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Careful with that nuke Britain had an atom bomb so big it could have gone off at any time

NUCLEAR bombs stored at British military bases in the late 1950s could have exploded by accident, according to declassified Royal Air Force papers. just one going off would have been like 25 Hiroshima blasts.

Rushed into service as a stop-gap while Britain developed its own H-bomb, the gigantic devices held so much fissionable material that they risked going critical when armed, the documents reveal.

Up to a dozen of the huge fission weapons, based on a design codenamed Violet Club, were supplied to RAF bases including those at Finningley in South Yorkshire, Scampton in Lincolnshire and Wittering in Cambridgeshire between 19S8 and 1960.

But the RAF was worried that when the bombs' safety mechanism was disabled there was a "risk of catastrophe". In one memo dated 12 January 1959, a Group Captain Tait wrote: "A high-yield nuclear explosion would be possible if the weapon were jettisoned, or in the event of a crash on retum, or an accident in de-bombing."

The evidence was unearthed from the Public Records Office in London by Lesley Wright at John Moores University in Liverpool, David Wright of the University of Manchester and military historian Nicholas Hill. They say each bomb held around 70 kilograms of uranium-235, enough to create a 500-kiloton explosion.

But each weapon, made by the Atomic Weapons Research Establishment at Aldermaston, was packed with 450 kilograms of steel balls while on the ground to separate the sections of the uranium so that it could not accidentally form a critical mass.

To minimise the risk of stray neutrons from one radioactive mass triggering a chain reaction in another, the RAF initially stored the bombs in separate buildings, but later they had only to be 1.8 metres apart.

The bombs also took too long to arm. In the event of a nuclear attack the RAF was meant to be able to launch a nuclear-armed aircraft within 15 minutes, yet Tait's memo warns that removing the metals balls that would arm a Violet Club bomb took at least 20 minutes.

Lesley Wright argues that the unwieldy weapon was imposed on the RAF because the British government wanted to keep up with the US and the Soviet Union, whcr were already testing fusion bombs with yields in the megaton range. "This is a prime example of how the pursuit of superpower status and fear overcame rational decision making,' she says.

A Ministry of Defence spokesman says the bombs were supplied as a kit for VWcan bombers "which could be assembled and deployed in a national emergency". But the MoD insists that there was "no risk" of an accidental explosion because it "took all the necessary precautions to ensure that [Violet Club] was transported and stored safely". Rob Edwards

Lost and found The Sun's missing neutrinos were there all the time

AT LAST physicists have solved a problem that's been plaguing them for three decades. Why does the Sun seem to emit fewer neutrinos than it should? It's simple. Neutrinos can change from one form to another.

Until now physicists had begun to think that either our understanding of the structure of the Sun was wrong, or that neutrino detectors did not work properly. But this week, a team of researchers from Canada, Britain and the US announced that neutrinos made in the Sun can change to other types en route to Earth. The other kinds are harder to spot, and so fool the detectors.

The team discovered that this 'neutrino mixing" was taking place using results from the Sudbury Neutrino Observatory (SNO), a giant particle detector buried 2 kilometres underground in a nickel mine in Ontario, Canada (see right). When they account for the effect, the results agree closely with accepted theory, says team member Nick jelley of Oxford University. "When you put the mixing in you find that the flux of neutrinos starting out in the Sun is completely consistent with the standard solar model," he says. 5 "I'm thrilled," says John Bahcall of the Institute for Advanced Study in Princeton, New Jersey, one of the authors of the solar theory. "A lot of my colleagues have been giving me high-fives today."

The results also confirm that neutrinos have mass, as first reported in 1998 by physicists at the Super-Kamiokande particle detector (Super-K) in Mozumi, Japan. This pokes a sizable hole in the prevailing theory of particle physics, the Standard Model, which predicts that neutrinos have no mass and cannot change type.

There are three types of neutrino: the electron neutrino, the muon neutrino, and the tau neutrino. Physicists are confident that nuclear reactions in the Sun produce only electron neutrinos, and the SNO experimenters concentrated on this type. Every second, more than a thousand billion electron neutrinos pass through the SNO detector, which comprises 1000 tonnes of heavy water surrounded by 10,000 electronic eyeballs called photomultipliers. But each day only a handful of the neutrinos interact with the heavy water and are detected. . In the interaction, a deuterium nucieusa neutron bound to a proton-absorbs an electron neutrino and decays into two protons and an electron. The electron carries away most of the neutrino's energy, producing a detectable flash of light.

The SNO team measured the flux of electron neutrinos and compared it with earlier results from Super-K, which used ordinary water. Super-K also detected muon and tau neutrinos, although not as well as it detected electron neutrinos.

They found that their electron-neutrino rate was much lower than Super-K's more inclusive rate. That means that some of the electron neutrinos generated in the Sun must be turning into muon and tau neutrinos, and that Super-K detected some of the converted particles, says Art McDonald of Queen's University in Kingston, Ontario. "More than 60 per cent are being transformed," he says.

Two years ago, the Super-K team confirmed that muon neutrinos can become tau neutrinos. The new results are the first to show that electron neutrinos also 'mix".

