Lecture 17 - Sleep Flashcards
(22 cards)
How long do humans spend sleeping and what does this suggest about its function?
Humans spend on average 175,000 hours of their life sleeping (more than eating and reproducing)
Suggests an important biological function
What are the three principle measures of sleep?
Electro-encephalogram (EEG) = head
Electro-oculogram (EOC) = eye
Electro-myogram (EMG) = neck
First day of sleep studies often difficult (sleeping in new location)
Other measures e.g. HR, blood pressure, respiration rates
What are pre-sleep Alpha waves?
Bursts of 8-12 Hz activity in low amplitude/high frequency waves
Describe the four stages of sleep
Progressive = increase in amplitude, decrease in frequency
Sleep spindle = 1-2s burst of 12-14Hz waves
K complex = single large upward, then downwards deflection
As we fall asleep, rapidly move into stage 1 sleep, and then progress into stage 2 (where we spend most of the night) – memory consolidation
Awake = low amplitude, high frequency
Describe sleep cycles
Each cycle lasts around 90 mins
As night progresses, spend more time in stage 1
REM only occurs after initial stage 1
Eyes move rapidly, other muscles relaxed
Short periods of wakefulness (don’t recall)
Is REM sleep correlated with dreaming?
Dement (1978):
80% awakenings during REM sleep = dream recall
93% awakening during nonREM sleep = no dream recall
nonREM dream recall = isolated experiences (e.g. perception of falling)
REM dream recall = more narrative
Not associated with sleep walking (due to atonia)
Is there an association between time in dream and time in reality?
Dement & Kleitman (1975):
Association between time in dream and time in reality?
Participants awoken 5 or 15 mins after onset of REM
Asked, on the basis of the dream events, how long they had been dreaming (5 or 15 mins)
Participants correct in 92/111 cases
Early studies of REM sleep indicated high rates of blood low, oxygen consumption and neural firing
Increase in variability of the ANS (blood pressure, pulse and respiration)
These REM sleep episode seemed emotionally charged
What are recuperation theories of sleep?
Being awake disrupts homeostasis
Sleep restores this e.g. sleep restores energy levels
What are evolutionary theories of sleep?
Sleep is not a reaction to homeostatic disruption
Sleep evolved (in humans) to prevent accidents and predation at night
Sleep is like sex – we don’t need it to stay alive but we are still motivated to have it
Describe sleep in animals
All mammals and birds sleep. Fish, reptiles and amphibians have periods of inactivity
Large species differences in sleep – not related to body size/temperature
Sloths hardly move, yet need 20 hrs/day (not consistent with recuperation theories)
Little/no effect of exercise on sleep duration in humans (Youngstedt & Kline, 2006)
Which sleep theory does sleep in animals support?
Sleep in animals not consistent with recuperation theories in sleep
Evolutionary theories – sleep related to: how vulnerable you are asleep, and time spend eating per day (e.g. sloths sleep in a tree, horses spend most of the day eating)
E.g. lions can do little else but sleep for 2 days after a kill
What do recuperation theories predict will happen as a result of sleep deprivation?
(1) Increases in physiological/behavioural disturbances
(2) After deprivation, missed sleep must be regained
Deprivation influences: mood, physiological function, molecular function (Cirelli, 2006)
Effects on executive function: assimilating changing information, updating plans, reference memory (Curcio et al., 2006)
What suggests these recuperation theories may be wrong about the effects of sleep deprivation?
But people recover well after sleep deprivation
(Dement, 1978): Randy Gardner – 260 hours awake
1st recovery night (14 hours sleep) … then back to normal
Studies on the impact of sleep deprivation are often correlational (sleep deprivation may itself be a consequence of something else e.g. anxiety, but sleep deprivation itself may also induce anxiety)
How does depression relate to sleep deprivation?
Vogel et al. (1975, 1990): preventing REM sleep acts as an antidepressant
Scherschlicht et al. (1982): examined effects of 20 antidepressants which all reduced REM sleep. Most increased slow-wave sleep
Preventing REM sleep makes the body want it more (Webb & Agnew, 1967)
Deprivation of REM sleep causes a transient rebound e.g. 30% of time spent in REM sleep compared to 20% (Brunner et al., 1990)
Few cognitive or emotional effects however
What is REM sleep for?
It is the default (i.e. hard to stay in nREM sleep)
It is more similar to wakefulness (people not tired after REM sleep deprivation)
Describe a study into the effects of sleep deprivation on animals
Two rats on a turn table between two chambers, if awake, dunked in water to wake up
After several days, experimental rats died
But, post-mortem revealed swollen adrenal glands, gastric ulcers and internal bleeding
Possibly a consequence of stress and physical damage?
How is the hypothalamus involved in sleep?
Contantin von Economo – studied the brains of those who died from the virus encephalitis lethargica
Victims who had difficulty sleeping – damage to anterior region (basal-forebrain area)
Victims who had difficulty staying awake – damage to posterior region (midbrain area)
Confirmed in lesion studies with animals (Saper et al., 2001)
What is the reticular system?
Complex network of brainstem nuclei and neurons
What did Bremer (1936) show about the reticular system?
Cerveau isole transection = slow-wave sleep pattern
Encephale isole transection = normal sleep-wake cycle
Thus, “wakefulness” area = somewhere in between the two
What did Mouzzi and Morgan (1949) show about the reticular system?
Stimulation of the reticular formation of sleeping cats woke them
Area became known as the Reticular Activating system – low activity = sleep, high activity = wakefulness
What is narcolepsy?
Narcolepsy is a rare long-term brain condition that can prevent a person from choosing when to wake or sleep
The brain is unable to regulate sleeping and waking patterns normally, which can result in:
Excessive daytime sleepiness – feeling very drowsy throughout the day and finding it difficult to concentrate and stay awake
Sleep attacks – falling asleep suddenly and without warning
Cataplexy – temporary loss of muscle control resulting in weakness and possible collapse, often in response to emotions such as laughter and anger
What is REM sleep without paralysis?
REM sleep without core muscle atonia
Schneck et al. (1986) - case study of the person having a dream that they were playing football and waking up having knocked things over and hit head and knee
