The mind at rest
The surprising science of sleep and daydreaming. Letting your mind wander involves complex brain activity and facilitates problem solving, creativity and even enhances our sense of identity. Also, scientific sleep studies are showing that our memory can be enhanced and we can learn new things ... all while we’re quietly snoozing. This program looks at the benefits of zoning out.
Lynne Malcolm: On RN, Lynne Malcolm with you for All in the Mind. Today, sleep and the wandering mind.
Muireann Irish: I think there's a common misperception that when we daydream we are actually being lazy and we are switching off from the present moment and not really doing anything specific with our brains. But converging research is now suggesting that when we daydream actually the brain is very hard at work.
Lynne Malcolm: And author JK Rowling would vouch for that; she came up with the magical Harry Potter stories whilst gazing out the window on a long train journey.
Muireann Irish: Daydreaming has been used to refer to all sorts of internally generated thoughts, such as when we reminisce over the past, when we plan for future events or we anticipate upcoming events, as well as a more social function when we infer and mentalise to consider the thoughts and perspectives of other people. And of course daydreaming also has been suggested to support creative functions. So helping us to have novel ideas and for more creative avenues to flourish.
Lynne Malcolm: More about daydreaming from Dr Muireann Irish later.
Now though, the surprising science of our sleeping mind.
Penelope Lewis: As humans we spend a third of our lives asleep. If you think about it, that's more time than we spend doing anything else, and it suggests that sleep must be doing something incredibly important. You also know this anecdotally because you feel absolutely rubbish when you miss out on a night's sleep.
Lynne Malcolm: Neuroscientist Penelope A Lewis is from the University of Manchester in the UK where she runs the Sleep and Memory Lab. In her recent book The Secret World of Sleep she explores the latest research about the night-time brain.
Scientists have been trying to work out exactly what are the most important functions of sleep for more than a century.
Penelope Lewis: This is really the million-dollar question; how important is sleep for us? We do know that it's important for things like your immune system, it's important to helping your body to maintain the correct temperature, and there are all kinds of negative side effects to sleep deprivation.
Some of the things are really obvious, that you might just not feel in a particularly good mood and you might feel tied the next day. But some of the other side effects are a bit more subtle. For instance, it's very hard for us to encode, so that's learn new memories, when we are sleep deprived, and there have been studies that show that the hippocampus, that's an area of our brain that is involved in learning new memories, has to work incredibly hard to code new material when we are sleep deprived. Not only that, but also our judgement seems a bit clouded when we are sleep deprived. So if we have to make a difficult decision or even a moral type judgement, that seems to be impaired and we might do things that we wouldn't normally do. We might take risks that we wouldn't normally take when we are sleep deprived. And simpler things like our reaction times are slowed down when we are sleep deprived.
Lynne Malcolm: So what's actually happening in the brain when we sleep?
Penelope Lewis: So, anecdotally many people seem to think that the brain just switches off when we are sleep because maybe that's what it feels like to us, but in fact scientists know from many studies that they've done, primarily with a technique called electroencephalography where we put little tiny electrodes all over the scalp to monitor brain activity, that the brain doesn't switch off when we go to sleep, instead it moves through an incredibly highly structured series of very specific sleep stages, and we call this a sleep architecture.
So each of these stages is characterised by different kinds of brain activity, and also different concentrations of chemicals in the brain. We think that each of these stages is important for different things and that they act together to build up or to support the overall functions of sleep.
Lynne Malcolm: The stages of sleep are defined by different levels of electrical activity in your brain. After moving through quiet wakefulness to stages one and two, you reach the deepest slow wave sleep. Then, the final REM sleep has some unusual characteristics. Although you're still deeply asleep, your eyes move rapidly beneath the lids, all your body muscles are paralysed and you have no temperature regulation. The whole sleep cycle takes about 90 minutes and it repeats through the night. Penelope Lewis's main focus is the relationship between these sleep stages and memory.
Penelope Lewis: Scientists think that the different kinds of brain activity in these different stages indicate that they are doing very different things, and what we are trying to work out at the moment is what those things are and how they map onto the different stages. With respect to memory consolidation, which is what I work on, I can say that there is lots of evidence that slow wave sleep, so these high-amplitude slow oscillations, are important for strengthening many kinds of memories, and potentially also for extracting out generalities out of the corpus of information.
