Lecture 12 Light regulation of sleep states Flashcards
Kleitman experiment
1930s
believed we only had a 24 hour clock as we adapt to the environment, experimented with longer 28hour cycles, believed efficiency would increase.
he was wrong
mammoth caves, no light, constant temp, 9 hour work/rest/sleep.
he couldn’t adapt but his assistant could.
Aschoff experiment
WWI bunker experiments.
let people control the environment themselves, ie lights.
people were ~ 24 hours.
some people were much longer however, up to 50 hours.
what is the opponent process model?
current leading theory.
2 opposing processes are occuring:
Homeostasis - the longer you are awake, the more tired you get, you sleep to relieve tiredness.
Circadian Clock - provides drive for wakefullness. increases during the day and decreases in the evening, SCN controls.
An SCN-dependent process actively facilitates the initiation and maintenance
of wakefulness, opposing a homeostatic sleep tendency that builds up while we
are awake.
what happens over 72 hour sleep deprivation?
overall fatigue reported increases, but still maintains a rhythm, 1st night more tired than 3rd day. higher night, less in day.
what happens in squirrel monkey SCN lesion?
What can this tell us about the opposite process model?
rather than long periods of wakefullness/sleep, constant napping and waking up occurs - arrythmic.
therefore without the circadian drive for wakefulness the homeostat maintains a low sleep load, it cannot build up.
Forced desynchrony?
Dijk and Czeisler (1994). looked at homeostatic effect.
strict 24hr cycle for first 5 days, 8hr dark/enforced sleep, prhibited rest.
this was to reset participants clock as a control.
Followed by 40 hours of dim light to check circadian phase, can sleep whenever they want.
then put on 28hr day, ~9.5hr darkness/enforced sleep, rest dim/prohibited.
measured body temperature to measure circadian phase, decreases when asleep.
usually body temp free runs ~24.5hr, so it matches up to the 28hr cycle sometimes. sometimes forced to sleep when clock wants you too, often not.
the sleep debt is therefore kept at a constant level.
polysomnography used to measure sleep, can measure wakefulness when scheduled to be asleep.
when forced to sleep and clock lines up, they stay asleep. otherwise often had periods of wakefulness.
at circadian phase 0, body temp low 36.5, <5 mins to sleep very quick.
at 37 phase 180, up to 20 minutes.
regardless of how long been asleep, chance of being awake <5% circ phase 0, 25-30% 180.
ignore phase, chance of being awake into schedulated sleep:
don’t instantly fall asleep, so modest chance awake still.
couple of hours in everyone asleep, then everyone asleep, percentage increases as night progresses as sleep bout decreases, increased chance of awaking.
look at circadian + homeostasis interaction to determine duration of sleep.
at c phase 0 doesn’t matter how long been asleep, all stay asleep.
at +/- 180 takes some time to fall asleep, and if been asleep >6hr increased chance of waking.
therefore consolidated 8hr sleep is only possible if go to bed between 10-11 to wake up for 8. don’t cross circadian drive for wakefulness.
why is sleep rhythm sometimes over 24hours?
in experiments sleep debt can be slow to build since little expenditure of energy.
sleep load may not be high enough to sleep at the end of the first day, the following morning the circadian drive for wakefulness occurs, so it isn’t until the second night they can sleep.
dementia and sleep disturbance?
show fragmented rhythm often.
increases in early night, have short inactive periods.
hard to care for, bad for cognition so exaccerbates problems.
often a decreased amount of natural light in homes so not activating that SCN baby.
If exposed to enhanced lighting in the house ~1200 lux over 400lux, rhythms become much more corrected.
night shift work and sleep?
subjective night exposed to at work is far dimmer than natural sunlight. ??
but also see natural sunlight on way to/from work.
their clocks often still sync to daytime, so go home to sleep in the daytime but drive for wakefulness increases before whole sleep debt can be paid.
then the following night the sleep load increases and drive for wakefulness decreases, have to go work.
night shift workers at power plant?
3-4am worst time.
questionnaire.
all fall asleep 1/week, often more.
1/3 admitted a serious error was caused/nearly caused from falling asleep once/year.
chernobyl/three mile island occured due to basic errors, 3-4am.
could make workplace light resemble daylight better.
Munich chronotype questionnaire?
measures sleep timing and duration on free/work days. huge dataset >150,000 in 2013.
work schedules cause sleep deprivation, highest in young adults, between 1-2hr difference between work/free days.
stabilises during retirement.
midpoint of sleep very close between <21, 21-30, >30 for work days.
for free days distribution varies more, <21 much later, >30 much earlier.
the midsleep point on free days can be seen the chronotype. good indicator of internal clock.
chronotype later for 20-30s, males also later than females.
3-4 average chronotype.
social jet lag and sleep deprivation
less sleep than required as clock later than work hours.
leads to less sleep on work days and catching up on free days.
location and chronotype?
germany questionnaire.
in coutnryside east later chronotype than west, sun rises in east.
still occurs in town cities but not as prominant.
the clock dictates when you sleep and homeostasis is how much.
wrong it’s an interaction between the two.
slow wave sleep in rats with SCN lesion.
still show sleep cycle in the absence of SCN, reduced amplitude, but driven by light.
EEG
