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Nature Podcast Digest, 2012/03/15

2012年5月6日

The original script of this podcast: http://www.nature.com/nature/podcast/v483/n7389/nature-2012-03-15.html

The audio file of this podcast: http://www.nature.com/nature/podcast/archive.html

 

分離脳(左右の脳の接続を切った脳)の患者は過去50年間、右脳左脳の働きの研究に貢献してきた。左目(右脳の視覚)が見たものを右脳は言語化(左脳の働き)できないが同じものを左手で指さすことはできる。一方同じ実験において左脳は(左脳の視覚では)見えていないものを指さす左手の動きを見て、論理的解釈(左脳の働き)をしようとする。現在の研究課題の一つは分離脳状態の社会的・倫理的判断への影響。

Kerri Smith: It’s been called split brain surgery. Only 50 to a 100 people worldwide have had this extreme procedure, which cuts the connection between the two sides of the brain. It’s a treatment for severe epilepsy for patients who’ve tried everything else. The idea is to separate the two halves of the brain to contain a seizure to one hemisphere. But what these patients probably didn’t realize was that their surgery would turn them into neuroscience celebrities. Mike Gazzaniga, a neuroscientist at the University of California at Santa Barbara has been studying split brain patients for five decades. Nature 483, 260–263 (15 March 2012)

Michael Gazzaniga: When I started in the ’60s there was a whole body of dramatic work that had been carried out on animals, on cats, monkeys and it showed that quite literally if your left hand did not know what the right hand was doing, that there was a major breakdown in information between the hemispheres and that we were beginning to figure out the actual pathways that were involved in particular kinds of, you know, kind of perceptual and cognitive tasks. And so the thought was ‘is that going to be true for humans?’. It was hard to believe that the left hand wouldn’t know what the right hand was doing. So, what I mean by that is that if I put an apple on your left hand and I ask you find the same thing with your right hand, it’s hard to even imagine you couldn’t and yet that’s the case following hemisphere disconnection. The information from one side just doesn’t get over to the other. Just seeing some of the basic phenomenon is riveting. And you’re seeing the process of consciousness being articulated and displayed in front of you and it’s a very, very serious and sobering moment and you’re always drawn into the studies. It’s anybody who isn’t, has got a problem.

Michael Gazzaniga: I remember 50 years ago, a patient came up to our labs at Caltech and brought him into the testing room and I told him to fixate on a screen and then on the screen I flashed various pictures to the right of where you fixate or to the left where one fixates and everything to the right of fixation easily named because that goes to the left-dominant speech hemisphere and everything to the left of fixation was not named, so nothing happened. He didn’t, he said, you know, like what are you asking this question for because I didn’t see anything. He was not giving a spoken response, but then I said well point anything you see and immediately the right hemisphere which could not say what it saw immediately pointed on the screen to where objects appeared and then when you get into more elaborate tests where you’re trying to understand why the person made particular responses and you challenge them why did you do that and they start interpreting the world in a particular way to explain why their left hand is doing something. That all, that gets into whole rich area that we’ve studied over the years.

Michael Gazzaniga: That’s a really great question because I think as you go through the decades since the beginning of the surgery, you didn’t know where it was going, one didn’t know where it was going and then all of a sudden there would be a question that would crystallize, so to say, what is in the future is a very hard thing to do. I can tell you one of the issues that we’re beginning to look at is whether the hemisphere disconnection anyway impacts on social and moral judgments that we make because there’s new work out now about how we assign beliefs to ourselves and to others and what parts of the brain are involved and because of that knowledge what might happen if the brain is disconnected and we have some preliminary studies which are interesting on that front. So, that would not have been asked, it was not asked for 50 years and it comes out of a current research that is going on in the field of social neuroscience that is quite fascinating.

