09. Sleep and circadian rhythms - Part 1 Flashcards
What is sleep?
Sleep is a natural, periodic state that involves reduced responses to environmental stimuli and decreased mobility
What species is sleep observed in?
All of them (even unicellular organisms)
What are the two drives of sleep?
Homeostatic
Circadian
What is sleep NOT?
- Coma (extended period of unconsciousness)
- Vegetative state
- Brain death (no sign of brain activity and no response to stimuli)
Two-process model of sleep (Borbély)
Concerns Homeostasis (S) & circadian rhythm (C)
Model is the interaction between Process S and Process C
What is the ‘gold standard’ of sleep research?
Polysomnography (Hans Berger, 1929)
How does Polysomnography work?
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
What does EEG stand for?
electroencephalogram
What does EOG stand for?
electrooculogram
What does EMG stand for?
electromyogram
What brain activity is observed during wakefulness?
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
Brain activity during sleep
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.
REM Sleep
- 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
Stages of sleep
We cycle through stages 1, 2, 3 (NREM) and REM stage
Dreams: experiments
If awakened from REM, participants report vivid dreams (Dement and Kleitman, 1957)
Dreams: Freud and Jung
- 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
J. Allan Hobson (2004) - hypothesis of dreams
- 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)
Dreams as a source of solutions
- They allow incubation of problems, and we come up with solutions
- E.g. Loewi’s experiment on chemical transmission (he dreamed it)
The Neural Basis of Sleep
What substances induce sleep?
- Adenosine
- Morphine
What is adenosine?
- It naturally accumulates during the day, after prolonged wakefulness and promotes sleep
- Caffeine antagonizes the effects of adenosine and decreases sleepiness
Encephalitis and sleep (Constantine von Economo)
- 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))
What is the vIPOA?
- 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
