Colour on the Brain - part 2

20 March 2020
Presented by Katie Haylor
Production by Katie Haylor.


colour chart for paint


This month - Naked Neuroscience continues its colourful journey! We're exploring amazing animal colour vision, colour perception and development, and how colour relates to emotion. Plus, some of the latest neuroscience news from our local experts... 

In this episode

Brain schematic

01:14 - Winning and losing - kids' circadian rhythms

Why children’s brains respond differently to rewards and losses at different times of the day…

Winning and losing - kids' circadian rhythms
Helen Keyes; ARU, Duncan Astle, Cambridge University

Perceptual psychologist Helen Keyes from Anglia Ruskin University and cognitive neuroscientist Duncan Astle from Cambridge University told Katie Haylor about some neuroscience news stories that caught their eyes this month. For Helen, timing is everything! She’s been looking at a paper about how children’s brains might respond differently to rewards (getting 50p) and losses (losing 25p) at different times of the day…

Helen - We know quite a lot about circadian rhythms. For example, humans tend to sleep at night and be awake during the daytime. And there are other changes like our body temperature and blood pressures vary through the daily cycle, with our lowest body temperature being at about 4:30 AM. But there are changes also in our hormones. So our cortisol and testosterone levels follow a daily cycle and they peak at particular times of the day. And this can impact on our neural patterns and even on our behaviour. So these authors we're looking specifically at children aged 7 to 11 and how their brains responded to rewards and losses taking into account these circadian rhythms. And they all took part in what we call a doors task. And this is a very simple computer game where you have two doors in front of you and you choose. And if you choose the right one, you win 50 pence and if you choose the wrong one, you lose 25 pence.

So the scientists used EEG, which records voltage differences across the brain, to measure the brain's responses to rewards and losses here in this game. And they did this across different time slots across the day for these children. And what they found was that for older children, so pre-teens, responses to gains were much stronger than the responses to losses in the early evening, so after 5 PM. And this was driven by the response to losses being really dampened. And so when the pre-teens experienced a loss, they lost 25 pence, their brains didn't really respond that much to that loss after 5 PM. However, they still responded quite highly to getting a reward. The opposite pattern was found for younger children. So children closer to age seven, researchers found that after 7 PM their neural responses to losses were greater than their responses to gains.

Katie - Does this have anything to do with bedtimes, do you think? I think it does perhaps fit in with what we know about bedtimes. So there's a phenomenon that we call "eveningness" in teenagers who have a preference for later sleep times. And we can certainly think about the earlier sleep times for younger children. I think it would be no surprise to parents that seven year olds respond very strongly to losses after 7 PM!

Katie - I've come across this concept of the "witching hour". I think it's - what is it - six till seven?

Helen - There you go. It fits right in with what we know about the witching hour in younger children, but it's really interesting that when these children become closer to adolescence, so when they enter the preteen phase, these younger teenagers might be experiencing greater urges to engage in rewarding behaviour later in the day. So considering that their brains aren't responding much to negative experience or to losses, we could conclude that these pre-teens are liable to just not be that sensible later in the day. And this might be something maybe that we should bear in mind when dealing with preteens or adolescents, but it might be something that we maybe shouldn't point out to them.

Katie - Do you think this study has any applicability in the learning environment?

Helen - It may well have applicability in the learning environment. We do know that there are peak times based on hormonal changes for alertness for example, and there are peak times for when we are best at committing things to our long term memory. So absolutely we should perhaps be taking these things into account in our education system. What times of the day match up quite closely with when adolescents' brains in particular are responding at their best.

Katie - Any advice for parents off the back of this study, do you reckon?

Helen - I think you should probably put your seven year old to bed as close to 7 PM as possible! And perhaps if your seven year old is responding quite negatively to losses, maybe use more rewards in the evening time, but I think in general it's what we might already have known for quite a long time that preteens, moving into adolescence, you perhaps respond not so sensibly to situations. And interestingly, this might be even more so the case in the early evening.

