Week 8: Sleep and Biorhythms Flashcards
Rhythm
Cyclic variation in a process over time
Circadian rhythm
Repeats approximately every 24 hours; sleep
Infradian rhythm
Repeats between 24 hours and one year; mating, breeding, migration
Ultradian
Repeats in less than 24 hours; eating/hunger
Bunker study
Method: secluded humans in a bunker with no access to light cues or clocks. Limit sense of time
Findings: Still followed a sleep cycle pattern similar to normal (about 25 hour cycle)
Suggestion: Cycles/rhythms are biologically hardwired, and can be adapted by external cues
Endogenous/free-running rhythms
Rhythms that exist even in the absence of cues. Can be changed by cue input.
Rhythm study in animals
Method: Submit animals either to constant light or constant dark. Observe activity patterns
Findings: In nocturnal animals, activity was heightened in constant dark and lessened in constant light. Vis versa for non-nocturnal animals. All animals still kept cycles, but they were altered
Supports notion of endogenous rhythms
Drosophilia studies (fruit flies)
Done in the 70s. Method: mutate the PER gene in flies and observe behavior
Findings: Disruption of gene led to disruption of rhythms
Suggestion: rare case where a process is directly related to one gene (PER).
Evidence supporting PER control of rhythms
Expression of PER varies with different levels of activity
Transplants of non-mutated PER genes would restore damaged cycles
Clock genes
PER and CRY (among others)
Clock gene circuit
Clock + Bmal1 -> CRY + PER -> inhibition
Internal clock and Bmal1 produces CRY and PER over time, which combine to make an inhibition factor on the clock. Over time CRY and PER levels decrease.
Self-limiting system, which creates the cyclic/wave pattern
Delayed sleep phase disorder
Habitual strong pressure to sleep and wake later than normal. Affects 1-10% of the pop. Related to CRY1
Familial advanced sleep disorder
Wake up early and go to bed late. Inheritable from genetics. Related to PER2
Suprachiasmatic nucleus (SCN)
Area of the brain in the hypothalamic nucleus located close to the optic chiasm. Aligns all the rhythm pattern in the body with each other. Designed/positioned to receive light as a cue to function (optic location). Will rhythmically fire even when isolated from cues
Affects of Lesion to SCN
Activity rhythm loss. Measured by watching wheel running behavior/patterns in rodents. Those with lesions had sporadic running patterns. Transplanting healthy SCN restores pattern, but of the host animal, not the receiving animal
Light sets rhythm
Retinal ganglion cells (RGNs) are reacting to light and producing melanopsin, which enacts rhythms. Cause of biologically set rhythms
Ways to improve sleep
Light exposure and activity early in the day, melatonin late in the day, no caffeine late in the day
Melatonin
Creates physiological pressure for sleep. Light inhibits production (less light, less inhibition, more production, more eepy). Produced by the pineal gland. Affects tissues across the body
Affect of individual light sensitivity
Melatonin production can vary, and thus determine the needed environment for beneficial sleep. Those with low sensitivity might have more melatonin production
Effects of electronics on sleep
More light leads to more sleep disruption via less melatonin production. Leads to poor sleep and mental health problems
Adenosine
Creates sleep pressure; increases during day, decreases during night. Weakened by caffeine
Cortisol
The stress hormone, involved in arousal. Begins rising before we wake up in the morning. Increased levels cause arousal, hence why you can’t sleep after stressful events
Exercise affecting sleep
Creates arousal, which inhibits sleep. Exercise early, sleep early; vis versa
Chronotype
Natural wake/sleep cycle predisposition. Influenced by age, gender, etc. Kids wake earlier than adults, women earlier than men
Early bird sleep type
“Morningness”. Associated with higher academic performance. Typically agreeable and conscientious
Night owl sleep type
“Eveningness”. Associated with higher cognitive ability and lower mental health. Typically high in neuroticism and sensation seeking
Variation in chronotype with age
Adolescents naturally wake up later than others. School theory: we should push start times so that kids are tested in their peak activity times
Zeitgeber
Cues that set rhythms
Entrainment
Rhythms that are set by zeitgebers are considered to be entrained
Factors that disrupt sleep rhythm
Light pollution (natural and electronic)
Jet lag (resolves quickly, shifts rhythms due to light cues)
Night shifts (hard to avoid, can lead to adverse mental health)
Implications of existence of bodily phases/rhythms
Drugs may respond differently depending on when in the cycle they are taken
Higher risk for metabolic disorder, cancer, and mental health events
Metabolic syndromes
Digestion may peak at certain times of cycles, and thus the time you eat potentially matters to efficiency of nutrient consumption
Mouse study of metabolic syndrome
Method: Gave two rats same amount of food. One rat was restricted to eating at a certain time, the other was unrestricted
Findings: The intermittent fasting rat weighed less than the normal rat despite eating the same amount
Suggests that intermittent fasting may be beneficial to weight loss, and that the metabolism may operate cyclically
Arousal circuitry
Involves the ventrilateral preoptic area and the locus coeruleus, as well as the reticular activating system (RAS).
