EEG and the stages of sleep Flashcards
EEG EOG and EMG
EEG measures cortical activity
- electrodes on the scalp at front, centre and back most important for sleep research
- bilateral in case on side comes loose during sleep
EOG measures eye movement
- corneoretinal potential (difference in potential between cornea and retina)
- electrodes above right and below left eye
EMG measures muscle tone
- electrodes under the chin
- muscle tone lowered during REM sleep
EEG stages of sleep
Deeper sleep = lower frequency
Wake
- alpha waves 8 - 12Hz
- beta waves
Stage 1
- Theta waves 4 - 7Hz
Stage 2
- Sleep spindles similar to alpha waves - more easily found by centre electrodes
- K complexes - large wave
- Can be up to 1/2 your sleep
Stage 3
- Delta (slow) waves 0.5 - 2 Hz
- Stage 3 and 4 now one type, known as N-3 sleep
REM
- slightly higher amplitude than wakefulness
- Theta and beta activity - waking- and light-sleep-type activity
Slow eye movement
Eyes slowly rolling back into the head
With theta waves as you fall asleep
- LAMF - low amplitude mixed frequency : ‘dropping off’
Discovery of REM sleep
Ladd 1892
- noticed eyes moving during sleep
- hypothesised they were watching their dreams
- idea of REM wasn’t popularised until
Aserinsky and Kleitman 1953
- EEG - into and out of deep sleep
- looked like they went back into stage 1 but there were also rapid eye movements — REM sleep!
- REM occurs periodically during the night
Berger & Oswald 1962
- EMG suppressed during REM - lungs and heart only muscles still fully active
Hypnograms
Show sleep architecture - transition through sleep stages during the night
REM periods get longer throughout the night - explains why when we wake in the morning we can remember long dreams - can be 40mins long!
Induction of SWS
Ngo et al., 2013
- 3 conditions
- with tones presented at a rate of 0.8Hz
- tones presented at random
- no tones (sham)
- acoustic stimulation began during wakefulness, through first 90mins of sleep
- 0.8Hz gave significantly delayed sleep onset and increased slow wave activity during sleep
- sleep after stimulation was not affected
Functionality of K complexes
Wauquier et al., 1995
- K complexes and sometimes spindles occur when there is external noise
- people with sleep disorders e.g. apnoea or insomnia have very few K complexes … K complexes keep you asleep
Amzica and Steriade 2002
- K complexes are more spontaneous than evoked
- generated spontaneously by slow waves
- impair transmission of incoming stimuli - keep you asleep
Functionality of sleep spindles
Can occur in response to environmental stimuli like K complexes (keep us asleep) but have recently been linked to memory consolidation _____ STUDY
Generated by the thalamus. As spindle power increases, the thalamus is less active
Veto sensory activation of the cortex
Slow wave sleep
Association with ventral medial pre frontal cortex (vMPFC) - generated here?
Confirms frontal predominance of slow wave activity during NREM seep seen in EEG studies
REM sleep
- PGO (pontine geniculate occipital) waves generated in the pons in the brain stem
- Which stimulates the geniculate area
- Which stimulates the occipital area
- Which stimulates the geniculate area
- Theta waves (4-7Hz) in the hippocampus and cortex during REM and wake
- associated with memory consolidation during REM
First night effect
Sleep architecture is slightly different from normal
- longer to fall asleep
- less REM, more time in lighter stages
- basic architecture is more or less the same
Often exclude first night data if using physiological data - not an issue if using dream data and REM sleep still occurs, just not as often as usual
Waking from sleep during the night
Agnew & Webb, 1972
- 44% woken from stage 1 or 2 said they weren’t asleep
- 15% woken from N-3 sleep said they weren’t asleep
Number of arousals during the night increases with age