The solar neutrino problem has vexed physicists since 1968, when Raymond Davis Jr of Brookhaven National Laboratory near New York built a neutrino detector in a gold mine in South Dakota and observed roughly half the neutrinos predicted by Bahcall's calculations. "It was fun in the early days," Davis says. "We had a lot of arguments. Some people said it just had to be wrong."

But experimenters tended to question the theoretical predictions rather than their own results, says Lawrence Sulak, a physicist at Boston University and a member of the Super-K team. "Most of us didn't put too much credence in the solar theory," he says. "But it looks like it's damn good."

Hans Bethe, a physicist at Cornell University in Ithaca, New York, agrees with that assessment: "John Bahcall went to great lengths to show from other properties of the Sun that the theory was correct." Adrian Cho

Insult to injury Rape seems more likely to make women pregnant than sex by consent

A SINGLE act of rape may be more than twice as likely to make a woman pregnant as a single act of consensual sex. That statistic will reopen the hotly contested debate over whether rape can be a successful reproductive strategy in evolutionary terms. It could help to explain why men raping women has been so common throughout history and across cultures, two American researchers told the conference. Previous studies found that rates of pregnancy resulting from rape could be anything up to 30 per cent, compared to a 2 to 4 per cent chance of getting pregnant from a single act of consensual sex. This led some biologists, notably Randy Thornhill from the University of New Mexico at Albuquerque, to parade the figures as evidence that rape is a natural way for men to spread their genes (New Scientist, 19 February 2000, p 44).

But in the ensuing controversy, the studies were all roundly criticised. Some rely on crime statistics, which may skew the figures: rape victims who become pregnant may be more likely to report the crime than those who do not. Others fail to measure the influence of contraception-either preventive or post-coital, such as the morning after pill. And some include acts of oral and anal rape, which cannot result in pregnancy.

Jon Gottschall, a researcher at St Lawrence University in Canton, New York, says the studies failed to answer the crucial question: 'What is the evolutionary success of rapists?"

To find out, he and his wife Tiffany Gottschall examined the results of National Violence against Women Survey, a study by the National Institute of Justice and the Centers for Disease Control and Prevention. The women studied were phoned at random and interviewed about their experiences. The Gottschalls focused on 405 women who had suffered a single incidence of penile-vaginal rape at some point between the ages of 12 and 45. Of these, 6.4 per cent became pregnant. But that figure jumped to nearly 8 per cent when the researchers allowed for the women who'd been using birth control-US government statistics show that I in 5 of the women in the sample were likely to have been using the pill or an IUD.

To complete the comparison, the Gottschalls needed to know how many women in that age group get pregnant from one-night stands and other one-off acts of consensual sex. The answer-reported this year in a separate study by Allen Wilcox, head of the epidemiology branch of the National Institute of Environmental Health Sciences-was a mere 3.1 per cent. "It was surprising to see this margin of difference," says jon Gottschall.

Crucially, he believes the difference cannot be explained away by the argument that women having regular consensual sex are, on average, more likely to be using contraception than rape victims. "All the women in Wilcox's study were trying to get pregnant, and not taking precautions," he says. A more likely interpretation, say the Gottschalls, is that rape really does result in more pregnancies.

One possibility is that women feel more attractive and sexy when ovulating, and unconsciously give off signals that rapists might pick up-although it's unclear whether men do in fact notice these signais (see p 12). Another, more likely explanation is that rapists target attractive and healthy-looking women-both characteristics that can indicate fertility. But whatever the reason, say the researchers, none of this absolves the rapist or means the victim is in some way to blame.

However, sociologist Frank Furedi of the University of Kent at Canterbury says that trying to answer questions about the reproductive success of rape is essentially meaningless. He believes that what constitutes rape or a consensual sexual act within a relationship can be extremely ambiguous and says

'Some biologists parade the figures as evidence that rape Is a natural way for men to spread their genes'

that phone surveys often push women into claiming they have been raped. "When relationships sour, women often redefine them in a destructive form," adds Furedi. Rape has also meant different things through history. 'Considering it as a strategy is essentially nonsense." Gottschall says women may also sometimes reinterpret a rape as a consensual act years later when the relationship has improved. He agrees that the data in the surveys is not perfect, "but the best information we have still all points in one direction".

One other question remains unanswered. For this form of rape to be a successful evolutionary strategy, the benefits of the crime have to outweigh the costs for the rapist. And the costs are extremely hard to judge. However, some surveys suggest that less than 1 per cent of rapists are convicted in the US, says Jon Gottschall. Even in traditional societies, a high proportion of rapists may have never been punished because of the costs to the victim of reporting the crime. Matt Walker

War of words Why women have more reason than men to fear the gossip's tongue

MOST women may be physically weaker than men, but they have a formidable weapon at their disposal: gossip. Nattering to each other in this way could be why women form such strong social bonds, says anthropologist Nicole Hess from the University of California at Santa Barbara.

In prehistoric times, men cooperated to hunt or see off rivals competing for their mates. But Hess wondered what made women first form cooperative social groups. "My feeling, growing up as a female, was that women also have strong coalitions. They form strong friendships too."

She thinks gossip could be the key. By chatting to each other, women have a powerful weapon that could be used to outcompete their rivals for precious resources.

