Snacking, craving and the microbiome! This month Naked Neuroscience looks at what's going on in the brain when we're hungry and thirsty...
In this episode
00:54 - Can dogs recognise their owners' faces?
Can dogs recognise their owners' faces?
Duncan Astle, Cambridge University; Helen Keyes, Anglia Ruskin University
First up is our usual neuroscience news segment, and cognitive neuroscientist Duncan Astle has been looking into a paper asking whether man’s best friend can recognise faces in the same way that humans can...
Duncan - So they've recruited 40 participants - 20 humans, and 20 family dogs. For the humans their average age was 32, and 47% had a Master's degree or equivalent and 37% had a Bachelor's degree. For the dogs their average age was five and to date, none had yet completed any higher qualifications.
[giggles].
So all of the subjects were put in the fMRI scanner - the functional magnetic resonance imaging scanner. And they were shown videos with human faces or human backs of heads, and dog faces or dog backs of heads. So we've got a two by two design. Face versus back of head, and species - human versus dog. And the stimuli were really carefully controlled. So for example, the dogs and humans would never look directly at the camera and that's because apparently that can be triggering for dogs and can make them anxious or aggressive. So they had to think very carefully about how they delivered the stimuli. What they wanted to explore is whether or not both species are sensitive to faces versus backs of heads, and whether they discriminate the kind of species that it is.
The headline result is that in humans, there are lots of visual areas that are very sensitive to faces, but not particularly sensitive to species. Whereas in dogs, there were lots of visual areas that were highly sensitive to species. So those brain areas seem to distinguish another dog from a human being. But not to faces ie they don't seem to distinguish the front of the head from the back of the head.
Now, amongst their analyses, one that they ran was called an MVPA analysis or a multi-voxel pattern analysis. What it's doing is testing what information is being represented in different brain regions. So that if we read out the activity in that brain region, could we predict whether the person was currently looking at a face, a back of the head, a dog, or a human?
In the dogs they found that the left medial and right caudal supra sylvian gyrus showed really good decoding for species. So the dogs had brain areas that seem to be quite specialized for distinguishing dogs from humans, but there are no significant areas that seem to be specialised for distinguishing faces versus not faces i.e. backs of heads. Contrast that with the humans, so in one particular area, the right middle temporal gyrus, you can decode species, so they can distinguish humans from dogs. And then in loads of areas, including the fusiform gyrus, sometimes called the fusiform face area, you see selectivity for faces, so a classic face response. In essence, it seems to be that while both species can decode the species of the person they're looking at, only the humans seem to have this kind of selective face processing set of areas.
And a final analysis they did was called a representational dissimilarity analysis, a look at different brain areas to see how well it distinguishes all of the different videos that people were shown. And then they can test whether there are parts of a dog's brain that has a kind of profile across those video clips that's very similar to a part of the human's brain and vice versa. So they can see whether there are analogous regions in the dog that seem to have a similar kind of representational profile of faces and species as a human would have. And they find that they do get some analogous regions for species, but not for faces. Again, supporting the idea that dogs don't really recognise the human faces or the dog faces. And that is that.
Katie - So overall, is what the papers saying that dogs are really good at telling that's a human that's a dog, perhaps not individuals so well. Whereas humans are really good at going “that's Duncan, that's Helen, that's Katie”.
Duncan - Precisely. There are all sorts of explanations as to why that might be. So for example, most dog owners tell me that their dogs recognise them. But if the dogs can't really recognise human faces, then how can they recognise their owners? So my guess is that they're using other things. So it may be that for human beings because of the way that our visual systems work, because of our language systems, needing to look at lips and so on, it may be that we've become highly specialised for decoding faces and distinguishing one person's face from another. Whereas for dogs, someone's face is just one of many useful cues for distinguishing an individual from another. And because they're not really looking at lips for language, the face is perhaps less vital than it would be for a human.
So it's obviously a really interesting paper. I mean the very fact they've managed to get people's dogs into an fMRI scanner, I think is itself quite impressive. But behind, you know, kind of the novelty factor, they're asking a kind of interesting question, which is, where does this special processing for faces come from? At what point in our kind of evolutionary past does it develop or does it emerge? And, you know, we know that higher order primates have similar face processing areas to human beings, but it's obviously not ubiquitous to all mammals because the dogs don't show it. So the question is, when does it crop up and why? So it may be that for instance, humans and other primates have a kind of uniquely sort of social interaction and social structure, where being able to distinguish one person's face from another becomes a really useful tool that perhaps was not there previously for other kinds of mammals.
