09. Sleep and circadian rhythms - Part 1 (Sleep) Flashcards
1
Q
What is sleep?
A
Sleep is a natural, periodic state that involves reduced responses to environmental stimuli and decreased mobility
2
Q
What species is sleep observed in?
A
All of them (even unicellular organisms)
3
Q
What are the two drives of sleep?
A
Homeostatic
Circadian
4
Q
What is sleep NOT?
A
- Coma (extended period of unconsciousness)
- Vegetative state
- Brain death (no sign of brain activity and no response to stimuli)
5
Q
Two-process model of sleep (Borbély)
A
Concerns Homeostasis (S) & circadian rhythm (C)
Model is the interaction between Process S and Process C
6
Q
What is the ‘gold standard’ of sleep research?
A
Polysomnography (Hans Berger, 1929)
7
Q
How does Polysomnography work?
A
Involves recordings of electrical activity from multiple sources – “poly”-somnography
EEG + EOG + EMG recordings
- EEG = neurons
- EOG = muscles near the eyes (eye movements)
- EMG = muscles of the body
8
Q
What does EEG stand for?
A
electroencephalogram
9
Q
What does EOG stand for?
A
electrooculogram
10
Q
What does EMG stand for?
A
electromyogram
11
Q
What brain activity is observed during wakefulness?
A
Beta waves
- irregular activity (13–30 Hz)
- occur when the brain is processing information
- person is alert and attentive to environment or engaging in cognitive processes
Alpha waves
- more regular activity (8–12 Hz)
- occur when a person is resting & not doing strenuous mental activities
12
Q
Brain activity during sleep
A
Beginning: a state of relaxation, feeling drowsy
- Stage 1: (3.5–7.5 Hz): presence of theta activity - transition between sleep and wakefulness
- Stage 2: Sleep begins: this stage consists of irregular activity & sleep spindles (12-14Hz) (also occur in other stages of sleep) & K complexes (only in stage 2)
- Stage 3: High-amplitude and low-frequency delta activity (less than 3.5 Hz)
- Synchronized, regular waves, reflecting synchrony and coordination in the activity of neurons in underlying brain areas
- There is a slowing down of brain activity as well as other bodily functions, such as heart rate, breathing, temperature, kidney function, etc
- Sometimes referred to as slow-wave sleep (SWS), or deep sleep.
13
Q
REM Sleep
A
- sleep phase characterized by increased brain activity and asynchrony in brain waves accompanied by muscle atonia
- “Rapid Eye Movement” (REM)
coined by Aserinsky and Kleitman - Michel Juvet, 1959: deep sleep, in terms of muscle activity, but light sleep, in terms of brain activity: “Paradoxical sleep”
- Facial twitches, erections, vaginal secretions and dreaming occur during this stage
14
Q
Stages of sleep
A
We cycle through stages 1, 2, 3 (NREM) and REM stage
15
Q
Dreams: experiments
A
If awakened from REM, participants report vivid dreams (Dement and Kleitman, 1957)
16
Q
Dreams: Freud and Jung
A
- Freud thought of dreams as the ‘royal route to the unconscious’ and an opportunity to realize our secret wishes
- Jung viewed dreams as a glimpse into the collective unconscious
17
Q
J. Allan Hobson (2004) - hypothesis of dreams
A
- they are meaningless
- during REM, brainstem is activated, frontal cortex is not activated
- therefore there is no logical meaning or progression in dreams
- we attempt to make sense of them when we wake up (bottom-up)
18
Q
Dreams as a source of solutions
A
- They allow incubation of problems, and we come up with solutions
- E.g. Loewi’s experiment on chemical transmission (he dreamed it)
19
Q
The Neural Basis of Sleep
A
What substances induce sleep?
- Adenosine
- Morphine
20
Q
What is adenosine?
A
- It naturally accumulates during the day, after prolonged wakefulness and promotes sleep
- Caffeine antagonizes the effects of adenosine and decreases sleepiness
21
Q
Encephalitis and sleep (Constantine von Economo)
A
- Patients with encephalitis had sleep issues
- Most had continuous sleepiness (would wake up only to eat and drink) - they had damage in the base of the brain
- Some had insomnia - they had damage in the anterior hypothalamus (ventrolateral preoptic area (VLPOA))
22
Q
What is the VLPOA?
