Brainwaves

Imagine a brain, like the one in the photo, made from a string of fairy-lights. Imagine billions of lights in the brain, all blinking in a seemingly random pattern, passing electricity onto each other in a pattern that only makes sense to itself. Now imagine that wires can grow directly between bulbs that commonly light at the same time, making a connection between them.

That's pretty much what is happening inside our brain, except the fairly lights are neurons and the wires are neural connections. The power comes via tiny electrical impulses and electro-chemical messengers.

Imagine that, like the one in the photo, your head is made of glass and that it were possible to record how fast and how bright the majority of surface lights in a particular area were flashing.

That's roughly what an EEG can achieve. 

It's complicated in there, and anyone who says that they have a complete grasp of what is going on inside is lying!

...but we have a few clues to guide us.

We can use an EEG to record the voltages that are present near the surface of various areas of the brain.

Essentially, an EEG is a volt-meter recording the voltages that escape to the surface via adhesive electrodes glued to the skin.

Straight away, this is a limitation because we are therefore oblivious to the voltages that are buzzing away in deeper areas of the brain and multi-lead EEGs can look at many areas of the brain at the same time.

However, we are still able to deduce an awful lot from a single site EEG.

These are slowly coming onto the market for consumer use, one that I've had for a while is the X-Wave. It's a large headset with a single forehead electrode and an ear-clip. The voltage from your forehead is monitored and by comparing the signal pattern to a known pattern for either "concentration" or "relaxation" the attached computer is able to deduce whether you are in either of those mental states. 

This is a neuro-feedback system. You can spend ages watching the flicking graphs and wiggling lines playing "trial and error" trying to make them respond as you wish. When you achieve the desired pattern you are given positive reinforcement by the computer, making it easier to achieve that state again. Oddly, being taught what to do is tricky, but given half and hour of experimentation you'll find that you soon pick up what to do.

With a little practice I was able to achieve 100% concentration...

...and around 80% "Meditation" which isn't that easy when you are desparate to grab a screenshot of being "relaxed"...

There are also computer games written for the X-Wave which allow you to control them by either concentrating, or relaxing. A good "real world" example is the "Star Wars Force Trainer" where you wear a similar headpiece and try various thought patterns until you find the one that makes the ball float.

I first purchased the X-Wave because I thought it would help me to determine sleep stages if worn when asleep. It would have been an uncomfortable night as the headset isn't really condusive to a good night's sleep. However, it doesn't (yet) have the ability to record and playback data, nor does it (yet) allow you to see the raw waveform, although I believe that this is something in the pipeline, although this would still leave the user needing a knowledge of EEG interpretation to be able to determine which sleep stage a sleeper was in.

The XWave may be useful for games and biofeedback, but it wasn't able to do what I wanted, nor did the PC interface become available as was available for pre-order on the website.

I then purchased the Zeo Bedside Sleep Monitor which uses EEG technology to do what I wanted (determine and record sleep stages automatically). Then, with updated firmware and a home-made lead, you can connect the Zeo to a computer and see an awful lot of what is going on in your brain. Granted, this is still a single channel EEG, so it is only looking at one area of the brain, but still the amount of activity that you can see is astounding!

First I'll mention some of the different types of brainwave that I've seen with this system. These waves are all recordings taken from my brain whilst I've been asleep. 

Generally speaking, the thing that determines one type of wave from another is its frequency (how many times it cycles per second), although some features jump off the screen at you such as "K-Complexes" and "Sleep Spindles", both features of Stage 2 NREM sleep.

It is possible that some features found in our brainwaves also serve a function, or at least they show when the brain is carrying out a particular function. For example, K-Complexes can be induced in a sleeping person by external noises. It is thought that the K-Complexes are a response to a noise that the sleeping brain has evaluated as not being a threat.

Sleep spindles also seem to be connected to the outside world. They represent when the brain is not consciously processing input from the world outside. In my oversimplified world I tend to think of them as little bundles of barbed wire that sit on the boundary of sleep and wake somehow shouting "La la la, we're not listening".

Like K-Complexes and Sleep Spindles, some wave patterns are closely related to sleep stages, such as Deep Sleep, which takes its correct name, Slow Wave Sleep, from the waves that are associated with it - Delta Waves, or Slow Waves.