Katie - Did they look at individual variation (in circadean rhythms)?

Helen - No, they didn't. And they'd, what would have been really nice would be if they had measured actual cortisol levels on the variation and how they mapped on to these changes, and they didn't measure that. So this is a very broad, vague study, but looking at 188 participants is pretty excellent for an EEG study. So I think we can be fairly confident and that they're fairly robust findings.

Duncan presented us with his own paper this month, in which he’s been MRI scanning the brains of children, in order to see if it’s possible to predict any cognitive difficulties...

Duncan - For a long time, lots of people have been interested in what is it about the developing brain that can give rise to different types of cognitive difficulty, like memory problems or listening problems. And the results have been super inconsistent. So, you know, if you choose children that have a particular diagnosis, like attention deficit, hyperactivity disorder, if you look through the literature, you can find studies that find brain differences all over the brain. And it's not really clear why that is. And so we wanted to see whether, if you scan the brains of lots of kids, and we had 480 kids in our study, could you predict the kind of cognitive profile that they have?

Katie - So what did you find out then? Can you, via MRI, categorise kids in this way?

Duncan - If you did a standard MRI scan of children's brains, and you use that to find information about grey matter in different parts of their brain, then that information is significantly related to the kind of cognitive problems that the child has. But not very much. So if you had the MRI information, you'd be about 4% better than chance, at predicting their cognitive difficulties.

Katie - Pretty low, right?

Duncan - Yeah. So it's significant because we've got 480 children, but it's a tiny, tiny amount. And that maybe goes some way to explaining why there's such inconsistency. And that's because rather than thinking: Oh what's the brain area for ADHD, or what's the brain area for a memory problem? Maybe the answer is that there is no brain area. And there's this interesting concept called equifinality, which is the idea that you might end up at the same end point, so the same kind of characteristics, but through multiple different brain roots. And that's what our data seems to suggest. Because when you looked at it, you could see that kids could have very similar cognitive problems but really quite different brains.

Katie - Do you think that language might be a bit of a factor here? I'm wondering how easy it is to put kids in particular boxes, say of dyslexia or dyspraxia.

Duncan - Do you mean the language of the labels?

Katie - Yeah.

Duncan - Totally agree. And that's why in this study we intentionally took those things out of the equation. So we had lots of different assessments of different skills in the children, and that's what we were trying to predict. So rather than trying to predict the label, for the reason that you say, that it could be that actually these things don't map on very neatly to underlying difficulties. We tried to predict specific types of cognitive difficulty they might have instead. And so having shown that there was this really poor relationship between the MRI scans and children's cognitive difficulties, we started to wonder why that was. And then we thought, well maybe, whether or not you've got more or less grey matter in this part of the brain, or that part of the brain, actually isn't really very important. What maybe is much more important, is how well those brain areas are connected to each other, and how they're organised. And so then we used a different type of brain scan called a diffusion tensor image, which sounds quite fancy.

But really what that's designed to do, is to measure the white matter tracts or fibers, that connect different parts of the brain. And with that information we were able to produce a, kind of, wiring diagram for each child's brain, showing how well these different areas are coordinated or connected with each other. And when we did that, we found that there was a really clear relationship between a particular type of brain organisation and children's cognitive strengths and weaknesses. And that was how well the brain areas were organised around hubs. And so a hub is just a very highly connected brain area. So if you imagine something like the tube network in London, King's Cross would be a hub, because it is really important for so many journeys and it's so well connected, versus something like Russell Square just down the track, would be a peripheral node in that network. And so what we've found is that the kids who had poorer cognitive abilities, the amount of gray matter in the different brain areas really didn't count for much. But how well those brain areas were connected to hubs counted for an awful lot.

Katie - So what relevance does understanding more about these hubs have in terms of helping kids who are struggling then?