Locus coeruleus
Involved in noradrenaline production
Reticular Activating System (RAS)
Provides cholinergic stimulation via basal forebrain. Arousal occurs via reticular formation stimulation. Damage here results in comatose state
Uses of sleep
Cleaning the brain, repairing damage, performing genetically programmed brain change (ontogenetic development), maintain learning, process memories. Possibly also adaptive as a way to save energy during a time when humans are not optimally functioning (night time)
Magic number of hours of sleep
Doesn’t exist, hasn’t been proven. Varies depending on the person
Efficient sleepers
Those who need less sleep to function. Related to DEC2 and ADRB1 (beta-adrenergic receptor 1). Inheritable and genetic. Suggested they spend more time in NREM3
Architecture of sleep
4 distinct sleep phase pattern identified via EEG (fast temporal resolution). NREM1, NREM2, NREM3/4, REM
Brain waves during sleep
Beta - awake; fastest
Alpha - resting
Theta - freshly asleep
Delta - fully asleep; slowest
NREM1
Alpha and theta waves, 4-7 Hz. Light sleep phase
NREM2
Middle sleep, shows sleep spindles
NREM3/4
Delta waves 1-4 Hz. Deep sleep stage, associated with feelings of restfulness
REM
Fast and random brain activity, stage where most dreaming occurs. Progressively get longer with each sleep cycle. Atonia kicks in here
Sleep changes with age
As you get older, you sleep less. More often brief awakenings and more sleep latency (falling asleep later)
Is REM necessary?
No identified use of dreaming as of yet. When REM is deprived, it will rebound/compensate, suggesting it’s important.
Low REM associated with low hippocampal neurogenesis, immune dysfunction, and mood disruption (not universal findings)
REM stage test
Method: allow people to reach REM stage, immediately wake them up, then allow them to fall back asleep. Essentailly replacing REM stage with wakefulness
Findings: no major adverse effects to restfulness or activity
Suggests that REM is similar to wakefulness
Sleep in memory
Replay or Preplay
Replay: reactivating memory traces to strengthen them
Preplay: building structures for future memories to be stored
Sleep memory study
PET scan of the human cortex in training phase of physical action and then during sleep
Findings: Motor areas activated in training were reactivated during sleep
Supports idea of REM sleep as replay memory processing
GPA study
Correlational study between GPA level and dim-light melatonin onset (DLMO) as well as sleep regularity. Found positive correlation btw GPA and regularity, negative correlation between GPA and DLMO
Suggests that regularity is the key to sleep being beneficial
Types of dreams
REM - 80% of dreams; emotional, illogical, sudden shifts in plot
NREM - 20% of all dreams; thought-like, repetitive, similar to daily tasks
Dream protection theory
Psychosexual theory. Suggests that suppressed desires emerge during dreaming, and interpretation can reveal things
Evolutionary theory
Dreaming serves to plan solutions and/or predict and prepare for the future or possible situations
Activation-synthesis theory
Neurobiological theory. Dreaming is the brain attempting to interpret random REM signaling
Sleep deprivation
Not a disorder, can be remedied easily. When prolonged, risk of general health increases. Potentially damaging if occuring during peak developmental periods (less sleep = less time for ontological development)
Insomnia
Difficulty falling or staying asleep. Of all cases, 90% are comorbid with other disorders like anxiety.
Cataplexy
Loss of motor control without loss of consciousness. Triggered by arousing stimuli, occurs in 70% of narcolepsy cases
Narcolepsy
Extreme daytime eepiness, frequent dozing
Characterized by rapid entrance to REM sleep phase.
Cause of Cataplexy
Orexin-expressing neurons limit function of inhibitory neurons that act on motor neurons. Loss of orexin neurons (in lateral hypothalamus) increases inhibiting factor on motor neurons, causing inappropriate atonia
REM behavioral disorder
Loss of atonia during sleep. Can be dangerous when people act out their dreams
Somnambulism / Sleepwalking
Movement during sleep. Likely occurs during NREM stages due to lack of atonia. More common in kids
Measuring sleep in the lab
???
