Sleep

Does the body generate its own rhythms?

yes!

• endogenous (will happen even if environment changes)

Describe endogenous in bears

• bears have to prepare for winter before hibernation sets in

• too late if the animal changes after the environment changes

• bears are able to prepare because of endogenous rhythms

circadian

sleep/wake cycle

circannual

happens across a year

Suprachiasmatic nucleus

• necessary for generating circadian rhythm, rhythms come from the SCN

• clock in the brain that generates a rhythm, located in hypothalamus

• activity level in SCN varies on 24 hour cycle

Suprachiasmatic nucleus activity in diurnal animals

high activity during the day, low activity during the night

what are the different types of studies

correlation, necessity, sufficiency

correlation study

ex. correlation between when SCN is active and when animal is active (don’t know if SCN causes animals activity)

necessity study

ex. is SCN necessary for activity? remove the SCN and see what happens

sufficiency study

ex. is the activity of the SCN sufficient to drive behavior

Neural activity in the SCN

• SCN neurons take out and put in a culture to record rate of action potentials

  • activity high for 12 hours, low for 12 hours

  • endogenously generating a pacemaker rhythm (no light or environmental input needed)

• Rate code is on a 24 hour cycle

• even single SCN neurons will fire rhythmically

Rhythm Genes

Clock is genetically controlled

3 major proteins in SCN neurons

period, timeless, and clock

levels of SCN proteins throughout cycle (period and timeless)

• period and timeless increase during the day

  • when they reach a threshold, they induce expression of clock

• pulse of light during sleep can inhibit timeless and decrease clock

levels of SCN proteins throughout cycle (clock)

• high levels make animals sleepy by increasing levels of clock

  • low clock = wake

  • high clock = sleep

• high clock levels correlated with reduced SCN action potentials

• pulse of light during sleep can inhibit timeless and decrease clock

why is sleep considered a behavior

because brain activity is in a different pattern from awakened, but is still active

how is sleep highly regulated

if a person sleep 4 hours one night, then a person will make up that sleep in later nights

regulated sleep in dolphins

dolphins make up sleep in a hemisphere-specific manner

waking brain waves

low amplitude, high frequency

slow wave sleep brains

high amplitude, low frequency

EEG for measuring sleep stages

• non-invasive measurement of avg. activity of 1000’s of neurons

• when neurons synchronized, amplitude of EEG larger and frequency lower

• when neurons de synchronized, amplitude is lower but EEG has higher frequency

synchronous pattern

neurons fire at same time; high amplitude, low frequency

asynchronous brain activity

neurons not firing at same time; high frequency, low amplitude

characteristics of deeper sleep

higher synchrony, more oscillation, except REM sleep

how many stages of sleep are there, and what are they

6; awake, stage 1, stage 2, stage 3, stage 4, REM

activity in awake stage

alpha and beta

alpha activity

smooth 8-12 Hz (relaxed)

beta activity

irregular 13-20 Hz (arousal)

stage 1 activity

theta

theta activity

3.5-7.5 Hz activity

stage 2 activity

sleep spindles and k complexes, beginning of high amplitude events

sleep spindles

short bursts of 12-14 Hz

k complex

sudden sharp waveforms

stage 3 activity

delta

delta activity in stage 3

less than 4 Hz (20-50%)

stage 4 activity

delta

delta activity in stage 4

less than 4Hz? more than 50%

rem activty

theta, beta