 

今あるノンカフェインコーヒーは普通のコーヒー豆に処理を施したもので、芳香が失われる。カフェインを出さないコーヒー豆を実らせる種の交配は失敗続きだが、いずれ成功するだろう。

Brendan Borrell: The current state-of-the-art is basically they take a bunch of the beans and they put them in super high pressure hot carbon dioxide.

Geoff Marsh: But the big challenge is to get rid of the caffeine and at the same time to preserve that complex flavour and the general feeling is that no one’s managed to do that yet.

Brendan Borrell: There are different species of coffee. We only drink two particular coffee species, what you know, Robusta coffee is kind of a low quality coffee and Arabica is what you’re going to drink at your fancy coffee shop and both of those have pretty high levels of caffeine, but there’s about a hundred other species out there in nature that you could potentially crossbreed that have lower levels of caffeine. Then there’s also the possibility there could be a mutant out there, somewhere growing in somebody’s farm or in one of these research stations like the research station I visited.

Brendan Borrell: There’s been this long history of excitement and disappointment. Early on, researchers had discovered some of these caffeine free plants and they thought it would just be an easy solution as to start to breed them with commercially viable plants, but coffee is just a very difficult plant to breed and also there’s all these other characteristics that you have to just keep in mind like the shape of the plant, how many beans it’ s producing and you know, one important attribute is that the beans are like ripening at the same time, so that somebody can go through and pick them off and coffee has also got really complicated genetics.

Brendan Borrell: Well, there’s been a kind of series of attempts to do that that did not always end up well. A group from the University of Hawaii, they thought they had created a caffeine free plant, but as the plants grew up, they ended up producing caffeine. People now think they had cloned and inserted the wrong gene. Later some Japanese researchers basically tried to do the same thing, but their plans are not flowering and producing beans 10 years later, so they’ve run into some other genetic roadblocks. And you know in this day and age many consumers are not going to drink a genetically modified coffee. So it’s kind of a pathway that is not going to come to fruition anytime soon.

Brendan Borrell: If you look at what’s out there today there’s basically three really strong contenders. The number one are the mutant plants that originally came from Ethiopia and have low caffeine and are currently being bred to be more commercially viable. There is a second plant in Brazil where basically the researcher has taken a bunch of coffee seeds and put them in a chemical that causes spontaneous mutations and he found some of these plants are low caffeine and he is trying to work through find that and the third possibility is somebody who has done a really funky crazy hybrid of like three different coffee plants and they manage to get pretty low caffeine levels. So those are all strong contenders.

 

コンピューターシミュレーションによると、10万年前の大型獣の大量絶滅の主な原因は気候変動と狩猟らしい。

Corie Lok: What killed the big beasts that roamed the earth one hundred thousand years ago? The answer to this question has been hotly debated for decades by scientists studying the ancient megafauna such as the woolly mammoth and sabre tooth cats. Competing theories have included climate change and hunting by humans. Now researchers at the University of Cambridge have attempted to set all the debate. They modelled extinctions on five different land masses running simulations that included climate data along with thousands of plausible combinations of human arrival and species extinction times. The combination that first predicted the timing of any given extinction included both climatic and human factors. The study was published in the Proceedings of the National Academy of Sciences. Nature 483, 249 (15 March 2012)

地中にしみ込んだ雨水により地震の横波が緩和されることが過去10年間の日本の地震観測データ分析で分かった。

This other paper that we liked looked at a type of seismic wave that is responsible for the worst damage seen during earthquakes. It seems that the velocity of these shear waves is reduced by rainy weather. Researchers in Colorado analyzed the average velocity of shear waves in nearly a 112,000 earthquakes recorded over ten years in Japan. They found that the velocities were lower than normal three months after a major nearby earthquake. In Southern Japan shear waves were also slower during rainy summers. The scientists think that the rain water soaking the ground increases fluid pressure which slows down the propagation of shear wave. The research is from the Journal Geophysical Research. Nature 483, 248 (15 March 2012)

 

