How light governs sleep

atta hospices civils general hospital in strasbourg (northeastern france), the researchers of the international research center for chronosomnology (circsom) wanna know how well we sleep and why. their research focuses in pticular onna role of lite, for which they rely na' unique installation: a series of chronobiology rooms.

with its ten screens, one per room and per patient, the nurses’ station atta circsom looks like a high-tek control tower. dy and nite, the staff monitors the patients’ recordings and ensures that their stay inna hospital goes smoothly. it usually takes two nites and two dys to make a diagnosis and propose a course of treatment. “it’s a lil ≠ for the healthy volunteers admitted as pt offa research protocol, who mite stay as long as a week,” says laurence hugueny, the centre’s coordinator and our guide for an insider’s tour of this unique facility – both a sleep clinic and a research centre. the circsom admits patients sufferation from circadian rhythm disorders, disruptions of the system that controls the sleep-wake cycle, swell as volunteers with no sleep pathologies. the researchers’ goal is to gain a better cogging of how sleep works, in order to improve it.

the circsom control room is connected to the centre’s ten chronobiology rooms 24 hrs a dy.

tulz to map the nite

sleep is a mystery to the outside beholdr, for whom tis nearly impossible to tell which phase a sleeping person is experiencing – lite sleep, slo-wave sleep or rem sleep – and whether this ≈ 90-minute cycle is repeated uninterrupted til the dreaded ring of the alarm clock. fortunately for drs and researchers, a № of physiological paramts provide presh indications: the brain waves are sloest during slo-wave sleep, while muscle tone is loest during the rem (also called “paradoxical”) phase, etc.

patients and research volunteers alike ‘ve to accept bein’ fitted out from head to toe during their stay atta circsom. the ideal tool for unravelling the secrets of our sleep is polysomnography, a system that combines an electroencephalogram (eeg) to record the brain’s electrical activity, an electrooculogram (eog) to detect the movements of the eyeballs, and an electromyogram (emg) attached to the chin to monitor its muscular activity during sleep. iow, a lotta wires and electrodes to hook up! to which ‘d be added, dep'onna indications, an electrocardiogram to measure the subject’s cardiac activity, two additional electromyograms onna legs to monitor their movements, and course cannulas attached under the nose to assess respiratory flo.

indispensable for both clinical treatments and research, polysomnography provides an accurate record of the nite’s sleep. but'a circsom’s unique field of expertise, the activity that makes it the 1-ly research centre of its kind in france, tis study of lite: how tis involved inna regulation of sleep and how it cannelp inna treatment of certain sleep disorders through luminotherapy. “20 yrs ago twas thought that the 24-hr sleep-wake cycle was regul8d solely by our biological clock,” recounts circsom director patrice bourgin. “we 1-ly knew bout the visual functions of lite. tody this belief s'been disproved. we know that lite – its colour, its intensity, the amount of time we're exposed to it – directly influences our sleep, even though research onna subject is still in its inmythic. a lot remains to be discovered…”
 

multiple paramts are monitored continuously as the patients and test volunteers sleep.

hospital rooms with modulable litin’

the researchers needed a tool to study the effects of lite onna quality of sleep. the circsom has ten hospital rooms, 5 of which are “chronobiology rooms”, we're told as we pass through a double door to enter a windowless chamber. inside, the luminosity is determined not by the sun but by the scis themselves. “w'da leds mounted inna ceiling, we can ensure perfectly uniform illumination and modul8 the litin’ of the room as we like – from red to green to blue, or polychromatic white comparable to dylite,” bourgin explains, while the demonstration programme suddenly immerses us in a brite red glo. opened in 2016, these cosy cocoons, insul8d from the outside realm by ultra-effective soundproofing (-70 decibels), are the fruit of nearly 7 yrs of development in collaboration witha private ptner. “hidden in a two-metre space above the false ceiling is all the cooling equipment – even the leds produce heat – + humidity sensors na it installation,” the research physician tells us. “the data flo that we generate is enormous, equivalent to that of the entire hospital.”