Hess and her colleague Edward Hagen tested the idea by asking men or women to imagine that they had discovered someone cheating in a competition, at the expense of a real-life friend. The cheater warned them to keep quiet, otherwise they'd be beaten or bad-mouthed. Depending on the scenario, the cheater was either alone, or backed up by a group of allies.

Men threatened with violence were less likely to expose a cheat if he had back-up. But if told they would be gossiped about, it made no difference whether the cheat had allies or not. For women, the opposite was true. The number of enemies was unimportant when violence was threatened. But if faced with verbal punishment, they were more likely to keep quiet if the cheater had friends.

Hess says this shows that women who share information within a group have a powerful advantage-they could use gossip to damage the reputations and social status of their rivals. This ploy may have helped them secure more food and material resources for themselves and their children.

Men competed in warfare and other physical or violent confrontations, and were judged on obvious traits such as strength and hunting ability. But women's key attributes of fertility and fidelity are less obvious, so they were more vulnerable to gossip, Hess says. ' Social anthropologist Camilla Power of the University of East London in Dagenham agrees. "It's a great idea," she says. "In evolutionary terms, gossip was started by women.' But she isn't convinced that gossip was the reason women formed groups in the first place. You need trust for gossip to work, otherwise no one will believe you, she says. And women would need to form coalitions for that trust to develop. Joanna Marchant

Not so jumpy Bacterial genes stayed put after all

PHEW! Our genome wasn't invaded by genes from bacteria.

Earlier this year, it was claimed that over a hundred bacterial genes had somehow jumped into the genomes of vertebrates. But Michael Stanhope and his team at GlaxoSmithKIine in Pennsylvania think the claims were based on faulty analysis. They say their findings should calm fears that genes from genetically engineered foods or bacteria could easily jump to humans.

When the first analysis of the human genome appeared in February (New Scientist, 17 February, p 4), researchers said they'd found 223 genes that were common to humans and bacteria but absent ftom evolutionary links between bacteria and vertebrates such as yeasts, worms and flies. They suggested that at least 113 genes had jumped straight from bacteria into vertebrates. But while bacteria regularly swap genes among themselves, Stanhope was sceptical that there had been so many transfers to vertebrates. "One or two would be very interesting," says Stanhope. "One hundred and thirteen? Incredibly extraordinary."

Stanhope's team picked 28 of the genes and used computer tests to study their evolution and relation to other genes more closely. The team also ran tests on a database the original study had overlooked.

They found no evidence of bacterial genes suddenly crossing to humans. Instead, they found that invertebrates such as flies and worms had similar genes, showing that all animals inherited them from a common ancestor after all. But there has been traffic the other way-they found evidence that one gene has jumped from humans to bacteria.

Other researchers have also cast doubt on the original bacterial transfer study (Science, vol 292, p 190), highlighting problems with the computational methods used.

"It's a bit symptomatic of the bioinformatics field at the moment-it's sometimes missing the biological perspective," says Stanhope. "We need to keep in mind that bringing order to genomic sequences is a biological issue." Claire Ainsworth More at: Nature (vot 411, p 940)

Hair today, skin tomorrow Now surgeons don't have to take skin to make skin

BY PLUCKING out a few hairs, doctors can grow skin grafts from a patient's own cells.

The technique could replace the painful method of taking skin from another part of the body for grafts or tissue culturing, Modex Therapeutics of Lausanne, Switzerland, told a conference in London last week. "We're changing patients' hair to patients' skin," says Edward Baetge, the company's chief scientific officer. Called Epidex, the technique uses the stem cells found in hair follicles, which can be transformed into skin cells. "Doctors can pluck hair from any point on the body,' Baetge says. Then they send between 20 and 100 individual hairs to Modex by post. The company grows the skin and sends it back in as little as a month. The technique compares very favourably with other tissue culture techniques that are available or under test at present, says Tania Phillips, a dermatologist at Boston University School of Medicine. "If you can do it by pulling out a few hair follicles, that's wonderful," says Phillips.

"It's a great development because to get cultured keratinocyte grafts ftom individual patients, you must take at least 1 centimetre of skin," she says. "With the hair cells, it sounds like you can provide skin coverage without hurting the patient." Thomas Hunziker and Alain Limat originally developed the technique at the University Hospital skin clinic in Berne. They

discovered that they could grow skin cells from stem cells and other versatile "transient amplifying cells" taken from a part of the follicle known as the outer root sheath. In the latest version of the process, the stem cells are deposited onto trays, which are placed above a layer of unrelated human skin cells. These secrete growth factors that transform the stem cells into basic skin cells called primary keratinocytes. If the patient is too sick to be treated, the keratinocytes can be frozen until he or she is ready. Otherwise, the next step is to expose the cells to air. This turns the layer of cells into proper skin, with a horny layer on top, a basal keratinocyte layer at the bottom, and stratified epithelium in between. The company sends back discs of skin about I centimetre across and a tenth of a millimetre thick. The discs are applied to half the damaged area, and grow to cover the entire wound in about three months. Last week, Modex released preliminary results of a trial on 80 patients with diabetic ulcers at 12 clinics in Germany and Switzerland. For the first 36 patients to be treated, the company says the technique has worked at least as well as the traditional grafting technique, called split skin mesh grafting. Baetge says that the results are very encouraging. He adds that while the technique is being tested only on fairly small ulcers, Modex is looking into its potential for treating larger wounds. Andy Coghtan

Forget digital encoding, conceal images in a sea of chaotic light

A MOVIE projector can transmit images from a strip of celluloid film directly onto a screen. But when you send cable TV pictures down an optical fibre, you need to process each image line by line, and send the details of each pixel encoded in a laser beam. If only there was a way to camouflage the pictures and send them directly down the fibre. Well now there is, and the secret is chaos.