Duncan - I think in the long run, what it means is that we have to radically rethink how these different types of difficulty might emerge over time. So rather than thinking that it's, sort of, the underdevelopment of, you know, brain area A, or brain area B. If it actually turns out that there's a more general global property of children's brains, which seems to be related to doing really well in terms of cognitive development, then a whole different set of mechanisms in terms of the genetics of those brain areas, in terms of the kinds of environmental influence are really much more important. And another second thing is that this key principle about, or being organised around, hubs cut across different diagnoses. So regardless of the child's diagnostic label, whether they had an ASD, or an autism diagnosis, for example, or an ADHD diagnosis, this principle held true throughout. And I think what it drives home is that relying on a child's diagnostic label to think about the ways in which you might help them, doesn't make great sense. Because as far as we can tell so far, those labels don't really map on neatly to underlying mechanisms. And so it's much more likely that interventions that are generally good for everybody or that are tailored to a child's specific difficulties, irrespective of their label, are much more likely to be effective.

Katie - This concept of brain connectivity, or crosstalk between different bits of the brain. It seems to be a bit of a recurring theme in some neuroscience, and certainly when I have a chat to people like you, do you think this way of looking at the brain has applicability beyond learning difficulties?

Duncan - Absolutely. So for instance, there's lots of work in things like schizophrenia, and other mental health difficulties. They seem to be sharing similar properties. Hub organisation seems to be a really important characteristic of an efficient and healthy brain. And so it's kind of an emerging area of science, that seems to cut across lots of different areas. And in aging, for example, it may well be that hub organisation is really important for continuing cognitive health into old age. Which is actually kind of encouraging to us that it seems that there are some more general principles, because rather than thinking of all of these different types of difficulty, like learning difficulties, or mental health difficulties, or aging as being totally distinct and separate, they might have some similar common underlying principles. And the organisation of the brain around hubs might be one of those principles.

Honey bees on honeycomb

16:28 - Visual visionaries of the animal kingdom

Which animal has the most impressive colour vision?

Visual visionaries of the animal kingdom
Professor Simon Laughlin, Cambridge University

Most of us humans have 3 different types of cone cells, which are responsible for the wide variety of colour we can perceive out there in the world. But we’re hardly known as a species for having the best vision on Earth, so how do our eyes compare with others' in the animal kingdom? Katie Haylor met Cambridge University neuroscientist Simon Laughlin at the university's museum of zoology, where he explained how us humans compare to other animals...

Simon - Well, the majority of mammals only have two types of cone. They have two colour channels. And this means that their colour vision is not as good as ours. In general a dichromat can only see something like one 10th the number of colours that are trichromat can see. In humans we have split the long wavelength part of the spectrum into two components, a green and a red. Whereas in most of the mammals, they have a blue or an ultraviolet and a green.

Katie - So what makes us so special? Why have we got three?
Simon - Almost certainly because a lot of primates are vegetarian. They eat fruit and leaves and trichromatic colour vision gives you much better ability to judge the colour, the quality, the ripeness of leaves and fruits. You can get around the world perfectly well with dichromatic colour vision. Indeed, as everybody knows from black and white photographs, you can see many of the objects that we're interested in without any colour vision at all. What colour vision is particularly good for is judging the quality of objects, things like ripeness, constituents, chemical composition, and also to produce signals which can be used for mate recognition and for feeding and pollination and all sorts of things like that.

Katie - So let's talk about another trichromat. We're standing in front of a pretty impressive collection of bees.

Simon - So what we have is a display of many of the different types of hymenoptera, the family of bees and ants. You can see there's an astonishing diversity among the hymenoptera in body form and size. There's a giant wasp here, which is almost as large as the palm of your hand.

Katie - Some would say it's terrifying, others might disagree!

Simon - They do sting, although many of them would prefer not to. Most of them are not as aggressive as say, wasps domestic wasps. So bees have three different colour types of photoreceptor, but compared with our visual system, they're displaced to shorter wave lengths. So they have an ultraviolet receptor, a blue receptor and a green receptor. And probably next to human beings, bees are the animal whose colour vision is best documented and best understood. It's been really intensively studied because bees use their sense of colour to identify flowers in order to get nectar and pollen.