Just as measuring the voltage from the screen of your television doesn't tell you what programme it's showing, measuring the voltage from your skull doesn't tell you what thoughts are being thought (although it's becomming ever closer http://www.ibtimes.co.uk/articles/290907/20120201/mind-reading-machine-scientists-computer-program-epilepsy.htm ) Trying to detmine what the person is thinking or dreaming about isn't as simple as looking at the brainwaves they produce and then comparing it to a vast dictionary of known squiggles. For one thing, the brain is capable of producing (and does so) many waves at the same time, in the same area of brain. The relative power of these waves can be separated out using FFT algorithms.

However, thoughts and sleep stages are completely different animals, and the Zeo is able to determine sleep stages with a high degree of accuracy (References Shambroom, Fabregas & Johnstone, also here and here), which is after all what it was designed to do. We are just piggy-backing off its ability to show EEG data.

The following is the raw data from a section of sleep. The bottom is a hypnogram (shows the stages of sleep) for a whole night (top-bottom = wake, REM, Light, Deep); the top is the raw waveform for the current 15 seconds) whilst the line in the middle is a record of about 45 minutes of data.

The middle one is the result of the FFT analysis (mentioned above) and represents the types of waveforms in proportion to each other. From this it is possible to determine which is the dominant waveform. 

A good example of this is observing the transition out of slow-wave sleep. (Note the steep drop in the red line).

Click for larger image

It's also interesting to see what happens to your brainwaves while awake and carrying out various tasks.

Normally, the frequency distributions seems to be fairly scattered (the lines are nicely spaced out), but one night I woke around 3am and couldn't get back to sleep, I kept the headband on. It seems that when I was concentrating on reading Twitter the various frequency brainwaves became more focused, leaving Alpha and Theta as dominant.

These grouped together even tighter when I actually tweeted and a form of Beta wave became dominant (although only slightly). I presume the tight grouping is because typing required more concentration and more focused thought. Oddly I received a phonecall while awake, and this shows another pattern.

  Click for larger image

Through playing around with this set-up you learn to spot patterns. For example if I am disturbed in the night by a sound that wakes me you can see a brief period of concentration before I go back to sleep. it would be fantastic to actually see the change in brainwaves during an episode of sleep paralysis or a lucid dream.

This would make a great neuro-feedback system and I plan to use it to test the claims of various products that they are able to "induce delta waves" or "cause trance like theta waves" etc.

Sleep Paralysis

 A sound wakes you up in the night. You sense that you aren't alone anymore - something is there with you.

You rationalise: someone has come into your bedroom, that must have been what the sound was. Cautiously you turn your head to see if you can see them, but it doesn't move!

You panic.

The intruder is pushing down on your chest making it hard for you to breathe. You can't take a proper breath, let alone call out for help. You might just be able to make a slight sound in the back of your throat. You can't even move your head down to see who (or what) is crushing you.

There's a noise in the room too - ripping sounds, it's loud as if it's right in your ears. All sorts of thoughts race through your mind, before you pass out with fear. Then it's morning and all is well. There's no sign of intruders, no damage to your body.

What I've just described was an episode of Sleep Paralysis, and as scary as it is, it isn't harmful.

Most would class this as a strange night, and to be fair it is.  However it actually happens to some people, and more accurately, it happens to me.

Folklore has many "explanations" for this, but they largely centre around applying cultural beliefs over the top of the facts. Explanations are as varied as:

• witches and old hags being the cause 
• demonic attacks 
• sexually active ghosts of both the male and female varieties (incubus and sucubus)

Many cultures have their own name and culprit responsible for Sleep Paralysis, and a comprehensive list can be found here. A more modern piece of folklore about Sleep Paralysis is that it is an alien abduction and that the noises you hear whilst paralysed are actually medical experiments that are being conducted on you. 

As the brain scrabbles to make sense of the situation it tends to fill in the gaps with dream-like hallucinations that are overlaid onto what you can see (remember that you have a fixed field of vision which is usually just your ceiling). 

