THE SCIENCE OF SLEEP
Agood night’s sleep might feel like one long, deep, velvety trough, but in fact it is divided into distinct phases that refresh the body and the mind.
There are two broad categories of sleep, says Motty Varghese ,a behavioural sleep therapist at the Sleep Therapy Clinic at St James Private Clinic in Dublin. There is REM (Rapid Eye Movement) sleep and Non-REM sleep and each occurs at different times. NREM sleep is further divided into three stages, each with its own characteristics:
Stage 1 NREM A transition phase between waking and sleep that lasts just a few minutes and occurs when you first fall asleep. Over an entire night, you probably spend just 5pc in this stage. Stage 2 NREM Slightly deeper than stage one, but you can still be woken quite easily. “We become a little bit detached from our surroundings,” says Motty. Your heart rate slows and breathing becomes more regular. You spend about 45pc of a night’s sleep here.
Stage 3 NREM If your stage two sleep is uninterrupted, it gradually progresses to stage three. “If you wake in the morning and feel like you had a great sleep, it’s very possible you spent enough time in stage three sleep which is very physically refreshing,” says Motty.
Then you shift back to stage two sleep, “and then you get your first episode of REM sleep,” says Motty. “REM sleep is the deepest stage of sleep.” It is also when we dream.
The entire sleep cycle takes about 90 minutes. “Ideally we should get five to six of those sleep cycles, which is seven to nine hours of sleep.”
The amounts of REM and NREM sleep we get in each cycle varies over the course of the night, with more NREM sleep in the first half — physically refreshing sleep — and more REM sleep (ideally 25pc or so) in the second half — the mentally refreshing part.
And if you are getting that quantity of sleep consistently, says Motty, there is no need to sleep in at weekend as you are not accumulating a ‘sleep debt’. You’re in the lucky position of getting enough healthy refreshing sleep each night.
SLEEP AND YOUR BRAIN
Neuroscientist Matthew
Walker, who has spent years researching sleep at the Center of Human Sleep Science in California, says: “We’ve not been able to discover a single cognitive operation that isn’t beneficially enhanced by sleep when you get it, or detrimentally impaired when you don’t get enough. This ranges from your basic ability, in terms of brain function, to focus and concentrate on information, to more complex things like decision making.”
REM or dream sleep, says Motty, has a big role to play in procedural memory — how to carry out a certain task — while NREM is involved in declarative memory formation — like who, what, when — very factual information.“Our memory formation and the consolidation of the information that we take in during the day by listening to the radio or talking to people or attending lectures or sitting in seminars in workplaces — all this information is processed during stage three NREM sleep.”
Matthew adds: “Sleep also involves balancing your reward circuitry in the brain so you don’t become excessively impulsive or sensation seeking or risk taking. Sleep seems to regulate and dampen that.
EMOTIONAL FIRST AID
But the function of REM sleep, our dream sleep, goes even further. “We’ve discovered that sleep provides a form of overnight therapy,” says Matthew. ”Sleep is a form of emotional first aid and will actually recalibrate the emotional circuits of the brain. Sleep will reconnect your prefrontal cortex, the part that makes us most human, the part that sits directly above your eyes, with the deep Neanderthal, emotional, reactive
brain centres, particularly a region that we call ‘the amygdala’. By way of reconnecting those two we wake up more rational — we wake up more emotionally stable rather than pendulum-like.”
Occasionally we all have bad dreams, says Motty. “It’s only a problem when those dreams are frequent. It is common in post traumatic stress disorder (PTSD), a big issue with war veterans coming from battlefield situations and going through a lot of emotional experiences. They struggle with recurring nightmares.”
Matthew, who wrote the groundbreaking ‘Why We Sleep: The New Science of Sleep and Dreams’
(Penguin), says: “We’ve found that for emotional memories, sleep will take those difficult, traumatic, painful experiences from the prior day and soothe them. It will take the emotional sharp edges off, and will actually divorce the emotion from the memory. It means that, when you wake the next day, you don’t feel as bad. Things don’t feel as terrible or depressing anymore.”
He describes how he found war veterans who visited his sleep lab, suffering from PTSD to have disrupted REM sleep. He hypothesised that their brains couldn’t effectively ‘detox’ the emotional memory. They also had high levels of noradrenaline, the stress hormone that is normally tuned down in REM sleep.
Together with Dr Murray Raskin of the US Department of Veteran Affairs, Walker discovered that the drug Prazosin, used to lower high blood pressure, also had the effect of lowering noradrenaline in the brain during REM sleep. As a result, the brain could deal with neutralising the traumatic memories and the recurring nightmares stopped.
“So it’s not time that heals all wounds,” says Matthew, “but it’s time within sleep, and particularly dream sleep, that provides emotional convalescence.”
For those who suffer from recurrent nightmares, rather than PTSD, there is a CBT treatment called Image Rehearsal Therapy, explains Motty. “You record the person’s nightmare, ask them to write it down, and then get them to change it in a positive way. They read it through a few times before they go to bed and gradually change the way they see the dream.”