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NS 22 jun2002

Brain food?

EATING soya for just a few weeks makes you smarter, by improving your memory and allowing you to think more flexibly. So says the author of a smalf new study, but other experts dispute the hndings. Soya is rich in chemicals that resemble human oestrogen. Some claim that these "plant oestrogens" have many benefits, from preventing breast and prostate cancer to easing the symptoms of the menopause. Other studies have revealed potential health risks (New Scientist, 11 May, p 16). But do plant oestrogens also affect our mental abilities? To find out, Sandra File and her team at King's College London put 27 students and 33 post-menopausal women on a diet that was either high or low in soya. After 10 weeks on the high-soya diet, both male and female : students showed improvements in memory and mental flexibiiity, File told a conference in London last month. For example, on average they recalled 14 pictures out of 22 instead 12. "That's a figure that would make a difference to your iife," she says. The post menopausal women also showed marked improvements in their mental flexibility and ability to pian ahead. They were better at remembering pictures, though other forms of memory didn't improve. But Sanne Kreijkamp-Kaspers at the University of Utrecht in the Netherlands thinks the improvements occurred because the diet relieved post menopausal depression, rather than affecting memory directly. She also points out that the number of participants was small. "I do not attach much conhdence to this study," she says. In a larger, longer-term study of 115 post-menopausal women, Kreijkamp Kaspers found no evidence that plant oestrogens improve brain function. But File says this study did not test the skills that showed the greatest improvements in her study. James Randerson

Ultimate prize
The competition to find a planet like ours is heatting up

FEELINGS among planet hunters are running high this week. While one team grabbed headlines with the firt sighting of a solar system similar to our own, another has quietly firmed up their claim to an'even greater prize: the first Earth-like planet orbiting a star other than the Sun.

Finding planets outside our Solar System has become a relatively common occurrence-around 90 have been found so far. But what astronomers really want to know is whether theryre more planets like our own out there, and whether they might be inhabited.

Planets, orbiting distant stars are far too dim to be seen directly. Instead, most planet hunters look for the effect of a planet's gravity on the host star. But the influence of small planets would be undetectable, so most of the planets found so far weigh in at several times the mass of Jupiter. This means they are too large and gaseous to support life.

A New Zealand and Japanese team headed by Philip Yock at the Uasses in front of another, it bends the light from the distant star like a lens, magnifying it tens of times. If the foreground star has planets, even small ones like Earth, the shape of the 'lens' should be warped in a way that depends on the planets' motion. Although relatively untested, so far it's the only method capable of spotting Earth-sized planets.

In 1999, Yock's team saw a blip in a microlens that could have been caused by a small Earth-sized planet, with an orbit between one and three times as far from its star as Earth is from the Sun. Critics said the blip was probably down to statistical noise. But the researchers have published their latest calculations this week, using a new, more accurate, image-analysis technique. They show that the chances of the blip being random noise are less than 1 per cent.

"The signal is stronger," says microlensing expert John Bennett of the University of Notre Dame in Indiana. But he wams that there could be other explanations, for example a third dark object coincidentally passing in front of the foreground star. Yock's colleague Ian Bond disagrees. 'I've been through the data so many times looking at other possibilities and that signal won't go away,' he says.

However, competing teams refuse to acknowledge the findings of Yock and his colleagues. Planet hunter Geoff Marcy at the University of California, Berkeley, has left the planet off his almanac of sightings at www.exoplanets.org, and refuses to comment on the microlensing result.

Marcy himself has been in the headlines this week after announcing the discovery of a solar system that looks a little like our own. He and colleague Paul Butler have found a system, called 55 Cancri, which has ajupiterlike planet orbiting its star at about the same distance as the real Jupiter orbits the Sun, a result that has taken 15 years of observations. There are also two other gas giants closer in, but computer modelling carried out by Greg Laughlin, also at Berkeley, suggests that a terrestrial planet could exist in 55 Cancri's 'habitable zone' (see Graphic). Planets here would have liquid water, something that's rare among other solar systems found so far. Bond is positive about Marcy's result, "T'here's no way of knowing if it has smaller planets like Earth, but it's an exciting candidate," he says. He and Yock refuse to be frustrated that Marcy's work has received so much attention when they believe they have already found an Earth-like planet. 'There's a bit of competition here because our method has come along later,' says Yock.

