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Professor Matthew Cobb

Matthew Cobb is a Professor of Zoology at the University of Manchester.  With an initial background in psychology, these days much of his laboratory studies involve working with maggots and focus on how the sense of smell works.  He has also published a number of books on both science and history, and his latest book focusing on the race to crack the genetic code will be published later in 2015.

Why would I be interested in maggots?

On earliest memories of science

Well, I remember when I was about five drawing a picture of my future of old me as an archetypal mad chemist in a lab coat holding up vials of chemicals and stuff.  I’m not sure where that came from, and for a long time after that I wasn't particularly interested in science, I was much more interested in thinking about politics and history, which I still have an interest in today.  But I wasn't certain whether I wanted to go to university or not and I picked up a prospectus for a university and it was the department of psychology and I thought, oh, that’s interesting, understanding behaviour, understanding why things work the way they do, and that made me decide to go to university for a start and not do one of the many alternatives I could think of at the time.  And the final thing that decided the last nearly 40 years is in 1976 I was a first year student and I read a New Scientist, they had this little paragraph summary about some scientists in America who had made a fly that couldn't learn, it was stupid.  So they'd made a mutation that they thought was just single letter of DNA being changed, and as a result this fly couldn't learn. And I looked at that and thought, that’s amazing, that’s what I want to do.

I was very lucky in that I was a student at Sheffield in the psychology department and that was one of only two places in the UK at the time where people studied fly behaviour and the genetics of fly behaviour and as it happened one of my lecturers was one of the founders of that area in the UK, so I was lucky that 1) I was inspired and 2) I was able to pursue that.

On studying olfaction

So my PhD was on fruit fly mating behavior: I watched fruit flies at it for about three years or so!  And one of the things that became apparent was that…we mainly looked at what they did and the males do a little dance around the female and he waggles his wing and in fact he sings to her, he makes a little noise to her.  And it became apparent that, years after I’d finished this research, they were communicating each other by pheromones, and I got a grant from the Royal Society to go to France to study with the man who was pioneering the study of pheromones, which are chemical signals between organisms which provide them with information, so it’s a bit like an informational smell.

And so I worked for three or four years trying to understand the role of chemical signals in fruit fly mating, and this is a model - a very well known model and now a very well understood model - for how all sorts of aspects of animal behaviour work.  And then we were thinking about how to broaden it out and we decided sense of smell was the big area - scientists generally call it olfaction but it’s just a sense of smell - and we decided we were going to use flies for the same reason other people use flies, because you can fool around with their genetics and get at underlying mechanisms.  And the bloke I worked with said, I really want to try using maggots and I said, maggots are boring, and he said, just do the experiment and then we can decide.

So I did the very simple experiment which I've subsequently spent the last 25 years doing, in which you get a plate with hard jelly on the bottom of it and you put these tiny maggots, fruit fly maggots, in the middle and you put a smell on one side and nothing on the other side and you put a lid on and you just wait. And I watched and all the maggots moved towards the smell and I thought, right, that’s what I’m going to do because having studied a lot of fruit fly mating,  fruit flies are a bit like humans, they're not always interested, you set everything up for the experiment, you've got lots of different flies ready to mate and they don’t do anything, whereas maggots are incredibly stupid, they're just interested in one thing which is to find a smell, eat if they can and get big and fat and turn into a fly. 

So the point of this rather long winded story, why would I be interested in maggots, they're stupid, is a really idiotic answer, that’s why you should be interested.  They move in two dimensions, they don’t fly, and they are not interested in sex, they’re just interested in eating, and so a sense of taste and a sense of smell.  So for the last 25 years or so, I’ve been studying a sense of smell in maggots. 

On not having a sense of smell

Well, often when I give talks on sense of smell I have people come up to me and say ‘I don’t have a sense of smell’, and there are a range of reasons for this, often it’s people who have had an injury. So in humans our sense of smell works by…we have these cells that dangle down from the bottom of our skull at about eye level to the bottom of our nose and if you bang your head then the skull moves across these cells and can cut them and they can’t regrow. So people who have had a traumatic head injury often lose their sense of smell.

