Module 13: Clock outputs: Circadian Organization of sleep and waking in humans

ultradian process

variations of sleep stages within sleep

• in humans, a 90 min REMS-NREM cycle

circadian process

variations in sleep propensity and sleep stages with time of day

• the time of day (more accurately, circadian phase)

homeostatic process

variations in sleep propensity and sleep stages attributed to duration of prior wake time

• how long have you been awake?

what are the states within the ultradian process and what are its characteristics?

• rapid-eye movement

• non rapid-eye movement

  • occurs first and it is initiated at sleep onset

what does the circadian process control?

• the timing of sleep (onset and the end)

• amount of REMS within each ultradian cycle

  • increases every cycle, is at maximal when body temperature reaches nadir approx. 2h before the end of sleep

what does the homeostatic process control?

• responsible for increase in sleepiness the longer we stay awake

• changes in sleep that occur following prolonged waking

what are some changes that occur during your sleep if you stay up longer?

• greater motivation to sleep

• onset occurs more quickly

• fewer awakening during sleep

• slow wave sleep (stage N3) is greatly increased

• sleep duration may be increases

what are the differences in domination between homeostatic process and circadian process?

• timing and duration of sleep bouts are dominated by circadian process

• duration of particular sleep stages are dominated by homeostatic process

in the wake extension study, what did they find when individuals started to sleep later at night?

• later you sleep, the less you sleep (up to a point)

at what time caused the least amount of sleep for those in the wake extension study?

slept the least when bedtime was delayed until 6am or 10am

at what time did the wake extension study show an increase in the amount of sleep after deprivation?

• 2pm

• 6pm

• and some 10pm

what did the temporal isolation studies (internal synchrony) find when it comes to wake and sleep cycles?

• when people choose on their own volition to wake and sleep, with no knowledge of time of day and no outside influence, the longer you choose to stay awake the shorter your next episode

homeostasis of tau

if you spend more time awake in one circadian cycle, then there is less time for that sleep in that cycle