Conventional images have to be digitised and encoded as a string of bits before they can be sent. The receiving unit decodes the data and reassembles the picture, a process which uses a lot of computing power.

Now jordi Garcia-Oialvo from the Technical University of Catalonia in Barcelona and Rajarshi Roy from the University of Maryland in College Park can encode and send whole images down optical fibres. They do this by mixing the images with a "chaotic optical signal", which is generated by repeatedly passing a laser beam containing the image through a non-linear crystala material whose light output is not proportional to the input intensity. This "messes up" the signal, but in a way that can be undone. You no longer need to digitise the image using complex codes. "It's a purely optical system," says Garcia-Ojalvo.

Chaotic communication first became possible about 10 years ago when engineers realised they could create chaotic signals in a transmitter and unscramble the chaos at the receiver. The signal to be sent is bounced around a cavity containing a set of four mirrors. Between two of the mirrors, a non-linear crystal renders the signal chaotic. In the receiver, a similar set of mirrors and non-linear crystal work in reverse to reconstruct the original message. The technique has already been tested with analagous equipment for radio transmissions. 'But optical systems are much faster

than electronic ones," says Garcia-Ojalvo. And because the researchers have worked out how to send entire images in one go without having to read them line by line, their technique is even faster. Garcia-Ojalvo says that although some fine-tuning is needed, they can already send pictures at speeds that would require gigabit bandwidths in a computer network. Chaotic signals have other advantages. They are resistant to noise, so do not require complex error-correction, and look very much like the hiss of background noise, making them hard to jam. 'They are naturally camouflaged and so have a low probability of detection," says Lou Pecora, a pioneer in the field of chaotic communications at the Naval Research Laboratory in Washington DC. "It may be that chaotic signals can carry video images more efficiently than conventional signals," he adds. "But we need more tests to find out for sure." Justin Mullins

Inner Visions

Tripping on hallucinogenic drugs reveals more about our inner selves than the hippies ever bargained for, says Dana Mackenzie

IN A DORM ROOM dimly lit by a lava lamp, a freshman awaits the beginning of his first LSD trip. Slowly, the walls come alive and begin to dance with colour. And then he sees whirling spirals of stars that disappear into the distance. A network of cobwebs that grows across the room. An infinite subway tube, surrounded by fluorescent lights...

Across campus, his science teachers experience their own psychedelic visions-but without resorting to illegal mind-altering substances. jack Cowan, a mathematician and neuroscientist at the University of Chicago, has built a neural network so powerful it can trip out. His computer's hallucinations match with almost spooky accuracy the visions of acid trippers, shamans and seers-visions that have always been interpreted as revelations from a transcendental consciousness.

Now, after more than two decades, Cowan and his team think they have found where hallucinations really come from. And there's nothing transcendental about it. An LSD trip is really a journey into the brain, says Cowan. "It's just the innate tendency of the brain to make patterns when it goes unstable."

Cowan's goal is to find out how the brain makes

sense of the visible world-not when we're tripping, but under ordinary circumstances. In the process, he may learn how it breaks down in other extraordinary conditions, such as migraine headaches. Hallucinations could even offer a route to the more profound depths of the mind, to emotions and conscious thought.

Hallucinations seem to come in an endless variety, as individual as dreams. So it seems improbable that they can even be categorised, never mind calculated by a computer. But in the 1920s, Heinrich Kliiver, a neuroscientist at the University of Chicago, discovered they did indeed fall into a number of distinct categories. Kliiver interviewed dozens of people who had taken the drug mescaline, and even took it himself. Keeping a commendably straight head, Kliiver eventually saw patterns in the patterns.

In the earliest stages of a trip, most subjects reported seeing abstract, geometrical images. Other writers have noted the same thing. "The typical mescaline or lysergic acid experiment begins with perceptions of coloured, moving, living geometrical forms," wrote Aldous Huxley in 1954 in Heaven and hell. "In time, the pure geometry becomes

