week 11: Sleep

Question 1

What does circannual cycles refer to?

Answer 1

Refer to yearly cycles.

Question 2

What does circadian cycles refer to?

Answer 2

Refer to daily cycles.

Question 3

The circadian cycles of flying squirrels is _____.

Answer 3

Less than 24 hours. They will sleep earlier and earlier each day if put in a dark room in the absence of external cues.

Question 4

How does circadian cycles in human change with age?

Answer 4

Young children are often morning people. Adolescents are often night people. As we get older, we become more and more morning people, but this depends on genetics.

Question 5

Many blind people report sleeping problems. Why?

Answer 5

They cannot adjust their circadian cycles using light, which is quite a powerful cue.

Question 6

Why aren’t we born with a perfectly synchronised internal clock rather than having to adjust a slightly-off internal clock everyday?

Answer 6

Because the length of day depends on seasons and geographical locations.

Question 7

Which part of the brain is involved in our body rhythms? Where is it located?

Answer 7

Suprachiasmatic nucleus located in the hypothalamus, just above the optic chiasm.

Question 8

Describe the sequence of neural mechanisms for body rhythms.

Answer 8

Photoreceptive RGCs → Suprachiasmatic Nucleus (hypothalamus) → Pineal Gland

Question 9

What is so unique about the RGCs involved in body rhythms?

Answer 9

These small population RGCs are more sensitive to short-wavelength (blue) light. These RGCs are photoreceptive (ie. they have photopigments). These are the only ganglion cells in the retina that have photopigments.

Question 10

The SCN receives projections from special retinal ganglion cells: photoreceptive ganglion cells, and not the other RGCs. Why do you think this is the case?

Answer 10

Because the SCN only cares about ABSOLUTE levels of luminosity, so it does not need complex retinal processing. This saves time and immediately senses light from this specific ganglion cell.

Question 11

Which 2 proteins are generated in the SCN? What is it created by

Answer 11

PER and TIM. Created by mRNA.

Question 12

What happens if you take one of these cells (PER & TIM) and put in a petri dish, outside of brain?

Answer 12

Cell activity will go up and down according to its circadian cycle

Question 13

What is the transcription factor? How is this a negative feedback loop?

Answer 13

proteins PER & TIM inhibit creation of themselves by inhibiting the genes that produce mRNA which produce them. When there are high levels of these proteins, it signals to nucleus of the genes to stop producing mRNA. When levels of proteins go down, inhibition decreases, cells produces proteins again.

Question 14

What are the functions of the PER and TIM protein?

Answer 14

They promote sleep. Increase in protein –> increase in drive to sleep.

Question 15

What does light do to the TIM protein?

Answer 15

Light activates an enzyme that breaks down the TIM protein, thus adjusting the cycle.
Breaks down TIM protein → problems falling asleep
Mutations in these genes (PER or TIM) will create sleep problems

Question 16

What is melatonin? Describe the pattern of melatonin levels throughout the night.

Answer 16

A hormone produced in the pineal gland. When pineal gland receives activation from the SCN, it releases melatonin into its bloodstream. Melatonin production/levels increases at night, reaches its peak at around 4am (deepest sleep) and then it drops in the morning so you can wake up.

Question 17

What is sleep?

Answer 17

A state that the brain actively produces.

Characterised by decreased response to stimuli

Question 18

What is comma?

Answer 18

Extended period of unconsciousness caused by head trauma, stroke, or disease.
Characterised by low brain activity, low response to stimuli, no purposeful movements.

Question 19

What is vegetative state?

Answer 19

Alternates between period of sleep and low arousal. Sleep processes are intact.
Characterised by low response to stimuli and no purposeful movements, but got brain activity.

Question 20

What is minimally conscious state?

Answer 20

Like vegetative state, but with occasional brief periods of purposeful actions and limited amount of speech comprehension

Question 21

What is brain death?

Answer 21

no brain activity

Question 22

What is fourier transform?

Answer 22

a method that translates this very complex signal into more digestible waves. Decomposes these signals into sinusoidal waves with specific frequency and amplitude.

Question 23

How do you measure sleep?

Answer 23

Using a combination of EEG signals and eye movement signals (measure eye muscle signal).

Question 24

During deep sleep, which waves are most dominant?

Answer 24

Delta wave

Question 25

What happens during the relaxed wakefulness stage?

Answer 25

High alpha waves; high power in alpha band
Cortex receives much high-frequency input. Most neurons are out of phase with one another, the EEG is full of short, rapid, choppy waves.

Question 26

What happens during stage 1 sleep?

Answer 26

Brief moment before you fall asleep
Irregular low-voltage waves
Activity starts synchronising a bit more

Question 27

Which 2 features characterise stage 2 sleep? Give a brief description of them.

Answer 27

K-complex - A sharp wave associated with temporary inhibition of neuronal firing
Sleep spindle - a burst of high frequency waves. Results from oscillating interactions between cells in thalamus and cortex

Question 28

Describe stage 3 & 4 sleep.

Answer 28

Deep sleep - slow, high magnitude; low frequency waves. Stages 3 and 4 differ only in the prevalence of these slow waves, and some authorities combine them as a single stage, slow-wave sleep (SWS). Slow waves indicate that neuronal activity is highly synchronized. Processing less information, less variability in response. (about 5-10% of cells are synchronised)

Question 29

In what ways is REM sleep similar to light sleep?

Answer 29

Low voltage waves just like in stage 1 sleep; increased neuronal activity

Question 30

In what ways is REM sleep similar to deep sleep?

Answer 30

Postural muscles relaxed, body is completely blocked from moving, except for eyes. During REM sleep, cells in the pons and medulla send messages to inhibit the spinal neurons, which control the body’s large muscles. During REM sleep, body is quite relaxed because of pons and medulla.