One problem for the microlensing team may be that they have been too lucky too soon. Astronomers have seen only a handful of microlensing events with as high a magnification as this one, and no one has found any other kind of planetary system to compare with the signal. Many feel that to jump straight in with such an ambitious claim is just not the done twing.

But one thing Yock and Bond can say is that their system is nothing like our Solar System, as they have only seen signs of one planet. if their other Earth is real, it's on its own. Eugenie Samuel and Jeff Hecht

More at: Monthly Notices of the Royal Astronomical Society (vot 333, p 71)

Biotech's cash benefits may not be what they seem

BIOTECHNOLOGY has been a huge economic success for American farmers. At least, that's what an industry-sponsored study released last week found. It says GM technology helped farmers save over $1 billion in production costs, grow almost 2 million tonnes of extra crops, and avoid spraying thousands of tonnes of pesticides last year.

But critics say this represents only a tiny saving to US agriculture as a whole, and that the study ignores some cheap alternative ways to combat pests. Even if the savings are real, they say, raising yields and cutting costs in the US will do nothing to solve the problem of food shortages elsewhere in the world.

The report was prepared by Leonard Gianessi and a team at the National Center for Food and Agricultural Policy in Washington DC, and partly funded by Monsanto and the Biotechnology Industry Organization. Gianessi's study looked at the costs and benefits of eight GM crops planted in 2001: herbicide-tolerant soybeans, canola, corn and cotton; insect-resistant corn and cotton; and virus-resistant papaya and squash.

The bulk of the improvements came from just two crops. Soybeans engineered to tolerate the herbicide glyphosate saved farmers $1 billion. And a GM variety of corn, designed to control the European corn borer by expressing the Bt toxin, raised yields by 1.58 million tonnes.

Critics, though, are suspicious of those numbers. Charles Benbrook, an agricultural economist often cited by GM sceptics,points out that soybean farmers didn't actually: spend $1 billion less by using glyphosate-: resistant soybeans. The $1 billion represents the estimated extra cost to GM farmers of; using alternative weedkillers to glyphosate. But farmers who don't use GM soybeans find other, often cheaper, ways of controlling weeds, including tilling their fields.

Benbrook's own calculations show that farmers who use glyphosate-resistant soybeans may find weed control easier, but they pay a premium for the technology and probably only break even financially.

Benbrook says the gains in corn yields make sense, because Bt corn is one of the few effective ways to fight the com borer pest. But while it sounds impressive, it only represents around 0.6 per cent of the 250 million tonnes of corn grown in the US every year. And the $1.2 billion supposedly saved on production costs on all crops is just 1 per cent of the $125 billion income from crop sales in the US.

Gianessi insists the improvements from biotech are significant, especially if you add potential gains from 32 other biotech crops that could eventually come on the market. But critics say that's not a huge improvement for a country that already has food surpluses, and where the government just decided to spend $180 billion on farm subsidies.

The savings probably make even less difference to world hunger, says Brian Halweil of the Worldwatch Institute in Washington DC. The World Food Summit in Rome last week concluded that local food production is more important than producing more food globally, Halweil says. And the majority of corn and soybeans grown in the US will be fed to livestock, he adds. Kurt Kleiner

Nature steps on the gas Is the rate of evolution going to speed up again?

RISING levels of carbon dioxide could speed up evolution. It seems that the higher the levels of C02 in the atmosphere, the faster new species appear.

University of Kansas researchers modelled how the amount of C02 in the atmosphere has changed over the past 545 million years. Levels of this greenhouse gas used to be up to 20 times as high as today.

Then they turned to the fossil record to work out the rates at which species of marine animals appeared and disappeared over the same period. When they compared the variation in C02 with the fossil data, they saw a close match between high C02 levels' and more new species.

Bruce Lieberman, a member of the Kansas team, says the correlation is striking. "The two curves match each other extremely well," he says.

