Sleep - Introduction
Occupies 1/3 of our time Individuals are often quite
active when asleep Sleep is not a loss of consciousness
It is a gradual descent into reduced awareness Sleep occurs in stages
Regular sequence of stages Qualitative differences between stages
Questions:
What happens when we sleep? What happens when we are deprived of
sleep? Why do animals sleep?
Why do different animals have different sleep patterns?
Electroencephalograph (EEG) Allows objective measurement of
sleep activity Electrical signals from brain
Measures: Amplitude: half the distance between high and low
points of an oscillation. Frequency: no. of
oscillations per second (Hz)
Alpha activity α
A smooth electrical activity of 8-12Hz Generally associated with a state of
relaxation and drowsiness Slow eye rolling Reduction in muscle tension and heart rate
Beta activity: β
Irregular electrical activity of 13-30Hz Generally associated with a state of arousal Waves slower and larger Duration 20 mins Still can be woken easily K-complexes still present
Theta activity: θ
EEG activity of 3.5-7.5Hz Occurs intermittently during early stages of
slow wave sleep and REM sleep Brain waves slow down “Descending the sleep staircase” Some sleep spindles
Delta activity: δ
Regular, synchronous electrical activity of less than 4Hz
Occurs during the deepest stages of sleep Hard to be woken Growth hormones now secreted Sleep walking/night terrors Body temperature drops;
need bed covers
REM (Rapid Eye Movement) Sleep Stage consists of beta (13-20Hz) brain waves “Paradoxical sleep” (Jouvet)
Eye movement, heart rate, etc. increased But body in state of near paralysis!
See
http://upload.wikimedia.org/wikipedia/commons/7/73/REM_-_Rapid_eye_movement_sleep_of_a_dog.webm
https://www.youtube.com/watch?v=nV4dkSLdtLE
Sleep cycle (ultradian rhythm) About 180 mins:
α β
θ δ
θ β
α About five ultradian rhythms during a night Less SWS, more REM as morning approaches
Sleep deprivation research - 1 Peter Tripp (a New York DJ) stayed awake for 8 days for
charity in 1959 Suffered delusions and
hallucinations (It is not a foregone conclusion
that the sleep deprivation caused these episodes.)
See https://www.youtube.com/watch?v=ko9MdrVWvHM
What are the limitations of this study?
Sleep deprivation research - 2 Randy Gardner remained awake
for 11 days in 1964 Toward the end he suffered from
slurred speech, blurred vision and paranoia
Afterwards he slept for longer than usual for a few nights But only recovered about 25% of the sleep lost
See http://keepingscore.blogs.time.com/2012/06/26/euro-2012-superfan-dies-from-sleep-deprivation/
REM sleep deprivation 1 (Dement 1960) Some participants were deprived of REM sleep over a
period of several days Others were deprived of NREM sleep
Results: Effects of REM sleep deprivation were more severe: increased
aggression, poor concentration Entered REM sleep 12x the first night but this rose to 26 on the
7th night When they were free to sleep undisturbed most spent longer than
usual in REM sleep This is known as the REM rebound effect
REM sleep deprivation 2 (Jouvet 1967) Method:
Placed cats on an up-turned flower pot on water Eventually they fall asleep
Result When the cats moved into REM sleep and lost muscle
tension they fell into the water They learnt to wake up when they felt their heads nod Eventually, they died
Conclusion: lack of REM sleep was fatal What else could have caused the deaths?
Sleep research … an evaluation Data about sleeping rhythms/dreaming often produced in
sleep laboratories Highly artificial conditions Participants often woken during sleep to ask about their dreams
What are the problems with conducting research in artificial environments?
Why do animals sleep?
Apparently, all animals sleep The area of the brain that governs sleep is the
oldest Why?
Animals are unconscious and defenceless when asleep So sleep is dangerous Therefore it must have a valuable function
Several theories have been proposed
Restoration Theory(aka recuperative, restitutive theories) Sleep allows
the body to get rid of an unwanted substance which accumulates during wakefulness
an essential process of chemical synthesis, which cannot occur during wakefulness
the recovery of neural components or pathways which fatigue during arousal
Without sleep, an animal's health (physical and/or mental) deteriorates
Restoration Theory - Evidence Berry & Webb (1983)
When people slept well at night their levels of anxiety were lower the following day than when they had a poor nights sleep
Insomniacs have less sleep and worry more but it is not clear whether this is a cause or effect
of sleep deprivation
Restoration Theory - Evidence Sharpiro et al (1981) studied runners who took part in a
marathon covering 57 miles Slept 1½ hrs longer on 2 nights following the marathon There was an increase in the amount of SWS
Newborn babies spend majority of time in REM sleep Horne and Minard 1985
When participants were given a number of exhausting tasks they slept faster
BUT not for longer
Evaluation of Restoration Theory For:
It seems logical: the more energy you expend the more you look forward to going to bed
Sleep is greater after periods of stress and improves mood
Against: Lack of exertion does not necessarily
mean you will sleep less It is unclear what causes insomnia REM sleep involves increase in energy
expenditure and blood flow, which inhibits protein synthesis
Ecological/Evolutionary Theory(aka behavioural theories) ‘Survival of the fittest’
Any properties we have now are a result of what has been useful in the past
Webb (1982) Proposed that sleep is useful in itself, because
those animals who slept more were more likely to survive
Webb’s theory is an evolutionary one, but is often called the hibernation theory of why we sleep
Ecological/Evolutionary Theory Sleep
Conserves energy when food gathering has been complete or is more difficult
Avoids damage from nocturnal predators or accidents by remaining motionless
Meddis suggested the duration of sleep a species shows depends upon its food requirements and predator avoidance
Evaluation of evolutionary theory Lions and squirrels do sleep longer, whilst
cattle sleep less Possible evolutionary arguments
(contradictory): animals sleep less to keep constant vigil Animals sleep longer to keep motionless, thus
staying away from harm
Learning While Asleep?
https://www.youtube.com/watch?v=Ye2_2osVCJQ