Question 31

How long is 1 sleep cycle?

Answer 31

~90mins

awake -> 1 -> 2 -> 3 -> 4 -> 3 -> 2 -> REM

Question 32

When in the night does deep sleep dominate and when does REM dominate?

Answer 32

Deep sleep dominates in the early stages of sleep (until 2am)
REM sleep dominates towards the morning.
The longer you sleep, the more you will have big chunks of REM sleep at the end of the night.

Question 33

Which 2 substances does hypothalamus produce that keeps us awake?

Answer 33

Histamine and orexin

Narcolepsy – a neurodegenerative condition that kills cells that produce orexin

Question 34

What substance does reticular formation produce that projects to the basal forebrain?

Answer 34

Acetylcholine.

Maintains arousal and is released when you are paying attention

Question 35

What substance does nuclei in the basal forebrain release to fall asleep?

Answer 35

GABA (inhibitory neurotransmitter)

Question 36

What is the local phenomenon?

Answer 36

Refers to the phenomenon that parts of brain can take turns to sleep. (eg. dolphins left and right hemisphere take turns to sleep) In humans, parts of the brain can also fall asleep. Electrodes measure local field potentials using EEG.

Question 37

How does the local phenomenon explain why our performance on certain memory tasks?

Answer 37

When we are tired, some parts of our brain go to sleep.

Question 38

What happens if I prevent you from entering into Stage 3 or Stage 4 of non-REM sleep? (ie. deep sleep)

Answer 38

You wake up, after a full night of sleep, feeling tired. As if you didn’t sleep well.

Question 39

What happens if I prevent you from entering REM sleep?

Answer 39

You wake up, after a full night of sleep, feeling rested. But if this is repeated over many nights, you may start hallucination during your waking time.

Question 40

What is insomnia and what are the possible reasons for it?

Answer 40

Inadequate sleep. Possibly due to:

• loud noises
• too hot/cold
• overuse of sleep pills
• stress
• drugs

Question 41

What is sleep apnea?

Answer 41

A sleep disorder characterized by inability to breathe while sleeping for a prolonged period of time.

Question 42

What are the long term consequences of sleep apnea?

Answer 42

Sleepiness during the day
Impaired attention
Higher propensity for depression
Heart problems (sometimes)

Question 43

What are the possible causes of sleep apnea?

Answer 43

Genetics, hormones, old age, obesity, deterioration of brain mechanisms that control breathing

Question 44

What are the possible treatment methods for sleep apnea?

Answer 44

Wear mask that forces oxygens into their airways

Question 45

What is narcolepsy?

Answer 45

A neurological disorder due to loss of neurons that produce orexin. Orexin-producing neurons in the hypothalamus die. Orexin is a hormone that keeps us awake! No good treatments available yet, same for many neurodegenerative diseases.

Question 46

What are the main symptoms of narcolepsy?

Answer 46

1) Attacks of sleepiness during the day
2) Occasional cataplexy (attack of muscle weakness when person is still awake)
3) Sleep paralysis (inability to move while falling asleep or waking up)
4) hypnagogic hallucinations (dreamlike experiences when awake)

Question 47

What is sleepwalking?

Answer 47

A phenomena where parts of the brain are awake while others are asleep. Happens more often in kids. Causes not well understood. Most common during dreamless slow-wave sleep.

Question 48

What are the 2 possible reasons from the evolutionary perspective as to why we sleep?

Answer 48

1) Sleep to save energy

2) Sleep to consolidate memories.

Question 49

What are evidences to show that we sleep to save energy?

Answer 49

Animals are awake when they need to be more efficient, and sleep to conserve energy. (eg. herbivores need to spend a lot of time eating grass so they only sleep for 2-3 hours each day, bats on the other hand sleep for 20h and are awake for 4h only to eat)

Question 50

What are the 3 possible mechanisms of sleep enhancing memory consolidation?

Answer 50

1) Memory replay
2) Synaptic downscaling
3) Sleep spindles

Question 51

How does memory replay in sleep enhance memory consolidation?

Answer 51

Measure cells in hippocampus during learning.
When learning, there is an activation sequence
Same activation sequence appears during sleep
Suggests animal is rehearsing the learning experience during sleep.
Found both forward and backward replay.
Rebuttal - such sequences also appear during waking period so this is not meaningful

Question 52

How does synaptic downscaling explain memory consolidation during sleep?

Answer 52

At night, synaptic downscaling takes place. Recall we need a balance between strengthening and weakening of synapses. Average increase is equal to decrease each day. Recent evidence showed that synapse size decreased after sleep; size decrease primarily in weak synapses. Best theory for now.

Question 53

How can sleep spindles possible explain memory consolidation during sleep?

Answer 53

Sleep spindles are high frequency fluctuations during stage 2 sleep. After a learning experience, there is an increased likelihood of sleep spindles. But hypothesis still not well developed.

Question 54

What happens in the long term if you get inadequate sleep?

Answer 54

1) more vulnerable to mental illness
2) less attentional capacity
3) poor memory consolidation

Question 55

What happens to nREM and REM sleep with age?

Answer 55

nREM sleep remains quite stable over time

REM sleep declines significantly with age

Question 56

What are the 2 possible theories as to why we have REM sleep?

Answer 56

1) motor memory consolidation
- motor memory is a form of implicit learning
- but people taking antidepressants which decreases REM sleep have no problems with motor memory so hypothesis likely false
2) shaking the eyeballs
Our corneas receive oxygen from the air and a liquid that surrounds it. Possible that REM sleep’s function is to move the eyes to shake the liquid and permit oxygen to reach the cornea. BUT people taking antidepressants (which significantly decrease REM sleep) have no damage to their corneas.