Week 8: Sleep - An EEG during sleep indicates 5 sl...

Week 8: Sleep  

An EEG during sleep indicates 5 sleep stages :  

• Awake  
• Low amplitude   
• Alpha activity (8-12 Hz)   
• Beta activity (13-30 Hz)   
• Stage 1 sleep   
• Theta activity (3.5-8 Hz)  
• If you wake during this period, you are  

not aware that you were asleep  

• Stage 2 sleep   
• Sleep spindle (12-14 Hz): activity in the hippocampus; memory  

formation   

• K-complex (suppression of cortical arousal in  

response to stimuli)  

• Stage 3 sleep   
• Delta activity (<3.5 Hz)  
• Indicates synchronous brain activity (the  

oscillations are more apart and higher in   amplitude)   

• Stage 4 activity   
• Highest amplitude  
• Delta activity   
• REM (paradoxical) sleep (activity similar to that of being awake)    
• Theta activity   
• Beta activity   
• No muscle activity; no acting on dreams   
• Almost always follows a period of slow-wave sleep   

REM sleep characteristics :   

• Rapid eye movements   
• EEG desynchronization   
• Ponto Geniculo Occipital (PGO) waves (just before REM sleep)   
• Activity from the pons to the lateral geniculate nucleus (LGN) of the  

thalamus and finally the primary visual cortex   

• Paralysis of skeletal muscles   
• Increased genital activity (also in small children)  
• Str

ong suppression of external stimuli (except for meaningful   sounds, such as someone calling ur now (brain activity present upon stimuli   although the present is asleep)  

• / 3

• Narrative dreaming   
• No logic continuity in space or time; caused by absent frontal lobe  

activity   

• At waking, immediately alert (mainly because the brain is active during REM  

sleep)  

• Chance of dream recall 75-95%   
• High probability of waking up spontaneously   

Slow-wave sleep characteristics (stages 3-4) :   

• Strong suppression of external stimuli   
• Low probability of waking up spontaneously   
• At waking, drowsy and disoriented   
• Chance of dream recall 20%   
• Fragmentary dreams (unrelated snapshots) with  

strong emotions (i.e., nightmares)    All mammals and birds need to sleep, even if it is not   convenient  

• The hemispheres of the bottlenose dolphin take  

turns in sleeping  

• A special function that has evolved   

Lack of sleep in patients (fatal familial insomnia) or animals   leads to   

• Loss of thermoregulation   
• Increased fat and sugar metabolism   
• Severe weight loss   
• Immune system disruption   
• Death   

However, in some people after voluntary deprivation (>10 days), no physiological   str ess is observed   

• Therefore, physical recovery does not seem to be the main function of sleep   

Sleep deprivation does lead to cognitive problems   (concentration/perception-hallucinations)   

• Sleep is required for recovery of the brain   

If sleep is possible after a period of deprivation there is no complete catch-up on the   amoun t missed out, but sleep is regained for stages 4 and REM   

• Therefore, these stages appear to be the most important to your brain   

The function of slow-wave sleep is primarily restorative  

• Build a sugar supply  
• Glycogen is built up in astrocytes during sleep, and when energy is  

needed, these astrocytes pass on the glycogen to the neurons  

• / 3

• When neurons use up too much glycogen, astrocytes release  

adenosine to signal the neurons to stop using up so much glycogen   

• Therefore, an accumulation of adenosine occurs throughout the  

day   

• Clearing of chemicals accumulated due to brain activity   
• Adenosine (inhibits neural activity when glycogen is low) is cleared  

a way  

• Learning (especially consolidation of declarative memory)   
• Remember events you can talk about  

The function of REM sleep :   

• Alertness (vigilance)   
• Brain development   
• Reduction in the proportion of REM sleep  

with age   

• Learning (in particular non-declarative)   
• E.g., hold a picture in front of a mirror and  

learn to draw it correctly   

Physiological mechanisms of sleep:   

- Possibility 1 (waking chemical): production during  

sleep of a chemical that keeps you awake    -

Possibility 2 (sleep chemical (i.e., adenosine):  

production during wakefulness of a chemical that   makes you sleep   

• Adenosine accumulates in the brain during waking  

(inhibits cells when energy is low)   Similar to sleep, there are also different levels of alertness during  

wakefulness. There are 5 neurotransmitter system involved:   

-Acetylcholine : cortical activation  

- Location: pons, basal forebrain, septum-hippocampus  

• / 3