Now if you listened to the last few episodes of Naked Neuroscience, you’ll know we’ve been pondering the subject of play. And perceptual psychologist Helen Keyes’ paper of choice this month - asking whether playing with dolls can impact social development - fits rather nicely into that theme...
Helen - Engaging in pretend play is really helpful for a child's development. It helps them to develop both cognitively and socially. And this study was looking at the neuroscience of this. So what's happening in the brain when children are engaging in this pretend play?
So pretend play or what you might call, make believe play, typically involves using toys or dolls to act out a pretend scene. And so you might be really putting yourself in the position of your toys or taking the perspective of your dolls as you're playing with them. And this type of pretend play usually emerges around the age of two. It can happen alone, or it can happen with a play partner, but even when it's happening alone, there's a lot of evidence that this is still social in nature. So you're kind of imagining an audience in this type of play or you're taking the perspective of others in this type of play. So it is particularly interesting to us as psychologists to ask whether this type of perspective-taking in pretend play does help to develop childrens' social brains, essentially.
So the scientists in this study used fNIRS, which is functional near infrared spectroscopy. And that essentially measures blood flow in different regions of the brain. An increased blood flow would be a good indication that that part of the brain is particularly activated. And here the scientists used this fNIRS to measure blood flow in the brains of 33 children who are aged between four and eight, while they engaged in different types of play, Either open-ended creative play on a tablet - so this would be where you are cutting hair or building towns on the tablets, open-ended play - or if you're playing with dolls and kind of doll sets. Both of these activities were recorded when the children were playing alone with these activities or when they were playing socially. So the research assistant was engaging in this play with them.
And the researchers were particularly interested in the parts of the brain that are strongly involved with social cognition. So empathy and perspective taking, and the particular part of the brain they focused on was the posterior superior temporal sulcus. What they found, interestingly, was that there was no effect of the age of the child or of the gender of the child here. So the findings I'm going to talk to you about applied equally for boys and girls.
They found that the social regions of the brain were really activated during joint play in general. However, during solo play, when you're playing with a tablet that activation dropped off. So that social part of the brain wasn't engaged, but that activation remained for solo play when the children were playing with dolls. So it looks like imaginative play using dolls engages the social regions of your brain. These regions involved with empathy and perspective taking, even during solo play.
Katie - That's so interesting Helen, because anecdotally, I've sometimes heard, you know, of parents who have a little one and then are expecting another baby might say things like, "We'll get our little one a doll", in some way kind of to prepare them for having a sibling. Do you think this kind of speaks to that in any way?
Helen - I think it does speak to that. It seems that playing with dolls or engaging in this type of imaginative play is a way of rehearsing your social skills and in a way of, of really thinking, encouraging our children to think about other people and that perspective taking. So absolutely I would recommend it to be a good idea to ask your child to engage in this type of doll play, to develop them socially.
Katie - But do we actually know if it makes a difference? I guess it's one thing to say these areas of the brain are highlighted, but has anyone followed kids up and thought, "Ah, these kids are more empathetic adults", or anything like that?
Helen - Well, engaging with this type of pretend play, yes, we do know that it's good for different areas of the brain. In general, engaging in pretend play is good for your cognitive skills and your social skills. So that's quite well established. What was interesting about this study, was it was showing that even in the absence of a playmate or that direct social stimulation, at a neural level we can see that engaging in imaginative play with dolls is, you know, recruiting those areas. In a way, making those areas practice your social skills. So yeah, we do know that engaging in pretend play is good for your social skills, but this is such a direct neural demonstration of that. It's just really strong evidence.
Katie - Do you think the tablet is a good comparison? I was just wondering about, you know, what, if you just give a kid some blocks or a stick or, or nothing, and just ask them to make up a game? Would that be more work for the brain?
Helen - The reason they didn't do that is if you give a child some blocks or some sticks, they will often engage in the type of pretend play that we would engage with when we're using dolls. They often won't, sometimes they will just stack the bricks or make rules for a game for themselves, but they really wanted to disentangle those social elements here by just giving a child a tablet and asking them to engage in a creative free play, not a rule based game, but it wasn't a social game.