The sleep spindles, the high-frequency activity that happens sporadically during stage two sleep, so that's an earlier stage of sleep, they seem to be important also for strengthening some kinds of memories, particularly procedural skills, so things like riding a bicycle or playing the piano, which you can do but couldn't tell someone else how to do. And those sleep spindles are really interesting because they occur specifically in the areas of cortex that were involved in learning, and we think they might indicate the replaying of memories that is thought to be really important for strengthening them.
REM sleep is a bit more of a dark horse at the moment. REM sleep has been linked to strengthening procedural memories, but now some of that research is being questioned a bit more. It is also thought to be important for processing emotions, so there's an idea that if emotional memories are replayed during REM sleep then that may help to sort of extract out some of the emotional content, so that when you think of those things next time when you are awake they are less upsetting. But again, that research is at early stages and we simply need to look at it a bit more.
Lynne Malcolm: So what's happening is that there is a type of rehearsal going on during sleep to help with your memory.
Penelope Lewis: That's what we think. So we know that many kinds of memory are strengthened during sleep, and one of the main theories about how that strengthening occurs is to do with rehearsal. So we know that memories of things that you were doing recently in the daytime, particularly things that are important to you, like they are really emotional or you've been told you need to remember them, are spontaneously replayed during the sleep that you get soon after that. And that replay seems to act like a kind of practice in the brain. So when we say 'replay', I mean that the neurons which were involved in doing that task and learning that information initially spontaneously reactivates or replay while you are asleep. So you can see how it's like practice in that it can strengthen up the connections between neurons that are involved in that representation.
Lynne Malcolm: So can we control this and use sleep to remember and learn better?
Penelope Lewis: We think that we can, and this is part of the reason this area of research is so interesting at the moment. Over the last five years or so there have been an increasing number of studies showing that we can actually trigger the replay of specific memories that we want to remember. So, for instance, one really compelling study got people to play a game which when I was a child we called the suitcase, so it's this game where you set out an array of cards and each card has a match, and they are all turned face-down and you get to flip over two cards at a time, and if they match then you pick those up and take them away. And so you need to remember where all the matches are. I think most people have probably played this game at some stage.
And so what they did in this study is they taught people…you know, people played this game with an array of cards that never changed, so they always left them in the same place. And so as people played it they learned where everything was, and at the same time as they played that they smelled the smell of roses. And once they had been doing it for a while they were tested to see how good their memory was, how well they could pick up all the cards. And then everyone went away and had a night of sleep and came back the next day and were tested again on the same array of cards.
But the trick is, different groups were given the smell of roses again at different times. One group was given it during awake, one group was given that smell during REM sleep, and one group was given the smell during slow wave sleep. And the fascinating thing is that the group who smelled the rose smell again during slow wave sleep actually performed much better the next day than any of the other groups. So they remembered those card locations better. And the reason for this we think is because the smell which was associated with that game and remembering those card locations, triggered a replay or a reactivation of that memory during slow wave sleep, and slow wave sleep is known to be important for strengthening memories. And so that triggering strengthened that memory and allowed them to perform better.
Lynne Malcolm: So there's a strong potential to influence certain aspects of memory during sleep. Penelope Lewis also says it's looking possible to teach people new information whilst they're asleep. A recent study showed this, using a form of conditioning with the sense of smell.
Penelope Lewis: It turns out that when people smell an unpleasant odour then they automatically sniff with smaller-volume sniffs than they would if it was a really pleasant odour or just a normal odour. So you imagine rotten eggs, you are not going to want to inhale it as much. And so what this study did was during sleep they gave people either a really horrible smell or a pleasant smell, and each one was paired with a particular tone. So the tone predicted what the smell was going to be like. And they found, as predicted, that when they smelled the horrible smell they sniffed less, and when they smelled the nice smell they sniffed more in their sleep.
But here's the tricky thing; later on they presented just the tones that had been paired with those smells and they found that the tones elicited the same behaviour. So people in their sleep had learned, you know, this tone means it's going to be horrible, and so I'm not going to sniff too much, and the other tone means it's going to be nice. And when tested the next day they found that this behaviour was maintained. So we'd call this a form of conditioning, and they were able to actually condition people during their sleep with this new material.
But it's not just about playing tones or smells during sleep, there are other things we can do to enhance our memory consolidation. So some really exciting recent work has suggested that we can actually increase the amount of slow wave sleep that we get, and this can be done either through electrical stimulation, which sounds rather macabre and people might not want to try at home, that's when we pass a current across the cortex at about the frequency of those slow waves or slow oscillations, and this actually entrains the activity and triggers more slow oscillations than you would have otherwise, that has been shown to strengthen the amount of consolidation that you would get to your memory, so you get better memory consolidation.
