xlvii. Distribution of early and late types

7 November 2009 at 02:23 | In Circadian rhythm | Leave a Comment
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Distribution, early and late types

The illustration above is adapted from Till Roenneberg et al., the team who invented the Munich Chronotype Questionnaire, MCTQ.  The MCTQ is a modern version of the Morningness-eveningness Questionnaire, MEQ, and it is considered to give the best estimate of morningness and eveningness chronotypes.  They have chosen to consider sleep onset at 00:30 and 01:00 as “normal” for the adult population.  Their results are 46.5% early types, 28.5% normal types and 25% late types — as shown in this table:

According to the illustration from MCTQ Percentage of population

Chronotype sleep time    % SUM
       
  

 

EARLY

 

TYPE

 

EXTREME

> 2.0 %

20.30 – 04.30 < 0.5     46.5 %
21.00 – 05.00 < 0.5
21.30 – 05.30 < 0.5
22.00 – 06.00    2.0
     
MODERATE13.0 % 22.30 – 06.30    3.5
23.00 – 07.00    9.5
     
SLIGHT31.5 % 23.30 – 07.30  14.5  
00.00 – 08.00  17.0
         
         
NORMAL TYPE 00.30 – 08.30  16.0     28.5 %
01.00 – 09.00  12.5
         
         
  

 

LATE

 

TYPE

 

 

SLIGHT15.0 % 01.30 – 09.30    9.0   

 

 

 

 

 

 

 

    25.0 %

02.00 – 10.00    6.0
     
MODERATE6.5 % 02.30 – 10.30    4.0
03.00 – 11.00    2.5
     
EXTREME

> 3.5 %

03.30 – 11.30    2.0
04.00 – 12.00    1.0
04.30 – 12.30    0.5
05.00 – 13.00 < 0.5
05.30 – 13.30 < 0.5
         
SUM         100.0 %

But isn’t 1 AM rather late at night to be considered a “normal” bedtime?  In my opinion, normal sleepy time would be no later than 11:30 PM, midnight and perhaps 12:30 AM.

Using my own idea of what is normal, I’ve reconstructed the table to show these results:  15% early types, 47.5% normal types and 37.5% late types, as shown here:

In my opinion, based upon their figures:

percentage of population

Chronotype sleep time    % SUM
       
  

 

EARLY

 

TYPE

 

EXTREME

< 1.0 %

20.30 – 04.30 < 0.5     15 %
21.00 – 05.00 < 0.5
21.30 – 05.30 < 0.5
     
MODERATE5.5 % 22.00 – 06.00    2.0
22.30 – 06.30    3.5
     
SLIGHT9.5 % 23.00 – 07.00    9.5
         
         
NORMAL TYPE 23.30 – 07.30  14.5       47.5 %
00.00 – 08.00  17.0
00.30 – 08.30  16.0
         
         
  

 

LATE

 

TYPE

 

 

SLIGHT21.5 % 01.00 – 09.00  12.5   

 

 

 

 

 

 

 

 

    37.5 %

01.30 – 09.30    9.0
     
MODERATE10.0 % 02.00 – 10.00    6.0
02.30 – 10.30    4.0
     
EXTREME

6.0 %

03.00 – 11.00    2.5
03.30 – 11.30    2.0
04.00 – 12.00    1.0
04.30 – 12.30    0.5
05.00 – 13.00 < 0.5
05.30 – 13.30 < 0.5
         
SUM         100.0 %

So I’ve also redone the figure at the top of this page to reflect my opinion of what is early and late: 

 Distribution, early and late types

What time do you think “normal types” go to sleep at night?

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Next: ~coming soon~

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xlvi. Guest Blogger: Breann Hays

11 October 2009 at 21:15 | In Circadian rhythm | Leave a Comment
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This post was written in response to one whose author also lives on a very strict schedule and thereby feels that he has “defeated” his circadian rhythm disorder.  Breann feels a bit differently about it.  Thanks, Breann, for letting me use this!

