5 - Homeostatic and Circadian Mechanisms

Question 1

What are the two obvious things that happen when you prevent someone from sleeping? What do these two things give evidence for?

Answer 1

• They become sleepy and tend to fall asleep rapidly and in unusual circumstances
• Sleep more than you usually would (rebound increase)

Physiological homeostatic stasis regulation. The tendency for the organism to maintain stability despite extreme changes in the environment and situation. Evolution has instilled in our genetics, optimal settings for homeostasis to maintain.

Question 2

What is the homeostatic regulator model?

Regulator, set point, error, big error, consequence.

Answer 2

Regulator: Measures the state of the system

Set point: The ideal state of the system

Error: Deviation from the set point

Big error: System sends out a signal (ie. drive) that activates behaviour relevant to that particular error

Consequence (feedback): Signal generated as consequence of the organism’s behaviour/output that signal to regulator to go back to the set point

Question 3

Why should a settling point model be used over the homeostatic regulatory model for physiological regulation of things like sleep?

Answer 3

Setting point model Example: Systems involved in burning up calories and systems involved in acquiring calories (body weight)

No such thing as a body weight regulator, the setting point is where the system comes into balance (no wisdom of the body/set point).

However, the sleep system behaves as if there were a set point.

Question 4

Describe the experiment from 1896 where Patrick and Gilbert kept themselves and another participant awake for 90 hours. (4)

Answer 4

They only recovered 16-36% of sleep on the first recover night (increase in the amount of sleep shown, but not 1:1 with the amount of sleep that they lost).

They suspected people of having microsleeps, these could help explain the missing sleep. Brief lapses in attention during memory/cognitive tasks.

They also found that recovery sleep was deeper than normal sleep, due to the fact that it was hard to wake them out of it. They proposed that this could mean that they were sleeping more efficiently, explaining for the missing sleep.

Found quiet wakefulness recovered a little bit of cognitive function.

Question 5

What are some faults in Patrick and Gilbert’s 90 hr sleep deprivation experiment?

Answer 5

• No EEG (wasn’t invented yet)

- Didn’t observe second recover night

Question 6

Who is Randy Gardner?

Answer 6

17 yo student in California that wanted to set a world record for staying awake. Kept himself awake for 11 days in 1966.

US navy neurologist Ross and William C Dement studied him.

Slept for 15 hours during his first recovery night (not much different from Patrick and Gilbert). He then slept for less time each night until he was sleeping just under 7 hours a night.

Question 7

What EEG change is observed in recovery sleep after sleep deprivation? What change in power spectra is observed?

Answer 7

• Increased slow wave sleep, especially early in the night
• Doing a Fourier analysis on an entire night of sleep shows a large increase in slow wave activity (not slow wave sleep).
• When sleep deprived, you sleep more intensely/deeply when you are allowed to sleep again, based on the Fourier analysis.

Question 8

What is slow wave activity?

Answer 8

Can be observed in any state

Proportion of power spectrum from Fourier analysis from .5 to 4.5 Hz

Question 9

Slow wave activity is a marker for _____?

Answer 9

Sleep need

The more sleep you need, the more slow wave activity is observed.

Question 10

How does slow wave activity appear to be homeostatically regulated? What is argument for this?

Answer 10

Increases linearly with amount of sleep loss

Having sleep after having a nap shows an amount of slow wave activity that is minus the amount of slow wave activity gotten during the nap

Question 11

Who is Borbély? Describe what he proposed and how he tested it.

Answer 11

Described process S

The need for slow wave activity building during the day and dissipating during sleep as an internal process.

Process S (sleep stuff) builds in brain as awake and dissipates during slow wave activity (doesn’t need to be a chemical, can be a process)

• Gave subjects diazepine that restricted slow wave activity. People still get restive sleep after this.
• Slow waves are not necessarily the mechanism that reverses the effects of waking, they are a convenient marker that Fourier analysis can observe

Question 12

What is chronic sleep restriction?

Answer 12

Getting less sleep than you physiologically need.

Most common type of sleep restriction.

