Wakefulness and Sleep
8.1 Rhythms of Waking and Sleeping
Endogenous Rhythms
Endogenous circannual rhythm = a rhythm that prepares birds for seasonal change
Endogenous circadian rhythm = lasts about a day, does not easily adjust to severe
departures from a 24-hour schedule (not only for sleep, also for eating, drinking,
hormone secretion etc.)
➔ people who tried to live in a different hour-schedule still showed wakefulness and
sleepiness on a 24-hour schedule
➔ genes controlling circadian rhythm are almost the same in mammals and insects
Setting and Resetting the Biological Clock
➔ circadian rhythms are not perfect, we adjust to stay in phase with the world
Zeitgeber = the stimulus that resets the circadian rhythm
➔ light plays an important role in regulating rhythm
➔ more than half of all blind people report frequent sleep problems (poor sensitivity to
zeitgebers other than light)
➔ people at the eastern edge of a time zone awaken earlier because the sun rises
earlier (=> sleep cycle is still affected by light when people go by the same clock)
a. Jet Lag
Jet lag = a disruption of circadian rhythm due to crossing time zones
➔ people find it more difficult to go to sleep before their usual time, therefore:
● going west: easier to adjust (phase-delay → sleep later, wake up later)
● going east: harder to adjust (phase-advance → sleep earlier, wake up earlier)
➔ adjusting to jet lag can be stressful => elevated cortisol => damage to hippocampus
b. Morning People and Evening People
➔ adolescents tend to stay up later and awaken later (consistent across cultures)
➔ people in big cities (with electric lights) tend to stay up later
Mechanisms of the Biological Clock
a. The Suprachiasmatic Nucleus (SCN)
Suprachiasmatic Nucleus (SCN) = part of the hypothalamus,
the main driver of rhythms for sleep and body temperature
➔ damage => body rhythms become erratic
➔ SCN neurons continue to produce a circadian rhythm of action potentials even
when separated from the body (e.g in a cell culture)
,➔ hamsters who received SCN cells from donors showed the circadian rhythms of the
donors, not of their own => rhythms come from the SCN itself
b. How Light Resets the SCN
Retinohypothalamic path = small branch of the optic nerve, from retina to the SCN,
conveys information about light to the SCN even without input from rods and cones
➔ comes from a special population of retinal ganglion cells with melanopsin (their
own unique photopigment), located near the nose
➔ ganglion cells respond mainly to short-wavelength light => short-wavelength light
from used electronics can phase-delay the circadian rhythm
c. The Biochemistry of the Circadian Rhythm
➔ Drosophila insects: two important genes: period and timeless, produce proteins
PER and TIM
➔ promote sleep and inactivity, oscillate over a day based on feedback amongst
neurons (high concentration during night, low during day)
➔ light activates a chemical that breaks down TIM => increase in wakefulness and
synchronicity with external world
➔ humans: mutations in PER => shorter circadian rhythm, preference for sleeping
early, depression
d. Melatonin
➔ SCN regulates sleeping/waking by controlling activity levels in other brain areas,
such as the pineal gland (endocrine gland posterior to thalamus, releases the
hormone melatonin → increases sleepiness in diurnal animals and wakefulness in
nocturnal animals; can reset circadian rhythm)
8.2 Stages of Sleep and Brain Mechanisms
Sleep and Other Interruptions of Consciousness
Coma = an extended period of unconsciousness caused by head trauma, stroke, disease
Vegetative state = alternates between periods of sleep and moderate arousal, although
even during the more aroused state, the person shows no awareness of surroundings
and no purposeful behavior.
Minimally conscious state = brief periods of purposeful actions and a limited
amount of speech comprehension.
Brain death = condition with no sign of brain activity and no response to any stimulus.
The Stages of Sleep
Polysomnograph = a combination of EEG and eye-movement records
,Alpha waves = characteristic of relaxation, not of all wakefulness
Stage 1 of sleep: irregular, jugged, low-voltage waves (brain activity is low but still
higher than other sleep stages)
Stage 2 of sleep:
● k-complexes → sharp waves associated with temporary inhibition of neuronal
firing
● sleep spindle → burst of 12 to 14 Hz waves for at least half a second
Slow-wave sleep = heart rate, breathing rate, and brain activity decrease, whereas
slow, large-amplitude waves become more common → input to cerebral cortex is greatly
inhibited, and most cells synchronize their activity
90 minute cycle: stage 1 → stage 2 → slow-wave sleep → stage 2 → REM
Paradoxical or REM sleep
Paradoxical sleep = deep in some ways and light in others, term used mainly for
animals without rapid eye movements
Rapid eye movement (REM) sleep = synonyms with paradoxical sleep, term used
mainly for humans; combines aspects of deep sleep, light sleep and features that are
difficult to classify as deep or light
Brain Mechanisms of Wakefulness, Arousal, and Sleep
a. Brain Structures of Arousal and Attention
➔ the midbrain has it own mechanisms to promote wakefulness
Reticular formation = structure that extends from the medulla to the forebrain; its
neurons with ascending axons are well suited to regulate arousal
➔ one part of it that contribute to cortical arousal is the pontomesencephalon
Locus coeruleus = small structure in pons, usually inactive
(especially during sleep), but emits bursts of impulses to meaningful events, especially
those that produce emotional arousal; it’s axons release norepinephrine throughout
cortex
➔ one axon pathway from hypothalamus releases excitatory neurotransmitter
histamine (arousal and alertness); antihistamines produce drowsiness (if they
cross blood brain barrier)
Orexin/hypocretin = peptide neurotransmitter, enhances wakefulness and activity,
especially important for staying awake; lack of it => alternates between sleep and
wakefulness
, Basal forebrain = its cells provide some axons that increase wakefulness and others
that inhibit it
b. Sleep and the Inhibition of Brain Activity
➔ neurons in the thalamus become hyperpolarized during sleep
➔ we remain unconscious during sleep because of inhibition → axons that release
GABA become more active
➔ during REM, cells in pons and medulla send messages that inhibit spinal cord
neurons (controlling body’s large muscles)
Brain Activity in REM Sleep
➔ REM is associated with PGO waves (pons-geniculate-occipital)
➔ path of axons in ventral medulla releases GABA promoting REM
➔ drug carbachol stimulates acetylcholine synapses moving sleeper into REM
(acetylcholine important for BOTH sleep and wakefulness – both brain arousal)
➔ serotonin and norepinephrine interrupt REM
Sleep Disorders
Insomnia → inadequate sleep; best determined by how someone feels the following
day, sleep deprivation impairs memory, attention, and cognition
a. Sleep Apnea
Sleep apnea = impaired ability to breathe while sleeping
➔ causes include genetics, hormones, age and obesity especially in middle-aged men
b. Narcolepsy
Narcolepsy = condition characterized by frequent periods of sleepiness during the day;
H1N1 virus (2009-2010) caused many cases of it
● attacks of sleepiness during the day
● occasional cataplexy (muscle weakness when awake)
● sleep paralysis
● hypnagogic hallucinations
➔ lack of hypothalamic cells that produce and release orexin
c. Periodic Limb Movement Disorder
Periodic limb movement disorder = repeated involuntary movement of the legs
and sometimes the arms during sleep
➔ mostly middle-aged/older people
➔ legs kick once every 20/30 seconds for minutes or hours, mostly during NREM
d. REM Behavior Disorder
REM behavior disorder = moving around vigorously during their REM periods,
acting out dreams;