 

I wouldn’t say that I’ve beaten DSPS.  I know that as soon as I stop doing everything right all the time, things will go back to the way they were.  I’ve been on the early morning schedule for about four months now, and my friends and family are really happy for me because they’ve never seen me do it for this long before.  (Sad but true :p)
 
But they also seemed to think that I would somehow have cured myself doing it  …  conveniently around the time they are getting sick of the unyielding restrictions on my time. 
 
One recently asked how much longer I would have to keep it up.  I said I was looking for new chromosomes, but they didn’t seem to have any at the store  :(  Then I felt bad for being mean, but it made me mad that she seemed to think that just because I was doing things differently it was going to really change anything.
 
Like I haven’t tried doing things differently a million times…  I have to keep reminding people that I have known how to operate an alarm clock for a long time, that’s not the part I had to learn… and none of this changes anything REALLY.
 
DSPS is a condition, not a habit.
 
Then she got kind of depressed and said it seems like a lot of work for nothing, then I got kind of depressed because it is…  But, oh well, at least I can say that I have a much better chance of at least graduating school.
 
I haven’t beaten anything…  I am just able to cope a lot better now.  And it took 3 years to get it down, too!

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xlvii.  coming soon

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xlv. Some helpful links

24 August 2009 at 19:27 | In Circadian rhythm | Leave a Comment
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Mailing list / support group:

Forums, some more helpful than others, my favorites at the top:

  • TalkAboutSleep is a message board with many categories including “Circadian Rhythm Disorders”. 
  • SleepDisorderChannel is another active message board with many categories, this one including “Delayed Sleep Phase Syndrome”. 
  • BrainTalk is less specific (lots of neurology problems) and less active; scroll way, way, way down to “Sleep disorders” in the alphabetical list. 
  • SleepNet has forums on sleep problems, not specifically circadian. 
  • Facebook has several DSPS groups.

 (In general, anyone may read these forums, while registration is required to post.)

→  Sites with information:

  • DSPSinfo.org is a page by and for people with DSPS.  It aims to be neither too pessimistic nor too optimistic.  See also the links at the bottom of that page.
  • Su Laine Yeo is the oldie but goodie!  The oldest DSPS information on the internet.
  • Busting myths surrounding Delayed Sleep contains a long list of links, many of them great! 
  • Night Owl Network is for and about the normal night owls, with, among other things, an article showing these survey results, very approximately:  25% evening people, 15% morning people and  60% intermediates.
  • The B-society is the English language version of a Danish organization working for recognition of the evening chronotype, not specifically DSPS.   Little activity lately.
  • See also these and other articles on Wikipedia .  Here listed alphabetically:  Chronotype, Circadian rhythm, Circadian rhythm sleep disorder, Delayed sleep phase syndrome, Melatonin, Non-24-hour sleep-wake syndrome, Phase response curve, Sleep medicine

 Posts on other blogs:

  • How I Learned To Live With DSPS is a stand-alone post on an otherwise business blog.  Good description of the disorder and well-written, for example:  “I felt like one of those 7 foot basketball players where doorways and airplanes seats never fit you. The world was just not designed for me.”
  • Defeating Non-24hr syndrome tells, in believable detail, how one person has beat Non-24 and the 15 rules necessary to maintain diurnality.  With bibliography.

 

  And do let me know of

any other good sites

that I may have missed, please!

 

All ready for work!

All ready for work!

If you must get up for work tomorrow and know how hard it’s going to be, it may be best to shower and dress the night before….

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Next, Guest Blogger: Breann Hays

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xliv. Rods and cones and the “new” ipRGC

30 July 2009 at 20:16 | In Circadian rhythm | 2 Comments
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We learned in middle school that there are two, and only two, types of light sensitive cells in the retina, rods and cones, right?  Right, that’s what we learned.  Could be the science teachers are still saying that, since the third type was discovered within the last decade. 

 

Mammalian retina

Mammalian retina

 

The mammalian retina consists of many layers.  One might think that light would first strike the rods and cones, the photosensitive cells we use for vision.  But our retina is “inside out” compared to the more logical layout found in the octopus and its relatives; light in our eyes must travel through the many retinal layers to reach our rods and cones.  