The other point I wanted to make was that this study was funded by Mattel who make Barbie. So while I'm very confident looking at the research methods and looking at the researchers involved in this study, that it was, you know, a proper legit study, it is important to say that it was funded by the makers of Barbie.
Duncan - fNIRS is great in that it's portable. The kids can play. We haven't got to slide them in a scanner. But also one of the challenges is that you don't necessarily get the same coverage. So one possibility is that whilst the tablets seem to be less engaging social areas, it may be that what kids can do on them is more cognitively demanding in other ways than playing with a doll. So for example, if they're building something on Minecraft on the screen, it may be that they're engaged in all sorts of other areas to a greater extent than playing with a doll. Different toys for different types of play, yielding different types of benefit. Do you think that's possible?
Helen - Absolutely. I think that is certainly the case. If we were asking a child to engage in rule-based play, we would almost certainly see frontal areas, the prefrontal cortex, recruited, much more than during doll play. So absolutely I would recommend that we should be encouraging our children into all these different types of play. So not, you know, doll play alone might be great for social skills, but not so great for cognitive skills and vice versa. I think what it really tells us, when we put all this research together, is it's a really bad idea to have children just playing with one type of stimulus or one type of game all the time.
15:40 - What is hunger?
What is hunger?
Giles Yeo, Cambridge University
What exactly is hunger? What does that rumbling feeling mean? And what's going on in the brain? Katie Haylor quizzed Cambridge University geneticist Giles Yeo...
Giles - So hunger is the drive to eat, right? Appetite drive to eat is what we're evolved to get so that we make sure we take on nutrients when we need nutrients. Okay. So let's go with that as hunger. But given that we only experience hunger within ourselves, then what is hunger? That feeling? And I think that's the real difficulty of it, you've almost asked a philosophical question! But in terms of signals, it's not just one signal. Your brain needs to know two pieces of information in order to modulate your food intake. The first piece of information your brain needs to know is, how much fat you are carrying on board? Why is this important? This is important because how much fat you're carrying on board is how long you will last in the wild without any food. Okay. Not a problem today. We have too much food. But a problem in the past where we never had enough food.
But then the second piece of information that your brain needs to know is what you are currently eating and what you have just recently eaten. So these are now your short term signals. And these short term signals are going to come from your gastrointestinal tract, your food to poop tube. And these signals are released because the moment we start eating and munching and swallowing, it goes through our stomach, our intestines, and out the other side, the entire tube gives off hormones, letting your brain know, not only how much you're eating, but what exactly are you eating? What the protein fats and carbs content is going to be. So your brain then senses these long and short term signals and influences your interaction with food. And so when you ask what is hunger, clearly hunger is when these signals - the short and long term signals - signal to your brain to say, uh, "I think you're going to need to eat some food now". That is hunger.
Katie - And what is the sensation that perhaps a lot of people will associate as being hungry? You know, when you've got that rumbling in your stomach and it's slightly uncomfortable, what actually is that?
Giles - The rumbling in your stomach and your intestines actually comes from the washing machine-like nature that your stomach does. Moving juices about. This process is called peristalsis. So in your stomach and moves things around like a washing machine around and around and around. In your small intestine, it moves stuff down in one direction towards the, towards the poop end. Now, what is interesting is that these actions actually happen all the time. However, the reason you hear it suddenly when you're hungry is because your stomach and your intestine is then empty. So the food that is normally there muffles the sound. And so if you're full now, because you've just had lunch, you won't hear it, because everything is actually muffling it out. The reason you hear it is because you have an empty stomach. And so therefore it is often associated with being hungry because A) your stomach and your intestines are empty. And B) so therefore you then hear the sound. And we've now been conditioned to think, "Ooh, my stomach rumbling. I am hungry". And so it's a link between the two.
Katie - You mentioned there's the long term context and the short term context to being hungry, but how much of being hungry is motivated by, say, your body responding to depleted reserves, or responding to some sensory information, like, well, like smelling something delicious or walking past a cake shop or something like that?
