Biological Psychology - Sleep

Which physiological functions show natural variability?

• Brain wave activity

• Breathing

• Heart rate

What physiological fu

What physiological changes occur during sleep?

• Overall physiological demands are reduced

• Bodily processes become more stable and predictable (e.g. brain wave activity, breathing, heart rate)

• Body temp decreases

• Blood pressure falls

• Metabolic activity slows

What are the three psychophysiological measures?

• EEG - measures brains electrical activity via small electrodes on the scalp

• EOG - records eye movements using electrodes placed beside the outer corners of the eyes

• EMG - records muscle activity using electrodes typically placed below the chin or on the leg to assess body movement during sleep

Describe stage 1 of the sleep stages in EEG, EOG, EMG readings

• EEG shows a mix of fading alpha and emerging theta, marking onset of true sleep (light)

• EOG records slow rolling eye movements

• EMG shows noticeable drop in muscle tone, but some twitches or hypnic jerks may appear

Describe stage 2 (sleep spindles and K-complexes) of the sleep stages in EEG, EOG, EMG readings

• EEG - theta waves punctuated by 1-2 seconds bursts of high frequency (12-14Hz) activity called sleep spindles. K-complex also observed - a very high amplitude pattern of brain activity

• EOG - Eye movement stops

• EMG - Muscle activity decreases further, steady but reduced; body is relaxed yet not fully still

Describe stage 3 (deep sleep) of the sleep stages in EEG, EOG, EMG readings

• Slow wave sleep/deep sleep occurs, growth and repair processes occur, hardest stage to wake from

• EEG - Dominated by delta waves - slow, high amplitude activity

• EOG - Eyes still, virtually no movement

• EMG - very low muscle tone, body fully relaxed

Describe REM of the sleep stages in EEG, EOG, EMG readings

• Occurs about 90 minutes after sleep onset, repeating several times through the night, brain highly active, vivid dreaming occurs here

• EEG - Low voltage, mixed frequency activity resembling wakefulness; brain highly active

• EOG

• EMG

Describe the sleep cycles

• Sleep alternates between Stages 1 and 3 and REM roughly every 90 minutes

• Early stages - larger proportion deep sleep

• Later stages - larger proportion of REM periods

What are the two main theories on why we sleep?

1. Recuperation theories - Propose that sleep serves to restore physiological balance disrupted by wakefulness (uses energy and stresses bodily systems)

2. Adaptation theories - view sleep as an evolutionary adaptation rather than a response to internal imbalance. Sleep evolved as part of a 24-hour circadian rhythm

What happens to the body and brain when deprived of sleep?

• Cognitive - poor focus, memory lapses, slower reactions

• Emotional - irritability, stress, intolerance, low mood

• Social/behaviour - reduced motivation, poor judgement

• Physical - immune suppression, appetite disruption, fatigue

What did Durmer & Dinges

The neurocognitive consequences of sleep deprivation

• Universally reduces daytime performance

• Causes microsleeps, lapses, and attention failures to wake-state instability

• Impairs key cognitive demands like memory, problem-solving and attention

• Prefrontal cortex functions are especially vulnerable

• Effects worsen over time

Kleitman’s sleep deprivation case study

students stayed awake for several nights, initially managed to study until 3am, when strong sleepiness set in. Stayed fairly alert when active but struggled to focus in quieter tasks and the cycle repeated.

It shows - the sleep-wake rhythm persists even without actual sleep (evidence for an internal adaptive clock)

Increasing fatigue and concentration problems support recuperation theory.

The case study of Randy Gardner in sleep deprivation

• Randy Gardner = 17 yo student, attempted to break the world record for wakefulness - stayed awake for 11 days

• During deprivation: distorted perception, mood changes, severe lapses in attention and motivation, impaired cognitive and motor functions

• After a few nights recovery sleep, normal functioning returned

• Demonstrates recuperation - lost sleep leads to deficits that are reversed through rest

  • First night he slept 14 hours - much longer than usual, then went back to normal 8 hours, suggests sleep is adaptive

Siegel

• Sleep is an adaptive behaviour shaped by ecological and evolutionary pressures

• Variation in sleep duration across species cannot be explained by the recuperation theory alone,

  • predators sleep much more than prey, suggesting ecological vulnerability determines sleep patterns

  • Sleep amount also correlates with metabolic rate and foraging needs, animals with high energy demands may sacrifice sleep to maximise feeding

Do all animals sleep (EEG-based evidence) - Siegel

• EEG-defined stages of sleep can be seen in mammals and birds, but not so clear in reptiles and fish

• Some species exhibit sleep-like states without the classic mammalian EEG signatures

• ‘sleep’ may have evolved differently in other species and have different functions

• Challenges idea that sleep is a universal recuperative function, but instead is flexible, taking forms that suit species’ adaptive survival needs

What is Rattenborg et al’s evidence that birds sleep in mid flight ?

• Birds can sleep with one hemisphere while keeping the other awake during flight (unihemispheric sleep)

• This is an adaptive solution to balance rest with ecological demands

• E.g. frigatebirds drastically cut their daily sleep showing that survival priorities override recovery needs

• Environmental pressures modulate sleep duration and type, not just by homeostatic pressure

Zimmerman et al.’s research into sleep as an adaptive trait

• Drosophila (fruit flies) - exhibit behaviour that meets the criteria for sleep (e.g. reduced responsiveness

• Zimmerman produced short sleeping and long sleeping mutants through genetic manipulation

• Short sleeping mutants had reduced viability, shorter lifespan, and lower reproductive success

• Sleep is under genetic control and subject to natural selection, rather than being a mere by-product of fatigue

• Shows that sleep is an adaptive trait coming from evolution

What are the main limitations of adaptive theories?

• Conclusions largely drawn from animal studies/observation

• Less directly testable than restorative theory

• Sleep has costs such as predation or lost foraging opportunities

• Doesn’t explain why lack of sleep can lead to physiological and neurocognitive collapses

What are the two theories as to why we dream?

1. Psychological theories - Freud, Threat-simulation theory, expectation fulfilment theory

2. Neurobiological theories - activation-synthesis theory, continual activation theory

Freud’s theory of dreams

• Dreams are triggered by unacceptable repressed wishes, often of a sexual nature

• Dreams we experience (manifest dreams) are merely disguised versions of our real dreams (latent dreams)

• The key to understanding people and helping them work through psychological issues is to expose the meaning of their latent dreams by interpreting their manifest dreams

• No evidence for this theory though

What is the threat stimulation theory of dreams (Revonsuo)?

• Dreaming can be thought of as an adaptive biological defence mechanism that prepares us for dealing with threats

• Dreams often contain threatening scenarios such as aggression, pursuit or accidents

• When threats are rehearsed in dreams, the neurocognitive mechanisms for threat perception and avoidance can be trained

What is the expectation-fulfilment theory? (Griffin & Tyrell)

• suggests that dreaming allows emotional arousals that haven’t been expressed during the day to be discharged

• This can free up space in the brain to deal with tomorrow’s emotional cues

• Experimental findings suggest that dream content is often emotionally charged and reflects waking concerns