Maybe a more user-friendly in-the-home technique that is being explored at the moment actually just uses sounds. So if tones are played softly at the frequency of slow waves, so that's about 0.75, 0.8 hertz, then these can entrain the slow oscillations, kind of tidy them up, they become bigger oscillations, they have a higher amplitude, and they have been shown to be more effective at memory consolidation as well. These are really new techniques. They are very much being explored at the moment, but we are quite hopeful that in the future we will be able to enhance people's sleep with these. That will enhance consolidation, and it might potentially also help people with conditions like insomnia.
There is a really important potential application in people who are getting older and therefore don't have as much slow wave sleep. So in people over the age of about 65, slow wave sleep reduces dramatically, this is thought to potentially be one thing that is linked to some of the symptoms of ageing like a memory loss, and even cortical decline in the frontal cortex. A recent paper came out last year which showed that the extent to which slow wave sleep is reduced in older people actually predicts the cortical decline. And so it is possible that if we can artificially increase the slow wave sleep that these people get, that we might be able to help to prevent some of those symptoms or postpone them or slow it down.
Lynne Malcolm: How often do you wake up in the morning and suddenly come up with a solution to a problem you were grappling with, or made a clear decision about something you were unsure about the day before?
It fits with the old adage to 'sleep on it'. Is there wisdom in that?
Penelope Lewis: I think it's fantastic advice. There has been quite a bit of evidence in recent years that sleep can actually help us to make tricky decisions, and it seems that this may be because it helps us not only to strengthen memories but also to sort of pull out the gist information from a set of memories, and pulling out the gist information often provides us with an overview, the big picture, which might then let us make a sensible decision.
So an example of a case where sleep has been shown to help with tricky problem-solving comes from a task that we call the rapid association task, and in this case what happens is people are given a sort of brainteaser. I might give you the words 'tooth', 'potato' and '16', and ask if you can think of anything that associates all of them. And the answer, which some of you may have come up with, is 'sweet'. So 'sweet tooth', 'sweet potato' and 'sweet 16'. So that binds together all of those words.
And it has been shown that if people are given a number of these problems and their performance is measured and then they are allowed to have a break of a couple of hours, with one group sleeping during that time and the other group not sleeping, then people who sleep and particularly people who have REM sleep in that time, seem to be better able to get the answer. And so that kind of data suggests that sleep is actually allowing us to pull out the associations between information that is linked, but the link is a bit more tenuous and maybe doesn't pop into our minds straight away.
So it may be something about the fact that this information is being subtly replayed in our minds while we sleep that allows us to make those linkages. That's an area that we still need to explore.
Lynne Malcolm: What about the connection between sleep and our emotions, the way we remember emotional events through sleep?
Penelope Lewis: This is a really interesting one. There's a bit of controversy in this area. There are two competing ideas, and one idea, which has been very popular and is very intellectually compelling, has been labelled the overnight therapy hypothesis, and this comes from Matt Walker, now at Berkeley. And the idea is this, we know that memories are replayed during sleep, and that includes emotional memories. During REM sleep our pharmacological milieu is such that even if we replay something that is very upsetting, then we can't have all of the bodily responses that are associated with this, and this is because a neurotransmitter called noradrenaline is at a very low level during REM sleep, and noradrenaline is in needed to experience these bodily responses. So that means our heart rate can't increase, our skin conductance can't increase, those kinds of things.
Those kinds of responses are necessary for experiencing an emotion, and so what Matt Walker says is that if you replay upsetting or traumatic emotional memories during REM sleep, then this will strengthen up the content of the memory but it may weaken the emotionality of that memory because you won't be experiencing those physiological responses at the time while you are replaying it. And the result of that could be that the next day or maybe after a week if you do this every night, when you remember that when you are awake it's not going to be as emotional, it is not going to be as upsetting as it was the first time around or prior to that kind of processing.
So essentially the idea is that replaying emotional things during REM sleep may diffuse them and reduce the emotionality, and this might be an important function of how our emotional system resets itself and deals with unpleasant things.
Lynne Malcolm: And so to dreams. What can neuroscientists tell us about them?