One of the first layers the light reaches is composed of the one and a half million ganglion cells, most of which are involved in processing visual (image forming) information.  Fewer than 25000, some say just a couple thousand, of these cells are themselves sensitive to light. They function as light meters and they function much more slowly than the rods and cones, not registering abrupt fluctuations in light intensity.  These cells project their axons to several brain centers including the suprachiasmatic nuclei, SCN, the “body clock” through the retinohypothalamic tract.  They thus provide the major clue for the adjustment of the body clock.  The incoming information about light intensity is also used to adjust pupil size (narrowing of pupils in bright light) and to regulate physical activity and melatonin synthesis. 

Newly discovered, they are called by many names:

  • intrinsically photosensitive Retinal Ganglion Cells (ipRGC, also pRGC)
  • photosensitive ganglion cells
  • melanopsin-containing retinal ganglion cells
  • melanopsin-expressing retinal ganglion cells (mRGC)

 Melanopsin jpg

Late in the previous century, scientists weren’t sure that there existed ipRGCs, and those who thought that they do exist were arguing about what opsin, what pigment, they use.  Is it  melanopsin or one of the cryptochromes, which also respond to blue light?  One argument against melanopsin was that it resembles invertebrate opsins and differs from other opsin photopigments found in vertebrates.  

Again, as with our hormone melatonin, it was research on specialized light-sensitive cells of frog skin which provided answers.  

It has been known for a while that even when vision is lost, the light-sensitive ganglion cells may function perfectly.  Recent research on mice at Salk Institute shows that the opposite also is true.  A way was found to knock out the ipRGCs while leaving the rods and cones alone.  The mice became arrhythmic, but still could see. 

One of the researchers speculates:  “It is entirely possible that in many older people a loss of this light sensor is not associated with a loss of vision, but instead may lead to difficulty falling asleep at the right time.”

Update:  I’ve just discovered a wonderful post, Why can’t human eyes detect all wavelengths?, on the blog of Xenophilius Lovegood (!?).  Xeno, claiming to be “a slightly mad scientist”, explains the physical / chemical / electrical changes in the rods and cones as they react to light.  He also has a bit about the ipRGCs.  Recommended.

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Next:  (coming soon)

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xliii. Blindfolding the blind

9 July 2009 at 00:54 | In Circadian rhythm | Leave a Comment
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MelSupprTest-1995

Blindfolding blind people sounds like an oxymoronic exercise.  But it is clear that some people with no visual light perception, do, in fact, entrain normally.  I believe it was Charles A. Czeisler who, about 1980, discovered that some blind people entrain normally to the 24-hour light/dark cycle while others do not.   

He and colleagues worked with a number of blind people throughout the 1990s, reporting the results in such papers as this one  from 1995 and this one from 1998.

These researchers, as well as others, worked on determining the circadian periods of individuals by the use of forced desynchrony,  so-called constant routines.  Conditions which are impossible to entrain to, allow mapping of body temperatures and melatonin levels. 

The illustration above, from the 1995 paper, shows two days and nights in the lives of a sighted (above) and a blind (below) *person.  They call this the “Melatonin Suppression Test”.   Circadian phase is determined in the first night: the high point of the level of melatonin in the blood corresponding more-or-less to the low point of the core body temperature.  The second night both subjects are submitted to 90 minutes of bright light (the white columns) at the time of their highest melatonin levels the night before.  And the melatonin levels go way down in both subjects! 

In a repeat of the test with the blind person blindfolded, the light had no effect.  Obviously, somehow, the light signal makes it to the body clock in some blind people.  More about how this works, for all of us, in the next post.

* (It seems to me to be not-too politically correct to call healthy volunteers “subjects” and healthy blind people “patients”.  Czeisler et co will have to answer for that.)

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Next:  xliv. Rods and cones and the “new” ipRGC

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xlii. Researchers mentioned here

13 June 2009 at 18:05 | In Circadian rhythm | 4 Comments
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Several researchers have been mentioned / cited here, and there’ll surely be more.  They are listed below. 