Katie - Does that mean when we look at a pretty flower and see the different colours, bees are seeing a whole host of other things going on in that same flower?

Simon - Yes. In the 1950s the famous bee neuroethologist Karl von Frisch took pictures of flowers in the ultraviolet and showed that they had patterns on them, very distinct ultraviolet patterns, that we couldn't see, but would be very salient for a bee.

Katie - I'm imagining they're a little bit like the air traffic control guys, who sort of signal a landing strip, that kind of thing?

Simon - So the flowers are using a combination of shape and color and odor to attract bees.

Katie - That's trichromatic vision. Does anyone have tetrachromatic vision? These are four types of cone cells.

Simon - Yes. In fact, tetrachromatic vision is probably the standard pattern for vertebrates. They're only eight and a half thousand species of mammal in the world, so they're really quite a small group of vertebrates.

Katie - So we're the odd ones out.

Simon - We're the odd ones out, yes. So fish and amphibia and reptiles and birds and therefore, by implication, dinosaurs, the standard pattern there is to have four different classes of colour receptor. And these generally extend from the UV through to the red, so they have the bee-type UV receptor plus three others.

Katie - Unfortunately, Simon didn't show me any dinosaurs, but we headed downstairs to find a rather impressive display of tetrachromats, some a little closer to home.

Simon - Down here we've got one of the smaller birds, which is commonly found in people's gardens. Many of you will have seen them. It's a blue tit. And the blue tit has this blue crown on its head. About 20 years ago it was discovered by taking images in the UV that in fact the crown is much more visible in the ultraviolet, to a blue tit's ultraviolet preceptors. And it led to a classic paper, which is called Blue Tits are Ultraviolet Tits. And this is a very nice example of animals generating a signal in a part of the spectrum that many other animals are unable to resolve. Mammalian predators like cats and so on will be unable to see this really vivid signal, which stands out to blue tits.

Katie - Oh, I see. So if you are blue tit and you're looking for a mate, then you can see this beacon flashing on their head that something that was trying to eat and wouldn't be able to see?

Simon - Yes. And there's some evidence that the brightness of the ultraviolet signal in your plumage is an indicator of what a good blue tit you are. You've been well nourished and so on. And so therefore you would be a more desirable blue tit to mate with. It's by using the ultra violet cone that the blue tits can see this very vivid signal. But of course, so can the eagle up there, and the hawks, it's not fail safe.

Katie - Back upstairs in the museum gallery, Simon and I continued upping the anti when it came to the number of cone cells in animal eyes. And this next creature is really impressive.

Katie - There's a lot of legs going on here, Simon! What's in the display cabinet in front of us?

Simon - Crustacea, that's crabs and lobsters. And we're looking at a particular group called the mantis shrimp. You can just about cover it with your hand. So it's a really big shrimp. So the mantis shrimp has the most complicated eye in the animal kingdom for analysing the wavelength of light coming in. It has 14 different colour channels. I should say that many birds have up to eight colour channels. Some butterflies have as many as 13. So having more than four colour channels is quite common, particularly among brightly coloured animals.

Katie - So what's the advantage of having such a massively complex visual system?

Simon - They probably do not have eight dimensional or 14 dimensional colour vision. It would just be too difficult for the brain to handle 14 different colour channels all at the same time. They're probably using very narrowly tuned receptors in order to be able to discriminate very vivid colour signals. The mantis shrimps are lethal animals. They have a giant claw on their forelimb, which they wind up with an elastic band. They release it and as it whips through the water, the tip of the claw actually is going faster than the speed of sound in water.

Katie - Wow.

Simon - And they smash it into shellfish and other crustacea and kill them instantly. They also kill and stun small fish. Now when you have such a lethal weapon, it's very important that you only use it on the right animals. And so the different species of mantis shrimp are very, very brightly coloured and they recognise mantis shrimps of the same species using these colours. And so they have this very accurate system for determining differences in the wavelength spectrum of light coming into the eye.

