#157 - Sleep Walking and Talking

0:02Matt Walker: Hi there, it's Matt here and welcome back to the podcast. Today, I want to talk about two of the stranger things a sleeping brain can do. Get up and walk and start talking. And I'd like to begin with something on the wall by your bedroom door. A light switch with only two positions and nothing in between. You're awake, then at some point after your head goes down, the switch flips. And in the morning, it flips back. Sleepwalking and sleep talking don't fit that picture at all. Tonight, I thought we'd have a go at both. We know from recordings made in sleep labs that the brain can be half awake.

0:40Matt Walker: These behaviors prove that beyond doubt. We'll have a look at what the evidence supports doing about them for adults and for children. Sleepwalking has been described as sleep and wakefulness coexisting in different parts of the brain at the same time. Let's have a look at why researchers think it happens and who is most likely to be affected. So how common is it to sleepwalk? Well, it depends who you ask, how they were asked, and over what time period. When 51 studies, including over 100 ,000 people, were pooled in a meta-analysis, it suggested around 7 % of people sleepwalk at some point in their lives.

1:22Matt Walker: Additionally, about 5 % of children sleepwalk each year and 1.5 % of adults. The researchers pooling the data did warn that risk of bias was present and suggested interpreting the results with caution. Next, in a telephone survey of 1 ,000 randomly selected adults living in Norway, 22.4 % reported sleepwalking in their lifetime, although the authors note limitations, including a low response rate and limited questions. Another survey approached over 19 ,000 American adults, got answers from nearly 16 ,000 of them, and found that 29.2 % had at some point in their lives wandered during sleep in what the researchers called an abnormal state of consciousness, and just 3.6 % had done so in the last year.

2:16Matt Walker: Talking in your sleep appears much more common. In that Norwegian survey, sleep talking had the highest lifetime prevalence of anything asked about at 66.8 % and 17.7 % had done it in the previous three months. In a representative birth cohort from Quebec, mothers filled in a questionnaire at each round of the multi-year study about how their kids slept. 84.4 % of the children were reported as sleep-talking between the ages of 2.5 and 6. In contrast, only 14.5 % were reported as sleepwalkers. When the Quebec researchers followed the children yearly to age 13, they found that sleepwalking was most prevalent at the age of 10, at 13.4 % of the 1 ,940 children.

3:08Matt Walker: The only earlier study to follow children year by year, a small Swedish one published in the 1980s, put the peak at around 11 to 12 instead. And in the Quebec kids, the rate didn't really fall after 10. It was still close to 13 % at ages 12 and 13. So it's unclear exactly when sleepwalking peaks and starts to fade. Either way, sleepwalking is something most people grow out of, while sleep talking does not fade in the same way. As many as one third of kids who start with sleep terrors, an issue we've already discussed here on the show, go on to also sleepwalk as they get a bit older. And in a Finnish cohort of more than 11 ,000 twins, over eight in 10 who reported sleepwalking as adults had also done so in their childhood.

3:59Matt Walker: Of those who had never sleepwalked as a kid, only 0.6 % did as an adult. In that same cohort, sleep talking as a kid and as an adult was highly correlated, so sleep talking often persists as people get older too. In a further analysis of the same cohort, this time more than 3 ,700 adult twin pairs, researchers used national registers of hospital admissions and long-term antipsychotic prescriptions and found psychiatric illnesses to be about twice as common in people who sleep-talked frequently. Still, the authors point out this means that most sleep-talking is not associated with serious psychopathology.

4:45Matt Walker: Then there's family. Among the 1 ,940 Quebec kids, 22.5 % sleepwalked if neither parent had, 47.4 % if one parent had, and 61.5 % if both parents had. That last number had a wide margin of error, but overall it does suggest an inheritance component. This was supported by a study of 100 adult sleepwalking patients from a sleep clinic in Montpellier, France, where just over half, 56.6%, reported a family history. The authors of the Quebec study said their findings substantiate a strong familial aggregation for sleepwalking. And in the Finnish cohort, identical twins were much more likely for sleepwalking than non-identical twins, which does suggest a pretty strong genetic component.

