Psychobiology Pt.2 Flashcards
The timing of sleep is determined by the
interaction of?
Homeostatic drive for sleep
❖ Process S
Circadian Rhythms
❖ Process C
Homeostatic drive for sleep (Process S)
❖ Sleep-dependent process
❖ Sleep drive
❖ As a function of sleep and waking, Process S
mediates the increase of sleep propensity during
wakefulness and conversely, its dissipation during
sleep
Circadian Rhythms (Process C)
❖ Sleep in-dependent process
❖ Wake drive
❖ Rhythmic alternation of high and low levels of
alertness over a 24h period
❖ Bimodal distribution
Interaction of Process S and Process C
❖ Under entrained conditions, Process S and
Process C interact to facilitate consolidated
periods of sleep and wakefulness
❖ The increase in the circadian drive for wakefulness as the
day progresses counteracts the increase in the
homeostatic drive for sleep, allowing the maintenance of a
consolidated 16h episode of wakefulness
❖ Similarly, the decreased circadian drive for wakefulness
occurring during the circadian nadir opposes the reduction
in homeostatic sleep propensity associated with
accumulated sleep, facilitating an 8h sleep episode
Three Psychophysiological Measures of Sleep
Electroencephalogram (EEG)
❖ Measures electrical activity in the brain by detecting changes in
voltage form neurons
Electrooculogram (EOG)
❖ Measures eye movements by detecting electrical activity in the
muscles around the eyes
Electromyogram (EMG)
❖ Measures muscle activity and tone by detecting electrical
signals in muscles
Stages of Sleep
Awake
❖ Fast, random, low voltage beta waves
Just before sleep
❖ Alpha waves
Stage 1
❖ Appearance of theta waves among alpha
waves
Stage 2
❖ Predominance of theta waves
❖ Sleep spindles
❖ K complex
Stage 3
❖ Delta waves
Physiological changes
during Slow Wave Sleep
-Reduced energy consumption by the brain
❖ Cerebral blood flow declines to ~25% of waking value
-Brain less responsive to external stimuli
-Reduced movement
❖ Moving sporadically once every 10-20 min to change body
position
-Increased parasympathetic activity
❖ Decreased heart rate
❖ Decreased blood pressure
❖ Decreased respiration rate
❖ Decreased body temperature
sleep cycle
❖ Sleep progresses through stages 1 → 2
→ 3 and then reverses back to stage 1
❖ Initial Stage 1 Sleep
❖ No significant eye movement or muscle tone
changes.
❖ Emergent Stage 1 Sleep
❖ Characterized by rapid eye movement (REM)
❖ Loss of muscle tone in the body’s core
❖ The sleep cycle repeats throughout the
night, lasting about 90 minutes per
cycle.
❖ As the night progresses
❖ More time is spent in emergent stage 1 (REM
sleep).
❖ Less time is spent in other stages, particularly
stage 3
REM Sleep
❖ Brain waves become faster and smaller with less amplitude, similar to beta
waves seen in wakefulness
❖ Oxygen consumption and blood flow in the cerebral cortex resemble wakeful
levels
❖ Marked loss of muscle tone (atonia), leading to temporary paralysis
❖ Phasic twitches occur in the eye muscles, fingers, and toes
❖ Paradoxical sleep: Brain appears awake, but the body remains paralyzed
(Michel Jouvet, 1967).
❖ Increased sympathetic activation:
- Increased heart rate
- Raised but fluctuating blood pressure
- Irregular respiration patterns
- BUT, body temperature drops to its lowest point
Dreaming in Rem Sleep
❖ 80% of awakenings from REM sleep result in dream reports (Dement &
Kleitman, 1957)
❖ Only 7 - 20% report dreams when awakened from Slow-Wave Sleep
(SWS).
❖ Loss of muscle tone in REM sleep may prevent acting out dreams
Freudian Theory of Dreams
❖ Sigmund Freud (1913) believed dreams represent repressed wishes, often
of a sexual nature.
❖ He proposed that manifest dreams (what we recall) disguise latent dreams
(true unconscious desires).
❖ No scientific evidence supports Freud’s theory, yet it remains popular.
Modern Research on Dream Content
❖ Dream studies rely on self-reports, which some argue may be unreliable
(Mangiaruga et al., 2018; Nir & Tononi, 2010).
❖ Others support self-reports as valuable insight into dream content (Cipolli et
al., 2017; Windt, 2013).
Key Findings on Dream Content
❖ Influence of Prior Experiences: Dreams often incorporate recent wakeful
experiences, even mundane activities (Cipolli et al., 2017; Fogel et al.,
2018; Vallat et al., 2017).
❖ Emotional Influence: Anxiety before sleep affects the emotional tone of
dreams (Sikka, Pesonen, & Revonsuo, 2018; Vallat et al., 2017).
why do we dream?
Activation –Synthesis
Hypothesis
- Hobson (1989)
- Dreams arise from random
brainstem activity during sleep - The cerebral cortex attempts to
make sense of these random
signals
why do we dream? Evolutionary theory of dreams
- Revonsuo (2000)
- Dreams serve a biological function
that enhances survival - They simulate threats (e.g.,
physical danger, social conflicts) to
help prepare for real-life challenges - This improves our ability to predict
and respond to dangers while
awake
why do we dream? protoconsciousness hypothesis
- Hobson (2009)
- Dreams are a training mechanism,
simulating real-life situation - Helps with cognitive development,
especially in early childhood - Supports future event prediction
and problem-solving
Brain regions involved in dreaming
Lesion studies
❖ Temporo-Parietal Junction
❖ Lesions here stop dreaming
❖ Medial Prefrontal Cortex
❖ Lesions also eliminate dreaming
❖ Medial Occipital Cortex
❖ Lesions result in loss of visual imagery in
dreams.