Bjorvatn, Bjørn (in post vii.), is a sleep researcher at the University in Bergen, Norway, and a co-founder of Bergen Sleep Center.

Czeisler, Charles A. (in post xliii.) has been researching circadian rhythms for several decades.

Dagan, Yaron  (in post xxxviii.) in Israel, often publishing together with Judith Abadi, stated in 2001: “Certain sleep-wake schedule disorders (SWSDs) cannot be successfully managed clinically (…).  …we propose new medical terminology for such cases–SWSD disability. SWSD disability is an untreatable pathology of the circadian time structure…  It is imperative that physicians recognize the medical condition of SWSD disability in their patients and bring it to the notice of the public institutions responsible for vocational and social rehabilitation.”  In almost all of his papers, he emphasizes that people with circadian rhythm disorders often are misdiagnosed because physicians don’t know (enough) about such disorders.  Here is a case study (abstract) about a 14-year-old boy whose other diagnoses fell as soon as his sleep disorder was diagnosed.  It should perhaps be obvious that I appreciate Dagan’s work and his opinion. 

DeCoursey, Patricia (in post xix.), is the grand old, grand old of the field of chronobiology.  In 1960 she invented the Phase Response Curve when the “daily” activity rhythms of her flying squirrels, kept in constant darkness, responded to pulses of light exposure. The response varied according to the time of day — that is, the animals’ subjective “day” — when light was administered. When DeCoursey plotted all her data relating the quantity and direction (advance or delay) of phase-shift on a single curve, she created the PRC. It has since been a standard tool in the study of biological rhythms.

Dijk and Lockley (in post v.).  Derk-Jan Dijk and Steven W. Lockley often publish together.  Dijk, who studies the regulation of sleep and circadian rhythms in humans, is director of the Surrey Sleep Research Centre in the UK.  Lockley, Assistant Professor of Medicine, Harvard Medical School, and Associate Neuroscientist in Sleep Medicine, Brigham and Women’s Hospital in the USA, is particularly interested in the effects of light on the circadian pacemaker in humans.

Horne and Östberg (in post xxxviii.) published their Morningness-Eveningness Questionnaire (MEQ) in 1976.   It is based on O. Öquist’s 1970 thesis at the Department of Psychology, University of Göteborg, Sweden: ”Kartläggning av individuella dygnsrytmer”, “Charting Individual Circadian Rhythms”.  This marks the beginning of modern research into chronotypes.  Olov Östberg modified Öquist’s questionnaire and, together with J. A. (Jim) Horne, he published the MEQ (pmid 1027738, abstract ) which still is used and referred to in virtually all research on this topic. 

Roenneberg, Till (in post xxxvii. and in post xlvii.), professor at the University of Munich, is one of the best-known chronobiologists in Europe, having received international prizes for both his research and his teaching.  He has built up the Centre for Chronobiology at the Munich Medical School with its database on the sleep of over 50 000 Europeans.  In 2008 in India he collaborated with and directed a project in Mangalore chronotyping the south Indian population, with data covering nearly 75 000 participants.  Roenneberg’s work ranges from the cellular/molecular mechanisms of the circadian clock to the consequences of shift work and, as mentioned, huge surveys.

Thorpy, Michael J. (post xxxii.), board certified in sleep medicine, is a sleep researcher and a professor of clinical neurology at the Albert Einstein College of Medicine in New York.  He has held high office in the National Sleep Foundation and in the Sleep Section of the American Academy of Neurology.  Thorpy was for many years editor of The International Classification of Sleep Disorders: Diagnostic and Coding Manual (ICSD) and has been publishing books and articles since the 1980s.

Uchiyama, Makoto (in posts xxxviii. and xxvii.), professor at the Nihon University School of Medicine in Tokyo and managing editor of Sleep and Biological Rhythms, the official English language journal of the Japanese Society of Sleep Research (JSSR), is a prolific co-author of studies on sleep, particularly on DSPS and Non-24, often in cooperation with Masako Okawa, chair of the Asian Sleep Research Society. (ASRS).  This research field is very active in Japan, where study subjects often are people with these disorders.  In the west, in contrast, studies are more often done on healthy, normal people with results extrapolated to effects in people with the disorders.  The Japanese researchers have shown, for example, that the interval between the lowest core body temperature and spontaneous awakening is much longer in people with Non-24 and DSPS than the “about two hours” which is considered normal. 