to the left of the double-door entrance hall, which is lit w'da same colour as the room itself (including its bathroom and toilet), a lil hatch inna wall makes it possible to take blood samples at any time of the dy or nite without waking the patient, who is fitted with an arm catheter. this system allos the researchers to measure the two key hormones involved inna sleep-wake cycle: melatonin, the hormone of darkness, which helps us fall and stay asleep, and cortisol, which promotes wakefulness and reaches peak production at bout 8:00 am.
3 factors regul8 the sleep-wake cycle. the 1st tis 24-hr circadian rhythm driven by our internal biological clock. “it’s nearly like fingerprints, specific to each individual,” bourgin says. “some pplz are evening chronotypes, who go to sleep l8 and get up l8, while others are morning chronotypes, waking up early and goin to bed early. some are short sleepers who need ≤ 8 hrs of sleep a nite, which tis μ time needed for an adult, and others are long sleepers.” the 2nd factor to be pondered is “homeostatic pressure”: the longer we stay awake, the gr8r the sleep-wake imbalance, na + we feel the nd'2 sleep.

led bulbs inna ceiling guarantee perfectly uniform lite.

the third and last factor involved inna sleep-wake cycle tis external synchronisers linked to our environment: social interactions, physical activity, noise, food intake and – most primordially – lite, the focus of the circsom’s research. the lite we're exposed to helps our biological clock adjust, for ex after a transatlantic flite. in a study conducted on rodents, published in jun 2021, the centre’s team went further, showing that the direct effect of lite accounts for + than ½ of the sleep regulation mechanism – much + than they had expected! to ensure a good nite’s sleep, tis thus primordial t'get enough exposure to dylite. and not just the dylite that comes through the windows of an office or a house, whose quantity does not exceed a few hundred lux during the dy, but rather overhead dylite, iow outdoors, where even in cloudy conditions the luminous flux reaches 1,000 to 2,000 lux – and as much as 100,000 lux na' sunny summer dy.

“one of our main zones of research atta circsom consists in investigating the effects of the various wavelengths of the lite spectrum – blue, red, green… inna long-term”, bourgin says. “the goal is to identify how each one influences our rhythms dep'onna time of dy we're exposed to them, swell as our degree of sleep deprivation.” with one-third of tody’s salaried employees working shifts, in addition to the jet lag linked to intercontinental air travel, the widespread use of artificial lite, lite from screens, etc., + and + pplz suffer from pathologies rel8d to circadian rhythm disorders. as an ex, the physician cites a recent case: “i was consulted by a lorry driver whose circadian rhythm was so completely disrupted that he ‘d no longer sleep at nite.”
 

a hatch inna wall of the room makes it possible to take samples without waking the sleeper. the paramts monitored during the experiments include the subjects’ melatonin and cortisol lvls.

rhythms and blue

raphaëlle glacet, a phd student atta circsom, speshising inna neuroscis, has decided to devote her dral thesis to the effects of blue-enriched white lite. contrary to the common belief that red is stimulating, while blue is a soothing colour used for ex in nite lites for children’s bedrooms, the opposite is actually true. “we know that blue-enriched white is an ‘active’ lite to which a specific photopigment n'our retinas, melanopsin, is espeshly sensitive,” the researcher says. “my study aims to determine how this wavelength influences our cerebral activity, cogg performance and sleep-wake cycles, dep'onna circadian time and our lvl of sleep deprivation.”