Neuroimaging findings
❖ fMRI studies show increased activity in:
❖ Temporo-Parietal Junction
❖ Medial Prefrontal Cortex
❖ Medial Occipital Cortex during REM sleep
❖ Supports lesion studies showing these areas
are critical for dreaming
Why do we sleep? Recuperation theories
◆ Sleep restores homeostasis disrupted by
wakefulness
◆ Three main functions proposed:
◆ Energy Restoration: Sleep replenishes energy levels.
◆ Toxin Clearance: Removes waste (e.g., beta-amyloid)
from the brain.
◆ Synaptic Plasticity Restoration: Maintains neural
connections.
◆ Sleep is triggered by homeostatic imbalance
and ends when balance is restored
Why do we sleep? Adaption theories
◆ Sleep is controlled by an internal 24-hour
clock, not just recovery needs
◆ Evolved to conserve energy, reduce nighttime
dangers, and enable brain functions
◆ Some theories argue sleep is not essential for
physiological health but is highly motivated
why do we sleep? Integrative view
Evolutionary programming determines sleep timing; recuperative needs influence sleep duration
The effect of sleep on learning and memory
❖ Sleep enhances memory retention
Two key roles
❖ Protects memories from interfering stimuli.
❖ Aids memory consolidation
Experimental Evidence
❖ Walker et al. (2002) study:
❖ Participants learned a motor task (finger-thumb
tapping sequence).
❖ Retested after 12 hours:
❖ No improvement after a full day awake.
❖ 20% improvement after a night of sleep.
❖ Effect was strongest in those who:
❖ Practiced in the evening.
❖ Had three nights of sleep before final testing.
Sleep in other animals
❖ Sleep observed in all mammals and most
birds (Manger & Siegel, 2020)
❖ Characterized by high-amplitude, lowfrequency EEG waves punctuated by
low-amplitude, high-frequency waves
❖ Less clear in amphibians, reptiles, fish,
and insects—some show inactivity, but
not confirmed as sleep (Siegel, 2008)
Sleep in other animals:
Key findings from comparative studies
1 Sleep serves a critical function
* Most mammals & birds sleep, even when it increases predation risk
* Some species have evolved uni-hemispheric sleep for survival
2 Sleep is not just for humans
* Sleep is unlikely to be solely for higher-order brain functions like emotional processing
3 Variation in sleep duration
* Some species thrive on minimal sleep (e.g., horses: ~2-3 hrs/day).
* Captive animals often sleep more than wild counterparts
4 Factors influencing sleep duration
* No strong link between sleep time and energy use, body size, or temperature (Siegel, 2005).
* Adaptation theories explain differences better:
* Short sleepers (e.g., zebras) need to graze & stay alert for predators.
* Long sleepers (e.g., lions) rest after large meals.
Sleep across the lifespan (Newborns and Infants)
❖ Sleep 16–18 hours/day, with 50% in REM
❖ Premature infants (~30 weeks gestation) spend
~80% of sleep in REM
❖ Infant REM differs from adult REM:
❖ No motor paralysis, facial expressions (crying,
anger, rejection).
❖ Laughter during sleep, including first smiles
(Trajanovic et al., 2013; Davies, 2018).
❖ REM decreases with age:
❖ 50% at 3 months → 25% at 1 year (similar to
young adults).
❖ Sleep cycles increase from 60 min (infants) → 90
min (older children).
The role of REM in Development
❖ Neural growth & brain maturation
(Roffwarg et al., 1966)
❖ REM sleep stimulates the cerebral cortex,
aiding nerve cell development
❖ Hubel & Wiesel’s kitten study: Deprived
visual input → impaired vision, cortical
degeneration.
❖ Possible role in processing sensory stimuli
& learning (Tarullo et al., 2011)
❖ Unclear link to later cognitive,
psychomotor, or temperament
development (Ednick et al., 2009).
Sleep across the lifespan (adolescence and Adulthood)
❖ By early adolescence, sleep
stabilizes at 6 – 8 hours/night, with
25% in REM
❖ Slow-wave sleep (SWS) declines
with age:
❖ By age 60: SWS reduced by half
❖ By age 90: SWS may disappear entirely,
potentially linked to cognitive decline.
❖ Poor sleep in old age → Increased dementia
risk (Kang et al., 2017).
❖ REM sleep remains relatively
stable, decreasing 0.6% per
decade
❖ Ages 76–85: Some studies show a slight
increase in REM.
The Stress Problem with sleep
Interpreting Sleep Deprivation Studies
-Effects of Sleep Deprivation:
❖ Leads to feeling out of sorts and impaired functioning.
❖ Commonly occurs due to stressors like illness, work,
shift work, drugs, or exams.
-Challenges in Studying Sleep Loss:
❖ Difficult to separate sleep loss from stress effects
❖ Even in controlled studies, the procedure itself can be
stressful.
❖ Results must be interpreted with caution
-Public Perception vs. Scientific Evidence:
❖ Media frequently links sleep deprivation to health and
accident risks.
❖ However, most studies cannot isolate sleep loss from
stress levels (Anafi et al., 2019).
❖ Therefore, they provide limited insight into the true
functions and necessity of sleep.
Predictions of Recuperation Theories about
Sleep Deprivation
Long periods of
wakefulness will
produce
physiological and
behavioural
disturbances>
These disturbances
will grow worse as
sleep deprivation
continues>
After a period of
deprivation has
ended, much of the
missed sleep will be
regained