concrete, and the visionary perceives, not patterns, but patterned things, such as carpets, coverings, mosaics." Kltiver classified these patterns into four types or "form-constants": tunnels, spirals, cobwebs and honeycombs. Unlike Huxley and Kliiver, Cowan has never sampled the drugs he studies. "I feel bad about it," he says. 'I have to rely on all these reports in the literature." He also hears plenty of personal accounts from students and others who attend his lectures. "Some people see these illusions when they're going to sleep or waking up," Cowan says. "People have seen them after taking anaesthetics. People claim to see them when they meditate, or have so-called near-death experiences." Cowan believes that the "tunnel of light" illusion commonly reported in near-death experiences is simply the first of Kliiver's four form-constants. Cowan was turned on to the study of hallucinations from an unexpected direction. In 1977 he was working on pattern formation with graduate student Bard Ermentrout when he stumbled across illustrations of Kliiver's patterns. "We saw immediately that the hallucination patterns were similar to convection patterns," says Cowan. The convection of hot water involves a delicate interplay of forces. When a pan of water is heated from below, the hot water at the bottom is more buoyant than the water above, and tries to rise. If the temperature difference is not too great, the lower layer sheds its heat by diffusion before it can rise very far, so the water remains stable. But at a certain critical temperature, diffusion is not enough to cool off the lower layer, so plumes of hot water start to rise. Between each pair of rising plumes, cold water descends, so a pattern spontaneously emerges: rolling tubes of water that form parallel stripes, or square or hexagonal cells. Cowan guessed that hallucinations must also be spontaneous patterns of activity produced by two competing forces-this time in the brain. One, like the water's buoyancy, tends to excite neurons while the other, like the diffusion of heat, tends to calm them down. He speculated that this could happen in the primary visual cortex, sometimes called Vl. This is a layer of tissue two to three millimetres thick at the back of the brain which serves as the first layer of processing for images gathered by the retina.


To test their idea, Ermentrout and Cowan developed a mathematical model of Vl and gave it a dose of virtual LSD. Their model reflects the fact that each neuron tends to excite its neighbours and inhibit those a little farther away. Then when the eye sees a large, featureless object, like a big red blob of paint, every neuron in the middle of the image will be excited by nearby neurons and inhibited by those farther away. So it receives no net input from other neurons. It's the brain's way of saying, "There's nothing interesting happening here." LSD upsets this balance. One of the effects of the drug is to allow neurons to fire when there is nothing in the visual field. Ordinarily, a neuron won't start firing unless the input from the retina and ftom neighbours exceeds a critical threshold. This ensures that if a neuron fires by mistake, it won't convince its neighbours to fire and the activity dies out. But drugs can lower the threshold-LSD does it by making the brainstem secrete less of the inhibitory chemical serotonin. If the threshold is lowered far enough, then excitation starts to beat inhibition, and spontaneous waves of activity form in the brain. It's like turning up the heat under the pan of water. The first patterns that form will be the same ones that are seen in the water: parallel stripes, checkerboards and hexagons. So why don't LSD users see parallel stripes across their visual field? Because these patterns are in the cortex, not the retina, Cowan reasoned. A lot of cortical real estate is devoted to objects close to the centre of the field of vision, where our sight is sharp, while relatively little is used for peripheral vision. Mapped onto the cortex, an ordinary scene is grossly distorted: objects near the centre loom large, taking up most of the brain area. When you run this distortion backwards, evenly spaced parallel lines in the cortex appear sucked together into the centre of the visual field, creating the visual impression of either a spiral or a tunnel. The regular checkerboard and hexagon patterns turn into spiralling squares or hexagons.

So more than half a century after Kliiver set out his form-constants, two of them were finally explained. LSD users see spirals and tunnels because those are the real-world objects that fit the patterns of neural firing in their cortex. Timothy Leary, the guru of 'tune in, turn on, drop out' fame, speculated in The Psychedelic Experience, 'These visions might be described as pure sensations of cellular and sub-cellular processes.' So just as Leary guessed, the spaced-out brain is tuning into its own architecture.

But what about the other two form-constants, the cobweb and honeycomb illusions? These are both lacy, filigree patterns, while water boils in fat rolls, so it's obvious the convection analogy won't work here. Cowan was confidant that his theory would provide the framework to understand these hallucinations, too. In the 1980s, it became clear that the neurons in Vl are not sensitive simply to the position of an image on the retina. Most of them are sensitive to edges, firing if they sense an edge passing through a particular point in the visual field but remain silent if that point is similar to its surroundings. These cells are arrayed in little patches called hypercolumns that represent a particular part of space (see Diagram, left). Within the hypercolumn, each neuron responds to an edge at a slightly different orientation.

Instead of signalling to their neighbours in the same hypercolumn, these neurons contact their counterparts in different columns, which represent similar orientations in slightly different parts of space. Then, if there really is an edge, neurons with the right orientation excite each other, so the brain is more likely to detect it.

These long-range connections seemed essential to understanding the last two hallucination types, but they added a new level of complexity to Cowan's mathematical model of the cortex. Hot water was no longer a good analogy, because the forces at work there-buoyancy and viscosity-are all short range. Now equations were needed to describe something long range and direction-sensitive. The maths turned out to be like those of a hot gas in a magnetic field.


Cowan and his graduate student Matthew Wiener programmed in these equations, and found many possible waveforms could result. But they couldn't tell which of'these patterns would be the first to appear spontaneously. They needed someone who could combine an expert's understanding of quantum mechanics and neuroscience, and in 1998, Cowan found just the person. Paul Bressloff of Loughborough University in Leicestershire had trained as a specialist in quantum gravity, then taken a detour into neural networks. In a few months of intense work at Chicago, he helped Cowan and Marty Golubitsky of the University of Houston work out the waves of activity that should emerge spontaneously among orientation-sensitive cells. The results appeared earlier this year in Philosophical Transactions of the Royal Society (vol 356, p 1).