Zivkovic, Bora, aka “Coturnix” (in posts xxxvii.xxxiii.xviii. and  xv.), should have had his PhD by now but the ideal job came along and his dissertation isn’t getting done.  He tells about that and about chronobiology and about lots more at ScienceBlogs

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Next:  xliii. Blindfolding the blind

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xli. Coincidence & update

6 June 2009 at 23:50 | In Circadian rhythm | Leave a Comment
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Chapter three begins a year-to-the-day after the end of Chapter two.   A coincidence.  (I so wanted to call it serendipity but don’t want to add to the misuse of that word.)

In this last year I’ve retired.  I’ve kept on with melatonin at night, my light box in the “morning” and keeping my sleep diary every day.  When I remember, I’ve added a tiny dab of melatonin late afternoon and yellow goggles in the evening. 

My schedule has not become as regular as I’d thought and hoped, even though I now only aim to be up before 1 p.m.  I see my sleep specialist about every other month.   He usually reminds me that he, at the beginning, had said that he couldn’t promise regularity, a “cure”.  And that he thought that my circadian period is “upwards of 28 hours”.

After five years of daily melatonin, I tried eight weeks without, thinking that, given the chance, my system might land on its own schedule.  Nope.  Those sleep diaries show chaos:  sleep whenever, rarely for 3-4 hours, often for 12-14 hours, night or day.  When I happened to get up between 9 a.m. and 2 p.m. I did use the light box.  There’s no sign of a system, most particularly not any sign of Non-24, for which I’m glad.  When I showed the diary to the specialist, he pointed at those eight weeks and asked: “What  happened here?”

It took only a few days back on melatonin to get back where I was before:

4weekDIARY jpeg

BTW, as you can see, I’ve simplified the sleep diary and now get four weeks on one page.  With 28 days across and 24 hours down, midnight in the middle as before, symbols at the top for melatonin use and at the bottom for use of light box, the filled in sleep parts of each column show clearly how (ir)regular my sleep pattern is.  Illustrated is, believe it or not, a month that the specialist was quite happy about:  “That may be the best month you’ve had.”

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Next:  xlii. Researchers mentioned here

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xl. The post-lunch dip

6 June 2008 at 16:10 | In Circadian rhythm | Leave a Comment
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Sleep timing, when not manipulated too badly, is controlled by body clock and homeostasis. Homeostasis starts building a need for sleep as soon as we wake up for the day, but at first it’s easy to ignore. For a normal or lark sleeper, that means until sometime between noon and two. At that point the body clock kicks with a need for wake which builds until just before bedtime. The sleep gate, a term used by some researchers, then opens and sleep occurs. 

During about the first half of the night, one sleeps away the built-up sleep need (as controlled by homeostasis). Some people wake up for a time at that point, which researchers are starting to see is normal and not a problem.

Then, normally about 2 a.m., the body clock kicks in with an intense sleepiness which dissipates through the next 4 hours.

So a normal lark is sleepy at 10pm (body clock’s need for wake gets turned off). The day’s sleep debt is paid off by about 2am when the body clock turns on a need for four hours more sleep. Happy lark awakens at 6am, raring to go, when neither homeostasis nor body clock craves sleep.

In theory, the body clock should kick in with its need for wake just before a big sleepiness hits at 2pm, but there’s often a bit of a delay, probably culturally encouraged in areas using the siesta, and that included/includes many agrarian cultures far from Iberia.  It is known that humans without electric light often experience an hour or two of wake in the middle of the night. (Said to be good for meditating, socializing and sex, not to mention nursing the baby.)

Thus, normal people are most intensely sleepy at 2pm and at 2am.

