Lecture seven - Intro to Sleep

Question 1

Do we definitively know why we sleep?

Answer 1

No. Some ideas, but not completely understood.

Question 2

Are we fully paralysed when we sleep?

Answer 2

No. Reduced muscle tone, but not complete paralysis.

Question 3

What are behavioural indicators of sleep?

Answer 3

-Humans - laying down.
-Cats and dogs - curled up.
-(Postural behaviours).
-Generally pretty inactive.
-Reduced-responsiveness.
-Rapidly reversible - one of the ways sleep is different to a coma.

Question 4

What are some ways sleep is measured?

Answer 4

EEG - electrocardiogram - brain activity, such as brain waves.
EOG -electrooculogram - eye movements.
EMG - electromyogram - muscle tone (generally placed under the chin).

Usually all three are used at once to measure states of sleep.

Question 5

When reading EOG traces, what is one way you can tell that someone is drifting off into sleep? (Stage 1 sleep).

Answer 5

When people drift off into sleep their eyes tend to slowly roll back in the eye socket. This movement is picked up on the EOG and is one way researchers can tell when someone is drifting off into sleep.

Question 6

What are the two distinct features of stage 2 of sleep?

Answer 6

Individual K-complexes and sleep spindles seen in EEG trace.

Question 7

What are distinct features of stage 3/stage 4 sleep?

Answer 7

Multiple K-complexes in a row called “delta activity”.
If a 30-sec epoch/EEG trace has 1/5 or 20% of the trace as this delta activity then this is considered stage 3 sleep.

Question 8

What stage of sleep do sleep spindles typically occur?

Answer 8

Stage 2 and 3.

Question 9

What is the difference between k-complexes and sleep spindles?

Answer 9

K-complexes are high amplitude, low frequency.
Spindles are lower amplitude, higher frequency.

Question 10

When people are woken from stage 1 or 2 sleep, might they be unaware they were asleep?

Answer 10

Yes.
In stage 3 sleep, however, people will be aware that they have been asleep.

Question 11

What are some characteristics of non-REM sleep (stage 1-3)?

Answer 11

Theta and delta waves on EEG.
Light, even respiration and regular heart rate.
Muscle tone.
Cognitive acitivity.
No dreams.

Question 12

What are key characteristics of REM sleep?

Answer 12

Rapid eye movements are picked up on EOG.
Some suggest that this occurs because we are looking at what we are seeing in our dreams.

Muscle activity is virtually ‘paralysed’ (limbs) as picked up by EMG. It is thought that this occurs to stop us reacting to our dreams in physical way.

“Saw-tooth” waves in EEG.

Respiration and blood pressure vary.

Vivid emotional dreams.

Sexual arousal.

Easy to wake a person during REM sleep.

Question 13

Does REM sleep tend to occur toward the end of a period of sleep?

Answer 13

Yes.

Question 14

What is the average length of a dream?

Answer 14

3 minutes.

Question 15

What is the average length of a sleep cycle, where an individual goes through all 4 stages of sleep as well as REM sleep?

Answer 15

90 minutes.

Question 16

Is it true that across a night of sleep, the frequency of slow-wave (stage 3/4) sleep is higher at the beginning of the night and there is less REM sleep, compared to later on in the night of sleep, where there is a higher frequency of REM sleep and lower frequency of slow-wave sleep?

Answer 16

Yes.

It’s harder to wake someone earlier in the night than later in sleep.

Question 17

Does the amount of time spent in REM and NREM sleep decrease across the lifespan?

Answer 17

Yes.

Question 18

How is sleep controlled and who originally proposed this mechanism of control?

Answer 18

Alex Borbley proposed that there are two processes that control sleep.

Homeostatic factor (process S).
Circadian factor (Process C).

Question 19

What do the two processes in Borbley’s model of sleep control do?

Answer 19

Process S - the homeostatic factor - refers to the regulatory processes and mechanisms the body has tp ensure that we get a certain amount of sleep. If we do not sleep enough ,we have to make up for it another night. If we do not sleep enough, there will be negative consequences.

Process C - circadian process - refers to internally generated processes that regulate sleep and wakefulness based on a 24-hour cycle.
Circadian rhythms were first identified by someone studying plants that open their leaves during the day and close them at night even when they are not exposed to any light.

Question 20

Why is it difficult to go to sleep a few hours earlier than your regular bed time?

Answer 20

We have a circadian push for wakefulness the few hours before our normal bed time. This occurs to stave off the sleepiness that would otherwise be quite inhibitory.

Question 21

Does the circadian alterness cycle continue it’s normal trajectory even when we do not get enough sleep the night before?

Answer 21

Yes.
An example of this is if you pull an all-nighter, the next day you will have an increase in wakefullness (compared to levels of tiredness across the night). It won’t feel the same as if you had had a good night’s sleep, though, as your homeostatic sleep process will be signalling higher levels of tiredness.