Giles - So all of it's going to be integrated. So it's very difficult to say what percentage it is. It's a whole, all your sensations, all your senses, that are there will actually feed into this input. And secondly, it's going to differ from person to person. We know people for example, who love their food. And so are probably going to be far more sensitive, far more sensitive to all of the tactile, the smell, the vision, you know, and all of the accoutrements that, that surround food. Okay. That's me. Just FYI! But I've got friends who consider food as fuel. And my colleagues sits in my office next to me and he eats the same damn cheese sandwich every single day and has for the past 10 years that I've known him. But he clearly gets hungry when he's hungry, but he doesn't necessarily think about food all the time, like I do. He doesn't know what's going to happen for dinner. He thinks about dinner when it's time for dinner when he's hungry. And so I think each of us have different thresholds for all the sensations molecular, hormonal or just for your eyes and the smells. And it's this interaction which therefore guides and influences our interaction with food, a menu, the restaurant, the refrigerator.
21:34 - How does thirst work in the brain?
How does thirst work in the brain?
Christopher Zimmerman, Princeton University
Here in the UK, we’re told to drink 6-8 glasses of water a day. But then chances are you’ve got a caffeine hit or two, maybe you have a fruit juice, a fizzy drink, some squash, the list goes on. And Naked Scientist Eva Higginbotham spoke to Princeton’s Christopher Zimmerman, who has recently been awarded the Eppendorf and Science Prize for Neurobiology for his essay describing his breakthrough research into the science of thirst, which has been upending the textbooks...
Christopher - My research asks a really simple question, which is, "how does the brain produce the sense of thirst? And how does it use this information to control our drinking behaviour"? There's a small group of cells located deep in the brain that we call osmosensors. And we call them osmosensors because they can sense changes in the osmolarity or the concentration of molecules and salts in our blood. And these changes in osmolarity are the main hallmark of dehydration.
From our understanding of these cells, we would say that the sensation of thirst is just how hydrated we are at any one given point in time, how changes in blood osmolarity are occurring. But we know from introspection and from a lot of research that that's not actually how we feel thirst. For example, when we've been quite thirsty or dehydrated, maybe after exercising and we drink water, our thirst is quenched almost immediately, even though that water won't actually enter the bloodstream and correct our deficit for many minutes. And it's really been unknown how the brain solves this problem.
We reasoned that what we needed to do is record the activity of these thirst located deep in the brain. Obviously this would be very challenging in humans. So we used mice just study this problem who have very similar brain structures and also drinking behaviour to humans. And we use new tools in neuroscience that allow us to put a fiber optic cable in the animal's brain and then record the activity of these cells in real time, as a mouse is freely behaving, so it can walk through its environment and eat, and drink and do anything it likes, and we can ask what these neurons care about as it does that.
Eva - And what did you find?
Christopher - So the first thing we found was that these neurons are osmosensors. If the osmolarity of the blood increases, the activity of these cells increases, and that makes the animal feel thirsty. What was really surprising is that for example, when the animal then went and drank water, rather than slowly turning off as the water entered the bloodstream, these neurons turned off almost immediately a little bit with every gulp or lick that the animal took, in a way that counted how much the animal is drinking. So they seem to be getting some anticipatory or predictive signal from elsewhere in the body that was letting them predict how the water would affect hydration in the future.
Eva - So it seems like really direct feedback then. How is it that they taste the water and immediately the brain is saying, "alright, we're getting some of what we need right now"?
Christopher - It's really interesting. There seem to be layers of signals that arise from different parts of the body as we drink. So for example, there's a first signal that comes from the mouth and throat that signals exactly how much. So the volume that we've consumed. And this involves as far as we can tell a number of sensory properties, including the temperature of the mouth, and maybe swallowing as well. And then there's another signal that arises a little bit later from the gut, from our stomachs and intestines, that tells these cells in the brain, not how much we drank, but what we drank. So was it pure water or how salty was it? And they can use this information to then decide how thirsty we should be in the future.
Eva - So how do you think these signals work?
Christopher - Yeah, that opens a really interesting set of questions to address moving forward. We never knew these signals existed before, and it's been really interesting to see how they affect our behaviour. But it also suggests that there are cells and molecules in our periphery - so in our mouth and throat and gut - that are initiating them. So cells in our mouth that express a protein that lets them sense water or fluids. Cells in the gut that express some protein that lets them sense osmolarity. And then neurons that take this information from those distal parts of ourselves and send it to the brain. And we're really only beginning to understand those pieces in this system and looking for and identifying them is going to be really exciting in the near future.
Hunger vs satiety
Giles Yeo, Cambridge University
Where do feelings of fullness come from? Katie Haylor spoke to Giles Yeo...