Daniel Rothman of the Massachusetts Institute of Technology had already suggested that levels of atmospheric CO, over the past 400 million years were linked to the amount of biological diversity. But instead the new work has found a better match with the rate at which new animal species were appearing and disappearing. It also extends the study back in time to encompass almost the entire history of aniihal life, including the initial burst of animal evolution known as the Cambrian explosion.

The researchers aren't sure how C02 levels could affect evolution. But if it is directly responsible for encouraging the formation of new and distinct species, or speciation, they say it's conceivable that the rise in atmospheric C02 predicted for this century might encourage new species to emerge, increasing biodiversity. But not for a while: any increase in the rate of evolution will not be enjoyed by our children or grandchildren but by whatever is inhabiting the planet 5 to 10 million years down the road, says Lieberman.

It's also possible that other factors, such as plate tectonics, could be influencing both evolution and levels of CO2. When continents break apart, the geological activity not only releases massive amounts of CO2, but could also drive speciation as populations become isolated. Either way, the researchers interpret the results as evidence that the planet is acting as a pacemaker for evolution.

But not everyone is convinced. While welcoming this new approach, Arnold Miller of the University of Cincinnati says the fall in average rates of speciation and extinction in marine animals since the Cambrian explosion could just as easily be explained by the disappearance of animals that evolve fast, such as trilobites, Dan Eatherley

More at: Proceedings of the National Academy of Sciences (vol 99, p 7832)

Fathering cancer Is the next generation paying the price for Sellafield after all?

WORKING at the Sellafield nuclear plant in Cumbria may have been harmful after all. Children of men who had been exposed to radiation while working at tht plant have twice the normal risk of leukaemia and lymphoma, according to a major new study sponsored by the nuclear industry.

Arguments have been raging for 12 years over whether radiation ftom Sellafield is to blame for a local cluster of childhood cancers. The suggestion that there was a link between the doses of radiation received by fathers and the incidence of leukaemia among their children was first made in 1990 by the late Martin-Gardner, an epidemiologist from the University of Southampton.

But his hypothesis has since been heavily criticised. Many experts have argued that large numbers of people moving in and out of the area, which is thought to spread infections that might increase the risk of cancer, can explain all the extra leukaemia cases seen around Sellafield.

Now, in the biggest and most comprehensive study to date, scientists from the University of NewcastIe have refocused the debate. 'Gardner may have been right," says Heather Dickinson from the university's North of England Children's Cancer Research Unit. She and her colleague Louise Parker compared the fates of 9859 children fathered by men exposed to radiation at Senafield with those of 256,851 children born to other fathers in Cumbria between 1950 and 1991.

Throughout the whole of Cumbria, they found that the incidence of leukaemia and non-Hodgkin's lymphoma was twice as high among the Sellafield children. The incidence was 15 times as great in Seascale, a small village next to the nuclear plant. Crucially, they also discovered that the risk to children rose in line with the radiation dose received by their fathers. Because a lot of people have moved in and out of Seascale, the researchers found that population mixing did account for most of the extra risk in that village, But for Senafield children throughout the county, mixing couldn't explain the two-fold increase in risk. There is growing evidence from human and animal studies that radiation damage can be passed ftom one generation to the next (New Scientist, I 1 May, p 5). But Dickinson and Parker point out that the risks are small: only 13 children of Sellafield workers contracted leukaemia over the 41 years. And because workers now receive much lower doses than in the past, there are unlikely to be implications for the current workforce. The research was part-funded by the Westlakes Research Institute, which is sponsored by British Nuclear Fuels (BNFL), the state-owned company that runs Sellafteld. 'This study is very reassuring for our workforce and confirms that the excess risk of leukaemia and non-Hodgkin's lymphoma, particularly in Seascale, can be largely attributed to population mixing,' says BNFI!s health director Paul Thomas. But local anti-nuclear campaigners see it differently. 'BNFL has tried to discredit Gardner's hypothesis for years,' says Janine Allis-Smith from Cumbrians Opposed to a Radioactive Environment. 'This study vindicates him and it is irresponsible of BNFL to ignore it." Rob Edwards More at: International Journal of Cancer 99, p 437)