In fact in my first episode of sleep paralysis (I was 12 or 13 years old) I remember that as I was trying to scream I was also remembering stories that our house was haunted. So, the logical thing for me to think at the time was that this was an attack by some sort of ghost and that I wasn't allowed to see whatever ghosts get up to in the night, so I was being held down. (Yeah, yeah, yeah. I was 12).

A nice (and rather famous) depiction of sleep paralysis is a painting by Fuseli called "The Nighmare" in which a sleeper (sleeping on her back - which is frequently the position that paralysis occurs) is being crushed by a demon-like animal whilst a presence watches in the room.

The Nightmare by John Henry Fuseli, 1781

...although a more modern take on this painting might be something like this:

What's the real cause?

When we dream, our brains are as active (if not more active) as when we are awake. Our brain is generating fake sensory input and processing it as if it were real. The only thing that stops us getting out of bed and running around acting out our dreams is that the brain induces muscle paralysis during REM sleep, with only a few essentials left un-paralysed. This is called "REM Atonia".

Ideally this paralysis is activated at REM onset, and de-activated as REM stops. But sometimes it can come on too early or switch off too late, not only can this happen at the beggining and end of a REM period, but it can also happen during a REM period if the sleeper is briefly woken in what is called "an arousal".

 
Whichever way it occurs, effectively, the brain is awake and conscious but the body is asleep.

I was chatting with a friend who confessed that she is woken by spiders in her bedroom, dangling from the ceiling and spends a while trying to get away from them before waking up fully and realising that nothing is there.

After chatting I suggested that she put a familiar object in the room, so that if she saw it when an episode of this occurred then it would remind her that is was just a type of dream and she would be able to calm down. This seems to be different from Sleep Paralysis, and I doubt that she is aware of her surroundings in the same way, so it may not be of any use, but...

I then decided to have a go at that idea myself and purchased a large copy of Fuseli's "The Nightmare", had it framed and placed in on my bedroom wall so that I would see if when I woke up paralysed and remember what was going on.

One night I was repeatedly woken by my son's oximeter, I had to keep getting up and dealing with things and then get back to bed. Each time I got into bed I found myself paralysed. The first time I was scared, as normal but the picture helped calm me down... By the third time I found it funny. I recognised the familiar feeling that seemed as if someone was deflating my muscles one by one. I then thought to myself, "Okay, your body is alseep, but you are awake".

I calmly looked around the room and decided that I would get up. I thought to myself that if my body wasn't going to bother getting up, then I would get up without it, and no sooner had I thought that then there was a buzzing crackling tearing sound and I found myself about two feet above my body looking at the ceiling.

I then moved down towards the foot of the bed, my feet descended to the ground and I was free. I could look back at my own body (I only saw my feet still in bed). Just to the left of the foot of my bed was a figure. I knew that this was the presence that I'd felt whenever I'd had sleep paralysis, but this time I could see it!

Having never left my body before I was feeling rather pleased with myself. I looked at the figure and he gestured for me to go past him. I did, straight into (and through) a mirror into the room next door!

From that day I haven't been worried about sleep paralysis, in fact I've welcomed it. I don't seem to be able to easily reproduce the feeling of leaving my body (more often than not I hear the buzzing ripping sound and the excitement wakes me before I can "leave") but I can quite easily turn the experience into a lucid dream.

With the folklore around such powerful events, there seems to be a specific term for the presence I saw:The Guardian of The Threshold. It seems that his job is to intimidate you into not proceeding until you are deemed "ready". I guess that this is similar to hallucinations, emotions and images that meditators see, and claim that their purpose is stall the meditators into staying in that particular level of meditation. 

However, for me, something seems to connect of Out of Body Experience and Lucid Dreams. It seems that I can't go through doorways in them, if I try to then I always end up somewhere else (usually on a high up place). I can go from room to room by walking through walls and mirrors easily enough, but for some reason never doors.

It's odd that now that I want it to happen more often, it seems to happen less frequently. Maybe the fear was a factor in causing it. What seems to happen is that as soon as I wake up and realise that I can't move I begin to think, "Right, let's see what we can do. Can I dream? Can I fill the room with dream imagery? Can I leave my body? etc". So the paralysis isn't the major event anymore, it's more of a gateway or a stepping stone.

Can anything help sleep paralysis? 

Speaking from my own experience, there are a couple of things that you can do.

