8. Sleep stages, why do we sleep

what is sleep, characteristics?

a period of natural rest, almost total unconsciousness

characterized by:

lack of movement

sleep posture (leaning)

less responsiveness to stimuli

reversibility

how can we measure sleep?

EEG
Electrooculogram EOG

Electromyogram EMG

EEG electroencephalogram

meaasure electrical activity

Electrooculogram (EOG)

electro - oculogram measures eye movements by putting electrodes near the eye to measure changes in voltage with eye movement

Electromyogram (EMG)

electro - myogram: measures muscle electrical activity

Polysomnography

goes into more details as it records brain activity, breathing, oxygen levels, heart rate, eye and leg movement while subject is asleep

comprehensive picture, good for episodes seizures

what are the Sleep-Wake states

Awake

Non-REM sleep (3 stages)

REM sleep

Awake state

we perceive the world/environment vividly

capable of logical thought

can move voluntarily

REM

rapid eye movements

Non-REM sleep (overall)

have less ability to sense environment (making it harder to wake)

we have occasional involuntary movements, no REM

REM Sleep

internally generated vivid sensation (dreaming)(

illogical, wild thoughts (plot is illogical bizarre we don’t question it)
Cannot move muscles (atonia), Rapid eye movements

sleep cycle

the repeating cycle/pattern of sleep stages through the night (typically 4-5 per night)

1 cycle is 90-110 minutes avg

order:

NREM 1 NREM 2 NREM 3

NREM 2 (brief), REM

paradoxical insomnia and NREM 2

half time of sleep cycle is spent in NREM 2 (light sleep)

so people with insomnia don’t perceive they have been sleeping

deep sleep (should we call police ex)

in deeper stages of sleep you are not as active as your regular self, so you will shrug off stuff. (NREM3 is deep sleep) REM sleep is the easiest time to be woken up at

what does the EEG measure specifically

measures the simultaneous occurrence of activity, not total neuron activity

measures:
Frequency:

Amplitude / Voltage

Frequency

how fast the waves are

measured in Hz (cycles per second)

Amplitude / Voltage

How large the waves are

measured in uV *millionths of a volt)

Amplitude : high and low on EEG

low amplitude (shorter faster) means activity is desynchronized (happens when awake and REM)

high amplitude (deeper slower waves) means activity is synchronized (NREM) different neurons that are acitve are active together - deep sleep

beta waves

have fast frequency 12-20 hz) and low amplitude amplitude (10-30 uV)

small waves, that move fast. is desynchronized and has a mix of frequencies

used when we are awake and alert

Alpha waves (awake but relaxed)

our eyes are closed, we are relaxed but awake the

frequency lowers/ slows down to (8-12 hz)

and amplitude increases, waves become deeper (50uv)

NREM-1 (what happens, EEG waves, body)

weird transition period: (shown on EEG)

alpha waves decrease and become lower in amplitude (smaller) and also irregular and there are occasionally vertex waves (wave spikes)

no REM but slow eye rolling movements

muscles are relaxed but not lost , heart rate slows

NREM -2

Almost identical to NREM–1 EEG (slowing alpha waves, can have vertex spikes, no REM)

but there are sleep spindles

short bursts of activity where frequency rises and amplitude softens : 12-14 hz, 50 uV

K complexes slow down freq and largen amplitude (0.5-1 Hz and 75 uV)

and consciousness fades

sleep spindles

periodic brief bursts of activity in NREM 2 where frequency rises and amplitude softens : 12-14 hz, 50 uV

may be important for memory storage

diff between sleep spindle and vertex waves

while both sudden vertex waves are more characteristic of NREM 1 and are sharp spikes,

while sleep spindles are in NREM 2 and waves are softer prick

K complexes

slow down freq and largen amplitude (0.5-1 Hz and 75 uV) during NREM 2

happens after some disturbance in the stage. suppresses arousal , dont wake up

NREM–3

characterized by slow wave sleep:

with delta waves: high amplitude (deeper 75 uV) and low frequency (longer, slow) 0.5-3 Hz)

synchronized, no eye movements, muscle control present but low, slow breath, heart

