done and what the journals and reviewers should have asked for, compared with what the authors did," says Ioannidis.

Many studies were not designed to test for a link between sex and gene variants, with researchers trying to extract associations from their data after the fact. Sample sizes were at least ten times smaller than they needed to be to yield statistically robust results, Ioannidis adds.

"This paper tells us that we don't have a clue whether gender is a real biomarker for any of the clinical areas assessed," says Howard McLeod, director of the UNC Institute for Pharmacogenomics and Individualized Therapy in Chapel Hill, North Carolina. "Gender, as well as age and race, are crude ways of understanding the complex factors regulating clinical effect," he adds.

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