The majority of my episodes have ocurred whilst sleeping on my back (leading me to link them with apnoeas), although I have had some episodes whist on my side (oddly, with a side-lying OOBE "I" still left my body in the same manner - chest first, then a turn to face the ceiling, then moving towards the end of the bed, then feet on the ground).

So...  

• Don't sleep on your back
• Have something in your room that you associate with Sleep Paralysis that you'll be able to see when an episode occurs. This will remind you that it's a trick and that you are safe.
• Relax if it does happen.
• Know that you are safe and that it will pass.
• Don't struggle, it seems that the more you try to breathe normally the more you are aware that you can't.
• Remember what the real cause is. Sooner or later you will either fully return to sleep or wake. 

Hypnagogia

You're tired and have just got into bed...

You close your eyes and stare at the blackness. Within a few seconds you see random sparks and colour flashes.

You've never really thought about them but if you have you've probably assumed that they're just the random firings of your tired optic nerves as they relax after a hard day.

It looks as if you're drifting through space floating past random galaxies and nebulae.

Then there's a bright flash to the bottom left of your vision, it whizzes off, it must have been a car driving past so, it becomes a car whizzing past on a dark road. Then there's another one. The lights are blurred, maybe it's raining and these are reflections of headlights on the wet road.

Why are you standing beside a road in the rain? Maybe your car has broken down and you are waiting for help. You sense someone behind you. Is it your passenger? Is it a stranger? Are you in trouble?

Fairly frequently, for me, this can evolve into a dream. Although many times these are just fleeting images on a black screen; sometimes they move (like the red blob that became an egg, which then hatched before vanishing) and sometimes they are just static images such as faces or objects. Most of the time the colours are exaggerated and over-saturated.

So what's going on?

My brain is doing what brains do best: it makes sense of the information that it is given. Sometimes it joins the information together to make a narrative, a story. More often than not, in a dream, it does this seamlessly so that you (as the observer, creator and participant of the dream) don't stop to think "Why is there a car driving past in space? Why am I now beside a road?", you just accept it as normal and carry on enjoying the story.

Sometimes as I watch the flashes and sparkles I am pretty much awake, certainly conscious. I am able to question those things and soon realise that the only way that I could have been in one place then magically transported to another place is if I am dreaming.

That's when sometimes I can separate out the creator / observer / participant aspects and consciously create the dream. This is called Lucid Dreaming.

I find that if I concentrate on the images as I fall asleep then as soon as I become conscious of them becoming a story that I wake up, almost as if that kick of consciousness drags me back to the waking world.

Or maybe this has happened to you...

You start to drift off to sleep when all of a sudden you hear your doorbell ring.

You jump up to answer the door only to find that there's no one there. So you go back to bed.

No sooner have you start to doze again than you hear another ring of the doorbell, but this time something is different - it's not YOUR doorbell, it sounds different. You sit up startled, and look around the room before getting back into bed.

Eyes closed, and then the phone rings once and stops. Tired, irritated, and a little scared that someone or something is playing tricks on you, you return to sleep.

Doorbells, phones, knocking, people calling your name, even short tunes wake me up, none of which are real. That is to say that none are generated by external stimuli, they are in fact hypnagogic hallucinations, and to the brain they are very real.

To be more precise, these images and hallucinations can be either hypnogogic or hypnopompic, but they are generally lumped together under the banner of hypnaogic.

Hypnogogic = going into sleep
Hypnopompic = waking from sleep

This is a well documented phenomena, and is nicely illustrated in the book "Head Trip - a Fantastic Romp Through 24 Hours in the Life of Your Brain". The whole book is illustrated in a similar fashion and is well worth a read. Original here: http://www.jeffwarren.org/illustrations/mavromatis’-four-stages-of-hypnagogia

So this is normal. This comes as a relief to me because I first became aware of these flashes and images in my late teens. I'd just started work which involved being on-call, hence my sleep was frequently disturbed and I found it difficult to sleep at night as I was forever listening out for my pager in case I was called out.

I found myself drifting off to sleep at any opportunity during the day, at a desk, in a chair etc. Then when I did sleep at night I had increasing spells of sleep paralysis, so I went to see a doctor and asked if there was anything that could be done to help, such as tablets to help me sleep when I wasn't on-call.

