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Part I：Speaker
【Rephrase 1】 Microbe Battery Makes Wastewater Worthwhile
[Dialog, 1:15]
MP3：
[Transcript hided]
Developed countries spend about 3 percent of all their electrical power treating wastewater. The juice purifies contaminated material so it can be returned safely to the environment. Now researchers think they can turn this power drain into a power source. Because a new kind of battery uses microbes to produce electricity from wastewater. The work is in the Proceedings of the National Academy of Sciences. [Xing Xie et al.,Microbial battery for efficient energy recovery] Like us, some microbes draw their energy from organic matter. And wastewater is chock full of such fuel. So scientists gave microorganisms polluted water and wired them up. When the microbes harvested electrons, the particles traveled through the electronic components to power a battery. This system had a net efficiency of 30 percent, about the same as a commercial solar cell. In theory, microbial batteries like this one could eventually be made more efficient, producing enough electricity to power the treatment of the wastewater three times over. Which gives a whole new meaning to the saying, “Waste not, want not.” http://www.scientificamerican.com/podcast/episode.cfm?id=microbe-battery-makes-wastewater-wo-13-09-18
Part II：Speed
Sleep therapy can change bad memories
Mitigating fears during sleep could help to ease anxieties felt when awake.
【warm up】
Forget the psychiatrist’s couch. Your own bed could one day be a setting for psychotherapy. Targeted brain training during sleep can lessen the effects of fearful memories, according to a study published today in Nature Neuroscience1. Researchers say that the technique could ultimately be used to treat psychiatric disorders, such as phobias and post-traumatic stress disorders.
Today, those conditions are most commonly treated using ‘exposure therapy’, which requires patients to intentionally relive their fears. With repeated exposures in the safety of a therapist’s consulting room, patients can learn to reduce their responses to traumatic cues — suggesting that memories are being altered. But the treatment itself can be intolerably painful for some patients, especially at first. In the latest study, neuroscientist Katherina Hauner and her colleagues at the Feinberg School of Medicine at Northwestern University in Chicago, Illinois, devised a form of exposure therapy that works while people snooze.
“It’s fascinating, and very promising,” says Daniela Schiller, a neuroscientist at Mount Sinai School of Medicine in New York. “We used to think you need awareness and conscious understanding of your emotional responses in order to change them.”
(words:186)
【Time2】
Instant replay
To create fearful memories, Hauner’s team delivered mild electric shocks to study participants as they viewed pictures of faces that were paired with a distinct odour, such as lemon or mint. People began to sweat slightly on seeing the pictures and smelling the odours, anticipating that they would get a shock.
Soon after the training, participants napped in the lab while the researchers monitored their brain waves with electrodes placed on their scalps. When the volunteers entered slow-wave sleep — a stage during which recent memories are replayed and reinforced — the team released one of the fear-linked odours. By administering the odour at 30-second intervals, the researchers were trying to trigger the memory of the corresponding face over and over again — this time without delivering electric shocks. Just like when they were awake, the sleeping subjects showed increased sweating when exposed to the odour, but the effect gradually subsided.
The reduced effect persisted after sleep. When awake, people showed diminished fear responses when exposed to the odour–face combination that had been triggered repeatedly during sleep. Activity changes in the amygdala, a region of the brain involved in emotion and fear, suggest that the treatment did not erase the fearful memory, but rather that it created new, innocuous associations with the odour–face combination. People who slept longer and received more treatment benefited most from the procedure.
“It’s really paradoxical,” says Jan Born, a neuroscientist at the University of Tübingen in Germany, noting that the spontaneous replay of memories during sleep is typically thought to strengthen rather than weaken learning.
Hauner explains that repeated activation of a single fearful memory during sleep probably works more like real exposure therapy and less like a natural replay of memories at night, in which memories are triggered haphazardly. More work is needed, she says, to determine how long the treatment lasts and whether overnight sleep might affect it.
As for using the technique therapeutically, Hauner notes that real traumatic memories, especially very old ones, could be much more complicated to treat than the simple scenarios engineered in the lab. “This is a very novel area,” she says. “I think the process has to be refined.”
(words:361)
http://www.nature.com/news/sleep-therapy-can-change-bad-memories-1.13792
How to learn in your sleep
Subjects trained to sniff pleasant smells while asleep retain the conditioning when they wake up.
【Time3】
It sounds like every student's dream: research published today in Nature Neuroscience shows that we can learn entirely new information while we snooze1.
Anat Arzi of the Weizmann Institute of Science in Rehovot, Israel, and her colleagues used a simple form of learning called classical conditioning to teach 55 healthy participants to associate odours with sounds as they slept.