Acute sleep restriction (every now and then) is less common.

Question 13

During chronic sleep restriction in rats, how does slow wave activity during a 24 hour period change? What happens during recovery sleep?

Answer 13

Stays the same during 20 hours of activity

Decreases during 4 hours of sleep

Net loss in slow wave sleep and delta power during the 5 days of sleep restriction. This isn’t recovered during recovery sleep (allostasis).

Question 14

What is allostasis?

Answer 14

Homeostasis fails and you physiologically adjust primarily through the activation through the HPA axis and other systems that try to make up for the fact that you have lost sleep (or starvation, etc.).

Other pathways try to make up for problems in one system.

The caveat, is that this causes physiological damage by using cortisol stress system.

Question 15

Why is allostasis only good for acute stresses and not long term stresses?

Answer 15

Allostasis causes physiological damage through stress responses

Question 16

If you sleep deprived rats, what happens to the nervous system?

Answer 16

It becomes hyper excitable via the stress pathways induced by allostasis

Question 17

What is the disk over water method?

Answer 17

• Two rats hooked up to polygraph and separated by barrier
• Disk attached to motor attached to computer
• Under disk is shallow pan of water
• Control animal can sleep whenever they want to
• When experimental animal falls asleep, EEG recorder activates motor which drives rotation of disk that rats are standing on. They will be dumped in the water if rats don’t get up and walked.
• Produces very long term sleep deprivation

Question 18

What happens when you are deprived of sleep and don’t have an opportunity to immediately recover?

Answer 18

• Allostatic response to make up for sleep that the animal cannot make up
• More delta, slow wave activity during wakefulness (maybe allostatic or homeostatic)

Question 19

Why are sleep deprivation studies never complete sleep deprivation studies?

Answer 19

There’s always a delay between procedures keeping animals awake. Can even be msec in EEG modulated waking.

Microsleeps confound the study and may reduce effect of sleep deprivation. May also bias slow waves during wakefulness.

Question 20

What do sleep deprivation studies show about producing frequencies?

Answer 20

The nervous system needs to produce slow waves. If this is prevented by sleep, it starts to happen during wakefulness.

Question 21

How is REM sleep modulated during recovery sleep after sleep deprivation? How do studies depriving rats of just REM or REM and NREM show?

Answer 21

It’s not the first thing you do, you get a lot of NREM first. But you do eventually get more REM after sleep deprivation than baseline.

If you deprive of REM sleep for a while, they’ll show a rebound in REM.

A deprivation in all sleep stages shows rebound in both NREM and REM sleep.

Question 22

What is HS1 in rats?

Answer 22

Equivalent to stage 2 sleep

Question 23

What is HS2 in rats?

Answer 23

Equivalent to stage 3 sleep

Question 24

When all sleep stages are deptived in rats for a few hours, what type of rebound is seen for HS1, HS2, NREM delta and REM in rats?

Answer 24

HS1: Negative rebound (get less)
HS2: Positive rebound
NREM delta: Positive rebound
REM: Positive rebound

Question 25

When all sleep stages are deptived in rats for ‘4 days’ hours, what type of rebound is seen for HS1, HS2, NREM delta and REM in rats? Is this a physiological response?

Answer 25

HS1: Positive rebound
HS2: Huge negative rebound
NREM delta: No big change
REM: Huge positive rebound

Not a physiological response, as it’s not enough sleep deprivation for that (only 24 hrs).

Explanation is that this is extremely effective REM sleep deprivation, due to the fact that they enter REM from nREM. They may have enough time to produce nREM sleep before the sleep deprivation disk starts turning.

Question 26

Why is REM sleep produced according to the hypothesis that being awake produces nREM sleep in rats? Is there evidence for this? What is the alternate hypothesis?

Answer 26

REM sleep a response to being in nREM sleep

nREM sleep is a response to being awake

Evidence? Long nREM episodes should have a long episode of REM. Not supported by data.

Alternate hypothesis is that there is homeostatic regulation for REM sleep.

Question 27

Is there a negative serial correlation between the length of a REM episode and the length of a nREM episode?