He asked me to describe what went through my head as I tried to sleep at night. When I mentioned the colour flashes he didn't really react, but when I said that I was always tired he decided that I must have "mild depression", he explained that it "wasn't clinical, but it was just being run-down"... and prescribed trycyclic antidepressants.

I clearly remember thinking that this was odd. I didn't feel depressed, just tired. The last thing I said to the doctor before taking the prescription was, "So these colour flashes are because I'm depressed, and these pills will stop them?". To which he replied, "Yes".

The antidepressants made me tired, which did help me sleep at night, but they also gave me disturbed dreams and nightmares and left me feeling even more tired in the day. Not a great solution, and one that I was quick to give up on.

That was nearly 20 years ago, and thankfully awareness of sleep medicine has moved on since then. Nowadays I would hope that most general practitioners would be aware of sleep paralysis and the effect of a disturbed sleep routine on general wellbeing. However, I doubt that many would be aware of the subtleties of Hypnagogia and the normal blurring of states of consciousness that every sleeper goes through on the journey to sleep - despite travelling through them themselves!

As I write this it's occurred to me that the hypnagogic sounds that I normally hear are all things that demand my attention: Phones, doorbell, children calling, explosion outside etc. Only once has it been a few notes of music that didn't cause me to sit bolt-upright in bed.

Maybe this is a hang-up from the being on call nights or having to wake at the drop of a hat to deal with my son's prolonged periods of apnea for many years?

Could it be that over the years a brain learns to be in a "hypersensitive" state, ready to wake up and so is fooled by dream sounds? If so, why would this only happen in REM. This may be similar to Wehr's experiment showing that if a subject expected to be disturbed then the hormone Prolactin wouldn't be released during sleep.

"Wehr quickly discovered that prolactin was vulnerable to almost any disturbance. Simply talking to the subjects would interrupt its secretion, as would their expectation that someone was going to talk to them. It was a fragile state: the subject had to be lying in the dark, expecting not to be disturbed, for the drug to work. But when it did work, it appeared to produce a period of gentle quiescence, a pleasant, meditative state in which time passed very quickly for the subjects.

In addition, each period of quiet rest, wrote Wehr, always emerged directly from “particularly intense” periods of rem sleep featuring vivid dreams, full of emotional resonance."

(Jeff Warren, "Head Trip, a Fantastic Romp Through 24 Hours in the Life of Your Brain)

Hormones aside, I know that certain things that I do can induce these sounds. One example is if I sleep with a fan on in the room. I suspect that this is because the fan generates "white noise" which makes it harder to hear if I am really called in the night, so my brain "plays safe" by alerting me to the dream noises that, if they were real, would demand my attention.

Hypnagogic hallucinations can be actually involve all the senses...

Someone saw the painting of Fuseli's "The Nightmare" on one of my walls and asked me a question. They asked, "Do you ever get walked on at night?". Needless to say this threw me and I wasn't quite sure where they were taking the conversation, but they continued.

They explained that they had been on a holiday in an old stone cottage recently and that during the night they felt as if someone had walked through the room, across the bed and up the stairs in the bedroom.

Already I suspected that this may have been a parasomnia and asked them to tell me more about the day.

I won't recant the whole tale here, but the beginning was enough to confirm that it was a likely hypnagogic episode or even a form of sleep paralysis.

"It'd been a long drive and it was late when I arrived. I made the bed up and got straight it. Just as I was dozing off I felt the bed crumple as if it'd been walked on. I laid there as I heard the footsteps walking up the stairs"

There are several pointers here:

• Strange room
• Tired
• Presence in the room

...and lastly (which is where this blog began)... 

• Tired and just got into bed

I'll go into more detail about this type of event when I blog about Sleep Paralysis.

I've got a particular fondness for hypnagogia (thanks to the episode with the doctor) so I tried to capture what is going on when it occurs. 

I don't have a full EEG to experiment with, but I do have the raw output from the Zeo's single channel EEG. Although this only looks at the front of the brain (combined with muscle tone and eye movements), it still gives a good guide to what is happening when these episodes occur.

I've concentrated on the episodes that take place in the middle of the night.