Giles - Feeling hungry is different to feeling full. You might think "well they're related". But they're two different processes. So the feeling fullness, interestingly enough, tends to come from the gut hormones. So I think our gut releases - and now I'm going to get this wrong. And people are going to @ me - at last count around 22 to 23 different hormones that we have identified from our guts. Okay. Now of these call it 22, it's going to be plus or minus, 20 of them - so the vast majority of them - make you feel full. Okay. And those are the full signals. Now, the fat signals, because they're long term, they're there to tell you, "okay, well, this is what the bank account looks like". Rather than the change in your pocket. So those signals, the signals from fat tend to signal starvation. Because clearly you're not going to be starving if you're feeling hungry, but you have plenty of fat, because you're not starving. So I think the feeling fullness comes from your gut typically, whereas the starvation signals - all the neuroendocrinology, all of the hormonal milieu that turns on when you're actually starving, those are going to come from your fat or lack or lack thereof.
Katie - In terms of the communication that goes along on the vagus nerve between the brain and the gut, I know it's two way, but am I right in thinking there's quite a big sort of bias, a big percentage of nerve fibers in the vagus nerve go from the gut to the brain?
Giles - You're right about the bias. It tends to go northward. So the stretch signals and any number of things will go from the gut directly, hardwired directly to the hindbrain. So the vagus tends to be directly, so the back of the head, tends to come up via that route. That is one set of signals that come from the gut. The ones that make you feel full, however, those signals tend to be hormonal. So in other words, they are hormones that are secreted into the blood, circulate, and then - so they are not hardwired, they are fly-by wired - like homing devices hormones.
Katie - Are we talking about ghrelin?
Giles - Ghrelin is one of them. Now, interesting you should mention ghrelin. I told you about the 22 different gut hormones, most of them making you feel full. Ghrelin is one of the two that make you feel hungry. There are two, the other one is called incident like peptide five and it's not as powerful as ghrelin. But ghrelin is one of the key "hunger hormones".
28:46 - Appetite and the gut microbiome
Appetite and the gut microbiome
Katerina Johnson, Oxford University
Now, we know we’re not alone in our bodies. We’ve evolved with all sorts of micro-organisms living on us and in us. And the gut, of course, has an important role to play in the process of digestion. Katerina Johnson researches connections between the microbiome, the brain and our behaviour, at Oxford University, and Katie Haylor asked Katerina how the microbes in the gut could be influencing our appetite...
Katerina - We think of our gut largely as somewhere that we digest our food. And obviously that that's a key part of it, but there's so much more that goes on beyond that in the way that our gut can communicate with our immune system, our nervous system and our hormones. And so one aspect to do with this is that we think that our gut microbes may actually have some effect on our appetite control and hunger, through interacting with our body's own hormones and also nervous system, especially the vagus nerve.
Katie - Now, last time we spoke, this was actually for another Naked Neuroscience episode about gut feelings. We talked a little bit about perhaps if what you eat is relevant in the question of how eating and gut microbes are related. But from what you said last time, I got the sense that we don't really know that much about the specifics in terms of specific dietary choices. Is that fair enough?
Katerina - Yes. The one definite is the fibre is really beneficial for our gut and gut health. And that's true also when it comes to potentially affecting our feelings of hunger and satiety. When our gut microbes break down our food, which we call microbial fermentation, they release lots of different chemicals. And in particular, when microbes break down fiber, they produce short chain fatty acids. And we actually know that these short chain fatty acids can affect the levels of hormones that are involved in appetite regulation. So that might actually be one reason why we feel fuller for longer when we eat a lot of fibre. Because actually, when this fibre is broken down, it produces these short chain fatty acids that regulate our gut hormones such as peptide tyrosine tyrosine, glucagon like peptide. And we actually know for example, that the short chain fatty acid butyrate promotes the feelings of satiety. These short chain fatty acids actually have a really diverse range of effects on the body and our physiology. So not only do they affect our appetite control, but they can also affect our behaviour and cognition. And they're actually small enough that they can, in some cases, cross the blood brain barrier so they can get directly from our blood circulation into our brain.
Katie - Now, there are a couple of different categories of fibre that we can eat. The type that Katerina is referring to in terms of fermentation is soluble fibre. Think soft, moist fibre - fruit, pulses that blend with water to make a gel. Perhaps less well known than its famous counterpart, insoluble fibre - think roughage, the stringy nature of celery, sweetcorn, things that don't match up. And fibre isn't the only context in which gut microbes get involved with our food.