So! It seems reasonable to me to apply this 12 hour difference to people with Delayed Sleep-Phase Syndrome, at least those who aren’t totally desynchronized internally. Take the classical DSPS example of sleeping 4am to noon. At 8am, the body clock has just turned on its intense need for continued sleep (making it impossible to hear an alarm clock or three). At noon we awaken (not quite as bushy-tailed as the lark was at 8am, perhaps because society has told us all our lives that “sleeping in” is BAD!).

Twelve hours after the intense need for sleep at 8am, we may experience the sleepy “after-lunch dip” at around 8pm. All times are approximate.

This explains, I think, why the long naps I used to take at 6 or 7pm abruptly ended at 10pm or so. Very tired larks may be able to sleep a couple-three hours at siesta time, but they won’t sleep for 8 hours then. Same with me; if I haven’t been up the previous 36+ hours, I won’t sleep longer than about four hours at my “siesta time”.

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Next:  xli. Coincidence & update

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xxxix. Guest Blogger

6 December 2007 at 16:42 | In Circadian rhythm | Leave a Comment
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Every now and then, someone on the mail list for DSPS and Non-24 just says it so well, often in a rant. I fell for this one by J., who has Non-24-hour sleep-wake syndrome. By permission:

 

It’s so funny to me how many things I keep on finding out might be related to my Circadian Rhythm Sleep Disorder that I always thought were just “quirks” of mine. First of all the odd sleeping, of course, but also the fact that I am always cold when no one else is… I always thought that I just had “temperature regulation” problems, for no specific reason. And it wasn’t a big deal, but EVERYONE always commented on it. Once in my very FIRST meeting with a new psychiatrist (bounced from neurology, of course) he mentioned it and then perhaps took it as a sign of my psychosis. Right, bro, right. How about I HAVE A CIRCADIAN RHYTHM DISORDER. Gahhhh.I have also been accused of wearing long sleeves in the summer just to hide track marks (yep, I’m a lazy, psychotic heroin addict now).

I am so sick of people viewing me as crazy and lazy, which, seriously, has been the case since this whole n24 thing hit when I was a teenager.

But now at least I KNOW and can EXPLAIN how maybe I’m not lazy after all. And, no, not a junkie either! In fact the ones feeding me the drugs… who was that?! DOCTORS. My sleep will never be normal. Trying to force it with daily drugs, morning and night, was wrong. Maybe my neurology in general will never be normal. My perception may never be normal.

I have finally started to accept it because that is the right thing to do. The doctors need to get on board with this if they want to “do no harm”.

And thanks for reading this far, if anyone did.
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xxxviii. Eveningness vs. DSPS

10 November 2007 at 07:00 | In Circadian rhythm | 1 Comment
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“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.
 
 It can be interesting to compare normal evening types with what we know about people with Delayed Sleep-Phase Syndrome.
 
Normal, healthy sleepers can be morning types (up to 25%), intermediate types (50% or more) or evening types (up to 25%). Any of them can be classified as long sleepers or short sleepers in normal distribution. They have normal “sleep architecture”, as do most people with DSPS.
 
Normal night owls who are good sleepers:
 

- 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.

CRSD [circadian rhythm sleep disorders] patients differ from night or morning type people … in the rigidity of their maladjusted biological clock. While “owls” and “larks” prefer morning or evening, they are flexible and can adjust to the demands of the environmental clock. CRSD patients, on the other hand, appear to be unable to change their clock by means of motivation or education,” according to Dagan, 2002 (PDF, page 3).
 
Or, as Wikipedia puts it: Attempting to force oneself through 9 – 5 life with DSPS has been compared to constantly living with 6 hours of jet lag.”
 
Uchiyama et al, 1999, found that people with DSPS do not evidence normal recovery sleep after sleep deprivation. They conclude that “[t]his suggests that DSPS may involve problems related to the homeostatic regulation of sleep after sleep deprivation.
 
Some of the characteristics of normal evening types may or may not also be characteristic of people with DSPS. If these points have been reported in the literature about DSPS, I haven’t seen them:
 

- 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.

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Next:  xxxix. Guest Blogger

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