Men with extra X chromosome father normal children

SEVERAL men with a serious genetic fault have been able to father normal children thanks to the controversial IVF technique known as ICSI. Men with Klinefelter's syndrome have an extra X chromosome. While many don't know about the condition until they discover they're infertile, others have symptoms such as mental retardation. Since the men cannot produce viable sperm, for the past few years Zev Rosenwaks's team at Cornell University has been retrieving immature sperm directly from their testicles. The best-looking ones are used to fertilise eggs from their partners using ICSI, or intracytoplasmic sperm injection, in which a sperm is injected into the e6g. Rosenwaks told a conference in Montreal last month that 9 of the 15 patients with Klinefelter's treated this way have managed to have children. All 14 babies have a normal number of chromosomes, even though some parents refused pre-implantation genetic diagnosis to ensure that this was the case.

The result is surprising because there's concern that ICSI allows genetic abnormalities to be passed on to the next generation. Indeed, at the same meeting David Page from MIT reported the results of treating 26 men who were infertile because of a deletion in their Y chromosome. Of these, 11 were able to have children thanks to ICSI, but all 10 sons inherited their father's deletion-which probably means they will be infertile when they grow up, Page says. Recent studies also suggest there is an increased, albeit small, risk of birth defects in children conceived with ICSI (New Scientist, 16 March, p 17). One of the boys in Page's study had a severe congenital heart defect, but it is unclear whether it was related to the defect in his Y chromosome or to the ICSI procedure, he says.

Rosenwaks adds that his team is also using the method of retrieving sperm directly from the testicles tolhelp men unable to father children after chemotherapy. "Those were patients who were thought to be sterile," he says. Sylvia Pagin Westphat, Montreal

The Grand Illusion
'THE last great mystery of science"; 'the most baffling problem in the science of the mind'; this is how scientists talk about consciousness, but what if our conscious experience is all a grand illusion?

Like most people, I used to think of my conscious life as like a stream of experiences, passing through my mind, one after another. But now I'm starting to wonder, is consciousness really like this? Could this apparently innocent assumption be the reason we find consciousness so baffling?

Different strands of research on the senses over the past decade suggest that the brave cognitive scientists, psychologists and neuroscientists who dare to tackle the problem of consciousness are chasing after the wrong thing. If consciousness seems to be a continuous stream of rich and detailed sights, sounds, feelings and thoughts, then I suggest this is the illusion.

First we must be clear what is meant by the term "illusion'. To say that consciousness is an illusion is not to say that it doesn't exist, but that it is not what it seems to be-more like a mirage or a visual illusion. And if consciousness is not what it seems, no wonder it's proving such a mystery.

For the proposal "It's all an illusion' even to be worth considering, the problem has to be serious. And it is. We can't even begin to explain consciousness. Take this magazine in front of your eyes. Right now, you are presumably having a conscious experience of seeing the paper, the words and the pictures. The way you see the page is unique to you, and no one else can know exactly what it is like for you. This is how consciousness is defined: it is your own subjective experience.

But how do you get from a real magazine composed of atoms and molecules to your experience of seeing it? Real, physical objects and private experiences are such completely different kinds of thing. How can one be related to the other? David Chalmers, of the University of Tucson, Arizona, calls it the 'Hard Problem". How can the firing of brain cells produce subjective experience? It seems like magic; water into wine.

If you are not yet feeling perplexed (in which case I am not doing my job properly), consider another problem. It seems that most of what goes on in the brain is not conscious. For example, we can consciously hear a song on the car radio, while we are not [email protected] conscious of all the things we do as we're driving. This leads us to make a fundamental distinction: contrasting conscious brain processes with unconscious ones. But no one can explain what the difference really is. Is there a special place in the brain where unconscious things are made conscious? Are some brain cells endowed with an extra magic something that makes what gois on in them subjective? That doesn't make sense. Yet most theories of consciousness assume that there must be such a difference, and then get stuck trying to explain or investigate it. For example, in the currently popular "Global Workspace" theory, Bernard Bears of the Wright Institute in Berkeley, California, equates the contents of consciousness with the contents of working memory. But how does being "th" memory turn electrical impulses into personal experiences? Another popular line of research is to search for the "neural correlates" of consciousness. Nobel Laureate Francis Crick wants to pin down the brain activity that corresponds to "the vivid picture of thcworld we see in front of our eyes". And Oxford pharmacologist, Susan Greenfield, is looking for "the particular physical state of the brain that always accompanies a subjective feeling" (New Scientist, 2 February, p 30). These researchers are not alone in their search. But their attempts all founder on exactly the same mystery-how can some kinds of brain activity be "in" the conscious stream, while others are n,ot? I can't see what this difference could possibly be. Could the problem be so [email protected] that we need to start again at the very beginning? Could it be that, after all, there is no stream of consciousness, no movie in the brain, no picture of the world we see in front of our eyes? Could all this be just a grand illusion?