Katerina - We do think that they play a role in laying down fat deposits and helping us to metabolise food. And it's quite a controversial area, but we think that some types of bacteria are better at extracting nutrients from food than others, other types of bacteria. And this might actually be one reason why some people are prone to putting on weight and some people tend to be quite slim. It might actually be that the slim people have less efficient microbes. So they extract less nutrients from their food.
Katie - Katerina explained to me that in general, more diversity in the microbes in your gut tends to be linked to good health. And more diversity in the diet tends to be linked to diversity in the gut microbes. After all different microbes like to break down different types of food. So, I wondered, could a problem with your gut microbiome lead to your eating behaviour changing for the worse?
Katerina - We don't know this area in detail, but we know that the gut microbiome interacts with lots of hormones and neuropeptides. And so for example, our hormones that control appetite, particularly, ghrelin, which is associated with the feeling of hunger and leptin, which is associated with us feeling full. So if we disrupt our gut microbiome, it may well influence these hormones and might make us, for example, more hungry.
Although on the other hand, we have to be kind of careful that we don't put too much agency on the bacteria. So there's this kind of temptation to think that they might manipulate our eating behaviour, you know, perhaps for their own means to make us eat certain foods. But if we consider this scenario using evolutionary theory, this kind of manipulation is unlikely to be the case because we have such an immense diversity of microbial species and strains that live in our gut. So for example, imagine if there was a bacteria that went to a bit of an extra effort to produce a signaling chemical term manipulate our eating behaviour, this bacteria wouldn't actually last very long in the gut, because it would be out competed by all the other bacteria that weren't making this additional energetic investment. So for sure our gut microbiome influences our appetite control, but probably not in a way that is kind of purposeful or to manipulate the behaviour of the host.
Katie - I see. And I guess you've got to be careful that you're not equating potential correlation to potential causation right? In this relationship?
Katerina - Sure. Yeah, exactly.
Katerina - Katerina shared a couple of other interesting research highlights from the world of gut microbes and appetite.
Katerina - We tend to think that when we feel full, it's kind of our stomach or intestines that, you know, have stretched. But there's some research suggesting that [gut microbes] might also be involved in, you know, effecting how full we feel. So basically the researchers looked at proteins that are produced by the common bacteria in our gut, E-coli. And they found that about 20 minutes after feeding, the study was done in animals, mice and rats, but the E-coli basically started producing a different set of proteins. And it was interesting that it was 20 minutes after feeding because that tends to be the amount of time that it takes someone to feel full. So they wondered whether these proteins produced by the bacteria were contributing to this feeling of fullness. So basically they took these proteins and injected them into rats and mice, and they actually found that the rodents reduced their food intake, independent of whether they were hungry or whether they'd just eaten. The proteins that are produced by the bacteria actually stimulated the release of hormones that we know are implicated in regulating our satiety. Another finding from their research was that the animals' bloodstream had a chemical in that derived from the bacteria, which actually increased the firing of brain neurones that helped to diminish their appetite. Yeah, it's quite interesting because these proteins that are produced by E coli can actually be involved in the same molecular pathways that are used by our own body to signal when we're full up.
36:28 - Stress, food relationships and lockdown
Stress, food relationships and lockdown
Giles Yeo, Cambridge University
So far this episode, we’ve chatted hunger, thirst, and how the microbes in the gut could be involved with our appetite. But hunger isn't the only driver for eating - some of us eat when we're stressed, or feeling a particular emotion. Katie Haylor asked Giles Yeo how these kinds of things work in the brain. But firstly, what science lies behind a food craving?
Giles - I think it feeds into the feeling of hunger. I think it modulates hunger. So let's simplistically split our brain - from a food intake perspective - into two major control centers. Now they're not separate, but conceptually. The first is the fuel sensing area. Okay. And this literally, I guess if we look at it simplistically, it senses how many calories you have used and therefore how many calories you need to eat in order to make up what you've used. Fuel sensor. Okay. And this sits in an area of the brain called the hypothalamus typically. But then there is also another part of the brain and this is called the hedonic region of the brain or the reward area of the brain. Now this is the part of the brain that makes eating feel good. It is also where it controls your cravings and your wants and your needs rather than necessarily how hungry in terms of, from a fuel perspective, you are.
