I. The Sleep Cycle in short:
"Initial" stage 1-> slow wave sleep -> REM sleep
Some Brain Waves (EEG's)
"Beta" waves - present when we're alert and awake, brain waves are fast (high frequency,
desynchronized, low amplitude waves)
Alpha waves - present when we are awake but relaxed and just before sleep, brain waves slow
down (larger amplitude, lower frequency waves)
Delta waves - present during "slow wave sleep" very slow (low frequency) high amplitude waves.
Reason why slow wave sleep is called slow wave sleep
Stage 1-"hypnogogic", dreamy state but not really. People claim they’re really not sleeping.
Stage 2- "sleep spindles and K complexes".
Bursts of firing that interrupt stage 2 slow waves
(sleep spindles). K complexes high amplitude waves.
Start of slow wave sleep. Stage 2 initial start
of slow wave.
Stage 3, dropped blood pressure and body temperature, Delta waves
Stage 4, Deep Sleep- Delta waves (high amplitude) predominate -> 3 ->2 ->
REM sleep -> 2 -> 3 -> 4 -> 3 -> .
.. like stage one sleep
Night time: Stage 1, 2, 3, 4, 3, 2 (about 50-90 min.), REM (10-20 min.), Stage 2-
REM to slow wave sleep cycle repeats about 3-5 times per night
As the night progresses, REM time per cycle increases slightly and deep sleep
Defined, literally, by the presence of rapid eye movements
Time of dreaming.
Found in placental and marsupial mammals
(Does this mean that non-REM species like the spiny anteater don't dream? Don’t know.)
EEG characteristic wave forms are similar to awake states
Powerful inhibition of motor neurons involved in movements of the extremities
Brain stem neurons are highly active creating diffuse activation of cortical regions
Changes with age- a greater proportion of time spent in REM sleep in babies
II. Some brain regions involved in sleep-
Regions of the reticular formation
some are involved in maintaining wakefulness, by stimulating the reticular formation.
Known for waking.
Caudal Reticular formation and Rem Sleep
Discrete regions of the caudal reticular formation are important for different
aspects of REM
Raphe nucleus – lesions here in cats produce insomnia, tend to not show as much rem
Basal forebrain – lesions here reduce sleep in cats, important for maintaining normal amounts of
slow wave sleep. Modulator of sleep rather than sleep control center.
Questions: Why do we sleep? Why do we dream?
REM – activity levels in the brain like while awake. eegs high freq low amp
III. Why do we sleep?
The major theories: