Is sleeping together good for my REM sleep?

Time for some Naked Neuroscience news, and this month cognitive neuroscientist Duncan Astle looked at a paper about cognitive health....

Duncan - So I've been working at home now for three or four months, and it's been a pretty sedentary experience. Most days, I'm wearing my pyjamas pretty much the whole day -

Katie - You're not supposed to admit that Duncan!

Duncan - And it got me wondering, what's the relationship between the kind of lifestyle we have, in terms of how sedentary or how active it is, and our cognitive health across the lifespan? And that's what this paper is all about.

Katie - Okay. So what did they do then?

Duncan - The story starts a long time ago, back in the nineties, when about eight and a half thousand people were recruited from GP surgeries in Norfolk. And a whole series of measures were taken including two physical activity questions. They were asked to rate their physical activity during work and their physical activity during leisure. And those measures were actually validated by fitting heart rate monitors, to people and checking whether or not they really correspond to physical activity. And they do.

Fast forward to about 2006, just over 10 years later, subjects are all seen again. And part of the measures that they are given this time round include a cognitive battery. So a battery of different attention, memory, reasoning, language tasks. And then what the researchers wanted to do was explore whether how active you were just over years ago during work, during leisure, is predictive of your cognitive health more than 10 years later.

Katie - So what did they find out then?

Duncan - They found somewhat counter-intuitively that if you're more physically active in your job, that's actually a risk factor for poorer cognitive health, more than 10 years later. Conversely, if you are more physically active during your leisure time, that's actually a protective factor for cognitive performance more than 10 years later. So there's no simple relationship between more physical activity equals better cognitive health later in life. The type of physical activity seems to be much more important.

Katie - What's going on? Is it that if you're more active in your job, perhaps you don't do the same level activity in your leisure? Because I can see why being active in leisure time is good for your brain, but I can't really see why being active in your job is bad for your brain, or is that not what they're saying?

Duncan - So the devil's in the detail. It's not that being physically active at work is bad for you. Not at all. The point that they raise in the paper is that the kind of job you do is much more complicated than just, "is it physically active or not?". So there are all sorts of other wider socioeconomic factors that also are predictive of the kind of job that you have. And we know that some of those are also associated with cognitive health across the lifespan. So for example, if you are on a lower income, then that is a predictor, a risk factor, for poorer physical and cognitive health across the lifespan. That also correlates with whether your job is more manual or more office based. All these kinds of specific economic factors come into play and might be really what's driving this apparent relationship with physical activity,

Katie - But is there anything positively, sort of, protective about having a desk based job?

Duncan - So they do say that having a desk based job reduces your risk of poorer cognitive health, more than 10 years later. So there is something protective about having a desk based job. But again, is it having a desk based job or is it all the things that are associated with it? For example, maybe earning more money, having more secure employment across the lifespan, and being less stressed in that respect. Are these the kinds of factors that are actually driving the better outcomes for those individuals? There are all sorts of factors like that, that it could be.

Katie - It sounds like what you're saying is it's probably a question of privilege, right? If you've got more money, perhaps you're more likely to have a better education, therefore a higher paying job, maybe it's a desk job, and maybe you have more means to enjoy active leisure time outside of work, cause you don't have two jobs. Is that a fair statement to make? Because I know it's quite a general statement!

Duncan - But I think that what you're essentially touching on is that socioeconomic status is what's really driving these relationships and that's what they allude to in the paper.

Katie - And that that is, is such a massive factor, that it outweighs the potential physical activity benefits of doing a manual job?

Duncan - Exactly that, because we do know that if you control for those things, and you look at people's cardiovascular health, then that does predict better cognitive health over the lifespan. So if you have better cardiovascular health, so for instance, like lower blood pressure, then you find that people do do better in terms of their cognitive health. So we do know that being more physically fit and healthy does predict better cognitive performance, but in this paper, because they're looking at the type of job you do, or how physically active it involves you being, what they're actually revealing is the kind of privilege that's enjoyed by people who have more sedentary well-paid desk based jobs.

Katie - There's quite a lot going on in this paper. What do you think that people should take away from it?

Duncan - I think that people should not be distracted from the idea that being physically active is good for you. I guess it also would make us think that even if your job is physically active, that doesn't mean that you shouldn't also try and be physically active in your leisure time.

Perceptual psychologist Helen Keyes looked over a paper that asks whether sleeping with a partner could help you get more and better REM...

Helen - It's where the good stuff happens - consolidating our memories, it helps to resolve some emotional distress. It also leads to increased social cognition. So REM sleep really ties in with a lot of improvements in people's lives, including having a positive effect generally on mental wellbeing. So REM sleep is really where it's at. And this study wanted to look at what's happening with REM sleep when you co-sleep with a partner.