The winning patterns were those in which the edges naturally close up into small square or hexagonal cells. Cowan's theory precisely reproduces Klilver's two missing form-constants. When the fine-edged squares and hexagons on the cortex are filtered back through the retinal map, they look like lacy cobwebs and honeycombs.

So far so good. But has Cowan done any more than confirm a wiring pattern for the brain that neuroscientists had already worked out? He points out that to understand how the brain works, we need more than wiring: we have to know how these circuits actually behave. In fact, Cowan's model does hint at this. One unexpected outcome is that subtle changes in the wiring of the model brain can cause significant changes to its preferred hallucination patterns. For example, if the longrange connections in the model always run between edge neurons that represent identical orientations, would generate hallucinations resembling herringbone twill. Clearly our brains are not wired this way; if they were, who knows what effect psychedelic visions of tweed blazers might have had on 1960s fashion. To produce cobwebs and hexagons, we actually need the connections to be a little more slapdash. Perhaps the human edgedetection system is wired this way because it helps us spot small, closed contours.

On the other hand, the herringbone patterns may emerge if the chemical stimulation is changed. Perhaps the theory can explain other kinds of visual disturbances that were thought to be unrelated to LSD hallucinations, such as the auras and zigzag patterns seen by people suffering a migraine attack. If so, it could tell us what changes in the brain cause migraines, and perhaps set us on course for a cure.

Lurking in the background is the much bigger issue of where the mind comes from. To what extent is the mind, and all the rich variety of inner experiences that gives us a sense of self, simply a product of physiological processes in the brain? Hallucinations could be a perfect place to start answering this question.

The apostles of the psychedelic sixties scorned the scientific approach to understanding an LSD trip. "Bobbing around in this brilliant, symphonic sea of imagery is the remnant of the conceptual mind," Leary wrote. "On the endless watery turbulence of the Pacific Ocean bobs a tiny open mouth, shouting (between saline mouthfuls), 'Order! System! Explain all this!"' To appreciate a hallucination, Leary said, you have to let go of the urge to rationalise it.

Tom Wolfe pitched in with The Electric Kool-Aid Acid Test. "The White Smocks liked to put it into words, like hallucination and dissociative phenomena. They could understand the visual skyrockets. Give them a good case of an ashtray turning into a Venus flytrap or eyelid movies of crystal cathedrals, and they could groove on that... That was swell. But don't you see?-the visual stuff was just the d6cor with LSD... The whole thing was ... the experience ... this certain indescribable feeling ... The experience of the barrier between the subjective and the objective, the personal and the impersonal, the I and the not-I disappearing ... that feeling!"

Cowan makes no apologies for being one of the White Smocks. He thinks that the "visual skyrockets" and that 'certain indescribable feeling" are part and parcel of the same experience. As the drug penetrates to deeper and deeper areas of the brain-visual layers, cognitive layers, emotional layers and, finally, whatever part of the brain gives us our sense of self-awareness-our subjective experience becomes enormously more complicated and richer. And yet what's going on at the cellular level may not be so different at each layer.

"Does that mean that everything can be observed and described?" Cowan asks. "I happen to believe the answer is yes. I don't think there's anything in the brain that science can't ultimately deal with." But the answers aren't going to come along tomorrow. "There are a hundred vision chips, a hundred sound chips. We now understand a bit more about one of the vision chips," he says. Cowan is already planning to look at other aspects of visual hallucinations, such as texture and size perception.

Journeying deeper still into the mind might not be much harder. The neocortex, the layer of the brain that includes V1, is the part that evolved most recently.

It is also the part that supposedly makes humans so intelligent. Because it hasn't been around long, its cells are all structurally quite similar, even if their func tions are quite different. "The reason this is a note for opti mism, " says Gary Blasdel of Har vard University, "is that when you really understand the oper ations that go on in a particular cortical area, it will generalise to other areas." Cowan's comput erised visions might just be the beginning of a really cool trip. D

Dana Mackenzie is a mathematics and science writer based in Santa Cruz, California

Further reading: The Doors of Perception by Aldous Huxley, Flamingo (1994) "Hallucinations" by R. K. Siegel, Scientific American, vol 237, p 132 (1977)

Stolen Fishery

FISHING used to be easy in the waters of the Banc d'Arguin National Park in Mauritania. "In the old days we could see the mullet coming," says Mohammed ould Swidi, chief of lwik village, as he looks out over the waters of the Atlantic. 'We just walked into the water with our nets to catch them." Not any more. Not since the rest of the world got wise to the riches here.

In oceans the world over, fishers have pillaged areas rich with fish. But that wasn't supposed to happen here, because the Banc d'Arguin is Africa's largest marine park. Set up in 1976, the park is a huge slab of empty desert flanked by mudflats and islands that occupies an open bay the size of Cyprus. It protects the prime breeding and nursery areas for one of the world's richest coastal fishing areas, stretching more than 2000 kilometres from Morocco to GuineaBissau. Its waters are open only to a few dozen local fishing boats equipped with small nets and sails. The park should have been a flagship for the growing body of conservationists who see marine parks as the key to protecting the world's surviving fisheries.