When a phantom doorbell rings (or whatever form it takes) then I look at the clock. More often than not I remember the time in the morning and check what the Zeo picked up at that time.

From this data I have learned that most of the hypnaggogic hallucinations occur when I am flitting between sleep stages.

Click for a larger image

The 5 minute eopch of the whole Zeo hypnogram (not shown above) showed me as being awake for this period, which is unsurprising as the live raw data and the 30 second hypnogram showed me as flitting between wake and N1/N2 (and having come from N2 - indicated by sleep spindles).

What isn't clear to me is whether these noises are the cause or effect of sleep state transition. ie, did I wake up then re-doze, dragging some lingering elements of consciousness to the sleeping world with, or did the noise (and presumable unremembered noises cause me to wake up)?

Sadly, without a more precise time that the event occurred and a more detailed EEG I doubt that I will be able find an answer, or be able to point at a wiggly line and say, "THERE is the noise that woke me".

What I can see from looking at the raw data is that the event occurred in the minute of 2322h and I stirred for a moment before looking at the time, resulting in w1 (wake 1 shown by a red peak representing delta waves along with the corresponding mass of noisy delta waves on the EEG line) at 2323:04h.

Interestingly, there is a spike (d1) of delta waves which are much neater in appearance, much like those of slow wave (delta) sleep a few minutes beforehand. This was interpreted as an awakening, but I suspect that it wasn't (it looks too noise-free). 

What I'll have to hope for is a more prolonged episode to look at, or perhaps being lucky enough to catch an episode of sleep paralysis whilst I'm recording the raw data.

REM Rebound

Looking back at my post about Sleep Debt, it seems illogical to me that I can be carrying round a lifetime's worth of sleep debt...

Why on the December 1st graph, didn't my brain arrange for all the debt to be paid back in one night, why do I not have solid nights of REM or SWS to catch up on all the lost sleep of my life?

It's clear to see from the following graph that I roughly caught up on the REM sleep that I missed out on, the area below the mean REM on the debt days is roughly equal to the area above the mean on the payback days.

In fact the figues bear this out too. Assuming that my 220 day mean figure of 99 minutes is my desired amount then on the two debt days I lost 73 minutes of REM, 60 of which I caught up on over the two payback days.

Why don't we just have a night of "super concentrated sleep" without any (N1 or N2) to help us catch up on REM and slow-wave sleep? 

Maybe light sleep (N1 and N2) also serves a purpose and is desirable to the body, hence it makes sure it has some each night, maybe the body actually needs N1 and N2 as a vehicle for REM and slow-wave sleep.

Maybe REM and slow-wave sleep don't need to be paid back on on a minute-by-minute basis.

From looking at the many nights of data that I have, I think it seems clear that I generally get my "normal" amount of slow-wave sleep, and that my issue is more with REM.

Perhaps each of us has an optimal amount of REM and more than that is unnecessary, perhaps it serves a function such as recharging the immune system or cognitive functions and their respective batteries can only be fully charged and no more. There is no point in over-charging a battery, so the body doesn't waste energy trying. Maybe the brain says "Okay, your immunity was low for a day, you were sluggish in thought too, you even dipped into your reserves, so we'll top you up with 'premium' rather than 'regular' tonight"

This is bourn out by this graph of the 13 nights where I had more than 140 minutes of REM sleep...

So, by selection, there is little change in the amount of REM (140 - 153) but there is a large variation in Light (N1 + N2) and Deep (Slow-wave) sleep. This shows something else besides total sleep time governs the amount of REM that the brain desires.

Yes, the total amount of sleep and REM can't be completely independent of each other because the total REM cannot exceed the total sleep, and the brain must also arrange time for slow-wave sleep too, but this suggests that if the brain desired more REM then it could arrange for a night of the "concentrated sleep" that I spoke of in the post about "Sleep Debt"

That describes conventional REM Rebound. However, as I said above I doubt that one is able to get more than a pre-set maximum amount of REM (which will vary for each person).

I think that the weekend of the Zeo Sleep Challenge goes some way to show this. 

