Lullaby for a lifetime’s deep sleep?

With our elec­tric blan­kets, pock­et-sprung mat­tress­es and draft-proof bed­rooms, we sleep bet­ter in the 21st cen­tu­ry than ever before. Yet to hear us talk, it would seem no one ever gets enough shut-eye.

“The more peo­ple wor­ry about sleep, the more they wor­ry and so sleep less,” says Jim Horne, pro­fes­sor of psy­chophys­i­ol­o­gy at the Uni­ver­si­ty of Lough­bor­ough, who is one of the UK’s lead­ing sleep experts and author of Sleep­far­ing. “Yet our sleep­ing cir­cum­stances are bet­ter than ever, and we under­stand more and more about the nature and pur­pose of sleep­ing and dream­ing.”

Recent research has chal­lenged the­o­ries about why we sleep. For exam­ple, research from the Cen­tre for Trans­la­tion­al Neu­romed­i­cine at the Uni­ver­si­ty of Rochester Med­ical Cen­ter in New York has demon­strat­ed for the first time that the space between brain cells may increase dur­ing sleep, allow­ing the brain to flush out tox­ins that build up dur­ing wak­ing hours.

“Sleep changes the cel­lu­lar struc­ture of the brain,” says Dr Maiken Ned­er­gaard, a leader of the study, which was pub­lished last Octo­ber in the jour­nal Sci­ence. “We need sleep – it cleans up the brain.”

It is clear that the night-time mol­e­c­u­lar pro­cess­ing – a sort of brain house­keep­ing shift – ben­e­fits our cog­ni­tive abil­i­ty as well as well­be­ing so that we wake refreshed in both cell and spir­it.

But how do we sleep? What hap­pens when we close our eyes and drift away to the Land of Nod? Tra­di­tion­al­ly, says Pro­fes­sor Horne, sleep has been analysed by chart­ing it in four stages, which cov­er the changes in our brain­waves, mea­sur­able by EEG – elec­troen­cephalog­ra­phy, the tech­nique that records the brain’s elec­tri­cal activ­i­ty – and includ­ing time when we are in REM (rapid eye move­ment) sleep and in non-REM (NREM) sleep.

Growth hor­mone is released dur­ing NREM, encour­ag­ing mus­cle and tis­sue repair, and stim­u­lat­ing the immune sys­tem to defend against infec­tions. REM is a peri­od for the brain to restore, clean­ing out all the “junk mail” that has accu­mu­lat­ed, and allow­ing the cap­ture of mem­o­ries and learn­ing.

The first stage is drowsy sleep. Our mus­cles are active and eyes roll slow­ly, open­ing and clos­ing mod­er­ate­ly. Num­ber two is “deep­er sleep”, when we may twitch slight­ly or move about, but we are def­i­nite­ly asleep; a stage which can take up almost half our sleep time.

Stages three and four fol­low; we are in deep sleep now and would be hard to wake. Through­out the night, these stages are inter­rupt­ed by 90-minute peri­ods of REM sleep, when we dream vivid­ly, twitch and may even wake briefly. This is the deep­est peri­od of sleep when blood pres­sure, heart rate and res­pi­ra­tion low­ers, and has been referred to as “human hiber­na­tion”.

If you have unhap­py thoughts dur­ing the day, you’ll have unhap­py dreams; hap­py thoughts dur­ing the day will see you hap­py in your dreams

Sleep clin­ics have used these dif­fer­ent stages for clin­i­cal and diag­nos­tic pur­pos­es to help those with insom­nia or oth­er sleep­ing prob­lems. But Pro­fes­sor Horne believes a fresh approach is need­ed that regards stages three and four as one phase of sleep. He feels that a bet­ter way to clas­si­fy sleep is to exam­ine the brain­wave pat­terns.

The fluc­tu­a­tions in activ­i­ty can trace the brain mov­ing between states of wake­ful­ness, like drowsi­ness or REM sleep, and peri­ods of deep NREM sleep. “To get into sleep, we must switch off wake­ful­ness,” he explains.

“In REM sleep, unlike NREM, the brain lis­tens to what is going on around, and the sleep­er can still decide whether any sounds are mean­ing­less, to be ignored, even incor­po­rat­ed into an ongo­ing dream, or if ‘emo­tive’ then there is an instant awak­en­ing, with the sleep­er alert and ready to react. In this lat­ter respect, REM sleep is like ‘screen­saver’ mode on your com­put­er – able to switch into imme­di­ate action.”

He adds: “In NREM sleep, your brain has been switched off prop­er­ly, whether that is in stage two or three/four. To wake up, your brain has to reboot, which is why it takes longer to ‘come to’ from NREM than REM peri­ods.”

NREM is prob­a­bly a peri­od of organ­i­sa­tion for the brain. Pro­fes­sor Horne believes it is not just for con­sol­i­da­tion of mem­o­ries, but retun­ing and redi­rect­ing links. He is cau­tious about the new US research sug­gest­ing it’s a time for tox­ins to be flushed away. “Inevitably some chem­i­cals will be drained away nat­u­ral­ly, but new ones will appear too. It’s more com­plex than just a deep-clean­ing mode,” he says.

But it is the pur­pose of REM sleep that per­haps looks most inter­est­ing for future study. We tend to think of this peri­od as dream sleep but, explains Pro­fes­sor Horne, even in NREM sleep the brain is think­ing about things. How­ev­er, we nev­er remem­ber any of this and only remem­ber dreams if we wake swift­ly after them, which is impos­si­ble from deep sleep, and then we can only recall the last minute or so of the dream. In fact, the actu­al process of dream­ing is facil­i­tat­ed by a dif­fer­ent part of the brain to that of REM sleep itself.

It seems the pur­pose of REM is about stim­u­la­tion, keep­ing our brains tick­ing over when there is no oth­er stim­u­lus. Babies enjoy REM sleep for well over eight hours a day in the womb. Once they hit the real world, full of new stuff, their need for REM sleep drops quick­ly, falling to about five hours a day at the end of the first year. Inci­den­tal­ly, sea lions don’t have REM while they are at sea and only expe­ri­ence it on land.

REM, peri­ods of which get longer and more intense as we approach morn­ing, seems to pre­pare us for wak­ing up after a peri­od of what Pro­fes­sor Horne has called “core sleep”, the first five to six hours of most­ly NREM sleep.

One the­o­ry con­cern­ing REM is that we use this time to process and arrange our thoughts from the day, hence the bizarre dreams which can include aunts, uncles, uni­corns and cab­bage.

Pro­fes­sor Horne doesn’t believe that REM and dream­ing sort out your psy­che: “If you have unhap­py thoughts dur­ing the day, you’ll have unhap­py dreams; hap­py thoughts dur­ing the day will see you hap­py in your dreams.”

He con­cludes: “A good night’s sleep comes with peace of mind.”