Lecture 10 Light regulation of sleep states

Question 1

Kleitman experiment

Answer 1

1930s

believed we only had a 24 hour clock as we adapt to the environment, experimented with longer 28hour cycles, believed (wrongly) efficiency would increase.

mammoth caves, no light, constant temp, 9 hour work/rest/sleep.

he couldn’t adapt but his assistant could.

Question 2

Aschoff experiment

Answer 2

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 (rare but happens).

Question 3

what is the opponent process model?

Answer 3

Diagram!!!

An SCN-dependent process actively
facilitates the initiation and maintenance
of wakefulness, opposing a homeostatic
sleep tendency that builds up while we
are awake.

Question 4

72 hour sleep deprivation

aka ignoring the sleep homeostat

Answer 4

overall fatigue reported increases, but still maintains a rhythm with consistent peaks, still more tired on first night than on third day

Question 5

what happens in squirrel monkey SCN lesion?

What can this tell us about the opponent process model?

Answer 5

constant napping and waking up occurs - arrythmic.

thus without the circadian drive for wakefulness the homeostat maintains a low sleep load (can’t accumulate, immediately dissipates)

Question 6

Forced desynchrony? (protocol)

Answer 6

Strict 24hr cycle for first 5 days, 8hr dark/enforced sleep, prohibited rest
(reset participant clocks)

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.

(look at circadian + homeostasis interaction to determine duration of sleep)

Question 7

why is sleep rhythm sometimes over 24 hours in sleep experiments?

Answer 7

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 might not be until the second night they can sleep.

Question 8

Dementia, sleep disturbance, and the problem with care homes?

Answer 8

show fragmented rhythm, increases daytime napping and nightime sleep disturbances

difficulting of caring for and declined cognitions exacerbates problems.

often a decreased amount of natural light in homes (not activating SCN)

Enhanced lighting in the house ~1200 lux (vs 400lux standard) rhythms become more regular

Question 9

Shift work and sleep (wrt to spectral changes, circadian processes etc)

Answer 9

Often subjective night is darker but still see sun to/from work ++ spectral changes so often clocks still synced to day –> drive for wakefulness increases before whole sleep debt can dissipate

Following night sleep load increases and drive for wakefulness decreases but have to go work.

Question 10

night shift workers at power plant?

Answer 10

3-4am worst time

60% fall asleep 1/week, 25% 4-5 times and 15% 10.

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.

Question 11

Munich chronotype questionnaire?

sleep timing on work vs free days in different age groups

Answer 11

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.

Question 12

social jet lag and sleep deprivation

Answer 12

less sleep than required as clock later than work hours.
leads to less sleep on work days and catching up on free days (but may not always be possible –> chronic sleep deprivation)

Question 13

location and chronotype

Answer 13

In countryside east later chronotype than west, sun rises in east.

Still happens in towns and cities but not as dramatic… countryside experiences least social jet lag

Question 14

Timing and amount of sleep driven by…

Answer 14

…interaction between circadian clock and homeostatic sleep

Question 15

slow wave sleep in rats with SCN lesion.

Answer 15

still show sleep cycle in the absence of SCN, reduced amplitude (still driven by light by mRGC projection to VLPO)

shown by EEG

Question 16

Bright light exposure to humans

permissible equivalent of SCN lesion studies

Answer 16

Sit in dimly lit room and expose to bright light box at different times of the day/night

When exposed sleepiness is reported lower, regardless of time of day or night.

Question 17

Light stimulation of murine sleep in wt mice vs melanopsin KO

Answer 17

(mice EEG/EMG, LD cycle then in early night give a light pulse)

WT and rodless coneless mice muscle activity stops and EEG shows SWS/REM sleep

Melanopsin KO, light does not stimulate sleep

Question 18

where else do melanopsin ganglion cells innervate?

how was this shown?

effect of lesions, etc, and function of this area

Answer 18

(tau::lacZ)

VLPO in hypothalamus;
ventrolateral pre optic area

Lesions disrupt sleep, active during sleep (generates SWS). GABA.
Switches off the ascending reticular activating system during sleep.

Question 19

lights effect on diurnal and nocturnal species?

Answer 19

promotes arousal in diurnal, sleep in nocturnal.

Question 20

rodents light and humans?

Answer 20

melanopsin ganglion cell projects to VLPO in mice, dunno about humans.

Question 21

How were circadian phases decreases measured in the forced desynchrony experiment?

Answer 21

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 thus kept at a constant level.

Question 22

When is uninterrupted sleep seen in forced deynchrony experiment?

Answer 22

When forced to sleep and clock lines up, they stay asleep. otherwise often had periods of wakefulness (polysomnography)

Question 23

Forced desynchrony conclusions

Answer 23

at c phase 0 doesn’t matter how long been asleep, all stay asleep.
at +/- 180 degrees takes some time to fall asleep, and if been asleep >6hr increased chance of waking.

Thus 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.

Question 24

Light activation of VLPO via melanopsin

Answer 24

c-fos expression (early gene sign of activity in neurons) increases at night if light pulse given.–> doesn’t occur in melanopsin KO mice.

Question 25

Sleep midpoint distribution on work vs free days in different age groups

Answer 25

midpoint of sleep very close between <21, 21-30, >30 for work days.

free days distribution varies more, <21 much later, >30 much earlier.

the midsleep point on free days = chronotype

chronotype later for 20-30s, males also later than females.
3-4 average chronotype.