The idea was to have a competition where the highest sleep score (ZQ) wins. The ZQ isn't the same as "Sleep efficiency", it can be made higher by the length of time that you sleep. So my idea was to partially deprive myself of sleep for the two nights leading up to it and hope that I caught up on them for the night of the challenge.

I thought that I'd also help my chances by depriving myself of REM sleep during the time that I actually spent asleep, causing more REM to be necessary on the challenge night, hence a higher score because Zeo awards bonus points for REM and slow-wave sleep. In essence I was hoping to make use of "REM Rebound".

William Dement did this with students who volunteered in his early work in the lab. He used an EEG to determine when they were in REM sleep. As soon as he saw evidence of REM he woke them. Then let them go back to sleep until he saw another REM period. Needless to say this annoyed many of the volunteers, and some gave up.

How could I manage to do this without employing someone to watch over me?

There is an excellent piece of software called ZeoScope that has been written by a Zeo user, Dan.

It was designed to work with the Zeo Raw Data Library, so that it receives the data from the Zeo and displays it on a PC. He also added in a function where the software can sound an audio alert when you have been in a certain sleep phase for a given period of time.

The purpose of this is to use as a trigger for a lucid dream (a dream in which the dreamer knows that they are dreaming and can consciously control the dream as if they were both the author and main character of the story).

It works well for this, if you select a nice quiet tone, such as raindrops or a soft voice telling you that you are dreaming.

I found a loud alarm clock tone and set it to play after I had 2 minutes of REM. I chose the alarm clock sound because I didn’t want to have a sound that I would ignore and incorporate into the dream.

After a couple of hours things seemed okay and I’d only been woken a couple of times, but as the night wore on the sounds became more frequent and persistent until I got annoyed and chose to get up early.

It was like being ripped out of another world, only to realise that you are in your bed and flapping an arm around trying to silence a non-existent alarm clock!

If I nodded off again quickly then I went straight back into REM and was greeted by an alarm again, so I quickly worked out that it was better to make sure that I was fully awake before going back to sleep.

It got to the point that as the flashing colours and shapes of dozing (hypnagogia) began to form coherent images the alarm would sound. Once I began to lucidly dream and remember thinking "Oh, I'm somewhere new... anytime now it'll go off..." and it did.

It turned out to be pretty effective...

I only clocked up 20 minutes of REM compared to my usual 1 hour and 40 minutes – mission accomplished!

I attempted to deprive myself of REM for the following night. 

I slept for longer that night and ended up with 40 minutes of REM, still an hour short of my usual amount. So if the hour-for-an-hour payback idea is correct then I would owe 2:20h of REM, which means that on the night of the challenge, all being well I'd end up with 2:20h plus my normal amount of 1:40h giving a total of 4h REM.

...but it didn't work out that way. In fact I had to force myself to stay asleep. I did manage to sleep for nearly 13 hours, but as you can see from the graph it was mainly filled with the "padding" of light sleep (N1 and N2). 

Compared to the hospital-payback night shown above I slept for 3:30h more, but only achieved 4 minutes additional deep sleep and 14 minutes additional REM. No one can say that I didn't give my body a chance to catch up on it's life long debt, and it failed to even catch up on the REM that it lost during the preceding two days.

Where is my missing REM?

Will I ever get it back?

Surely I gave my body enough chance to catch up on some much needed REM? Why did it squander the chance by filling the night with light sleep (N1 & N2)?

William Dement suggests that payback occurs over the course of many nights. That fits with my "hospital debt" being largely paid back over two nights. He recommends a period of a few weeks where you have no obligation to stay up late, or be forced awake by an alarm clock. Then after paying back the debt, your sleep will normalise into a pattern that is right for you.

I am torn between the conventional wisdom and what I experience firsthand. Perhaps the only way to reconcile them is that my awakenings during REM are the problem.

I guess that I am trying both approaches: sorting out the cause of my REM interuptions and trying to schedule my day in a way that is more friendly towards sleep.

Maybe one day I'll have a week of solid REM.

Sleep Debt

Imagine that it's midnight: you are sound asleep and the alarm is set for 5:30am as usual.

A noise wakes you up! You sit bolt-upright in bed trying to work out what it was. Eventually you get up to have a look and can't find anything so you go back to bed.