5:38Matt Walker: Genetic studies of the parasomnias suggest they are familial, but haven't pinned down the genes involved or how they act. In the Finnish twin data, the closest genetic overlap between any two parasomnias was between sleepwalking and sleeptalking, which appeared to share about half their genetic influence. A variant of a gene called HLA-DQB1 was present in 35 % of 60 people who slept-walked and 13 % of 60 with no diagnosed sleep problem. A later study of 74 adults with non-REM parasomnias found the same gene variant was more common than in the general population, whether the person had sleepwalking, sleep terrors, or confusional arousals.

6:25Matt Walker: Though the comparison was against population figures rather than matched controls, and the authors themselves described the genetic evidence as scarce.

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9:01Matt Walker: A recent review concluded that genetic studies of sleepwalking have so far been too limited to draw any firm conclusions. Now, before I go any further, let me explain what I mean by parasomnia. The term is used to refer to a group of sleep disorders involving unusual movements and behaviors. They can occur distinctively in REM sleep or in non-REM sleep or in both. Sleepwalking, like two related conditions, sleep terrors and episodes of confused behavior immediately after waking, called confusional arousals, is known as a non-REM parasomnia, or more tellingly, a disorder of arousal, since it involves only a partial rousing.

9:46Matt Walker: Unlike acting out dreams, a separate condition which usually happens in the second half of the night, disorders of arousal usually occur when emerging from slow wave or deep sleep, which is concentrated in the first half of the night. Overnight video monitoring of 45 adults covering 334 episodes found that 72 % of sleepwalking and other arousal episodes occurred in the first third of the night, and 80 % arose from slow-wave sleep. In effect, about three times out of four, sleepwalking happens in the first third of the night. Sleepwalking is like turning on only some of the circuits in the house.

10:31Matt Walker: A recent study placed 256 tiny electrodes on the heads of a group of sleepers, 19 children and 22 adults, and monitored them overnight to map their brain activity. Across 84 parasomnia episodes, most of them were confusional arousals rather than full sleepwalking. The researchers found that parts of the brain involved in awareness, sensation and movement towards the back of the skull looked awake, but others involved in judgment and control of emotion towards the front of the skull appeared to still be asleep. The authors suggest that the key problem in disorders of arousal is that the brain's regions fail to wake up together and describe it as a failure of arousal integration.

11:19Matt Walker: An earlier study from the same group used the same 256 electrode setup. This time it was a single participant, a single 12-year-old, and the researchers found a mixed bag of awake and asleep types of brain activity during his parasomnia episodes. And recordings taken directly from within the brain of a 20-year-old man with a difficult-to-treat form of epilepsy confirm the split personality of sleepwalkers' brains. This marker of the non-REM parasomnias is known as sleep-wake dissociation. In that epilepsy patient, during a brief episode of confusional arousal, Some brain areas, including those for motor control and the cingulate cortex, which plays a role in emotions, showed brain activity found only in wakefulness.

12:09Matt Walker: Whereas others, including the frontal and parietal association cortex, which are areas needed to make sense of the world, displayed the slow waves of deep sleep. The brain is asleep and awake at the same time, like a house in which all the upstairs lights are blazing, but only one bulb downstairs glimmers. A review in Nature Reviews Neurology argued that this dissociation between behavior and awareness is a key feature of the non-REM parasomnias. Sleepwalkers also seem to have reduced slow wave activity, the brain waves associated with deep sleep, in the cingulate cortex and the brain areas for movement and sensation.

12:52Matt Walker: In one study, high-density EEGs were recorded over a single night from 15 adult patients with a history of sleepwalking or sleep terrors and from 15 good sleepers. Looking only at stretches of sleep at least a minute away from any arousal, the patients showed selective decreases in slow-wave activity in those regions. There was a trend in the same direction during REM sleep, and while they lay awake before sleep too, though it didn't reach statistical significance, which led the authors to suggest this may be a trait-like feature of sleepwalkers' brains. Sleep deprivation is a well-known trigger of sleepwalking episodes, presumably because it increases the pressure for slow-wave sleep, which in sleepwalkers seems to be unusually unstable and prone to incomplete arousals.

