Why doesn't my own snoring wake me up?

Why doesn't my own snoring wake me up? What actually happens when we die? Why does my helium balloon get more squishy? Can humans really live for 200 years? What is vascular dementia? Plus, why is there always room for dessert? Chris Smith joins Aubrey Masango to answer your science questions...

Aubrey - Scientists have discovered the part of the brain that still finds room for a slice of chocolate cake even when we're full!?

克里斯,我知道!我们都有这样的经历n't we, where you think you're full up, and then someone wheels out the sweet trolley and, all of a sudden, you find a corner of your stomach that just about has a chocolate cake-sized space left in it, and we eat it! Now this is a chap who works in America who's called Saleem Nicola, and they've been interested in this question because the world is getting fatter. Obesity has reached epidemic proportions all around the world. Within some countries maybe half the population overweight and a third of the population obese. And this carries enormous health consequences because obesity is the number one risk factor for diabetes, and diabetes has all kinds of health consequences. So it's very important we understand why this happens and we see if we can find ways to help people. And the thing is we, according to what Salim Nicola has found, we're almost certainly a victim of our ancestry because he's been looking at a region of the brain which is called the nucleus accumbens ,which is part of the brain's pleasure center. And there is a population of nerve cells that they've discovered there which when you are full, but not when you're just hungry when you're full, this population of nerve cells, using the same receptors that morphine binds to, activate and they tell you to feel hungry but only for highly appetizing energy rich foods. So in other words when you're just normally hungry you don't feel a particular preponderance to eat any selective foodstuff, you'll just eat because you're hungry. But once you are full, your appetite normally switches off but the fullness then turns on this additional group of nerve cells that then make you want to have food which is sweet and calorie rich. And the reason he thinks this is there is because historically when we didn't have supermarkets on every corner, when we didnt have access to food and high calorie foods and drinks and things on demand, we didnt know where our next meal was coming from, so it would have benefited our ancestors to really make hay in a dietary way when the sun shone. So in other words when there was the opportunity cram in as many calories as possible. And it's unfortunately we're falling victim to this evolutionary history and it's making us want to crave these foodstuffs even when we're full and we don't need the energy in the modern era. So we now know which bit of the brain is responsible. At the moment we can't turn it off though, so the next step will be to try and investigate the circuits there, see how they work, and see if we can find a way to maybe develop a drug or some other molecule to subvert this system so that we don't get so taken with the chocolate cake when the opportunity arises. Unless we need to of course.

Aubrey - That was going to be my question. Yeah, that was going to be my question. Now that we know that there is a particular place in the brain that's responsible for us bingeing on chocolate cake, can we switch it off but you're saying that it can't at this stage Dr Chris?

Chris - Well what we need to do is is to investigate how the system works and then see if there are any simple molecules that could be used in order to change the behaviour of this brain area. Because the thing is, let's face it, not everyone has a problem and not everyone wants to cure their problem, they don't think they've got a problem. So, at the end of the day, it will be an additional tool that people could use if they want to change their behaviour. And understanding how the system works in the first place - how the clockwork ticks if you like, you need to understand that before you can work out how to throw a spanner in the works and stop the clock ticking and stop your waistline expanding. But this is the first step, so a very interesting finding.

Aubfrey - Indeed. On the SMS line, Caroline asks: Why is it a person who snores doesn't hear themselves yet everyone in the entire village hears them? Their ears and head is closed to them than others is the question that Caroline asks Dr Chris?

Chris - Hello Caroline. Well part of the reason they don't hear is because they're asleep usually, and when you're asleep you're much less sensitive to stimuli going on around you. There's probably another reason as well, which is that the brain has a system in it for cancelling out internally generated sensations. In order to enable us to focus on things we need to notice, so stimuli that are coming in from outside, the brain has a system which is at the junction where your parietal occipital and temporal lobes all meet. And this region has a cancellation function so that things that you do to yourself are anticipated, and when the sensations come in from those actions they are negated so that they don't distract you away from what you need to notice. And this is partly the same reason, probably, that you can't tickle yourself. And so what's probably happening when you snore, because your body is in that pattern of breathing, it knows that you're going to breathe in. There is suppression of the incoming stimulus from yourself so you don't notice the racket you're making because you're anticipating it, and it's not being used to arouse you and wake you up. Other people, they don't know when it's going to happen. Their nervous system is therefore seeing it as a change, a sudden noise in the environment or a stimulus and they attend to it because that could be a danger sign that something in our evolutionary past was about to jump on you and eat you. So we're primed to notice things that are changing and respond to them.

Aubrey - Leander in Kempton Park. Hi.

Leander - Yes guys how are you?

Aubrey - Very good thanks. Go ahead Leander.

Leander - I want to know the real cause of death? Cause some people who just fall, some are shot. What happens in the body when one dies?

Aubrey - Interesting question, Dr Chris.