原始的な脳を持つ生物(ギボシムシのような半索動物)の遺伝子レベルでの脳の土台が脊椎動物と同じであることが分かった。この土台は体の区分に関係がある。脊椎動物の大きな脳がどのようにしてできたのかは謎だが、この原始的な脳の土台にもその謎を解く鍵が隠されている。

Kerri Smith: Looks can be deceiving, take the Acorn worm, it’s a lowly sand burrowing creature without much of a brain just a rudimentary system of nerves but it’s offering important clues about the evolution of much more complex vertebrate brains. Acorn worms and other hemichordates branched off the evolutionary tree from chordates the group that include vertebrates more than 500 million years ago. Surprisingly developing acorn worms activate the same molecular programs that help form the big complex brains of vertebrates. Ewen Callaway spoke to Chris Lowe at Stanford University in California.

Chris Lowe: There are different approaches where you can study by an evolution. One is the local morphology of the brain. We look in to neurons, we can look into the actual morphological structures of the brain and then the more recent approach is to understand the brain evolution is to look at the molecules that are actually involved that the genes are actually involved in setting up the major regions of the brain. You think of brain as an analogy as a house, the genes are kind of the scaffolding. And so what we did was to look at an animal that belongs to the phylum called hemichordates. If you look at their nervous system, morphologically looks really different from an vertebrate brain and yet if you look at those molecular scaffolding molecules they are really involved in setting up the main structures of vertebrate brain. Our study showed that there was an unexpected degree of concordance in a way that that scaffolding was setup during the development of this animal and the vertebrates. And in many ways it showed more similarities with the vertebrates and then some of the elements of amphioxus and tunicate brains.

Ewen Callaway: What are they using these molecular scaffolds for? They don’t have complicated brains I mean what do you think they’re doing with them?

Chris Lowe: So that’s a very good question that’s one we are trying to think a lot about. In our studies where we actually manipulated these scaffolds, so these genetic tools you can use to interfere with the formation of these scaffolds. For the most part what we found is that it seems that the scaffolding is not just involved in nervous system formation but involved in the general patterning of the entire body and so they seemed to be deployed at the boundaries of the vertebrate brains, so they were important in defining the main regions of the brain and during vertebrate development. And when we look at these boundary forming scaffolds in a hemichordate they seemed to be deployed at the boundaries between some of the major anatomical divisions of the body. So, when I introduced the animal, the acorn worm, and it has its large proboscis that is involved in digging and feeding and then that’s give rise to the middle region of the body and it’s between that boundary of the proboscis in the middle region that one of the key signalling centres and is deployed. So it suggests that it may be involved in not just in nervous system patterning but also perhaps in dividing the body.

Chris Lowe: The part of the scaffold that we’re talking about, are clearly key components of the development of the vertebrate brain. What we’re saying is that they weren’t the key innovations made on in vertebrate brain evolution, they were incorporated from a previous existing structure,during the development of the vertebrate brain but they weren’t assembled at the base of the vertebrate say are much more ancient than that. So I am not saying that these centres are not importance of vertebrate brain evolution quite contrary the very key but it’s very difficult with our current understanding to really identify what were the key changes that rose the expansion of the vertebrate brain. And I think many of those findings have definitely come from looking within the bottom, looking within the chordate but also some of the clues have come from the very early vertebrates that man stopped the lineage of vertebrates and before going for very big.

 

肉食獣に甘味の味覚がないのは、肉食化により炭水化物用の味覚が失われたためだと考えられる。味覚の退化は食生活に左右される。雑食動物には甘味の味覚は残っており、食べ物を丸のみするイルカには味覚がほとんどない。

Richard Van Noorden: This is the interesting finding that many animals that eat meat. Carnivores have completely lost their ability to take sugars. We already knew apparently, I didn’t know but apparently we did already know that cats cannot taste the difference between sugar water and normal water and nor can tigers and nor can cheetahs and they all have mutation in their gene that renders their sweet taste receptor completely inactive.