13:42Matt Walker: In 124 adults with a history of sleepwalking, the total number of episodes almost doubled during recovery high slow-wave sleep after 25 hours of wakefulness. The percentage of participants having episodes in the lab increased from 48 to 63%. When researchers played tones to 10 sleepwalkers during slow-wave sleep, 3 out of the 10 could be made to sleepwalk on a normal night. During their high-pressure post-sleep deprivation deep sleep, all 10 had episodes compared with none in a matched group of healthy volunteers. The researchers behind these studies argue that this trouble-sustaining stable slow-wave sleep makes sleepwalkers especially vulnerable when sleep pressure is high.

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15:51Matt Walker: Sleepwalking episodes can have a mental component too. For example, psychological stress was by far the most commonly reported trigger of sleepwalking, named by 95 % of 188 adults diagnosed with sleepwalking when given 24 options to choose from, and by 80 % of a separate group of 45 patients with disorders of arousal who were asked in an interview about stressful and positive emotional events. Stressful life events were also listed among possible sleepwalking triggers in a UK survey of almost 5 ,000 people. Other common triggers reported by the 188 sleepwalkers included bad dreams and nightmares, 78%, and sleep deprivation, 60%.

16:39Matt Walker: Sleepwalkers aren't always blank inside either. Of 38 interviewed people referred for severe sleepwalking or sleep terrors, 71 % reported at least one dreamlike experience related to one of their episodes and the action in the dream matched the behavior reported during their episodes. 95 % of the hundred or so experiences reported were a single visual scene rather than a moving sequence and were often unpleasant. 84 % involved some feeling of apprehension or fear and whenever aggressiveness was part of the dream, the dreamer was always the victim. One review article speculates that maybe sleepwalkers are really dreamwalking.

17:25Matt Walker: When asked about their mental experiences during sleepwalking, 14 out of 20 children surveyed remembered nothing, but 16 out of 25 adults recalled at least one mental experience. The International Diagnostic Criteria, meanwhile, describe these episodes as coming with no mental experience at all or very little, and the large clinic cohort counts dreamlike experience as an integral part of adult sleepwalking. Sleepwalkers, it seems, haven't been reading their own criteria. So what does the sleeping brain say? Sleep talking is more common than sleep walking in the general population. In one study, a sleep clinic in Paris analyzed speech recorded on overnight videos from 129 people being evaluated for REM sleep behavior disorder, 87 being evaluated for sleepwalking or sleep terrors, and 15 normal controls.

18:24Matt Walker: 92 % of the sleep talking came from the parasomnia patients, and 59 % of a total of 883 speech episodes were non-verbal like shouts, whispers, and grunts. In total, there were 3 ,349 intelligible words, with the most commonly spoken word being the eminently sensible sounding no. Overall in the study, saying no or something similar featured in around one word in five, a quarter of episodes featured a question, and almost one in ten featured a swear word, with men both talking and swearing more than women. Speech also kept the same grammatical structures and lengths of pauses as normal conversation.

19:09Matt Walker: Saying no, questions, and swearing featured more often in non-REM sleep. All in all, sleep talking is strikingly similar to waking speech in structure and meaning, as well as its use in conversation.

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21:01Matt Walker: As for the brain activity and sleep stages involved, one lab-based study found that sleep talking could happen in all stages of sleep, but is more common in non-REM sleep. 13 healthy young sleep talkers were recorded in the lab over 28 nights in total. And compared to matched controls, they spent less time in REM sleep and more in non-REM sleep. In six of the sleepers, the researchers looked in detail at 21 utterances and 21 non-linguistic vocalizations during stage two non-REM sleep and found a change in brain activity over the left hemisphere just before the words came out, which they cautiously interpret as consistent with language being processed much as it is while awake.