Katie - I see. So you've got a really precise visual system because you don't want to mistake a potential mate for lunch.

Simon - Yes, that's right. But they go much further. If you think that you had a retina with 14 different receptors, then any point on the retina is only going to be monitoring a small portion of the visual field and they get round this problem by putting all of the receptors in a big fat band across their compound eye. All the photoreceptors in that band are all looking in the same direction, and then they scan the band across the image to determine the spectrum of light at different locations.

this is a colourful flower

25:36 - How and why colour makes us feel

Why do we have cultural, linguistic, and emotional associations with colour?

How and why colour makes us feel
Professor Anya Hurlbert, Newcastle University

Over the course of this and last month’s Naked Neuroscience episode, we’ve discussed how colour vision works in humans, how colour vision can vary and how it’s tested for, and how our colour-sensing abilities compare with those of other animals. But what about our cultural, linguistic, and emotional associations with such a ubiquitous thing as colour? Newcastle University’s Anya Hurlbert spoke to Katie Haylor. And as it turns out, light is far from just being a visual experience…

Anya - We respond to light coming off objects in order to see objects, but we also respond to light itself and our eyes are flooded with light from the room, from the surroundings, from the environment, generally we call that ambient illumination. And the light that's flooding our retinae at the back of our eyes is also stimulating receptors that are not involved in conscious vision, are not involved in helping us to reconstruct colours of objects and recognise them. They're involved in modulating our overall mood, behavioural level of alertness, sleep/wake cycle and our overall behavioural and cognitive function. And these receptors are part of what we call the non visual pathway. So we not only see light and see objects, we also feel light and respond to it in non-visual ways.

Katie - Is this part of the reason why, say if you've got somebody who's very poorly in hospital, say they're in intensive care, and they're in a coma, maybe they're not conscious, but light is still really important in terms of stimulating their circadian rhythms, which may be a bit lacking if you're in a hospital.

Anya - Yes, exactly. In fact, getting the light environment right in hospital rooms, which are not exposed to daylight is really important and is now being made more possible by the advances in lighting technology so that light spectra can now be tuned in real time to match natural daylight. And this is really important in helping to regulate the sleep wake cycles, not only of patients but also of the staff.

Katie - So from the unconscious to the conscious then, I want to ask you about emotion because colours are loaded culturally, linguistically! You know, "I just saw red", and maybe went into a rage. There is so much going on.

Anya - Yes!

Katie - What is the science behind colours affecting how we feel?

Anya - It really is true that colours, sort of more than any other visual attribute like texture, or emotion, seem to reach right down there into emotion and they have a close connection to the limbic system. And that's true anatomically. So the areas in the brain that analyse colour are actually located quite close to the deep seated emotional areas of the brain. And I don't think it's any accident, therefore, that colours readily evoke intense feelings in people. Vision scientists think that there might be a link in evolution between the emotional responses that objects aroused in us and the colours that they are. So that we developed a means of using colour as a sort of proxy for other properties of objects. And then we transferred those properties of objects to our feelings about the colours.
So that might sound sort of abstract, but we can think about the classic one of trying to find red berries amongst green foliage. So we're looking for the ripest, juciest, most maximally nutritious berry. We just scan for a deep saturated red and we find that and we pick that and that makes us survive better and it makes us feel good. So we start to associate that positive feeling with that deep saturated red. And eventually we abstract our response to the berry and apply it to the red.

Katie - Oh I see, so if a colour affects your emotion, then it can also affect your behaviour?
Anya - Yes.

Katie - If you're someone like me who loves listening to, reading about, watching interior design shows, you hear a lot about colours, you know, painting your bedroom, a certain colour, or your bathroom a certain colour. How rigorous is the science when it comes to creating your environment to be a certain colour to affect how you feel?A classic example is sleep, are there colours that are just genuinely better for sleep?