Yet the flagship is foundering. The problem? African n;tions may want to protect their valuable fish stocks, but their governments feel the need to sell fish to the rest of the world in order to make money. Also, while the boundaries of the park may be fixed, the fish stocks are not. As the fish swim in and out with the seasons, tens of thousands of traditional fishers from all along the coast lie in wait-and beyond them, cruising the horizon, are hundreds of giant foreign trawlers, whose catch dwarfs that of the traditional fishers. "I'm not optimistic about

the survival of the fisheries here,' says Pierre Campredon, a French marine biologist who advises the Mauritanian government on fisheries management. If he is right, then conservationists worldwide would do well to pay close attention to the Banc's fate. Otherwise hopes for the success of marine reserves wfll be dashed.

The Banc's vast expanse of shallows and mudflats harbours a cornucopia of marine life. The park's chief scientist, jean Worms, says it Is unique in all Africa, probably the world. The park's large area of shallow water on the shores of the Sahara desert is certainly special. It gets plenty of sunshine and, thanks to an adjacent ocean current, it also receives nutrient-rich waters carried up from the ocean depths. Plankton grows in profusion and seagrasses spread across the mud. These food sources sustain a complex food chain of fish and millions of seabirds, including some two million winter migrants from Europe.

This food chain supports a fishery that is West Africa's single most valuable natural resource. And as other spawning and nursery grounds along the coast have been lost to coastal development, dams, pollution, trawling and the dynamiting of reefs, the Banc's importance has grown dramatically. A decade ago, only the people of the park, a clutch of poor desert communities called the Imraguen, took any interest in its fish. Now, because of overfishing elsewhere, the whole world does. The waters that border the park send shrimps to Spain, lobster to japan, grouper to Portugal, the fins of sharks and rays to Asia, shark meat to half of Africa and almost anything to Dutch fishmeal factories.

Back in lwik, Swidi tells me that the mullet have fallen victim to Senegalese fishers sailing north and fishing on the park boundary after their own fish stocks collapsed. The early 1990s saw a twentyfold increase in the Mauritanian mullet catch, thanks to a new market for mullet roe in Europe-where it fetches $150 a kilogram. It was this, not fish for their own tables, that drew these fishers north. Not surprisingly, stocks collapsed. "All our efforts at conservation were completely cancelled out in just a few years," says Campredon. Now other fish are heading toward the same fate. When the mullet stocks collapsed, the fishers turned to sharks, with dramatic effect. I watched on the beach at lwik earlier this year as villagers gutted a hundred sharks, rays and guitarfish caught by one boat. A trader had driven 200 kilometres up the beach from the capital Nouakchott to buy the meat for Ghana. The fins would later be sold for the soup dishes of Asia. Some species, such as hammerhead and tiger sharks, are almost gone from these waters. It's hardly surprising. Sharks reproduce slowly compared to other fish. They have long lives, mature slowly and have few young-when they get the chance to breed at all. At lwik, I saw dozens of unborn young being cut from the female sharks and thrown aside.

Empty seas

Information on fisheries is hard to come by in West Africa. Marine research is underfunded and in its infancy. But the marine scientists I spoke to in Mauritania, Senegal and GuineaBissau are all in agreement. As Cherif ould Toueilib, director of the Mauritanian government's two-year-old fisheries research bureau, puts it: "The cake is getting smaller with more eaters." Even without hard numbers it is easy to see that a crisis is developing. Dimas Santos, who exports fresh Mauritanian grouper, bream and hake to European restaurants, looks gloomy in his packing plant behind the beach at Nouakchott. "The fish just aren't in the sea any more. I can only buy half of what I could get two years ago. We are paying the price of years of overfishing," he says. Many of his suppliers are Senegalese, the most enthusiastic of the local fishers. From the coastal villages of Senegal, thousands of open motorised boats, called pirogues, sail the length of the West African coast laden with boxes of ice to preserve their catch. But their journeys get ever longer because fish are in shorter and shorter supply. On Hann beach just outside Dakar, the Senegalese capital, fisherman Bira Gueye says that it now takes him four hours to reach fish shoals instead of 20 minutes. Many Senegalese fishers go out for a fortnight at a time, travelling the 600 kilometres to the Banc d'Arguin. But, as another fisher in Dakar puts it: "It's worth it. It takes two weeks to catch here what you can get in a night on the Banc."

Because the pirogue fishers are so visible, they often bear the brunt of the blame for declining fish populations specially since many stray across the park boundary to poach in the Banc's rich nursery areas. Indeed, the poachers probably take far more fish than the local villagers. Lamin, a 19-yearold Gambian poacher I met as he waited to reclaim his impounded boat, boasts he can enter the park with impunity at night. He only got caught when he lost -his bearings and failed to make himself scarce at dawn.