Let's just take an example. We know that when we are really, really, really hungry, the simplest foods in the world taste delicious. A piece of cheese, a little bit of bread, some rice. Hmm, Hmm. But then, the fuller you become, the more picky you become with your food. Okay. So, we know this phenomenon, we go through it every single day. So there, we have an example of when you're really hungry and so therefore you need fuel, your fuel sensor's going "empty, empty, empty", then you're craving levels for certain things either change or the threshold drops because the bread and cheese and simple foods taste absolutely delicious. Whereas the fuller you become, because your fuel sensor's saying "we don't need that much fuel", suddenly what it takes to trigger your cravings, what it takes to trigger your reward pathway is completely different, right? So suddenly bread and rice - ah no. You need a chocolate cake, right? You need something which is highly energy dense to trigger that area of the brain. So those cravings are going to come more from the reward and hedonic areas of the brain, but it influences and speaks to the fuel sensor part of the brain.
Katie - So aside from hunger then, if someone's inclined to eat through stress or particular emotional states, say you're sad or something, is that then tapping into the hedonic pathway that you mentioned, rather than the fuel sensing pathway?
I'm gonna answer this in a sense where we don't actually know with a capital N.... K capital K! I have a PhD, you know... You're absolutely right. There are some people when they're stressed who eat, and some people when stressed don't eat. And this is a different type of stress than tiger stress that is run, run the hell away from, from anything. Everyone universally responds to tiger stress. Otherwise we're going to be dead. Whereas with chronic stress there's a diametrically opposite response to how we actually respond to the stress. And it's the same hormone it's cortisol, right? It's not even different hormones. Exactly the same hormone. And I think where people are going with this is that, stress is unpleasant. And so you want to try and remove that stress. For some people removing that stress is food. Other people maybe need drugs. They may need alcohol. Maybe they do bungee jumping, you know, and maybe they go running, you know, these, these, these crazy people, they go run when they're stressed. So, so, but because it makes them feel better. So I think that's probably where we are.
Katie - It might seem like I'm asking a bit of a flippant question, but I don't think I am actually, when we first started talking, I mentioned I've been visiting the biscuit cupboard more because I'm working from home and I'm socialising virtually from home. I'm basically living in my house, exclusively. What do you sort of forecast as being the consequence of the way that we eat, considering a lot of us have been in our houses for quite a lot of the time over the past six months? How do you feel about our relationship with food collectively, I guess is my question.
Collectively is a strong word. I think that depending on your response to food and how you behave around food, I think the lockdown will have a number of different effects, some positive, some negative. So for me, I found out at the beginning of lockdown, for instance, on a Tuesday, going down before starting the daily routine and make cornbread. Who the hell wakes up at eight in the morning and makes cornbread on a Tuesday? But I love my food! Whereas other people might have gotten stressed during lockdown. And so suddenly there was this chronic stress that was there and you happen to be closer to your fridge, to your kitchen and being able to do what you want. And so therefore those people may have actually ended up, ended up eating more than they would have liked. And obviously then there are people who really love to do their exercise because that was a good outlet for them, but then they didn't actually manage to do that. And so as a result, didn't burn off the calories, which they wish they ate as well. So I think it all depends on who you are.
Now on top of that, I know I was fortunate in lockdown. I was fully paid through lockdown because I had a job. Whereas there were a lot of people who lost their jobs. And so therefore they were then going to have a completely different relationship with food. Because what kind of food was available to them? Did they have to turn towards cheaper foods with longer shelf life? So-called ultra processed foods, for example, which are high in fat, sugar and salt. So I think there's a very complex answer to give into how we would, as a homogenous blob, respond to lockdown and food.
But I think what lockdown would have done, and this is the critical thing...Because our behaviour around food is governed not only by our genes, but by the genes' interaction with the environment, and lockdown was a very, very significant environmental impact, the like of which none of us have seen in our lives, I don't think. This is a very new type of scenario we will be facing. So there will be undoubtedly a huge influence influencing the relationship of many, many, many different people in different ways to food. And let's see what happens, to be fair. I think there will be studies in a few years time looking back upon this time and upon how lockdown has actually influenced average BMI, rates of disease, you know, and everything else. I don't think it's a flippant question at all. I think it's a very, very relevant question. I just can't give you an easy answer.
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