REM stage

increased EEG activity during sleep that mimics when were awake *like beta waves, super active:

unsynchronized: fast/ mixed frequency (15 - 20 hz), low amplitude (10-30 uV)

has eyes move rapidly, breathing is irregular, vivid dreams, full loss of muscle control (limp)

dream have quality of a movie

Do dreams only happen during REM

no, we used to think dreams happened only in rem but they also happen in NREM stages

from experiments: 80 of people reported dream during rem sleep

and few woke up from NREM with dreams

Posterior cortex

includes some of parietal, temporal, occipital.

active when a person is dreaming in REM / is associated with vivid dreaming

but sometimes active in NREM

(if you woke person while it was active they would report dreaming 91%)

sleep pattern for mammal infancy

mammals sleep more when younger than when adults.

infants have short sleep cycles, 50% REM sleep compared to adult’s 20%. so theory that REM could be key to development of NS

sleep pattern for mammal old age

old people sleep less, awake more, and spent less time in NREM 3 deep slow wave sleep

SWS

slow wave sleep associated with delta waves, NREM 3

How much sleep do we need

it is said 7-8 hrs for avg adult but it can vary from person to person

some people are good with 5 or 10hrs

correlational study of sleep time and morality

one study over 10 yrs found that those who slept for longer or shorter than 7 hrs had a higher mortality rate

7 is the sweet spot but this is just a correlation

Evolutionary basis for sleep: what sleep stages do some animals follow

most mammals, birds, reptiles sleep to some capacity. sleep varies widely between species

others have periods of slience rather than sleep but may be sleep, (need awareness?)

mammals show REM, NREM

birds SWS and REM

lizard, fish: REM like state

what is unique about Dolphin sleep

this animal cannot deeply sleep since they need to come up for air. so they don’t have REM because there is muscle antonia

their brain hemispheres are unilaterally SWS. one side rests while the other stays active

why do we sleep (name theories)

ENBM

Energy conservation

Niche Adaptation

Body/ Brain Restoration

Memory Consolidation

Energy conservation theory + evidence

we sleep to conserve energy, reduces the load on our metabolism if we rest. cheaper to run our body

physical: muscles, heart, BP, temp, breathing are reduced

evidence:

there are correlations between the amount of time you sleep and your metabolic rate: small herbivores with higher metabolism (use a lot of energy, lack storage) sleep more

doesn’t apply to predator species: sleep more than prey

Niche Adaptation hypothesis and evidence

we have evolved to be inactive for certain periods because being active at those times (ex. night) would put us at risk

stay hidden or quiet when its dangerous to be outside

decent amt of evidence since pattern of activity lines up with this, ex. if its time for mating stop sleeping

Body/Brain Restoration hypothesis, evidence plus critique

the body needs sleep to repair itself: cells, proteins

evidence: growth hormones is most released during SWS and there are links between poor sleep and poor immune function. no sleep can be fatal

and waste removal by glymphatic system (spine fluid) is active during sleep (blood moves from brain to system)

critque:

when we dont get enough sleep we still stay up, and dont sleep longer next night although we should need to make up for the repair

Memory consolidation theory (+evidence, possible mechanisms)

sleep is necessary for memories to be better consolidated, helps learning, and neural connectivity

evidence: verbal and non verbal tasks, tested with/out night of sleep

possible mechanisms:

synaptic homeostasis

Active system consolidation

Synaptic homeostasis (possible mechanism for memory consolidation theory)

when we sleep synapses are downgraded so they are filtered out, leaving synapses that more relavent, and can continued to be strengthened

(rid of random noise, preserve strong connections)

Active system consolidation (possible mechanism for memory consolidation theory)

when we sleep we rehearse something that happened when we were awake, to help learning, and strengthen memory