A
- The ventrolateral preoptic area
- It contains inhibitory neurotransmitters (GABA)
- Damage to this area causes insomnia in rats, and they eventually die
- Electrical stimulation of this area causes sleepiness and sleep
23
Q
What is the key brain area for sleep?
A
VLPOA (ventrolateral preoptic area)
24
Q
What is the key brain area for wakefulness?
A
RAS (Reticular activating system)
(AKA reticular formation)
25
What is the RAS?
Wakefulness system
Location: Brain stem
Projects to: forebrain
26
What does the RAS consist of?
A group of nuclei in the brainstem:
- Locus coeruleus (LV – NE/NA)
- Raphe nucleus
- Tuberomammillary nucleus (TMN-Histamine) (produces antihistamines)
- Nucleus basalis of Maynert (NBM-Ach)
27
Who discovered the RAS?
Moruzzi and Mogoun (1949)
They accidentally discovered that stimulating the area in sleeping cats would wake them.
28
What is the flip-flop switch?
- Mutual inhibition between sleep-promoting VLPOA and wakefulness-promoting RAS
- When one is activated, it inhibits the other - a 'flip-flop' in control
29
Who discovered the 'flip-flop switch'?
Cliff Saper, 2001
30
According to the 'flip-flop switch', what happens in the waking state?
- Flip-flop is 'on' (person is switched 'on')
- The wakefulness-promoting brainstem (RAS) and forebrain areas are activated
- They inhibit the sleep-promoting VLPOA
31
According to the 'flip-flop switch', what happens in the sleep state (slow-wave sleep)?
- Flip-flop is 'off' (person is switched 'off')
- VLPOA is activated
- It inhibits wakefulness-promoting brainstem (RAS) and forebrain areas.
32
What molecules increase wakefulness?
Orexin AKA Hypocretin
(a peptide hormone released from lateral hypothalamus)
33
What effect does orexin (hypocretin) have on the body?
- maintains wakefulness
- its malfunction is linked to narcolepsy
34
What does 'sleep is ubiquitous' mean?
Everything sleeps (or has a sleep-like resting state)
35
What does sleep deprivation do to rats?
Causes them to...
- stop grooming
- stop eating
- lose ability to thermoregulate
- lose weight (but eat more)
- eventually, die
(Rechtschaffen et al., 1983)
36
Why do we sleep?
Sleep is...
- Adaptive
- Restorative
- Developmental
- Cognitive
37
How is sleep adaptive?
- The original function of sleep was probably to conserve energy
- Decrease in body temperature of about 1-2 degrees Celsius in mammals
- Decrease in muscle activity
- Increase in sleep time when there is scarcity of food
38
How is sleep restorative?
- Sleep takes place at night, at the end of a busy day and helps us to feel refreshed and energized the next day
- Activity during wakefulness causes accumulation of free radicals (oxidative stress) and potentially toxic waste (such as amyloid beta).
- During sleep, the body removes free radicals and toxic waste
39
How is sleep adaptive?
- it conserves energy (probably original purpose)
- less muscle activity
- decreased body temperature (1-2°C in mammals)
- we sleep more when food is scarce
- decreasing mental activity decreases energy usage (brain normally uses ~20% of energy)
40
How is sleep restorative?
- Activity during wakefulness causes accumulation of free radicals (oxidative stress) and potentially toxic waste (such as amyloid beta).
- During sleep, the body removes free radicals and toxic waste
41
How does sleep promote development?
- during stage sleep, growth hormone (GH) levels are at their highest
- infants sleep more than adults (they need to grow and develop their body & brain)
- REM sleep in adults is 20-25% of sleep, in infants it is 50% of sleep
42
How does sleep promote cognition?
- it enhances learning and memory
- it allows us to incubate a problem & reach solutions
- we go over the day's events, process them and retain them (Wilson and McNaughton, 1994)
- different types of learning are supported by different types of sleep (stage sleep vs REM and declarative vs non-declarative)
43
Are we sleeping enough?
No, especially children and young people
