The nature of sleep
Link to Biological Rhythms
• Sleep wake cycle is a _________ rhythm
• This is controlled by endogenous
pacemakers such as the ________.
• It is fine tuned by external sources
otherwise known as ________
_________.
• Sleep cycle becomes an ultradian rhythm
when we look at the changes within the
stage.
Two Toed Sloth – 20 hours
If all animals sleep, what does this tell us?
Giraffe – 3 hours
Glossary
Frequency
Amplitude
The nature of sleep
What does EEG stand for?
What does it allow us to measure?
What are the two main classes of sleep as
identified by Aserinsky and Kleitmen
(1953)?
* Show slideshow EEG
Glossary
Desynchronised EEG
A reading that has no regular pattern
of electrical activity. This is typically
recorded when brain is active.
Synchronised EEG
A reading that has a regular pattern
of electrical activity. Repeated waves with
a particular amplitude and frequency.
Sleep Spindles
Bursts of high-frequency (12-16 Hz) electrical
Activity seen in deeper stages of NREM.
Delta Waves
Seen in EEG in deeper stages of NREM.
Large amplitude and a frequency of about
1-4 Hz.
Up and down the “sleep escalator”
• Most people have 5 cycles of sleep a night that last
approximately 90 minutes. Slow-wave sleep (SWS)
occurs in only the first two cycles; REM sleep occurs in
all of the cycles, and increases during the course of the
night’s sleep.
• Electroencephalographs (EEGs) measure electrical
activity or brain waves, electro-oculograms (EOGs)
measure eye movement, and electromyograms
(EMGs) measure muscle movement and have been
used to distinguish the stages and cycles of sleep. EEG
readings are normally used as frequency and amplitude
differ depending on the stage.
• Traditionally, self-report data was used before the
development of the recording technology
Up and down the “sleep escalator”
•
•
•
•
•
1, 2, 3, 4, 3, 2, REM
2, 3, 4, REM
2, REM
2, REM
2, REM
• 10, 10, 40, 60 (for how long the REM cycles are)
Can you think of a rhyme
That will help you remember?
The nature of sleep
NREM – Slow Wave Sleep (SWS)
Stage 1 and 2
Hypnogogic
Heart beat
Waves
Spindles
Frequency & Amplitude
Stage 3 and 4
Waves
Frequency & Amplitude
REM
REM
Paradoxical
Eyes
Motor
Frequency & Amplitude
Sleep stages
• Dement and Kleitman (1957) demonstrated a
link between REM sleep and dreaming.
• How do you think they measured this?
• They woke participants up at times when their
brain waves were characteristic of REM sleep
and found that Ps were highly likely to report
dreaming.
• However – dreaming was also reported outside
of REM sleep
• What is a problem with this research method?
• Correlation – can we establish a cause?
• Sample – mostly men and small sample
Research
Jouvet (1969)
Found that the control of REM and NREM lies in the ascending
reticular formation (a network of millions of neurons buried
deep in the brain).
Jouvet used techniques such as lesions and electrical stimulation of the brain
and found the two critical areas of the brain are:
NREM – raphe nuclei
REM – locus coeruleus
In addition, he found that certain neurotransmitters were involved in
Different stages:
NREM – serotonin
REM - noradrenaline
Would you say this is reductionist?
Task
In continuous prose, write 50-100 words on
the differences between slow wave sleep
and REM sleep
*Make into a mind map
Evaluation of cycles of sleep
Objective evidence
EEG, EOG and EMG provide objective measures of sleep –
this means they are less subject to bias. Self-report is
vulnerable to bias and distortion, due to researcher effects
and participant reactivity, therefore it may lack validity.
Artificiality of sleep laboratory
The sleep lab is an artificial condition and
people are “wired up” to machines. The
sleep lab is reductionist as it does not reflect
many factors that can influence sleep in real life.
The research lacks mundane realism and this
means that the findings lack generalisability and
ecological validity may be lacking.
Universality
There are some universal
characteristics of sleep as
stages 3 and 4 occur only
in the 1st two cycles and
REM sleep always
increases in duration with
each successive cycle.
Individual differences
Most people have 5 sleep cycles
and sleep for around 8 hours. But
many people sleep much less than
this and much more. Patterns of
sleep vary from each individual.
Weakness of the self-report method. The self-report method yields subjective data
compared to the objective measurements of EEG, EOG and EMG.