psych201 1

While awake and relaxed you produce…

alpha waves on an EEG, as you drift off these slow down

NREM Stage 1

very easy to wake you, body starts to relax

NREM Stage 2

Deeper - heart rate slows, body temp drops. Sleep Spindles appear.

What are Sleep Spindles?

bursts of EEG activity that help memory consolidation

REM (Rapid Eye Movement)

your eyes dart around closed lids. Your brain is almost as active as you are when awake. Vivid and Emotional dreams can happen and Body is temporarily paralyised. Critical for emotional processing and memory consolidation

How often do you cycle through these stages?

You can cycle in and out of these stages throughout the night

More REM sleep appears in…

later cycles of the night, so if you sleep longer, get more REM

NREM Stage 3

slow wave/deep sleep. The most restorative stage Hard to wake. Growth hormone is released here. Your brain's waste clearance system is most active

What is the brains waste clearance system called?

Glymphatic System

Circadian Rhythm

a clock ticking inside your cells, working through a negative feedback loop. like a thermostat which turns itself off when it gets too hot

Clock Protein

a master switch that turns ON the genes for Per and Tim proteins stimulating their productions

Per and Tim proteins

once they build up enough (takes a long time), they team up and travel inside the nucleus to switch off clock. This stops more Per and Tim being made

The Clock Cycle

Morning → Clock is active → Per & Tim build up during the day → Evening → Per & Tim inhibit Clock → Per & Tim break down overnight → Clock becomes active again → repeat.

Zeitgeber ("time-giver")

The clock isn't exactly 24 hours, so it needs resetting. the main reset signal is light. This is why screens before bed is bad, it tells your brain it is still daytime

The suprachiasmatic nucleus (SCN)

located in the hypothalamus, right above where the optic nerves cross. It is the master clock of the brain, it keeps it ticking even when removed from the brain

The SCN receives light signals from.

specialised retinal ganglion cells that contain a pigment called melanopsin, which are sensitive to blue light and are slow to activate and switch off

The pineal gland is?

The SCN signals for it to release melatonin (the darkness hormone) at night which tells your body it is time to sleep

reticular formation (brainstem)

has both wake promoting and sleep related pathways. The pontomesencephalon recieves sensory information and generate activity with circadian rhythm

locus coeruleus

releases noradrenaline

what does noradrenaline do?

increases alertness and attention when active

hypothalamus releases…?

histamine (alertness) and orexin (keeps you awake). loss of orexin neurons causes narcolepsy

GABA

source: interneurons throughout brain, effect: promotes sleep, shuts down the thalamus so sensory information can't reach the cortex

Acetylcholine

source: brainstem (pontomensencephalon), effect: promotes wakefulness and REM sleep

glutamate

source: widespread, effect: promotes wakefulness

noradrenaline

source: locus coeruleus, effect: increases alertness (antihistamines make you tired)

orexin/hypocretin

source: lateral hypothalamus, effect: promotes wakefulness, stabilises wake state

insomnia

too little sleep

sleep apnea

breathing repeatedly stops during sleeping causing brief awakenings

Narcolepsy

sudden, uncontrollable urges to sleep. Often triggered by strong emotion. reduction of orexin

sleepwalking

most brain regions are asleep, but the motor cortex is still active. More common in children (5%) than adults (1.6%).

lucid dreaming

being aware you are dreaming. Occurs in ~23% of people regularly. Associated with frontal and temporal lobe activity during REM sleep. Tests have been run for people to hear and do maths in lucid sleep.

body temp while sleeping is

slightly lower than during the day

cortisol (stress hormone) while sleeping is…

stress levels are down at night, before you start to wake up cortisol levels increase and as the day progresses they decrease

age and gender with circadian rhythms

males and females follow similar pattern, males tend to wake up and go to sleep later than females around 20-30. during adolecense midpoint increases

older people do what during the night, and have less of?

they wake up more and slow wave sleep is lesser

hypothalamus controls:

circadian rhythm, temperature control and thirst and hunger

for animals that don't sleep during the night…

still produces a lot of melatonin at night but it produces wakefulness

caffeine blocks…

melatonin

histamine (NT)

source: hypothalamus, effect: increases alertness

Sleep processes increase…

GABA actvity which decreases activity in the thalamus, inhibiting sensory information reaching the cortex

GABA neurons are small and so the effect of increased GABA can be

local, some parts of the brain might be sleeping when others are not

why do we sleep?

restorative function, hormonal regulation, immune function consolidation, cognitive and memory function and memory consolidation.

cognitive and memory function

this involves synaptic homeostasis hypothesis (noise reduction) - synaptic pruning happens during the night, you make new synapses during the day and ones that are not useful are removed at night

immune function consolidation

low levels of inflammation while sleeping

hormonal regulation

growth hormone are very high at night and stress goes down at night. No sleep and cortisol does not move smoothly

threat simulation theory

dreams to rehearse mechanisms for survival

emotional regulation hypothesis

therapy session in low stress environment, dream about ex but without emotion

predictive processing theory

running generative models unconstrained by sensory input