HUF 2-61 Sleep and consciousness

Question 1

What is sleep?

Answer 1

A state of

• reduced consciousness
• rhythmic, cycles of NREM and REM sleep
• decreased sensory input
• decreased motor activity
• decreased metabolism and energy use
• temperature regulation maintained

Question 2

Comparing sleep with other altered state of consciousness

Answer 2

1. Different from hypnotic and dissociative state (variant of waking state, waking EEG, acting under suggestion, focused attention span)
2. Different from comatose state - unarousable, malfunction of CNS

Question 3

Function of sleep

Answer 3

1. Restoration and repair (rest and detox)
2. Hormonal surge and growth
3. Immunity
4. Offline memory consolidation

• Glymphatics: removal of neurotoxic waste from brain
• 60% ↑ in interstitial space
• ↑ Exchange of CSF with interstitial fluid
• ↑ Removal of neurotoxic waste (e.g. β amyloid)

Question 4

Synaptic homeostasis hypothesis of sleep

Answer 4

• Consolidation as by-product of global synaptic downscaling during sleep
  => Reuse synapses for future encoding
• Slow oscillations showed max amp. at beginning of sleep when overall synaptic strength is high
• Gradual synaptic depotentiation => ↓ amp across SWS (Rest → Reuse)

Question 5

Offline memory consolidation during sleep

Answer 5

• Memory encoded at daytime
  => Replay and reactivation during diff. sleep stages (NREM, REM)
  => Consolidation (synaptic homeostasis, active system reorganisation)
  => Transfer of memory representations to other neuronal networks for long term storage

Question 6

Cycles of NREM and REM sleep

Answer 6

Stage 1:
- θ 4-8Hz (light sleep)

Stage 2:
- Sleep spindles at 12-14Hz; High voltage multiphasic K-complex (light sleep)

Stage 3:
- Slow δ wave at 1-4Hz (deep sleep)

Stage 4 (REM):

• Vivid dreams
• Stage 1 like EEG activities
• Mixed freq. of low amp
• Rapid eye movement
• Loss of muscle atonia

Question 7

EEG

Answer 7

• Scalp EEG: recording of electrical activity of cortical neurons along scalp
• Thousands of neurons excited simultaneously
  => One large surface signal
• Asynchronous activity => Irregular signals

Question 8

NREM sleep vs. REM sleep

Answer 8

NREM

• Eye movement: slow
• Muscle tone: present
• Autonomic activities: ↓
• Dream reports: thought-like process (10-20% of dreams)

REM

• Eye movement: rapid
• Muscle tone: atonia
• Autonomic activities: enhanced or variable
• Dream reports: colorful and emotional (80-90% of dreams)

Question 9

Circadian rhythm

Answer 9

• Control of rhythm: internal clocks and external cues
• Paired suprachiasmatic nuclei (SCN) of hypothalamus
  => Pacemaker function, central master clock
• Genes: CLOCK, PER, CRY
• Feeding schedule, light, activity
• Melatonin, cortisol, core body temp
• Disordered sleep <=> impact on mood, behaviour, metabolism
• Melanopsin in retinal ganglion cell
  => Retinohypothalamic tract
  => SCN
  => Light as important clue in circadian rhythm

Question 10

Light and melatonin suppression

Answer 10

• Melatonin suppression more prominent with light of short wavelength (esp. blue light))
• Blue light: therapeutic tool in circadian rhythm disorders
• Impact of blue light on sleep

Question 11

Circadian and diseases

Answer 11

Sleep disorders

• Delay sleep phase
• Advance sleep phase
• Jet-lag

Physical illnesses
- cancer, metabolic disorder

Mental illnesses
- Affective disorders

Question 12

Sleep / wake NT and modulatiors

Answer 12

Wake:

• NA (antidepressants)
• 5-HT (antidepressants)
• ACh (antidepressants)
• Histamine (antihistamine)
• DA (amphetamine)
• Hypocretin (narcolepsy - hypocretin deficiency)

Sleep

• AD (caffeine)
• GABA (BZD)
• Galanin
• Melatonin (dim light melatonin onset)
• IL-1 (fever)

Question 13

Diff sleep problems

Answer 13

Initiation and maintenance of sleep

• Insomnia, sleep deprivation
• Circadian rhythm sleep disorder
• Narcolepsy

Abnormal state arise from sleep
- Parasomnia (sleepwalking)

• Obstructive sleep apnea syndrome (OSAS)

Question 14

Sleepwalking

Answer 14

• Ambulation during sleep (altered consciousness)
• NREAM slow wave sleep
• Difficult to be aroused during event
• Amnesia about the event
• Interactions with environment / surroundings
• Topographic orientation
• Preserved motor control
• Genetic predisposition: DQB1 gene
• Dissociation of arousals and awareness

Question 15

Sleep disorders

Answer 15

• Comorbid (mental, physical)
• Excessive daytime sleepiness (ED)
  => Impair daytime performance (work, school)
  ↑ Risk of traffic / industrial accidents, sleep related injuries
  ↑ Risk of future mental illnesses and physical morbidities

Question 16

Normal sleep vs. sleepwaling

Answer 16

Sleepwalking

• Activation of ant. cerebellum (vermis) and pos. cingulate cortex (Area 23)
• Highest ↑ of regional cbf (>25%) compared with quiet SWS
• Deactivation of large areas of frontal and parietal associative cortices
• Frontal-parietal associate cortices: EEG delta burst
• Motor and cingulate cortex: fast activity before onset of episode

Normal sleep

• Frontal-parietal associative cortices: deactivated
• Cingulate cortex: deactivated
• Motor cortex: deactivated

Sleepwalking

• Frontal-parietal associative cortices: deactivated (lack of insight and recall)
• Cingulate cortex: ACTIVATED (autonomic and emotional responses)
• Motor cortex: ACTIVATED (motor responses)