克里斯-早上好。一旦我们撒手西去,effectively, the big bag of chemical reactions which is your body with all of the cells talking to each other, that communication system, that chemical environment becomes disrupted and it fails. Now usually death doesn't just happen abruptly. In people who have grown old and they die, dying takes a number of weeks to days and we see people gently tail away and fade off. And, effectively, their biochemistry goes off and things will begin to just gently shut down and eventually things become so disrupted chemically that then your heart just stops, for example. I mean that's one thing that can happen. The other cause of death can be an abrupt sudden death, which is much more catastrophic, much less expected and much less often associated with old age, although it can be associated with old age, and this will be things like strokes or heart attacks. Two very common causes of death. In a stroke, either a blood clot has formed and blocked a blood vessels supplying the brain or a blood vessel bursts inside the head and bleeds into the brain. In both cases you deactivate a very significant proportion of your brain and you need all of your brain. And this causes loss of consciousness which can then lead to injury or it can lead to the systems that keep your body going, the physiological systems going, that can shut down and that can cause you to die. If your heart suddenly stops because you have a cardiac arrest, perhaps because of a very large heart attack or for some other reason, if your heart stops you stop supplying life giving blood, which has got oxygen and energy in it to all of your tissues all at once. The most vulnerable organ is your brain and so you immediately lose consciousness and because you can't restart your heart because you can't resuscitate yourself you are therefore destined to die. So the process of dying is a complicated procedure. It can be something that happens over a very very slow course or it can happen abruptly. And the reasons can be different but the outcome is usually the same.

Aubrey - Barrus in Bloomburg. Good morning to you.

Barrus - Good morning Chris. Morning. I saw one of those Get Well helium balloons, the silver ones that you get. And it's nice and firm and I brought it home now and I've noticed that it seems to have lost its ability to be firm. What is what is changing in the helium that it's losing it's ability that it seems to be dropping?

Chris - Morning.

Barrus - I'm sure the structure should be solid, so why?

Chris - Yeah. Well there's two reasons to consider. One is that helium is a very tiny atom. It's second only to hydrogen in the periodic table for the lightest atom. And this means that the particles can sneak out between the materials that make the fabric of a balloon. And this is why normal balloons don't stay inflated with helium in them for very long because the helium slowly works its way out between the strands of rubber and leaks away, and is lost from the Earth forever because it's so light Earth's gravity can't hold onto helium and it escapes into space. So that's one reason. The reason you use foil balloons for helium is that by illuminizing them like that it generally produces a better barrier that keeps the helium in, so it leaks out more slowly. There's also potentially a thermal effect. If you bought your helium balloon on a day itwas nice and hot and sunny and the person filled that balloon up on a nice hot sunny day. So the rubble was nice and stretchy, and the gas got hot and inflated the balloon very hard, then that could mean that the gas had expanded on a hot day. If you then put your balloon in a colder environment then the gas, because of Boyle's Law, where you increase the temperature of the gas and it's going to increase its volume, the gas is going to shrink a bit. So it might be that your balloon is in a colder environment than it was where you got it and that means that it's shrunk a bit, so I think both factors You could try warming the balloon up a little bit but, unfortunately, helium - tiny particle, easy to leave a balloon material and escape into space. I suspect that's where your helium's gone.

Aubrey - Let's take one call before break, Dr Chris. Arthur in Clermont. Hi.

Arthur - Good morning Aubrey and Chris. Chris, this report about humans living to two hundred years or even a thousand years. How feasible is this, and if it's not feasible what is the maximum age you think that humans can live to? Thanks, I listen on the radio.

Aubrey - Thanks very much Arthur. And I believe it's an advert that's doing the rounds at the moment, Chris. Some insurance companies are beginning to sell that story to us. I've seen it myself. Is it true, can we live up to 200 years?

Chris - Hello Arthur. This is something that people have been speculating on for a long time. The reason we age is probably because the body has to make a compromise between repairing itself, regenerating itself and then spending its precious resources on things like reproduction, to make sure that we actually have our genes going into a fresh new young body that'll carry our genes on in a new body and reproduce to make more children into the future. Now, if we could turn off that ageing process then potentially we could live for much longer. There are animals that do. If you look at say whales, there are some Bowhead whales, for example, that can live for extraordinary lengths of time, 150 years or so. People have found evidence of these animals with harpoons that were not made for 150 years still embedded in them from people attempting to catch them. People have looked at the lens material in sharks and found that the lens material in there eye, if you carbon date it, shows some of these animals to be 500 years old. So it's certainly possible to live for a very long period of time. Is it possible to do this to a human? Well nothing is impossible. In medicine, you never say never because otherwise someone will prove you wrong. At the moment with present technology, no I don't think it is. We've made enormous strides in longevity owing to improvement in our environment, improvement in our food, improvement in provision of freshwater. And medicine has also made a contribution, although the biggest one comes from improved living conditions and nutrition. At the same time, those gains have bought us about a hundred years of relative health. To get that to be doubled is a big ask and that's going to take a lot of technology. And really we have to ask ourselves do we want to go there. Do we want to do that or actually are we better not doing that because theres a huge price for the planet to play if we decide to go down that road.

Aubrey - The Naked Scientists. Dr Chris Smith is my guest. We're talking matters scientific. Please give us a call on 0118830702 or 0214460567. Roy in Glenvista. Good morning to you.