Penelope Lewis: We really don't know a whole lot about dreams is the honest answer. Neuroscientists have explored the physiological basis of dreams, and we know that there are particular areas in the brain that are necessary for people to have dreams, and if those areas are damaged or if those systems are damaged then dreaming can be reduced or even completely lost. And there are different ideas about what the functions of dreams actually are, and also how dreaming might relate to replay of memories and memory consolidation.
So one hypothesis is that although most of the replay of memories that happens when we are sleep is subconscious and we are completely unaware of it, it's possible that occasionally that replay is strong enough that it reaches consciousness and manifests itself as a dream. So that if that view is correct then our dreams could be indicators of what we are replaying and what's getting consolidated. So they are sort of epiphenomena, if you like, of that process that's happening anyway.
Lynne Malcolm: And we'll delve further into the world of dreams on All in the Mind next year.
Penelope Lewis is director of the Sleep and Memory Lab at the University of Manchester, and author of The Secret World of Sleep, published by Macmillan.
You're listening to All in the Mind on RN, Radio Australia, and online. I'm Lynne Malcolm, and we're discovering what happens when our minds are at rest.
Are you a daydreamer? Do you often find yourself gazing out the window in a world of your own thoughts? It can feel like a waste of time but it's actually an essential part of human life and sets us apart from other animals.
Daydreaming is the passion of Dr Muireann Irish who's from Neuroscience Research Australia. She says there's lots going on in your brain when you 'zone out'.
Muireann Irish: Actually neuroimaging studies are now showing that when healthy individuals daydream and simply rest in the scanner, the brain is hard at work. We see deactivation of the attentional networks and then an increase in activation of what is known as the default network of the brain. This default network kicks in to engage in these fanciful forms of thought where we reminisce, we imagine, we socially introspect, we mentalise and we engage in creative thought.
And so these functional neuroimaging studies have demonstrated that in fact there's a widely distributed neural network of the brain which activates or lights up, and this incorporates many different structures that are essential for many complex functions that we engage in. So some of these structures that activate are in the frontal lobes, they are in the medial temporal lobes of the brain, including the hippocampus which is essential for memory, and also more deep posterior parietal structures. In fact it's this widely distributed network that hast to activate to support this function which really suggests and speaks to the complexity of the whole process of daydreaming.
Lynne Malcolm: So how does daydreaming, for example, relate to our creativity?
Muireann Irish: Well, this is one of the more interesting aspects of the whole daydreaming field, and so it has been suggested that in fact when we daydream we are loosening our associations for a particular problem. So sometimes in everyday life we may get stuck, we can't puzzle out particular items that have been troubling us for a while, and then it seems that when we actually put that idea to one side and then engage in some other sort of zoning out or tuning out sort of activity, in fact the creative breakthrough happens.
And so some researchers have suggested that we need these periods of incubation where we are really not focusing on the problem per se, but in the background our daydreaming is facilitating us to bring different ideas together and to make associations that we may not necessarily have made before. And then we have this creative breakthrough.
And so some famous examples of people who have had inspiration in unlikely places are people like Woody Allen. He attributes some of his best ideas to just tuning out in the shower. Or the author JK Rowling who actually came up with her idea for the Harry Potter novels just daydreaming on a long train journey. So it seems that inspiration can actually strike us in very unlikely places.
Lynne Malcolm: So in a sense there is a whole mechanism going on behind the scenes that we actually don't have any control over.
Muireann Irish: In a way, yes. So the healthy brain is constantly engaging in all sorts of machinations that we may not be overtly aware of but that when the product of these emerges it seems to benefit us in a very evolutionary adaptive way.
Lynne Malcolm: So could you say that the more one daydreams, the more creative you can be?
Muireann Irish: I'm not sure if we can make that leap just yet, but certainly I think there is a time and a place for daydreaming and that it definitely would have a number of important functions in everyday life. There is the other side of the coin that if we daydream too much we are not being attentive to the present moment and we are not focusing our attention on tasks that do need it. So I think it's a question of balance probably.
Lynne Malcolm: So what can happen if you really lack daydreaming?
Muireann Irish: Well, this is one of the avenues that I've been pursuing with my own research, and I've been investigating the capacity for introspection and daydreaming in conditions such as dementia. And so we know now that given these complex regions of the brain that are so important for daydreaming we know that there is significant atrophy or brain shrinkage in dementia in these regions. And so I've looked in a number of different ways at how this impacts upon the person's ability to just spontaneously reminisce or to imagine the future or to even introspect and then mentalise to consider other people's perspectives.
