Tags: Body clock, Circadian rhythm, Hypnogram, Nap, Sleep architecture, Sleep research, Sleep stages
Sleep researcher Sara C. Mednick has written the book Take a Nap! Change your life. (Workman Publishing, NY, 2006)
Yes, it continues in the over-enthusiastic, cheer-leading tone seen in the title, and no, it doesn’t address circadian rhythm disorders. The book is so popularized that it doesn’t even have an index. But it’s interesting and it’s based on solid science. It tells about sleep stages, what they are for and their circadian rhythms.
Though we spend about half our total sleep time in Stage 2 sleep, it’s been known for some time that most deep sleep appears in the first half of one’s night, and most rapid eye movement (REM) sleep appears in the last half. Here’s a hypnogram from Wikipedia showing a normal night’s sleep with its sleep stages:
Deep sleep (slow wave sleep) is stages 3 and 4 where Stage 3 includes 20-50% delta waves and Stage 4 includes over 50% delta waves. The illustration clearly shows deep sleep in the early part of the night (more clearly than a more modern one might, as stages 3 and 4 often are combined into one, at least in the USA).
It would never have occurred to me, but Dr. Mednick has shown that this early night/late night division into predominantly deep sleep and predominantly REM sleep is just part of a whole circadian cycle: a morning nap will include more REM sleep while an afternoon/evening nap offers more slow wave sleep. Sleep cycles generally contain the lowest amount of REM a couple of hours before bedtime and the greatest amount twelve hours later. I’ve tried to illustrate this here:
And should we care which sleep stages we are getting in a nap? In a nap of 20 minutes or less, the answer is no, as that nap includes only stages 1 and 2. But in a longer nap, up to an hour and a half or so, we go through a whole sleep cycle and it may indeed matter which type of sleep we are wanting.
The short “Stage 2 nap” increases alertness, stamina and physical dexterity. Drowsy drivers have a lot to gain from a 15-20-minute nap.
The morning nap, with more REM-sleep, inspires creative insight, heightens sensory perception and consolidates newly learned material including spacial orientation. The evening nap, with more deep sleep, provides tissue repair, improves memory and clears the mind (“prunes deadwood”).
On one point, Dr. Mednick disagrees with other experts. She says a nap no longer than three hours ending no later than three hours before bedtime will not interfere with nocturnal sleep and may even improve it!
Take a Nap! provides detailed instructions for planning your ideal nap. NB! if you are not well-rested, sleep debt will demand the repaying of SWS first, whether or not that’s what you want most of. See also Mednick’s website: www.takeanap.info
( posted by D )
Next post: #55. Chronotherapy: balancing benefit and risk
Tags: Chronotype, Circadian rhythm, Core body temperature, Cortisol, DLMO, DSPS, Eveningness, Jet lag, Melatonin, MEQ, Morningness, Shift work, Sleep architecture, Sleep deprivation
“Well, I don’t like getting up before seven either,
but I have to, and I do.”
Implication: and you can, too.
But, is that true?
The article on Wikipedia about Chronotypes, morningness/eveningness, reports what researchers know so far about these normal variations, which have been studied since about 1970 and are measured by the Horne-Östberg questionnaire, the MEQ, a short version of which can be found online at Bruce Logie’s interesting site.
It can be interesting to compare normal evening types with what we know about people with Delayed Sleep-Phase Syndrome.
- like to sleep in and don’t like to go to bed early.
- are more alert in the evening than just after awakening, as opposed to morning types.
- can take a nap at 10 a.m. or noon after a night with less sleep than usual, while morning types generally don’t want a nap until 2 p.m. or later.
- experience both Dim-Light Melatonin Onset (DLMO) and the minimum of the daily cortisol rhythm later (clock time) than morning types.
So far, it sounds like people with DSPS are evening types, as the properties above apply to both groups. However, normal evening types:
- after starting a new routine requiring them, for example, to start work earlier than before, will adjust their sleep-wake schedules to the new times within a few days.
- awaken spontaneously earlier in their circadian phase than morning people; that is, the interval between the low point of the body temperature and wake time is shortest in evening types. In people with DSPS, it’s notably much longer than average.
People with DSPS do not adjust to a new schedule easily, if at all.
- Evening types have a core body temperature which is a bit lower than average, both day and night. Is this also true for people with DSPS?
- Evening types have a melatonin profile which declines much more slowly after midpoint, as compared with morning types. Is this also true for people with DSPS?
- Evening types take a long time to “get going” after awakening. In relation to the timing of spontaneous awakening, the following points contribute to this for evening types, and possibly also for people with DSPS:
- the timing of lowest body temperature,
- the timing of the cortisol minimum,
- the timing of melatonin offset, and
- the slower decline of blood levels of melatonin.
