Sleep

Revision: biological rhythms

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?

WHAT HAPPENS WHEN WE SLEEP?

Interesting facts from research

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)

Stages of Sleep: Physiological and Behavioral Description

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 Hz 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!

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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

WHAT HAPPENS WHEN WE ARE DEPRIVED OF SLEEP?

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  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

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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?

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? VCJQ VCJQ

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