You are no longer sleepy, in fact you are now lying awake looking at the numbers on the clock as they get ever closer to the time that the alarm is set for. You stare at the clock for a whole hour...

...then eventually drop off to sleep.

The alarm goes off and you get up feeling a little more groggy than usual.

What you didn't realise is that while you were staring at the clock, you were racking up debt - sleep debt.

You don’t need to try very hard to build up a sleep debt.

Imagine losing just an hour of sleep a night for a week, the odd late night here, early morning there etc – that would take nearly a whole night of its own to pay off, not to mention the 8 hours that you’d normally spend asleep on that night.

You've been deprived of seven hours of sleep, and your brain is not going to let you forget it! The debt is going to come looking for you when you least expect it. You might be watching the TV, or sitting at your desk, or worse - driving when it creeps up on you and demands that you pay it back!

…and pay it back you will. It has a long memory as far as sleep debt is concerned... or so the current thinking says.

In his book, “The Promise of Sleep”, Dr William Dement (the sleep pioneer who named the stages of sleep and conducted many groundbreaking experiments into sleep and sleep deprivation), states that as far as his experiments were concerned, the sleep debt was still valid for at least two weeks after it was racked up. That isn’t to say that after two weeks, the debt is forgotten, but just that experiments had only explored sleep-debt for two weeks.

But what does that actually mean in practice? Does it mean that you need an additional seven hours of sleep to rebalance things? To be honest, there is division about how much of the debt needs paying back, and it may well vary from person to person.

I decided to look at my own data to see if I could find any clues.

This is a night of my sleep while I was in hospital recently with my son. I had to wake up every two hours to perform a procedure. 

There are solid chunks of wakefulness throughout the night, along with a significant drop in REM.

I normally get around 1:40h of REM and 40m of deep sleep. It's interesting that although my REM suffered, my deep sleep didn't. This suggests that the brain values deep (slow wave) sleep more than REM, so it makes it a priority before it catches up on REM.

Then the following night we were able to have a lie in on the ward, during which we caught up and paid back some of the debt (resulting in more REM and a higher score). 

The bulk of the debt was paid back on the first night, although the debt continued to be paid back the following night too. 

This is easier to see with the following graph covering the two consecutive nights of sleep debt (the first of minor debt and the next of more significant debt shown above) along with the two nights of payback. 

Besides charting your sleep every night, there are other ways of measuring sleep debt. 

People get used to being tired in the day and consider it to be normal, so simply asking someone how tired they are is a little too subjective. The Epworth Sleepiness Scale was designed to be more objective.

You can take the short test here http://www.predictonline.com/epworth.htm

Most of us are familiar with the fact that if you are tired then you can pretty much drop off to sleep as soon as your head hits the pillow. The technical measure of the time it takes to get to sleep is called "Sleep Latency".

Sleep latency is actually a good marker of sleep debt - the quicker it takes for you to get to sleep, the greater your debt. Eventually the time to sleep onset reaches zero, then you have what is called a "sleep attack" - when the brain's desire for sleep is so great that it just blacks you out, even if just for a few moments. This can have disasterous effects, especially if you are driving at the time!

The brain is choosy about the currency that you use to pay back the debt. If you missed out on REM then it wants REM paid back (this is called REM-rebound). If you missed out on slow-wave sleep (deep) then it wants paying back in slow-wave sleep. 

This screenshot of the week leading up to (and including) the sleep debt shows how an unusually low amount of REM is caught up on:

I imagine that the brain would arrange the payback at the expense of the light sleep (N1 and N2) which largely appears to me to be "padding" to keep us asleep and out of trouble (evolutionary hang-up) or a vehicle necessary for the two types of restorative sleep: REM and SWS. I tend to think of this as a "more concentrated" form of sleep.

This is nicely shown by this graph of my REM for the above period, shown as a percentage of total sleep:

When the need arises, REM can form a larger part of total sleep, proving that it isn't accrued in relation to time spent asleep, that is to say that there isn't a formula that says "For every hour of sleep, 15 minutes of it will be REM".

So it seems unlikely that a total-sleep payback of an hour-for-an-hour of whole sleep is likely, although this may be true for REM and slow-wave sleep.

This all seems very well for small debts but it didn't seem to work for a larger debt...