They repeatedly exposed the sleeping participants to pleasant odours, such as deodorant and shampoo, and unpleasant odours such as rotting fish and meat, and played a specific sound to accompany each scent.
It is well known that sleep has an important role in strengthening existing memories, and this conditioning was already known to alter sniffing behaviour in people who are awake. The subjects sniff strongly when they hear a tone associated with a pleasant smell, but only weakly in response to a tone associated with an unpleasant one.
But the latest research shows that the sleep conditioning persists even after they wake up, causing them to sniff strongly or weakly on hearing the relevant tone — even if there was no odour. The participants were completely unaware that they had learned the relationship between smells and sounds. The effect was seen regardless of when the conditioning was done during the sleep cycle. However, the sniffing responses were slightly more pronounced in those participants who learned the association during the rapid eye movement (REM) stage, which typically occurs during the second half of a night's sleep.
(words:243)
【Time4】
Pillow power
Arzi thinks that we could probably learn more complex information while we sleep. “This does not imply that you can place your homework under the pillow and know it in the morning,” she says. “There will be clear limits on what we can learn in sleep, but I speculate that they will be beyond what we have demonstrated.”
In 2009, Tristan Bekinschtein, a neuroscientist at the UK Medical Research Council's Cognition and Brain Sciences Unit in Cambridge, and his colleagues reported2 that some patients who are minimally conscious or in a vegetative state can be classically conditioned to blink in response to air puffed into their eyes. Conditioned responses such as these could eventually help clinicians to diagnose these neurological conditions, and to predict which patients might subsequently recover. “It remains to be seen if the neural networks involved in sleep learning are similar to the ones recruited during wakefulness,” says Bekinschtein.
The findings by Arzi and her colleagues might also be useful for these purposes, and could lead to 'sleep therapies' that help to alter behaviour in conditions such as phobia.
“We are now trying to implement helpful behavioural modification through sleep-learning,” says Arzi. “We also want to investigate the brain mechanisms involved, and the type of learning we use in other states of altered consciousness, such as vegetative state and coma.”
(words:223)
http://www.nature.com/news/how-to-learn-in-your-sleep-1.11274
Earth's days are numbered
Researchers calculate that the planet will leave the Sun's 'habitable zone' in about 1.75 billion years.
【Time5】
Earth will be able to host life for just another 1.75 billion years or so, according to a study published on 18 September in Astrobiology1. The method used to make the calculation can also identify planets outside the Solar System with long ‘habitable periods’, which might be the best places to look for life.
The habitable zone around a star is the area in which an orbiting planet can support liquid water, the perfect solvent for the chemical reactions at the heart of life. Too far from a star and a planet’s water turns to permanent ice and its carbon dioxide condenses; too close, and the heat turns water into vapour that escapes into space.
Habitable zones are not static. The luminosity of a typical star increases as its composition and chemical reactions evolve over billions of years, pushing the habitable zone outward. Researchers reported in March that Earth is closer to the inner edge of the Sun’s habitable zone than previously thought2.
The inner edge of the Sun’s habitable zone is moving outwards at a rate of about 1 metre per year. The latest model predicts a total habitable zone lifetime for Earth of 6.3 billion–7.8 billion years, suggesting that life on the planet is already about 70% of the way through its run. Other planets — especially those that form near the outer boundary of a star’s habitable zone or orbit long-lived, low-mass stars — may have habitable-zone lifetimes of 42 billion years or longer.
The authors suggest that scientists searching for life on other planets should focus on those that have occupied their habitable zones for at least as long as Earth has — such as HD40307g, which is 12.9 parsecs (42 light-years) away from Earth.
(words:287)
【Time6】
Life is complicated
But it is possible that Earth took an atypically long time to develop advanced life, says Caleb Scharf, an astrobiologist at Columbia University in New York. “It’s the age-old problem of over-interpreting a single data point,” he says. Study co-author Mark Claire, an astronomer at the University of St Andrews, UK, agrees, but adds that if he were running a mission to find life on a terrestrial planet, he would probably point his telescopes at planets that had been in the habitable zone for as long as possible.
Critics also suggest that the formula the researchers used is too simple. The model assumes that extrasolar planets have Earth-like atmospheres, compositions and tectonic-plate action. Colin Goldblatt, a planetary climatologist at the University of Victoria in Canada, says that without including climate dynamics such as atmospheric composition and volume, the results are not very useful for predicting habitability. “If you want me to build a habitable planet where Venus is, I can do that; if you want me to build a dead planet where Earth is, I can do that,” Goldblatt says.
“There is plenty of room for new formulations of the habitable zone,” agrees Claire. For now, researchers don’t know much about these extrasolar planets. But habitable zone calculations could prove interesting closer to home as well.
