Understanding sleep paralysis

Katie Haylor spoke to Cambridge University neuroscientist Baland Jalal about his work on sleep paralysis...

Baland - Imagine lying in your bed, sleeping, but then realising that you're actually awake, but you can't move or you can't speak. Suddenly you feel like, “Oh, there might be some ominous ghostly presence in the room”. Before you know it, this evil thing’s on your chest choking you, suffocating you, your limbs are being held down. And perhaps you might even see this ghostly figure in front of you. This could be a classic scenario of sleep paralysis. So quite frightening.

Katie - Sleep paralysis occurs at the intersection of being awake and asleep. It's not always, though it is mostly, a negative experience and the phenomenon isn't fully understood. Baland reckons about 20% of people may have had at least one experience of sleep paralysis of some kind.

Baland - This window, this borderland situation where you find yourself between REM and wakefulness. In fact, when we do EEG studies or whatever, we find that it's really a strange state that has elements of wakefulness and elements of REM sleep colliding. You have REM physiology paralysing you and being active, while your wakefulness centres are slowly becoming more active.

Baland - Your physiology is very different during REM sleep, you have rapid breathing. Pulse rate is elevated. As you said, you have these vivid and crisp dreams during REM. And so when you go in and out of REM, that's where you have a lot of interesting things going on

Katie - For one, Baland says the structures responsible for your sense of self, the temporo-parietal junction, take a nap during REM sleep, which he said explains why sometimes when you're dreaming, you might actually be looking at yourself like you're watching yourself in a documentary, rather than feeling like you are yourself in the first person.

Another bit of the brain, he told me, that is less active during REM sleep is the dorsolateral prefrontal cortex - important for us creating a logical, sensible, cohesive world. So your sense of perception can go awry.

Baland - So you might find yourself on the moon, opening a fridge, you're taking snacks, but then suddenly you’re in Buckingham Palace having tea with the Queen and everything is messed up - time, space, people. REM sleep has all these interesting signatures which really play into then how things like sleep paralysis are experienced because it's very much a REM sleep phenomenon.

Katie - So what is going on then in an episode of sleep paralysis? Baland told me that the paralysis is a defence mechanism against potentially hurting yourself, or a sleeping partner, by moving around whilst asleep, and is controlled by neurotransmitters in the brain stem.

But sleep paralysis is a system glitch. You’re in REM sleep (and therefore paralysed) while the outer layers of your brain are waking up. He theorises that, a bit like with phantom limb sensations, your body is sending the “move” commands that are instinctual with being awake, but as you’re paralysed, there's no feedback coming back from your limbs to your brain.

Baland - When you just keep sending those signals - move, move - lacking this proprioceptive feedback, then that will feel like something is holding you down. Or they feel like it's pain or spasm, which is interpreted as somebody, or something, is holding you down. Same with breathing. When you try to control your breathing manually, and it's automatically breathing, you can't, it will feel like a pressure or suffocation sensation.

Katie - And he reckons there may be a similar explanation for the ghostly presences some people experience.

Baland - It has to do, we believe, with our sense of self being distorted. So we talked about a little bit on how the sense of self is scaffolded and created in certain structures in the brain, in the parietal lobes. When we disrupt these regions using electrical current, you might feel like a ghostly other person is mimicking your postures. These structures are involved in this. A theory that we proposed is that during sleep paralysis, you're sending all these commands from your motor cortex, responsible for movement saying “move”. And since there's no feedback coming back from your limbs - your body - telling your brain how to create a body image, your sense of self gets distorted. And so what we believe it does, then it sort of fills in the blank for you, like Google autocorrect. It projects your body image out there in space. So call this an out of body experience.

More typically you see this intruder-like creature, and this could just be understood as a different type of hallucination, where you create a scenario of fear around that projected self, being out there in space, so you create a story around this. And so when you have fear, when you have anxiety, emotional parts of the brain that are responsible for fear being hyperactive, your brain creates a story around that. And that would typically entail a ghostly creature in your room. And so we actually believe it's at your own projected body image. So that is one theory.

Katie - Is having sleep paralysis necessarily an indication that something is wrong?

Baland - No, not at all. So a lot of people have these from time to time without having a mental condition or psychiatric condition per se. So it's, it's not dangerous in that way. It tends to be more when you have frequently occurring, fearful sleep paralysis. So when it repeats itself and becomes a chronic phenomenon, and that would potentially be a reason for concern slightly in terms of your wellbeing.

Katie - What can actually be done then to help people who experienced sleep paralysis? Besides the usual sleep hygiene stuff you might expect and getting help with any underlying conditions that might be triggering it, the UK national health service website mentions cognitive behavioral therapy and low dose antidepressants. Baland has recently published a pilot study about a psychological sleep paralysis treatment that he's come up with called meditation relaxation therapy. Step one - he says, get rid of the panic

Baland -  you would tell yourself, this is not a demonic figure or whatever, this is common all around the world. It's benign, it's temporary and finding ways to reappraise or re-interpret the dangers of it.

Katie - Step two - try to emotionally and psychologically distance yourself from the experience. And step three - direct all your attention to something positive.

Baland - Since you have limited attention, and we know this from neuroscience, you might as well hijack the system for your own benefit and focus all your attention on something extremely positive and centre all your emotions on this object in order for you to, in effect, take control and be in charge of  what's going on. This is a way to divert your attention away from potential hallucinations.

Katie - Step four - Don’t try to take control over your movement.

Baland - This goes back to some of the theories that we've proposed in terms of when you try to act out your movement, you will feel like there's a spasm and there's pain in your limbs. And then could go into the interpretation of a ghostly figure and whatnot.

Katie - It sounds deceptively simple, but anyone knows who's been in a panic that trying to think logically when you're panicking is incredibly difficult.

Katie - Baland’s done a pilot study of this approach with 10 people suffering from narcolepsy.

Baland - And there, we found that applying this treatment did improve sleep paralysis by around actually 50%. So this was eight weeks of applying this, so it was a big effect. But obviously we have to be cautious in interpreting these findings. So this was an extremely small study, basically a study that would then give us a rationale for going into bigger studies, but we can't infer that it's effective. Right now we are actually running a larger study. So this is not narcoleptics, but people in the general population that have a frequently occurring sleep paralysis. So a large study with a placebo condition... we’ll see if it works.