Policing is far from perfect, admits Antonio Araujo, the park's conservation officer. Two of his three patrol boats are out of action, and he has no night binoculars or searchlights. The radar that scans the seas for ships cannot see the pirogues because they are too small. But despite the poaching, the fish catch within the park is a fraction of the harvest just outside. 'Pirogue fishing causes little harm compared with the big trawlers," says Campredon. Peering at a radar screen at Mamghar in the south of the park, Araujo points out the slow-moving white blobs of around 40 large trawlers from Spain, the Netherlands, Ireland, japan and China "fishing the line" close to the park boundary. It's a fair bet that among them is one of the world's largest fishing vessels, the Irish-owned Atlantic Dawn, which is 144 metres long, has a crew of 60, can hold 7000 tonnes of fish, and is dedicated full-time to Mauritanian waters. The European Union bought the rights to take 250,000 tonnes of fish a year from Mauritanian waters-half of the foreign take-and more in neighbouring Senegal and Guinea-Bissau. It pays the Mauritanian government one Euro per kilogram, though the deal is up for renewal. And all told, the 600 or so foreign trawlers catch 30 times more than the pirogues. The European Union's fisheries policy stipulates that all fishing should be 'sustainable", and Kevin McHugh, who owns the giant Atlantic Dawn, does not feel he is damaging Mauritania's prime resource. "Those waters down there are alive with fish,' he says. "There are very strict controls. But they like to see us coming, because we are paying for our investment and there is a direct return to that state." But Callum Roberts of York University, one of the world's leading experts on marine reserves, has a different view. "Foreign trawlers are strip-mining African waters of their fisheries resources,' he says. "It is a scandal. They have signed up to international treaties that promise sustainable fishing. But having failed to do it at home, they are wrecking the future of African fisheries."

In theory, decisions about how much fish to take are down to the host governments. But such is their dependence on fishing that they are under strong pressure. The fish here provide hundreds of thousands of jobs, especially among communities who fled to the coast during the great West African droughts of the 1970s and 1980s. They also provide up to 75 per cent of national protein, and, through the sale of licences to foreign trawlers, up to half of government revenues. "These countries have big debts. They have to pay it back. Until they do, they say they cannot refuse the EU,' says Campredon.

While foreign trawlers dominate outside the park, the pirogue fishers they displace are pressing to be allowed inside. Sid Ahmed ould Abeid, president of Mauritania's National Fisheries Federation, a trade organisation, summed up their predicament: "The fish come into the area from the south, swim into the park, spend three months there, where only the park villagers can catch them, and then swim straight out into the deep water where the trawlers get them." If the pirogue fishers are to make a living, they need access to the park, he says. Privately, European park advisers concede that it may be politically impossible to keep out the pirogues while local fishers have the run of the place. There is a strong political lobby among rich absentee boat owners in Mauritania who want to open up access. But, says Araujo, "if we did set up a licensing system for outsiders to come in, we just don't have the resources to police it".

What is to be done? Clearly, fish habitat needs to be protected. The Mauritanian authorities are setting tougher laws against poachers. And in Senegal, where many old fish nurseries among the mangroves have been lost and coral reefs are being dynamited or ripped up by trawlers, the environment minister Lamine Ba says he wants to create a string of marine parks.

In reserve

Such parks have had a dramatic effect on fish populations elsewhere i the world, according to a recent detailed study by marine biologists at the National Center for Ecological Analysis at the University of California, Santa Barbara. Even small reserves can rapidly double fish populations, increase fish size by 30 per cent and triple the amount of offspring, says Bob Warner, an ecologist at the centre.

But most researchers believe that for such reserves to be effective, there cannot be any fishing within the area. Even a small amount of fishing will tend to pick off the biggest

fish, which produce the most eggs, having a disproportionate effect. "Full protection is essential," says Roberts. One way forward for the Banc d'Arguin, he suggests, would be to identify key spawning grounds within the park and ban all fishing within those areasa kind of reserve within a reserve.

And by themselves even the best parks aren't sufficient to save a troubled fishery like that of the Banc, says Roberts. "Marine protected areas are not a solution here. Not until the trawlers issue is tackled, anyway." They only work in the context of a wider conservation framework. If, as at the Banc, hundreds of trawlers are "fishing the line" on the edge of the protected area, then they have little chance.

Fixing the trawler problem won't be easy. West Africa badly needs foreign revenue from fishing. But trawlers are not the only route to that. Santos believes the future should lie in line-fishing small numbers of high quality (and therefore high-priced) fish for sale to European markets and restaurants. Sport fishing may also play a role. High-rolling tourists spend a lot of money, but take only a few fish. They are already cruising in small numbers among the picturesque mangrove-fringed islands of Guinea-Bissau. There, in waters too shallow for big trawlers, they fish in small boats with rod and line. 'Last night I had a dream about bream," drawled one American over breakfast at the Tubaron Club on Rubane Island. Such dreams could also prove lucrative among the islands of the Banc d'Arguin.

Where does all this leave the pirogue fishers? They are the ones who must live in the region. Campredon believes that if they can get rights to a greater share of the catch, it may give them the long-term interest needed to manage the fisheries better. "They are the key figures, the primary managers of ecosystems and their resources. It is only by working with them and helping to address their concerns that we will be able to better manage the coastal zone," he says.

But whether such responsibility is possible in a global marketplace is less cleat On the beaches from Hann to lwik, the local residents have to fish to live. And market forces will encourage them to go fishing, however empty the seas. Fish in the markets behind Hann beach fetch 20 times what they did a generation ago. There may no longer be plenty more fish in the sea, but-for the moment at leastthere is still money to be made. The brutal logic seems clear. If the trawlers keep up their 'strip-mining", and if the current free-for-all persists, it will continue to be every fisher for himself. And as scarcity pushes prices up, the park will succumb, and nobody will stop till the last fish is gone. It happened on the Grand Banks of Canada. It can happen again. 1:1