Rhythms of Sleep Flashcards
Sleep Deprivation Studies: Humans
3-4 Hours Deprivation:
- Increased sleepiness
- Disturbances of mood
- Poor performance on tests of vigilance
2-3 Days of Continuous Deprivation:
- Experience microsleeps, naps of 2-3 seconds
Longer Periods of Deprivation:
- No effects on motor performance
- No effects of cognitive performance
- May affect creativity
- Correlated with dementia
Circadian Rhythm
Any biological process that displays endogenous, entrainable oscillation for an average of 24 hours
Ex. sleep cycle
Infradian Rhythm
A biological rhythm that lasts longer than 24 hours, but less than a year
Ex. Menstrual cycle
Ultradian Rhythm
A biological rhythm that occurs repeatedly throughout the day
Ex. Microsleeps, blinking
Zeitgebers
Environmental cues that entrain circadian cycles (light-dark tides)
- Without Zeitgebers, animals display “free-running
rhythms”
- Humans average around 25 hours
- The circadian clock is located in the suprachiasmatic
nucleus
- Even when isolated, it shows cycles of electrical,
metabolic, and biochemical activity
- The Retinohypothalamic tract connects the retina with
the SCN
- Photoreceptors that entrain the SCN are light-sensitive
ganglion cells
Suprachiasmatic Nucleus (SCN)
- Light information is sent directly to the SCN (in the hypothalamus)
- SCN: primarily biological clock, receiving projections from retinohypothalamic pathways
SCN Signaling of Pineal Gland
- SCN signals the pineal gland about light/dark phases
- Pineal gland secretes melatonin during dark phases
- Lesions of the SCN or pineal gland disrupt rhythms controlled by light/dark phases
- Create free-running circadian rhythms
- Abolish annual breeding cycles
Function of Melatonin
- Synthesized from serotonin in the pineal gland
- Melatonin is not a sleep aid
- Pineal gland is main source of melatonin
- just one pineal gland
Sleep Cycles
4 Stages:
1. Stage 1 (non-REM)
2. Stage 2 (non-REM)
3. Stage 3 (non-REM & slow-wave sleep)
4. REM
Stages Differ By
- Neural Activity
- Eye Movement
- Muscle Activity
Studying Sleep
Electro-oculogram (EOG): monitors eye movement
Electromyogram (EMG): measures muscle activity
Electroencephalogram ( EEG): measures brain waves
EEG Activity
- Delta
- Theta
- Alpha
- Beta
Wakefulness
Beta: irregular, low amplitude, typical of alertness & active
thinking
Alpha: regular, medium frequency, typical of resting
PGO Waves
- Distinctive patterns of high amplitude electrical potentials known as PGO waves
- Waves neural activity begins in the pons, followed by lateral geniculate nucleus of the thalamus, and then in the occipital cortex
- REM deprivation results in high density of PGO waves when allows to sleep normally
When Sleep Begins:
Stage 1: Alpha to Theta waves with vertex spikes;
transition from wakefulness to sleep
Stage 2: Theta waves continue, but now marked by sleep
spindles and k-complexes
Stage 3: Beginning of deep or slow wave sleep & involves a
combination of Theta and Delta
- The deep, restful sleep, where it’s hard to wake you up
- High amplitude, low frequency
REM Sleep & Dreaming
- External stimuli can be incorporated into dreams
- Dreams run on “real time”
- Virtually everyone dreams
- Sleepwalking, sleep talking, and bedwetting occur more frequently during SWS than during REM sleep, when core muscles are relaxed.
Lucid Dreaming
- Dreams in which the sleeper realizes they are in a dream
- Can be trained through intention setting before bed, as well as use of a different electronic devices
- Studies of this experience has allowed the understanding of the experience of time in dreams
Forebrain System (Basal Forebrain)
Generates SWS
Brainstem System
- Medulla, Pons, etc
- Reticular Activating System
Activates the forebrain to wakefulness
A Pontine System
Triggers REM sleep
Why Do We Sleep?
- Energy Conservation
- Niche Adaptation
- Restoration & Recovery
- Memory Consolidation
A Hypothalamic System
- Makes sure we keep a stable system
- Coordinates the other three
Dreaming To Forget
- REM sleep erases spurious associations between neurons before they can inappropriately trigger synaptic plasticity & learning
Reverse Hebbian Rule: weakens connections when a dream co-activates neighbouring neurons
- Weak associations are actively down-regulated by random input
Sleep Disorders in Children
- Night terrors & sleep enuresis (bed-wetting) are associated with SWS
- Somnambulism (sleep walking)
occurs during stage 3 SWS- May persist into adulthood