We have a disorder which, without treatment, forces us to fall asleep even later than evening types. Simply trying to enforce conventional sleep and wake times does not advance the circadian markers. It seems almost impossible to wake us much earlier than our pre-programmed wake time (as my siblings will attest). The disorder is chronic, changing little or not at all after the age of 20.
When normal chronotypes shift their schedules, all the body’s rhythms catch up and are synchronized to each other within a few days. In DSPS, the dissynchrony may continue as long as the shifted, “unnatural” schedule lasts, even for years or decades, leading to physical and psychological disorders.
It’s clear that people with DSPS who (try to) work days, have much the same set of problems that many shift workers have, whether these always work nights or are on a rotating schedule. However, shift workers’ problems receive sympathy and understanding while people with DSPS are commonly stereotyped as undisciplined and lazy. Dagan again (PDF, page 7), on adolescents, points out that “[f]requently, the patients’ parents, teachers, doctors, or psychologists believe that the patients’ biological sleep-wake problem and the accompanying dysfunction at school are motivational or psychological in nature, a belief that during the years, the patients tend to adapt themselves. This attitude toward CRSD patients, to which [they have] been subjected since early childhood or adolescence, adds psychological distress to the practical difficulties of coping with life.”
Like normal people, we do adjust (entrain) to the earth’s 24-hour rotation, but, without treatment, we don’t “learn” to wake up at a conventional, early time of day.
Tags: ASPS, Body clock, Chronobiology, Chronotype, Disability, DSPS, Eveningness, Genetic mutation, Japanese study, Light therapy, Morningness, Non-24, Prevalence, SAD, Sleep architecture, Sleep disorder
There are a great many sleep disorders. I read recently that an official list of them had been pared down to about 70. Many have to do with not getting enough sleep, or getting sleep of poor quality by several criteria. Some have obvious causes, such as chronic pain, frequent stops in breathing etc.
My interest is in the timing of sleep as my sleep seems otherwise normal. As the experts put it, I have normal “sleep architecture”. (For a good, short explanation of sleep architecture — stages and brain waves — see this page from Feinberg School of Medicine at Northwestern University in the USA.)
Nearly all of us can reset our clocks daily, adjusting the various rhythms to 24 hours. As much as I’ve read about it, I’ve not found a good enough explanation for being able to adjust to 24 hours while not being able to adjust to sleeping midnight to eight or so.
I’m not immune to the light/dark cycle. I need to get up at noon. I fly 8 hours east or west, go through jet lag like anyone else and within days I need to get up at noon in the new location. This is built in. I’m not the only one. I’d just like to understand it better.
A Japanese paper (2004) suggests these possible mechanisms:
- reduced sensitivity of the oscillator to photic entrainment,
- an intrinsic period beyond the range of entrainment to the 24 hour day, and
- abnormal coupling of the sleep/wake cycle to the circadian rhythm.
One of the most rare disorders which occurs naturally is called Non-24. Sufferers simply(?) live on a 23, 25 or 26 hour cycle, getting up one hour later each day for example, thus coming in sync with the earth’s rotation every few weeks. Their rhythms are in sync internally, just not with the light/dark cycle outside. Most, but not all, of these people are blind.
ASPS, Advanced Sleep-Phase Syndrome, is also rare. These people fall asleep and awaken much earlier than normal. The disorder runs in families, and an American family has been studied intensively the last few years. Research on their genetic mutation was published in 2001. “Detailed sequence studies of the candidate human gene, hPer2, in the affected family members, revealed a key change in a single amino acid — from serine to glycine — at position 662 in the hPer2 protein.” The alteration “occurred in the portion of the hPer2 protein that governed binding to an enzyme called casein kinase one-epsilon (CK1e ).” In animal models, this enzyme regulates “proteins involved in controlling the length of circadian rhythms.”
Now this is beyond me, but it would appear that these disorders may be genetically programmed. Though ASPS is rare, it seems reasonable that researchers start there, since one can compare the DNA of people who are related to one other.
Another disorder which may be related to the others is Seasonal Affective Disorder, SAD. Sufferers are normal in summer, have problems of mood, weight gain etc. when days get shorter and can often be treated successfully by bright light therapy. It seems likely that they may have a mild form of ASPS or DSPS which is “treated” by morning/evening daylight when days are long.
Diurnal preference, spoken of as “morningness”, larks, and “eveningness”, owls, is also a subject of study, the field of chronobiology. This is, reasonably enough, connected to one’s circadian rhythms. However, it does not appear that ASPS is an extreme morningness chronotype nor DSPS an extreme eveningness chronotype. The internal relationships among the various rhythms do not place these conditions on a simple continuum.