chapter 9: sleep and biological rhythms

circannual vs. circadian cycles

circannual: yearly cycles (e.g., migration, hibernation). circadian: daily cycles (~24 hours, e.g., sleep-wake cycle). endogenous factors (like the scn) maintain internal rhythms. exogenous factors (light, temperature) help synchronize them to the environment.

free-running rhythm

a rhythm that persists without external cues (e.g., light/dark). it varies slightly among animals, not always 24 hours.

daily rhythm resetting

light exposure, melatonin, social cues, and physical activity can reset circadian rhythms.

zeitgeber

a time cue (e.g., sunlight) that helps regulate biological rhythms.

eeg (electroencephalogram)

measures brain's electrical activity; reveals different brain states like sleep stages.

emg (electromyogram)

measures muscle activity; low during rem sleep use to atonia.

eog (electroculogram)

measures eye movements; detects rem sleep through rapid movements.

alpha, beta, theta, delta waves

alpha: relaxed wakefulness. beta: alert, awake state. theta: light sleep (stage 1/2). delta: deep sleep (stages 3/4).

synchronous neuronal activity

characteristic of sleep, especially slow-wave sleep.

brain waves during wakefulness

mostly beta (alert) and some alpha (relaxed).

4 sleep stages + rem

stage 1: light sleep, theta waves. stage 2: sleep spindles, k-complexes. stages 3 & 4: delta waves, deep slow-wave sleep. rem: rapid eye movement, vivid dreams, muscle atonia.

slow-wave sleep (sws)

deep sleep; stages 3 & 4 marked by delta waves.

sleep spindles

bursts of 12-15 hz activity; occur in stage 2.

k complex waves

high-amplitude waves in stage 2; response to stimuli, promote memory consolidation.

rem = paradoxical sleep

brain is active like wakefulness, but body is paralyzed.

nightly sleep progression

cycle through stages 1->2->3->4->rem; repeat ~90 mins. rem gets longer later in night.

most rem sleep

occurs in the latter half of the night.

sleep deprivation effects

more rebound rem and slow-wave sleep during recovery.

3 theories of sleep

repair/restoration, evolutionary/circadian, and synaptic homeostasis (a synthesis).

repair and restoration evidence

for: growth hormone release, recovery from fatigue. against: sleep doesn't always correlate with exertion.

evolutionary theory evidence

for: sleep helps avoid predators. against: sleep can be risky for survival.

learning during sleep

no; conscious learning requires awareness.

rem sleep and memory

enhances procedural and emotional memory.

slow-wave sleep and memory

aids declarative (fact-based) memory consolidation.

what promotes learning during sleep?

replay of neural patterns (hippocampus) during rem and sws.

sleep across lifespan

more rem in infants; sws decreases with age.

passive sensory theory

sleep is due to reduced sensory input.

rejection of passive theory

active neural mechanisms promote sleep (e.g., vipoa inhibition).

transection techniques

cerveau isolé: cut at midbrain; eeg shows continuous sleep. encephale isolé: cut at spinal cord; normal sleep cycle. caudal transection: preserves arousal; sleep/wake remains.

reticular activating theory

reticular formation stimulates wakefulness.

single locus for arousal?

no, arousal is mediated by several interconnected systems.

acetylcholine & cortical desynchrony

enhances alertness and eeg desynchrony in waking and rem.

cholinergic drugs

agonists increase arousal; antagonists reduce it.

endogenous ach activity

high in waking and rem; low in sws.

norepinephrine (ne) role)

increases alertness and vigilance via locus coeruleus.

adrenergic drugs

stimulation increases arousal; inhibition reduces it.

catecholamine agonists

promote alertness (e.g., amphetamine).

endogenous ne activity

high in waking; low in rem.

serotonin role

helps initiate sleep but not maintain rem.

serotonin blockers

reduce cortical arousal.

endogenous 5-ht activity

high during wake; decreases in rem.

histamine role

promotes wakefulness from the tuberomammillary nucleus.

antihistamines

induce drowsiness by blocking histamine receptors.

histamine activity

high during wake; low during sleep.

other name for orexin

hypocretin.

orexin in arousal

stabilizes wakefulness and prevents inappropriate sleep.

orexin activity

high during wakefulness; low during sleep.

modafinil

promotes wakefulness, likely via orexin and dopamine systems.

adenosine role

accumulates during wake, promotes sleep.

caffeine

blocks adenosine receptors, increases alertness.

adenosinergic activity

high during prolonged wakefulness; reduced by sleep.

suprachiasmatic nucleus (scn)

in hypothalamus; master circadian clock.

scn input

retinohypothalamic tract, signals from retinal ganglion cells.

melanopsin

light-sensitive pigment in retinal ganglion cells that signal the scn.

scn pacemaker activity

neurons show ~24-hour rhythms in electrical activity.

scn genetic mechanisms

clock genes (e.g., per, cry, bmal1) regulate circadian cycles.

chronotype

individual differences in circadian preference (morning/evening).

pineal gland function

secretes melatonin, regulates sleep-wake timing.

melatonin timing

elevated at night; inhibited by light.

melatonin & aging

secretion decreases with age.

melatonin-regulated cycles

sleep-wake, reproductive cycles, seasonal rhythms.

pgo waves

pontine-geniculate-occipital waves; occur before rem, linked to dreaming.

activation synthesis hypothesis

dreams result from brain interpreting random rem activity.

dorsolateral prefrontal cortex

inactive during rem; explains lack of logic in dreams.

thalamus in rem

relays dream imagery to cortex.

pons role

triggers rem and muscle atonia.

primary visual cortex in rem

not strongly active.

secondary visual cortex in rem

active; processes visual imagery of dreams.

amygdala in rem

highly active; processes emotional content of dreams.

postural paralysis region

sublaterodorsal nucleus (sld) in pons.

two circadian rhythm sleep disorders

advanced sleep phase disorder and delayed sleep phase disorder.

onset vs. termination insomnia

onset: trouble falling asleep. termination: waking up too early.

maintenance insomnia

difficulty staying asleep or frequent awakenings.

narcolepsy

sleep disorder with sleep attacks, often caused by orexin deficiency.

cataplexy

sudden muscle weakness while conscious, often triggered by emotion.

sleep apnea

breathing stops briefly during sleep, causes daytime drowsiness.

sleep paralysis & hypnagogic hallucinations

paralysis upon falling asleep or waking; vivid dream-like hallucinations.

rem behavior disorder

failure of rem atonia; person acts out dreams.

fatal familial insomnia

genetic disorder causing inability to sleep, leading to death.