Just as the sun brightens and the Earth becomes too hot for life, Mars will be entering the habitable zone. “If humans are going to be around in a billion years, I would certainly imagine that they would be living on Mars,” Claire says.
(words:260)
http://www.nature.com/news/earth-s-days-are-numbered-1.13788
Part III： Obstacle
An embryonic idea
A group of stem-cell biologists have grown an “organoid” that resembles a brain
【Time 7】
REGENERATIVE medicine, the science of producing tissues and organs from stem cells, is a rapidly developing field. This week, however, it took a leap forward that was big even by its own demanding standards. A team of researchers led by Madeline Lancaster of the Austrian Academy of Sciences, in Vienna, announced that they have grown things which, while not human brains, resemble brains in important ways.
Dr Lancaster’s organoids, as she calls them, are a far cry from the brains in jars beloved of the writers of horror movies. But they do contain several recognisably different types of nerve cell and have anatomical features which look like those of real brains. They might be used to study, in ways that would be unethical in a living human being or impossible even in a mouse, the crucial early stages of brain development, and how they can go wrong. They could be employed to test drugs in ways that mere cell cultures cannot be. And because they can be made, if needed, from the cells of living people, they might even illuminate the particular problems of individual patients.
To make an organoid, Dr Lancaster’s team start, as they describe in an article in Nature, with what is known as an embryoid body. Just as an organoid has some features of an organ without truly being one, so an embryoid body has some features of an embryo without actually being one. Embryoid bodies can be grown either from natural stem cells—themselves derived ultimately from real embryos—or from what are known as induced pluripotent cells, which are made from adult cells (usually skin cells) that have been treated with four crucial biochemical factors which cause them to forget their identity and behave like embryonic cells.
Embryos have three layers: endoderm, mesoderm and ectoderm. Each turns into an eclectic mixture of body parts in the complete organism. Nervous systems grow from the ectoderm (which also contributes dental enamel and the skin’s epidermis, among other things), so the team put ectodermal cells into droplets of gel and then floated the droplets in a nutrient broth in a gently rotating bioreactor (which allowed the cells to grow without being shaped by the constraint of a vessel such as a Petri dish) to see what would happen.
Though the result (pictured above) may not look much like a brain to a layman, to an expert the resemblance is remarkable. After ten days the organoid has developed neurons. After 30 days it has regions recognisably similar to some of those in a real brain. And though, because they lack the blood supply of a real brain, organoids never grow much bigger than 4mm across, they live a long time. Some are now a year old and still going strong.
Real brains consist in large measure of layers of neurons called the cortex. This surrounds fluid-filled spaces known as ventricles. That is more or less the anatomy of an organoid. Many of them also contain areas which look like choroid plexuses. These are places that absorb nutrients from the bloodstream and dump waste into it. They also generate the cerebrospinal fluid that fills ventricles.
Signs of other structures turn up too. The various lobes of a real brain sport different mixtures of neurons. The team see signs of this in the organoids. They found evidence of retinas (the back of the eye is an outgrowth of the brain), of meninges (the membranes that surround the brain) and of hippocampal cells (the hippocampus is a part of the brain which is crucial for memory formation). The organoids, then, look as though they are making a fair fist of trying to become real brains.
So the method clearly works. The next question was whether the team could do anything useful with it. And they could. They were able to realise one of the desiderata of stem-cell science and investigate the condition of a particular individual who has microcephaly.
Brainwave
Microcephaly, as its name suggests, is a developmental condition in which someone’s brain fails to grow as much as it should. The consequence is that his head is small and he suffers a range of debilitating symptoms.
Microcephaly is hard to study in a laboratory because tinkering in mice with the genes that cause it in people does not replicate the severity of the condition. The team therefore wondered if they would have more luck by growing an organoid derived from their patient’s skin. And they did.
First, the organoid actually grew, proving the method works with induced cells as well as natural ones. Second, it showed that what seems to be going wrong in microcephaly is that the process of development is running too fast. Neurons differentiate more rapidly than they should. And once that has happened, the brain’s growth slows down.
This is no help to the patient. No one thinks microcephaly can be reversed. But if it were better understood, it might be prevented—as might a host of other neurological problems whose roots lie in the brain’s early development. Schizophrenia and autism, for example, are both suspected of being caused by mistakes in the migration of developing nerve cells through the early embryonic brain. Dr Lancaster hopes the group will be able to model these processes in the future.
Dr Lancaster’s organoids, then, would seem to have a bright future, helping scientists understand both how the brain works and what has gone wrong when it doesn’t. Small though they are, they could be the start of something very big indeed.
(words:923)
http://www.economist.com/news/science-and-technology/21584319-group-stem-cell-biologists-have-grown-organoid-resembles-brain
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发表于 2013-9-24 00:08:42
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