You might want to protest. You may be absolutely sure that you do have such a stream of conscious experiences. But perhaps you have noticed this intriguing little oddity. Imagine you are reading this magazine when suddenly you realise that the clock is striking. You hadn't noticed it before but, now that you have, you know that the clock has struck four times already, and you can go on counting. What is happening here? Were the first three "dongs" really unconscious and have now been pulled out of memory and put in the stream of consciousness? If so, were the contents of the stream changed retrospectively to seem as though you heard them at the time? Or what? You might think up some other elaborations to make sense of it but they are unlikely to be either simple or convincing.

A similar problem is apparent with listening to speech. You need to hear several syllables before the meaning of a sentence becomes unambiguous. So what was in the stream of consciousness after one syllable? Did it switch from gobbledegook to words halfway through? It doesn't feel like that, it feels as though you heard a meaningful sentence as it went along. But that is impossible.

The running tap of time

Consciousness also does funny things with time. A good example is the "cutaneous rabbit". If a person's arm is tapped rapidly, say five times at the wrist, then twice near the elbow, and finally three times on the upper arm, they report not a series of separate taps coming in groups, but a continuous series moving upwards-as though a little creature were running up their arm. We might ask how taps 2 to 4 came to be experienced some way up the forearm when the next tap in the series had not happened yet. How did the brain know where the next tap was going to fall? You might try to explain it by saying that the stream of consciousness lags a little behind, just in case more taps are coming. or perhaps, when the elbow tap comes, the brain runs back in time and changes the contents of consciousness. If so, what was really in consciousness when the third tap happened? The problem arises only if we think that things must always be either 'in" or "out" of consciousness. Perhaps, if this apparently natural distinction is causing so much trouble, we should abandon it.

Even deeper troubles threaten our sense of conscious vision. You might be utterly convinced that right now you're seeing a vivid and detailed picture of the world in front of your eyes, and no one can tell you otherwise. Consider, then, a few experiments. The most challenging are studies of "change blindness" (New Scientist, 18 November 2000, p 28). Imagine you are asked to look at the lefthand picture in the illustration below. Then at the exact moment you move your eyes (which you do several times a second) the picture is swapped for the one on the right. Would you notice the difference? Most people assume that they would. But they'd be wrong. When our eyes are still we detect changes easily, but when a change happens during an eye movement or a blink we are change blind. Another way to reveal change blindness is to present the two pictures one after the other repeatedly on a computer screen with flashes of grey in between (for an example see http:// nivea.psycho.univ-parisS. fr/ASSChtmi/ kayakflick.gif). It can take people many minutes to detect even a large object that changes colour, or one that disappears altogether, even if it's right in the middle of the picture.

What do these odd findings mean? At the very least they challenge the textbook description that vision is a process of building up representations in our heads of the world around us. The idea is that as we move our eyes about, we build up an ever better picture, and this picture is what we consciously see. But these experiments show that this way of thinking about vision has to be false. If we had such a picture in our heads we would surely notice that something had changed, yet we don't. We jump to the conclusion that we're seeing a continuous, detailed and rich picture. But this is an illusion. Researchers differ in how far they think the illusion goes. Psychologists Daniel Simons of Harvard University and Daniel Levin of Kent State University, Ohio, suggest that during each visual fixation our brain builds a fleeting representation of the scene. It then extracts the gist and throws away all the details. This gives us the feeling of continuity and richness without too much overload.