Anya - Well it's very interesting because there's so many different factors that can affect your emotional response to colour and the way it makes you sleep or the way it keeps you awake. And so teasing those apart is quite important because we have individual differences in our preferences for colour and they might depend on, in our lifetimes, which particular objects have we associated with particular colours. So I might particularly like green because my room was painted bright green when I was a child, but other people might look at green and think of snot or slime and therefore have a rather bad reaction to it. So there are individual differences in our preferences for colours. And that might influence, say, what colour we like our walls to be. That's one area.

Then we have the other area of our non-visual response to light. And the fact that there's this non-visual pathway that feeds directly into the parts of our brain that set our circadian rhythm means that, universally, very bluish light will tend to wake people up. And that's something we can say that's absolutely true. Whatever your preference for object colour. So a light with more short wavelength content, bluer light, with enough power in the short wavelength part of the spectrum will tend to keep you awake and that will then affect your sleep. So you really do need to think about responses to colour and responses to light on many different levels in order to understand why something might or might not help you sleep.

Katie - I've got to ask, do you have a favorite colour?

Anya - I do have a favorite colour and you know, I'm just very, very common in that way. I like blue and I mean way back, you know, at the Chicago world expo in the late 1900s, Joseph Jastrow showed that about 4,000 people picked blue as their favourite colour. So not unique!

Katie - We mentioned colour and emotion and you said it's not massively surprising to you that they are so closely linked. I think you're looking at this in the context of development though, right?

Anya - I'm also interested in at what stage of life these colour preferences develop, yes. But also whether there are any universals in colour preference. There are, as I said, universals in terms of non-visual responses to light. But can we pin down any universals in terms of emotional responses to colour? I'm not so sure. We know there are huge cultural influences. We know there are huge sex differences, but at what stage in development these arise is still not really clear.

Katie - Another thing we mentioned in terms of culture was language. You hear that some languages have so many different words to describe certain colours, but certainly if you go into a paint shop, there's myriad list of different adjectives that we put on colour. Do we know very much about language and colour? I'm wondering if people who speak certain languages have different relationships with colour than other people?

Anya - Absolutely. And it's been shown by many other groups that where certain languages such as Russian have different words for light blue and dark blue, they actually perceive those as different categories in the same way we Westerners perceive blue and green as very distinct categories. So there is definitely a relationship between language and perception and this does appear to come about at the stage of development where you would expect it to come about when language terms are being learned. There's a hypothesis, which there's a lot of evidence for, that language helps to shape perception, that the meer learning of linguistic terms helps to shape the colours that one perceives in terms of creating the boundaries between colours that we clearly put into different categories.

Katie - That's so interesting. Does that therefore mean that if you develop a bit differently to most people, your perception of colour and your emotion to it could be different?

Anya - Short answer - absolutely, yes. I think the individual variations in the way people see, respond to, and label are enormous and that each individual sees the world completely differently and there's really no way to get inside somebody else's head and perceive and respond to colours in the same way they do.

Katie - Oh, so does that mean the age old philosophical question that kids ask, "is that green, my green, the same as your green?" Is that always just going to remain a question?

Anya - I think it will, but I don't think that's a problem, I don't find that a kind of cop out or anything. I just think it means we have lots more to study.

Katie - And finally, on the subject of green, there is a lot of association at the moment with green and wellbeing. Do I need to paint my house green? Is this going to make me feel better?

Anya - Only if it really would make you feel better, for whatever reason! Your personal preference should be the thing that absolutely holds sway. Green doesn't necessarily have the same connotation for everyone, and green tends to be a background colour, because in the natural world it's foliage or it's grass. It takes up huge swathes of visual space that's meant to be sort of background against which other objects appear. Flowers or fruit or people. So green, you might think, "well, yes, it's probably quite a good colour to put on walls because it will sort of fade into the background and that's what you want walls to do". But you should never paint a room simply because someone tells you should paint it that colour! [laughs].


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