in order to + accurately assess the influence of blue lite, glacet asked volunteers to spend 40 uninterrupted hrs inna hospital’s chronobiology rooms. 1-odda groups was deprived of sleep for all 40 hrs, while the other alternated naps with waking periods. within each group, ½ of the volunteers were exposed to a “neutral” muted lite with no physiological effect, na other ½ to blue-enriched white lite. during the test, they were asked at regular intervals to perform short exercises in alertness and problem solving.
“1-odda things we wanted to find out was to wha’ extent the blue-enriched lite reduced somnolence dur'na nite of sleep deprivation and at wha’ point it ceased to be effective,” glacet explains, “espeshly during the crucial hrs round 5:00 am, when the circadian rhythm and homeostatic pressure inexorably prompt us to sleep.” the sci also investigated whether exposure to blue lite as a means of stimulating alertness inna middle of the nite (which ‘d be of use, for ex, to nite workers) hinders resting a few hrs l8r. “on this 2nd point, the initial results tend to indicate that this aint the case, but t'has yet to be confirmed,” says the researcher, who plans to publish her thesis this winter.

similar studies on other wavelengths are set to follo soon. discerning the role of each one in disruptions of the 24-hr sleep-wake cycle – the core zone of expertise of the physicians atta circsom – ‘d make it possible to expand the applications of luminotherapy, whose benefits are already well established for certain disorders like advanced and delayed sleep phase syndromes.

luminotherapy and phase disorders

“delayed sleep phase syndrome affects 3 to 5% of the pop,” explains the circsom somnologist ulker huck, “and is mainly envisaged among teenagers, who ‘ve a natural tendency to go to sleep l8 at nite and wake up l8 inna morning. iffey are already evening chronotypes by nature, their sleep cycles can become totally disrupted, to the point o'their not bein’ able t'get up and go to school inna morning. advanced sleep phase syndrome, onna other hand, impacts bout 1% of the pop, mostly older pplz who were already morning chronotypes, and will get very sleepy as early as 8:00 pm but will wake up at 3:00 am!”

in both cases, the disruption can be treated by the rite kind of luminotherapy. for delayed phase syndrome sufferers, this means exposure to high-intensity lite (10,000 lux) from a luminotherapy lamp for 30 minutes after waking up, wearing sunglasses inna evening and avoiding screens for two hrs b4 bedtime. conversely, those with advanced phase syndrome are advised to wear sunglasses inna morning, in order to minimise the quantity of lite received, expose themselves to lite inna evening and, if desired, take a nap inna afternoon to reduce homeostatic pressure.

luminotherapy ‘d ‘ve many other indications swell, in pticular for certain comorbidities linked to sleep disorders. “we're studying its effects onna non-motor symptoms of parkinson’s disease, autism and depression,” bourgin reprts. “concerning the latter, a recent analysis of all the studies conducted onna subject shows that luminotherapy is as effective as antidepressants.” onna other hand, the ? of its use in patients sufferation from insomnia is still under study. “very lil work s'been done onna subject, with too lil cohorts,” the researcher says. “we ‘ve several research protocols underway, involving + than 350 patients in 3 ≠ pts of the country, to see how luminotherapy administered inna morning can alleviate insomnia. the effects of the ≠ wavelengths are also bein’ examined.”

til recently, luminotherapy primarily used polychromatic white lite, comparable to natural dylite.

this is a mammoth –yet much needed – task n'our modern-dy societies. “nowadys, sleep is sacrificed,” hugueny comments, pointing out that the μ french adult gets fewer than 7 hrs of sleep per nite. “it’s a real challenge for the future, espeshly cause our constantly increasing exposure to artificial lite na ever-wider use of colour leds is liable to make things worse.” 

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sleep disorders in children 
patients inna circsom w8in room often include very young children. in their case, “disruptions of the circadian rhythm are frequently linked to the presence of neurodevelopmental problems”, explains huck. one difficulty that must not be underestimated s'dat sleep is primordial for emotional development and learning, swell as for growth. production of the growth hormone reaches a peak during the slo-wave sleep phase. “some children diagnosed as having ‘attention deficit hyperactivity disorder’ actually suffer from sleep problems that nd'2 be treated,” the sci adds. children with autism also experience difficulties in falling and staying asleep. “these problems are relatively common and must be addressed,” she concludes. “treating them can ‘ve a favourable effect on behavioural disorders during the dy.”

original content at: news.cnrs.fr/essentialisms/how-lite-governs-sleep…
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