Answer 27

No

Not evidence for the opposite.

Question 28

What two controls of REM sleep might co-exist?

Answer 28

?

Question 29

Under the BRAC hypothesis, what type of REM control do you predict?

Answer 29

An internal oscillation of cycles. Evidence does not support this.

Question 30

Is there a positive serial correlation between the length of nREM sleep and the length of REM sleep? Where is a correlation found?

Answer 30

No

There is a link between the length of REM sleep and the length of the proceeding nREM sleep. Ie. a very long period of REM sleep decreases the amount of time for the next nREM sleep and therefore increases the amount of REM after that.

Question 31

What is evidence that a lack of REM doesn’t lead to more REM (simple homeostatic regulation of REM sleep)? When might a need for REM arise?

Answer 31

When people are kept in temporal isolation and get a full night’s sleep (so to speak), and are then asked to sleep some more, they generate a lot of REM sleep.

ie. a lot of REM sleep is generated after a night of REM sleep.

There may be a demand for REM when there’s physiological damage in the cortex from SWS

Question 32

Is there a consequence for extra REM sleep? SWS?

Answer 32

REM: No damage from extra sleep

SWS: May cause damage from extended levels

Question 33

If you have long term REM sleep deprivation, how do you respond? How do rats respond?

Answer 33

Humans: Increase in other types of sleep, then a bit more REM later in sleep

Rats: immediate extra REM sleep

Question 34

What are ultradian and infradian cycles?

Answer 34

Ultradian rhythms are recurrent periods or cycles repeated throughout a 24-hour circadian day. In contrast, infradian rhythms, such as the human menstrual cycle, have periods longer than a day.

Question 35

What is the two process model?

Answer 35

Two processes:

• Homeostasis (process S)
• Circadian clock (process C)

A model to account for how sleep is regulated. Process S and process C affect each other.

Question 36

What does the homeostasis model of the two process model of sleep predict? What type of correlation is this? How is this refuted?

Answer 36

The length of deprivation should be linearly or parabolically related to the strength of the drive.

The drive is not monotonic. If you stay awake all night, you will be most sleepy at some times more than others.

Question 37

Patrick and Gilbert in 1986. What did they observe about sleepiness over time after 3 days of sleep deprivation?

Answer 37

The increase in sleepiness was not monotonic. It was stronger at some times in the day.

Question 38

How does the circadian clock model affect the two process model of sleep?

Answer 38

It increases the drive for sleep at specific times, regardless of the amount of homeostatic need for sleep.

Also known as process C, the circadian system modulates the thresholds for falling asleep and waking that are baseline dictated by homeostasis (process S)

Question 39

The circadian system is an open loop system, What does this mean? What is the homeostatic system?

Answer 39

Open loop: Feedback doesn’t modulate the system

Closed loop: (eg. homeostasis). feedback returns to modulate the system

Question 40

In a time free environment, when do people fall asleep relative to their body temperature?

Answer 40

In the trough of their body temperature (usually around 4 am), this causes shorter sleep than regular as the circadian clock begins to bring you out of sleep.

OR

Just in the beginning of circadian clock sleep phase, cause very long sleep (~10 hr) as they go through the whole phase.

Question 41

What have mathematical models of the two-process model of sleep regulation predicted? Does evidence support this?

Answer 41

• How pressure for sleep builds up homeostatically
• How sleep is discharged

Predicts sleep pressure accurately in humans and small mammals. But not necessarily in other animals.

Question 42

True or false? Duration of the delta power regulated by circadian factors

Answer 42

True for monkeys but not humans.

Slow wave activity and duration of sleep regulated homeostatically in humans. In monkeys, there is circadian regulation of SWS when they are studied in constant in dim light (not how we study humans, so this should be taken with a grain of salt)

This suggests that sleep regulation by circadian rhythms and homeostatic regulation may not be same for all species.

Question 43

If you are awake for five minutes, that creates a little bit of a homeostatic drive to sleep, but not much. Homeostatic drive to sleep increases as you’re awake.

After more than 12 hours awake, will there be a homeostatic drive to sleep in the early evening?