Ronald Rensink of the University of British Columbia in Vancouver goes a little further and claims that we never form representations of the whole scene at all, not even during fixations. Instead we construct what he calls "virtual representations" of just the object we are paying attention to. Nothing else is represented in our heads, but we get the impression that everything is there because a new obqect can always be made "just in time" whenever we look. Finally, our ordinary notions of seeing are more or less demolished by psychologists Kevin O'Regan of the CNRS, the French national research agency in Paris, and Alva No@ of the University of California, Santa Cruz, who first described vision as a grand illusion. They argue that we don't need internal representations at all because the world is always there to be referred to. According to their "sensorimotor theory of vision", seeing is not about building pictures of the world in our heads, it's about what you are doing. Seeing is a way of interacting with the world, a kind of action. What remains between eye movements is not a picture of the world, but the information needed for further exploration. The theory is dramatically different from existing theories of perception. It's not clear who's right. Perhaps all these theories are off the mark. But there's no doubt about the basic phenomenon and its main implication. Searching for the neural correlates of the detailed picture in our heads is doomed because there is no such picture. This leaves another problem. If we have no picture, how can we act on the things we see? This question may seem reasonable but it hides another false assumption-that we have to see consciously in order to act. We need only think of the tennis player who retums a serve before consciously seeing it, to realise that this is false, but the situation is odder than this. We probably have several separate visual systems that do their jobs somewhat independently, rather than a single one that produces a unified visual world. David Milner of the University of St Andrews, and Melvyn Goodale of the University of Western Ontario, argue that there is one system for fast visuomotor control and a slower system for perceiving objects. Much of their evidence comes from patients with brain damage, such as DF who has a condition known as visual form agnosia. She cannot recognise objects by sight, name simple line drawings, or recognise or copy letters, even though she produces letters correctly from dictation and can recognise objects by touch. She can also reach out and grasp everyday objects (objects that she cannot recognise) with remarkable accuracy. DF seems to have a visual system that guides her actions, but her perception system is damaged. In a revealing experiment, DF was shown a slot set randomly at different angles (Trends in Neurosciences, vol 1 5 p 20, 1992). She could not consciously see the orientation of the slot, and could not draw it or adjust a line to the same angle. But when given a piece of card she could quickly and accurately line it up and post it straight through. Experiments with normal volunteers have shown similar kinds of dissociation, suggesting that we all have at least two separate vision systems. Perhaps the most obvious conclusion is that the slow perceptual system is conscious and the fast action system is unconscious. But then the old mystery is back. We would have to explain the difference between conscious and unconscious systems. is there a magic ingredient in one? Does neural information turn into subjective experiences just because it is processed more slowly? Perhaps the solution is to admit that there is no stream of conscious experiences on which we act. Instead, at any time a whole lot of different things are going on in our brain at once. None of these things is either 'in' or "out" of consciousness. But every so often something happens to create what seems to have been a unified conscious stream; an illusion of richness and continuity. It sounds bizarre, but try to catch yourself not being conscious. More than 100 years ago, psychologist William James likened introspective analysis to "trying to tum up the gas quickly enough to see how the darkness looks". The modem equivalent is looking in the fridge to see whether the light is always on. However quickly you open the door, you can never catch it out. The same is true of consciousness. Whenever you ask yourself, "Am I conscious now?' you always are.

But perhaps there is only something there when you ask. Maybe each time you probe, a retrospective story is concocted about what was in the stream of consciousness a moment before, together with a "self" who was apparently experiencing it. Of course there was neither a conscious self nor a stream, but it now seems as though there was.

Perhaps a new story is concocted whenever you bother to look. When we ask ourselves about it, it would seem as though there's a stream of consciousness going on. When we don't bother to ask, or to look, it doesn't, but then we don't notice so it doesn't matter. Admitting that it's all an illusion does not solve the problem of consciousness but changes it completely. Instead of asking how neural impulses turn into conscious experiences, we must ask how the grand illusion gets constructed. This will prove no easy task, but unlike solving the H Problem it may at least be possible.

Susan Blackmore is a psychologist, writer and lecturer based in Bristot Further reading:Consciousness Explained by Daniel Dennett, Penguin (1993) O'Regan and NoO's ideas wit[ soon be debated in a speciat issue of Behavioral and Broin Sciences