We tend to think of being asleep or awake as an either-or prospect: If you’re not asleep, then you must be awake. But sleep disorder specialist and neurologist Guy Leschziner says it’s not that simple.

“If one looks at the brain during sleep, we now know that actually sleep is not a static state,” Leschziner says. “There are a number of different brain states that occur while we sleep.”

As head of the sleep disorders center at Guy’s Hospital in London, Leschziner has treated patients with a host of nocturnal problems, including insomnia, night terrors, narcolepsy, sleep walking, sleep eating and sexsomnia, a condition in which a person pursues sexual acts while asleep. He writes about his experiences in his book The Nocturnal Brain.

Leschziner notes that the different parts of the brain aren’t always in the same stage of sleep at the same time. When this happens, an individual might order a pizza or go out for a drive — while technically still being fast asleep.

“Sometimes these conditions sound very funny,” Leschziner says. “But on other occasions they can be really life changing, resulting in major injury or, as one of the cases that I described in the book, in a criminal conviction.”

Interview highlights

On what we know about recall after a sleepwalking episode

We used to think that people don’t really remember anything that occurs in this stage. That seems to relate to the fact that the brain in parts is in very deep sleep whilst in other parts is awake. What we have learned over the last few years is that actually quite a lot of people have some sort of limited recall. They don’t necessarily remember the details of all the events or indeed the entirety of the event, but sometimes they do experience little snippets. … On one occasion, [a patient] dragged his girlfriend out of bed in the middle of the night because he thought that a tsunami was about to wash them away, and those kinds of events with strong emotional context are often better remembered.

On how sleepwalking demonstrates the brain can be in multiple sleep stages at once

Certain parts of the brain can remain in very deep sleep … [such as] the frontal lobes, which are the seats of our rational thinking or planning or restricting on normal behaviors, whereas other parts of the brain can exhibit electrical activity that is really akin to being wide awake. So, in particular, the parts of the brain that [can seem to remain awake] are [the ones] responsible for emotion, an area of the brain called the limbic system, obviously the parts of the brain that are responsible for movement. And it’s this dissociation, this disconnect between the different parts of the brain in terms of the sleep stages, that actually give rise to these sorts of behaviors.

On what causes sleepwalking

We know that sleepwalking and these related conditions seem to run very strongly in families. So there seems to be some sort of genetic predisposition to being able to enter into this disconnected brain state, and we know that anything that disrupts your sleep if you have that genetic predisposition can give rise to these behaviors. So, for example, I’ve seen people who have had non-REM parasomnia events [such as sleepwalking] triggered by the fact that they sleep in a creaky bed and their bed partner rolled over [or] sometimes a large truck [drove] past in the street outside the bedroom.

But there are also internal manifestations, internal processes that can give rise to these partial awakenings. So, for example, snoring or, more severe than snoring, sleep apnea, where people stop breathing in their sleep … anything that causes a change in the depth of sleep in people who are predisposed to this phenomenon of being in multiple sleep stages at the same time can give rise to these behaviors.

On sleep apnea

Sleep apnea describes the phenomenon of our airway collapsing down in sleep. … Our airway is essentially a floppy tube that has some rigidity, some structure to it as a result of multiple muscles. And as we drift off to sleep, those muscles lose some of their tension, and the airway becomes a little bit more floppy. Now when it’s a little bit floppy and it reverberates as we breathe in during sleep, that will result in snoring — the reverberation of the walls of the airway result in the noise.

But in certain individuals, the airway can become floppy enough or is narrow enough for it to collapse down and to block airflow as we’re sleeping. It’s normal for that to occur every once in a while for everybody, but if it occurs very frequently, then what happens is that sleep can be disrupted sometimes 10, sometimes 20, sometimes even 100 times an hour, because as we drift off to sleep, the airway collapses down, our oxygen levels drop, our heart rate increases, our brain wakes up again and our sleep is essentially being disrupted. …

We are now aware that obstructive sleep apnea has a range of long-term implications on our health in terms of high blood pressure, in terms of risk of cardiovascular disease, risk of stroke, impact on cognition and mental clarity. And there is now an emerging body of evidence to suggest that actually obstructive sleep apnea may be a factor in the development of conditions like dementia.

On the importance of having positive associations with your bed

If you’re a good sleeper, you tend to associate being in bed with being in that place of comfort, that place where you go and you … feel cozy and you drift off to sleep and you wake up in the morning feeling wide awake and refreshed. But for people with insomnia, they often associate bed with great difficulty getting off to sleep, with the dread of the night ahead, with the fact that they know that when they wake up in the morning they will feel horribly unrefreshed and unrested. And so the environment that we normally would associate with sleep becomes an instrument of torture for them. And so a lot of the advances that have been made in this area about treating insomnia are really directed towards breaking down those negative associations that people have with their sleeping environment if they have insomnia and rebuilding positive associations. So trying to utilize the brain’s own mechanisms for drifting off to sleep and trying to reduce the anxiety surrounding sleep in order to reestablish a normal sleep pattern.

On the problem with taking benzodiazepines and Ambien for insomnia

There has been a bit of a sea change in the last few years away from these drugs. We know that these drugs [are] sedatives. So the first thing to know is that they do not mimic normal sleep. They’re associated with some major problems. So some of these drugs are, for example, associated with an increased risk of road traffic accidents in the morning, because of a hangover effect. They’re associated with an increased risk of falls in the elderly, for example. And we know that people can develop a dependency on these drugs and can also habituate, by which I mean that they require ever-increasing doses to obtain the same effect.

In the long term, there are now some signals coming out of the work that is being done around the world that suggest that some of these drugs are actually associated with an increased risk of cognitive decline and dementia. And whilst that story is not completely understood — and it may be that people who have insomnia in themselves are predisposed to dementia or actually that insomnia may be a really early warning sign of dementia — [it] certainly gives us cause for concern that perhaps we shouldn’t be using these drugs quite as liberally as we have done historically. And so therefore the switch to behavioral approaches, approaches like cognitive behavioral therapy for insomnia, has been really driven by some of these concerns.

On his recommendation that you read before bed

Provided you are not reading on a tablet or a laptop, [and instead an] old-style analog book, I would highly recommend. It’s a good way of reducing your light exposure. Keeping your mind a little bit active so that you’re not concentrating on the prospect of having to drift off to sleep until you’re really tired. It’s a very good way of keeping your mind occupied.

Sam Briger and Mooj Zadie produced and edited the audio of this interview. Bridget Bentz and Molly Seavy-Nesper adapted it for the Web.

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