And across-the-board it seems that the damage that we see to the neural networks in dementia conditions really limits the ability of the person to take themselves away from the present moment, to remember past events, to anticipate and envisage the future, and to consider the thoughts and feelings of other people.
So there's widespread damage to the brain and it really impacts upon them in an everyday level. So if we think about how important it is to remember past events for our identity and our sense of self, that's really damaged in dementia conditions such as Alzheimer's disease. And then we see socially relevant mentalising and daydreaming, that can be affected in certain conditions known as frontal temporal dementia where patients are really limited in their social interactions because they can't do this social daydreaming to imagine what other people are thinking or feeling.
And then across-the-board in dementia we also see that patients are unable to imagine or envisage future events, and that's really limiting. It means that they can't look forward to events possibly with their family at a future time point. It may lead to apathy or even feelings of depression. So I think the fact that we can engage in daydreaming so readily and so easily, we often take for granted just how important it is on an everyday level in our lives.
Lynne Malcolm: And are there other associations between daydreaming and other mental health issues?
Muireann Irish: Yes, I think it's really interesting when we consider the other side of the coin when maybe these daydreaming ruminative functions are perhaps overly expressed. And so two conditions that spring to mind in this case are anxiety and depression. And so in depression for example we see individuals who are caught in a process of thinking too much in a negative way about their past, and they are very maladaptive ruminative forms of thinking. And then in anxiety it's nearly the other side where they are constantly envisaging the future in a negative way, in an anxious way and ruminating on what might happen or what could happen. And so in that sense I think it's nearly a question of how could we apply some of the mindfulness literature to help these individuals perhaps rein their thoughts in a more positive and constructive way.
Lynne Malcolm: These days where it seems that many of us are spending less time on the bus, for example, gazing out the window, instead we are hooked into our digital devices, are we finding it harder just to have that space, and what impact might that have?
Muireann Irish: Yes, certainly I think this is probably an issue to consider, particularly with children and the huge role that imaginative play can serve in helping to develop their social skills and just their general creativity. And I do think when you see we're checking our emails on the bus on the way to work, we are not really taking the time out to just make castles in the sky or take a lion in for a walk and draw pictures any more…
So I think we really need to be mindful of how we are encouraging especially children to use this capacity for daydreaming. It's so fundamental to who we are as human beings and it really makes us unique, in a way, elevating us above other primates. So it's possibly a question, again, of balance. How do we set aside time to foster and really encourage this form of thought, particularly in the schools, without also compromising the need for focused attention on basic lessons such as maths and reading. Engaging in imaginative play as well is very important for helping to foster the child's sense of self, sense of identity, and their hypothesis testing within social scenarios.
I often find that when I actually do stop paying attention to a problem, that's when I get my best source of inspiration. I find myself that I tend to have a lot of my good constructive forms of thinking late at night, to the point where I used to keep a notebook by my bed to write down ideas. Sometimes even I would find that when I woke up that overnight, through dreaming,different associations had come together, and that certainly can happen during our waking moments as well.
But I think, yes, there is a time and a place for us just allowing ourselves to maybe down-tools for a moment and just allow our minds to wander and to see what the product of those loosening of the associations could bring.
I think that looking at these higher-order forms of thought, it's really bridging the gap between mind and brain, and trying to determine what regions of the brain do we really need to engage in these uniquely human functions. It seems like we've evolved to have these fanciful forms of thinking to escape from the present moment, and so what are the purposes that these forms of thinking must serve. Which begs the question; how does it impact on the individual when they lose that function? And so that's the area that I want to keep driving my research in.
Lynne Malcolm: Muireann Irish, senior research officer at Neuroscience Research Australia and research fellow at the University of New South Wales.
Go to the All in the Mind website for more information, including the book details related to today's program. While you're there, leave a comment about your sleep and daydream experiences, and you can also share those on the All in the Mind Facebook page. Don't forget you can download previous episodes of the program on the All in the Mind website from abc.net.au/radionational.
I'm Lynne Malcolm, thanks for your company. Next week tune in at the same time to hear about Fast Minds, and adult ADHD.
- Dr Muireann Irish
- Senior Research Officer, Neuroscience Research Australia
- Penelope Lewis
- Neuroscientist, University of Manchester
- The secret world of sleep
- Penelope A. Lewis
- The Role of Sleep Spindles and Slow-Wave Activity in Integrating New Information in Semantic Memory
- The Journal of Neuroscience Sept 2013
- Lynne Malcolm
- Katie Silver
- Sound Engineer
- Leila Shunnar