Answer 43

No. Seville calls this the forbidden zone for sleep onset. Probably allows for extended time awake.

The flip side of this, is a zone in the early morning that prevents you from waking up, even when you’ve gotten enough sleep by then.

These are set by the circadian system.

Question 44

Why would you, through evolution, come up with a system (circadian system) that ignores homeostatic need for sleep and makes you sleepy or need to wake up at specific times. Especially at the forbidden zone for sleep, where sleep need has not been met, but you can’t sleep.

Answer 44

Visual system that is actively engaged during environment during the day, but really bad during night.

The circadian system avoids us from wasting energy during a time of day (night) where we are bad at improving our fitness. We can improve our fitness much more efficiently during the day, and so we use energy (be awake) then. This is a genetic temporal program that is in our genomes because it has served our species well in the past.

Question 45

What is the biggest detractor against polyphasic sleep in humans (eg. Überman)?

Answer 45

The circadian system.

We evolved to be awake during the day and asleep at night. There are periods at night where we are kept awake, despite homeostatic need for sleep. And a period just before night where we are kept awake.

This is a genetic temporal program that is in our genomes because it has served our species well in the past.

Question 46

How can genetic temporal programs (eg. the circadian system) fail? What can compensate for this?

Answer 46

When energy deficits arise due to unpredicted disturbances during periods when the system predicts sleep.

Homeostatic regulation can kick in when it detects deficits, which the genome cannot predict.

Question 47

Why has the prevalent (incorrect) theory been that homeostasis rules for all behaviours?

Answer 47

Because traditionally, much research in the area has been in the lab. Animal’s motivation can be manipulated extremely effectively to induce wanted behaviour.

Because you can manipulate these factors in the lab and produce complete control of behaviour, this doesn’t mean that this system works/exists in nature.

Based on evolution, we exist in systems that keep us alive and reproductively active (predictive homeostasis). Your gene’s create a program of activity that keeps you from developing homeostatic deficits.

Homeostatic deficits do not motivate behaviour themselves, rather, programs proactively produce behaviour that would prevent homeostatic behaviour in the first place.

Question 48

What is reactive homeostasis?

Answer 48

Where homeostatic mechanisms cause you to seek relief when in a deficit.

This is rare. Usually animals have genetically programs that proactively prevent deficits from ever arising. And prevent reactive homeostasis.

Question 49

Predict how much food rats would eat after the following periods of food deprivation at the cycle indicated:

14 hours (during light cycle)
25 hours (during dark cycle) 
42 hours (during light cycle)

Why?

Answer 49

14 hours (during light cycle): 27%
25 hours (during dark cycle): 50%
42 hours (during light cycle): 27%

The homeostatic model would predict that after 42 hours you would eat more than 25 hours. However, they eat more after 25 hours IF the 25 hour period occurs in the dark stage (because rats are nocturnal)

The genetic temporal program can override even very strong homeostatic pressure. This is analogous to the set point changing at different times of the day. This is called rheostasis

Question 50

What is rheostasis?

Answer 50

Rheostasis refers to biochemical and physiological processes that, through graduated quantitative regulation, serve the adaptive needs of an organism facing internal or external environmental challenges. Physiological rheostasis operates much in the way an electrician’s rheostat graduates current.

Setting the setpoint depending on differing need of the organism

Question 51

What is a delta wave defined as?

Answer 51

Being between 75 and 140 mV

Question 52

Describe how the results of a study of sleep deprivation in squirrel monkeys contradict the usual finding in human studies that SWS and delta power are homeostatically regulated and largely unaffected by circadian phase.

Answer 52

• In squirrel monkeys, periods of sleep deprivation under constant lighting conditions led to only moderate increases in sleep duration and in delta power during recovery sleep
• These measures were heavily modulated by circadian phase.
• In human studies, circadian phase has little effect on SWS and delta power, which are more strongly regulated by homeostatic mechanisms.
• As a result, the impact of homeostasis on these sleep parameters in monkeys was relatively small compared to that observed in humans (homeostasis more important for humans)