It was a sleep lab study. In this case, they were measuring EEG (so looking at the electrical activity in participants' brains) when they were sleeping. They asked 12 heterosexual couples to come in over two weekends, and on one of those weekends, the couples slept in the same bed together while their electrical brain activity was being measured. And in the other weekend, and they slept in separate beds in separate rooms in the sleep lab. That same electrical activity was measured again. The couples also completed questionnaires about their relationship quality. So the depth of their relationship, the amount of conflict in their relationship, the support they felt from each other. And also got to complete the passionate love scale of their relationship.

Katie - Were these couples people who slept together, normally?

Helen - Couples who'd been together for at least three months in a situation where they were sleeping together every night or almost every night for the last three months. So yes, they were certainly couples who did normally sleep together. Tended to be rather young couples. So the average age was 23, but they were in fairly solid, committed relationships. And the authors found that the couples spent a higher proportion of sleep time in this REM sleep when they were bed sharing, compared to when they were sleeping alone. This REM sleep that they engaged in was also less disrupted, so better quality, when they were sleeping together. So that's really lovely. They found a really nice effect that might explain why they had more REM sleep. They found there was greater synchronisation of sleep cycles when couples slept together, more so than when they slept alone. This synchronisation between your sleep cycles was strongly correlated with the depth of your relationship. So the deeper your relationship was, the better the quality of your relationship, the more synchronised those sleep cycles.

Katie - That's very cute.

Helen - That is very cute. I agree.

Katie - What about deep sleep? Do we know if this has any effect on the other bits of sleep? Cause I know REM sleep is really important, but it's not the only type is it?

Helen - Not the only type. And we generally go down through stages of sleep. So when we talk about, you know, the architecture of sleep, you're going down from stage one, stage two, stage three, stage four into deeper sleep. It tends to be after that very deep period, sleep that you can then go into this REM sleep. But these periods of actually quite high electrical activity in the brain, that's what's happening during REM sleep, they seem to be really key to people feeling that they've had a good sleep. So if you are just engaging in other types of deep sleep, you don't feel as refreshed. You don't feel that you've had as good a sleep. And continually depriving people of REM sleep -e ven if you're allowing other types of deep sleep - can lead to quite serious psychological problems. It's just really essential to humans on other animals that we engage in this REM sleep.

Katie - As we're such a social species as humans I can see the logic of why having a closely bonded relationship and sleeping in the same place would be good for your sleep. But do we know what's actually going on to make it that way?

Helen - We don't know. So it could be that, you know, you just feel safer when you're sleeping with a partner and that would tie in nicely with the correlation with the depth of your relationship. That makes sense from an evolutionary point of view. If you feel safer, you can enter into that deeper sleep cycle. And then the other aspect that could be driving it is this synchronisation. So if you have a deep relationship with someone, and your sleep cycles are somehow synchronising with each other, perhaps that just spurs a more, a better rhythm of going in and out of these sleep cycles. We don't quite know why, but that synchronisation seems to be key to both people getting a better night's sleep and getting more REM sleep.

Katie - Do you think it could be influenced by just what you're used to? Because sleep for me is associated with routine. I have a sort of bedtime wind down routine, and I'm just wondering if these couples habitually sleep with their partners, in a study when you're sleeping by yourself it might just feel a bit weird and you might just sleep worse.

Helen - It's absolutely a good hypothesis. There has been other research looking at people who are single and how they sleep. That's a great question. And we have found in the literature that people who are in couples generally sleep better and report subjectively feeling that they've slept better than people who are single and sleeping alone. So that research has been done, but I don't think it's been done in this detail looking at actual electrical activity in the brain.

Because REM sleep is so associated with this social cognition and sociality, it's really interesting that there can be kind of a positive spiral happening here. The authors say it's likely that this has a really nice effect. You sleep together with your partner, you have more REM sleep, which in turn needs to more positive mental health and more prosocial behaviour, and your willingness and ability to engage in social behaviour. Which can be obviously very nice for a relationship! It also would you think twice about perhaps, you know, sleeping on the couch, if you're having a fight with your partner, because that potentially could lead to worse sleep, less sociality, leading to less sleeping together altogether! So it does seem to have a nice positive pattern there, sleeping with a partner.

Katie - What do you do if you're in a really deep relationship with someone, but they snore and it's a nightmare for you?

Helen - You're in a conundrum! So what was really nice about this study, they didn't find any results specifically around snoring, but this may be because they looked at participants who had an average age of 23. So I would suggest they come back in 20 years and look at these data! But they did look at body movements during sleep. They found, what had already been established in the literature, that people who co-sleep engage in more body movements during the night. But really nicely, they found that that didn't affect the quality of sleep at all. So that's lovely. So even though people are being disturbed more from that physical movement of a partner in bed, it's not affecting their sleep quality or the amount of time they spend in REM. Now the same, I imagine couldn't be said of snoring. I think that's a whole other study. And I really think if you are unfortunate enough to have a partner who snores, you're going to have to wait this one up carefully, I think!