21:49Matt Walker: The next study was done in people's homes with 29 sleep talkers and 30 matched controls across seven days. The study used a phone app to record their talking plus sleep diaries. The results show that people talked more often when their sleep was more fragmented and sleep talkers rated their sleep poorer. Adult sleepwalkers may suffer other effects too. The sleep center in Montpellier compared a hundred adults who sleepwalk with a group of a hundred matched controls. Nearly a quarter had episodes every night and about one in 10 had been badly enough injured on at least one occasion to require medical attention, rising to one in six if you count bed partners who needed treatment after being attacked.

22:35Matt Walker: Compared to the control group, the sleepwalkers reported more daytime sleepiness and tiredness, more insomnia symptoms, more symptoms of depression and anxiety, and poorer health-related quality of life. So, adult sleepwalking can't be written off as the mostly harmless continuation of a childhood habit. Some adults, perhaps those unlucky enough to end up at a sleep center, are having a pretty rotten ride. In a separate study from a sleep center in Montreal, 32 of 70 adult sleepwalkers who filled in a standard questionnaire could be classed as sleepy. This wasn't explained by any evidence of disturbed sleep on their overnight recordings or by any other sleep problems.

23:19Matt Walker: So the authors suggest that the sleepiness may be part of the sleepwalking itself. The Montpellier researchers also raised another mystery. Of their 100 adult sleepwalkers, 47 recalled being injured and in pain on at least one occasion. But 37 of them, 78.7%, hadn't felt any pain at the time. It had only become apparent once they came round later the same night or on waking the following morning. In only 10 of the 47 had pain from an injury been bad enough to wake them. In almost four sleepers out of five, sleep had prevailed. Yet the sleepwalkers in the group were more likely than controls to have a history of headaches and migraines.

24:03Matt Walker: The authors are happy to call this discrepancy a clinical enigma and speculate that there is a connection between problems of pain perception and the half-asleep state. Pain signals are damped down during sleep, and the half-asleep brain may block them from reaching the cortex. though they couldn't measure pain sensitivity directly. All this is based on sleepers' memories of events and comes from just one center, keep in mind. Put all of that together and sleepwalking and sleeptalking come down to a brain that can wake up in pieces with some circuits back on and others still off. It runs in families and is brought out by lost sleep.

24:44Matt Walker: Sleepwalkers themselves add it can happen by stress too. In children, sleepwalking mostly fades with age, and for most people, sleep talking is benign. This is a clinical topic, and none of what follows should be taken as direct advice. Simply, a list of some things worth knowing based on what the research shows. First off, address sleep problems and poor sleep habits. Not enough sleep was among the most commonly reported triggers at home, named by 6 in 10 sleepwalkers. Lost sleep almost doubled the rate of sleepwalking episodes in lab experiments, the best evidence for any trigger. Second, discuss ways to cope with stress.

25:26Matt Walker: Stress was the most commonly reported trigger for people who sleepwalk. That same home questionnaire study also suggested stress management as part of treatment. Psychological treatment helped some in clinic studies. Third, keep the bedroom safe to help prevent injury. About 1 in 10 adults who sleepwalk in the Montpellier series needed medical treatment after a sleepwalking episode. 1 in 6, if you include injured bed partners. And most of those hurt felt no pain until waking up. So if you are a sleepwalker, it's a good idea to make bedrooms and any potential routes safe to prevent injuries. Lastly, especially in children, sleepwalking usually improves with age.

26:11Matt Walker: In the Quebec cohort, it peaked at 10 and was still at much the same level at 13, though an earlier Quebec study, relying partly on mother's recall of the early years, did report it falling off substantially through childhood. As to whether to wake somebody mid-episode, most people in one study said they'd had a conversation during an episode at least once in the past year. However, a clinical review advises that parents or bed partners should not wake the individual or engage with them, as this can worsen and prolong the episode. None of this is the complete answer, but the science so far has given us something real to work with.

26:54Matt Walker: Overall, the light switch metaphor isn't quite right. The brain is more like a fuse box. Some circuits can be on while others are off. During sleep, the circuits that relate to motor behaviors can be switched on, whereas the circuits in charge of overseeing those behaviors remain switched off. Thank you so much for listening to today's episode. I really do appreciate you giving me your time and attention. Please take good care of yourself. Enjoy your waking days and have a walking and talking free night tonight. Bye for now.

27:34Thank you.