Richard Van Noorden: They’ve lost it exactly, there’s no selection pressure, there’s no need for them to taste sugar because their diet does not really include vegetables which is the main source of sugar and it turns out that this trend is actually wider than we thought. There’s a study published this week in the Proceedings of the National Academy of Sciences. This is a team from the Monell Chemical Senses Centre in Pennsylvania and they went and looked at as well other carnivores, sea mammals, hyenas, dolphins and they found that in many of these animals as well, they also couldn’t taste sugars and again they had a broken copy of this gene.

Richard Van Noorden: Well, what was interesting was that although they all have this mutated gene, they didn’t have the same mutations. So that suggests that they independently lost their ability to detect sugars. This is a kind of example of convergent evolution and the team also found that some of the carnivores have lost their ability to taste other flavours. So bottle nose dolphins and sea lions, they can’t taste the (21.26) savoury flavour that is mono sodium glutamate flavour and dolphins also can’t taste bitter compounds and again probably because they just don’t need to, there’s no advantage and so when the genes goes wrong there’s no disadvantage. Dolphins really just swallow things whole. So they have very few taste buds.

Richard Van Noorden: Well, it turns out that some carnivores can still taste sugars and there’s one called the insect-eating aardwolf which is a name I love. It’s very closely related to the hyena and it can still taste sugars and of course omnivorous meat eaters who eat a little vegetables like the spectacle bear. They can still taste sweet food. But really what this study is showing overall is that feeding ecology is really a major force shaping the evolution of taste.

 

発電ナメクジ、発電ゴキブリ、発電ネズミ等々。 血中の糖分を燃料にする生物燃料電池の研究が進んでいる。サイボーグや心臓のペースメーカーの動力源として応用。ただし、電球1個をともすのにナメクジ1000万匹が必要。

Richard Van Noorden: These guys are incredible, so just think normal brown garden snails crawling around in a sort of plastic box of moss in a lab, but they have a super power, they can produce electricity. So, this is work from Evgeny Katz in New York and it seems implanted tiny biofuel cells into the snails and the biofuel cells run on the glucose and oxygen in the snail’s blood. So when you hook-up the electrodes to an external circuit you get electricity and the snails live quite happily for half a year and every time they were hooked up you could get the electricity out again.

Richard Van Noorden: It is amazing and what’s even more amazing maybe is that snails are just the latest creature to be electrified like this. Just last month some reporters led by Daniel Scherson, Western Reserve University in Cleveland, they reported doing this in cockroaches and we’ve also had biofuel cells implanted into beetles and that work hasn’t come out yet but it is from the University of California, Berkeley and just a few years ago we also had a slightly different kind of biofuel cells implanted into rats.

Richard Van Noorden: Well, it’s going towards two very different practical areas. So for many years the Department of Defence in America has funded ideas to try and make effectively living cyborgs, insects with electronic circuits within them that allow them to sense chemical or something about their environment and an antenna that lets them send this information by radio signal. But these have been using very bulky batteries which will obviously run out and the point of a fuel cell is you’re tapping into the creature’s own metabolism, You’ll never run short of fuel because the snail or the cockroach itself is just eating more food. So that’s the idea on that side of things, the real limitation there’s how much power can you actually get and from the snail you could only get microwatts of power. Now that isn’t enough, probably hundreds of microwatts is definitely enough to send back a radio signal, Scherson says he has already done in cockroaches but there are still imitations here. Completely on the other side, the work in rats comes with the idea of implanting biofuel cells into ourselves in to humans in order to run things like pacemakers from the glucose and oxygen in our own blood.

Richard Van Noorden: Well that’s an interesting one, so a snail can produce about 7 microwatts at peak, of course the fuel cells are quite small so that’s why, so that would mean 7 microwatts, so that would mean a million snails would be 7 watts and 10 million snails would be 70 watts, which is about what your light bulb is. Incidentally one human puts out of about 80 watts a day, so one human would also be one light bulb, so 10 million snails.

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