Roy - Good morning Aubrey. Morning Chris. Quick question. We've had hours of conversation over this. Why is it that a plastic container containing carbonated cold drink goes flat so quickly?

Aubrey - Interesting. Dr. Smith...

Chris - I haven't seen any evidence that it does. But the bottom line is when you have a carbonated drink, carbon dioxide has been forced into solution. In other words, to dissolve in the drink fluid under pressure. When you decant the drink, bubbles form because there's less pressure above the liquid now to hold the gas in solution, but also it starts to release the gas at what we call nucleation points. So in other words, it's far easier to form a tiny bubble within a liquid wherever there is a rough surface on a surface. Because of that point there will be a tiny bubbles of air trapped already and the gas can therefore join in with its partner gas molecules to form a bubble because it's really hard for a bubble, for reasons of surface tension, to get started. And once you've got a little bubble it's much easier to make another bubble or a bigger bubble. That's why the bubble stream off of one place on a surface where there is a small imperfection or a rough patch. Now it may well be that in the plastic container that you've been putting your carbonated drinks into, the surface is rougher compared to another vessel or a glass surface, for example, and it may well be that that roughness is causing more nucleation and more gas to come out of solution more rapidly, and that's why your drinks are going flatter. But there's no chemical reason why a plastic surface should be more likely to release gas than say a glass surface. It will probably come down to, as I say, temperature, because if you if you make the liquid warmer then it can hold less gas so it would evolve the CO2 faster, and the roughness of the surface which would encourage it to happen.

Aubrey - Barbara in [**]. Good morning to you.

Barbara - Hi.

Aubrey Hi. Go ahead.

Barbara - My name's Barbara and I'm just asking what exactly is vascular dementia and what is the long term prognosis?

Aubrey - Vascular dementia and what is the long term prognosis, Dr Chris?

克里斯,你好,芭芭拉。痴呆,首先,是the loss of cognitive faculties, often with age, and that's why we often add the phrase or the word 'senile' to the expression with senile dementia. Senile meaning with age. One important cause of dementia is when the blood supply to the brain doesn't work as well as it should, and if you look at the brain you see that there is a structure called the blood brain barrier. And this is because brain tissue is very delicate and chemically very sensitive and the blood contains lots of substances which could irritate the brain, so you have a blood brain barrier which keeps the blood away from the brain tissue allowing through the things you want to get into the brain like sugars, important molecules for making nerve transmitters and repairing nerve cells, and oxygen. And it can that you throw away the waste but it doesn't let other stuff through. If, with age and with other problems such as smoking or diabetes and other health problems, if you damage the integrity of this blood brain barrier what can happen is that chemicals and nasties from the bloodstream can go across the blood brain barrier, enter the brain substance and begin to irritate or damage nerve cells and cause nerve degeneration and nerve cell loss. And that progressive nerve cell loss leads to dementia or loss of cognitive faculties which manifests in much the same way as if you had Alzheimer's disease, which is another form of dementia or loss of nerve tissue leading to a loss of your cognition.

Aubrey - All right. Ed in [**] asking a similar question or a related question. Ed go ahead.

Ed - Yes well, that's what I was actually asking. Apparently there are some books out now which claim that you that Alzheimer's can be reversed or even and prevented by lifestyle changes and various supplements or good foods and exercise as well has some specifics to it I suppose. And I know it seems like glucose is a baddy. But is this true, I mean, reversed and prevented?

Aubrey - Thank you very much for the question Ed. Dr Chris.

Chris - Regrettably no. Alzheimer's disease and other dementing diseases, which are largely diseases of longevity, are set to become much more common. In fact, the worry is that within the next half century probably one person in three in some populations of some countries owing to the ageing population are likely to have some kind of dementia or Alzheimer's disease. This is a huge problem. And the reason we get Alzheimer's disease is because there is a build up in the brain of a pathological or harmful protein called beta amyloid. This is naturally made in the brain, but normally the brain gets rid of it. But, under certain circumstances, it builds up in a toxic way and then damages nerve tissue. Its likelihood that that will happen increases with age, and so therefore the longer you live the more likely you are to succumb to this. The likelihood of it not happening can be reduced by doing sensible things like exercise, like eating healthily, like not smoking, not drinking too much. And also having good genes because Alzheimer's disease has a genetic component as well. It may also have an infective component. There's research out this week suggesting that certain virus signatures keep cropping up in the brains of people who have Alzheimer's disease and therefore infection may also play a role. So the best advice is that there's not a lot you can do about your genes, but what you can do is to minimise your lifestyle factor risks. So doing all the things I've suggested is probably a good idea. Keep an eye on your blood pressure, keep an eye on your cardiovascular health, and eat a healthy diet. And don't smoke because smoking is a huge risk factor for Alzheimer's disease and, actually, many other diseases. So that's the best way to reduce your risk nd hope that medicine, in the meantime, can come up with a way to save us all before we succumb. So we're all crossing our fingers.

Aubrey - Sage advice as always Dr Chris Smith. Thank you very much for joining us. We really appreciate it.

Chris - It's a pleasure. Thank you. See you soon everyone!