Another way is getting older: these cells regenerate, they’re about the only part of your brain that does regenerate, they're continually regrowing, so as long as the pathways remain intact, new cells will appear and they'll find their way to where they're meant to go in the brain.  As you get older, that process of regeneration declines and your sense of smell declines, and one of the things we know about old people is that they think food doesn't taste of very much, and this might be because they're in a horrible home where the food doesn't taste of very much, but almost certainly in most cases it’s in fact because their sense of smell is declining. So that’s a problem, whatever age you are: if you can’t smell you will have a relatively rudimentary taste.  People generally know you've got salt, sour, sweet, acid as your main taste domains; you've also got hot spicy, you've also got kind of very, very cold and they're kind of linked, and there’s also umami which is a kind of meaty taste. So, that’s it, but smells are kind of infinite and when you add smell and taste together, that’s when you get your full gastronomic experience, whether it’s eating fish and chips or lobster thermidor in a swish restaurant, it’s the mixture of smell and taste that gives you the full experience.  So if you have a cold, if you smoke or if you’ve had an injury or you're getting very old, your sensory of eating is much reduced.

I have on one occasion [met someone?] who genetically could not smell: it’s relatively rare, in fact, there are a handful of genetic disorders which mean people have never been able to smell and cannot do so, there’s no solution to it.  In terms of the problems that poses in everyday life, you may not know that you smell,  gas, you left the gas on…natural gas doesn't smell of anything, they have to put something in it called mercaptan which has a very, very strong smell so we know if we’ve left the gas on and can immediately smell it, but clearly if you've got no sense of smell, there are a whole other set of problems, you don't know when the milk’s off, other things that you can’t actually tell, so it is in fact quite a problem and it means you've lost an aspect of your sensory world.

On current smell research

Up until spring this year, whenever scientists like me spoke about how many smells we could detect we all said human beings can detect up to 10, maybe 20,000 smells, and people who work in the wine industry or perfume who have a very refined sense of smell which they train, they can maybe detect 25,000 smells.  Now nobody really knows where that figure comes from and everybody’s said it, but it doesn’t seem to have any basis at all, and earlier this year colleagues at the Rockefeller University in New York actually tried to test this idea, a complicated experiment in which they used a combination of smells and saw how many of these combinations people could discriminate and detect the differences between.  And, quite amazingly, the figure that they've come up with is that humans can detect at least a trillion different odours.  Now that’s very surprising on one level in that it’s much bigger than the 20,000 figure that we thought, when you consider that we’ve got 400 different kinds of cell, each kind of cell can detect many, many odours, each odour can be detected by many, many different kinds of those 400 cells, and in the world there are an infinite number of potential molecules that could smell of something, it’s in fact not that surprising.

Now somebody’s gotten very grumpy on the internet about this and suggested it isn't true and there’s some basic flaws in their calculations, because they didn't actually make people smell a trillion smells, they did a complicated sum, but all the smell scientists I know say the mathematician who suggests we’re all wrong doesn't really understand the complexities of actually how the sense of smell works in our being able to detect very, very rich complexes of atoms and molecules stuck together, but if you think about it, we know what the dimensionality of colour is, so light we can measure in wavelength and intensity and so on, and you can do the same with hearing, again, wavelength intensity.  Taste, well perhaps intensity and maybe five, six, seven dimensions; smell, the only way you can talk about smell is in relation to another smell, you can’t give an actual definition, like 27 nanometers or something like that.  So the complexity of our perception of it in fact reflects the complexity of the underlying physiology and ultimately genetics of what enables us to sense such a wide range of odours.

On smell and Alzheimer’s

Because smell is so important, although people generally don't recognise it, people are getting interested in when you lose your sense of smell, is it a signal of something going wrong, and there is a lot of evidence now that one of the signs of early onset Alzheimer’s - and perhaps Parkinson’s as well - may be the loss of certain aspects of smell, so people who are looking to try and screen Alzheimer’s patients before they are really beginning to lose important parts of their memory are using smell tests to try and see whether there’s an aspect of general sensory processing which is also being affected before you can actually see the more classic symptoms. It’s still something that is being developed but I think people are extremely interested, both the smell scientists and the people working on Alzheimer’s.

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