Dreams For No Reason

Question 1

Glial cells

Answer 1

Extra cellular physical support
Provision on nutrients
Maintenance of extra cellular fluid around synapses
Types; oliogodendrocytes, asteocytes, microglia

Question 2

Cerebrospinal fluid

Answer 2

Clears waste

Maintains homeostasis

125ml at any point & 500ml generated every day

Question 3

Brain is richly supplied with blood

Answer 3

Dense capillary system in brain

20% of all blood pumped to brain

60% of all glucose used by brain when at rest

Comprises only 2% of body’s mass

85 billion cells, 1,000-10,000 connections

Question 4

Lymphatic system of brain

Answer 4

Drains fluid back into heart from lymphatic nodes

Question 5

Ventricles of brain

Answer 5

Cerebrospinal fluid

Fluid washes the brain, removing by-products

Question 6

Thalamus: specific relay nuclei

Answer 6

Vision: lateral geniculate nucleus

Hearing: medial geniculate nucleus

Sensation: central posterior nucleus

PGO (pons, LGN, occipital cortex) waves frequently referred to in discussion of sleep REM & are invoked to explain source of dreaming

Question 7

Thalamus; non-specific

Answer 7

Intralaminar nuclei & midline nuclei- diffuse projections to the cortex, general altering system

Reticular nucleus of the thalamus- coat over the thalamus, involved in sleep & wakeness

Question 8

Why do non-specific neurone matter?

Answer 8

Input from the senses pass through this layer before reaching their specialised processing sections of the thalamus & been passed to specialised processing sections of the cortex

Activity here has the ability to greatly waken all external input- ability to fall asleep & not be woken by external stimulation

Activity here has the ability to amplify input from specific senses or all- arousal/wakefulness

Changes the balance of cortical input from external to internal sources- dreaming

Neurons exist in tonic mode or burst mode

During sleep most are in burst mode (many during wakefulness)

No info can be transferred when rhymic bursts happen

Question 9

Thalamus: association neurons

Answer 9

Pulvinar- visual info & eye movement, probably attention

Input from distributed cortex & eye movement area

Output to secondary visual cortex in parietal/temporal area

Question 10

Neurotransmitters involved in sleep & dreaming

Answer 10

Release neurotransmitter wide, extremely long axons which terminate all over cortex

Acetylcholine- involved in muscles, released during sleep before REM initiated

Norepinephrine

Serotonin

Neurotransmitters manufactures & stored in axon terminals, then bind to receptor sites, opens/closes channels

Question 11

Synthesis, packaging & transport of neurotransmitters

Answer 11

Calcium influx causes vesicles to blend with membrane

Small molecule neurotransmitters- very important in sleep, in the terminal button by the Golgi complex

Large molecule neurotransmitters- in the cell body & transportes down to the terminals

Some neurotransmitters manufactured in axon terminal, some in cell body packaged & actively transported down axon terminal via micro tubules

Question 12

Metabotropic receptors

Answer 12

Can open ion channels from inside the cell

Slow developing, long lasting, varied in kind

Typical type for neurotransmitters involved in sleep

Can activate a cascade of enzyme production

Metabolic receptors work differently

Diffused vs localised release- localised release is very specific but general is diffuse so can affect more cells

Question 13

Neurotransmission

Answer 13

Local

Specific

Brief

Fine control

E.g. switching off wakefulness

Question 14

Neuromodulation

Answer 14

Widespread

Non-specific

Long-lasting

Increase of cortical stimulation

Question 15

Computational unit

Answer 15

Electrical charge inside next neuron will significantly change if the effect of many post-synaptic intervals are added

This will be most effective if they arrive about the same time in same part of next neuron

Question 16

Excitatory neurotransmitters & inhibitory effects

Answer 16

Effect of summing the inputs to give a cell body of neuron is that it either produces AP’s or doesn’t

If it produces AP’s this can lead to release of excitatory or inhibitory neurotransmitters

If it releases inhibitory neurotransmitters then the cells it contacts with become less & less likely to produce nerve impulses

Question 17

Neurotransmitters

Answer 17

Amino acids- glutamate (dominant excitatory neurotransmitter), GABA (inhibitory)

Monoamine neurotransmitters- serotonin, dopamine, norepinephrine (control sleep, brain stem neurona with diffuse branching)

Acetylcholine- involved in sleep & transmission to REM (dreaming?)

Neuropeptides- look & act like neurotransmitters, orexin (sleep control)

Question 18

Recycling of neurotransmitters

Answer 18

After the neurotransmitters have had their effect they are typically reabsorbed back into the neuron that released them (pre-synaptic cell)

Question 19

Theories from REM observation

Answer 19

A perspective that studies REM sleep & makes inferences about dreaming

Many variants but share a conclusion

Dreams are a by-product of brain activity, they have no meaning or purpose

Brain is active, sometimes more active than wakeness

No perfect correspondence between dream & REM, perception cannot be equated to brain activity, some other property of consciousness, dreams not reducible to physiology

Seems to be random, chaotic activity from pons & medulla

Brain still working so still get some experience but doesn’t mean anything

Most popular explanation

Question 20

Aserinsky & Kleitman (1955)

Answer 20

Only in 20/27 cases when people were woken from REM did they report having dreaming

Question 21

Vertes & Eastman (2000)

Answer 21

Slow wave sleep (deep sleep)- brain activity is very different from wakefulness

REM sleep- the brain activity is more similar to wakefulness

Theory; REM maintains CNS activity throughout sleep- keeps it active so when wake up brain can function

REM eases sleeper back to wakefulness

Implication- dreams are a by-product of this biological necessity as activity approaches that of consciousness

Question 22

Sleep cleans the brain

Answer 22

Xie et al (2013)

Cerebrospinal fluid flows through the brain & clears out toxins through a series of channels that expand during sleep

Distorted processing occurs (dreaming)

Question 23

Reverse learning

Answer 23

Crick & Mitchinson (1983)

No function of dreaming (by-product of cognitive neural change)

In order for brain to function when awake, neurons have to be in autonomous state, in sleep neurons out in this state so when wake up neurons can respond

Question 24

Purpose of REM sleep

Answer 24

Dreams are still meaningless

You are the passive observer as memories are unlearned

Experience old memories being discarded (rubbish in the brain, stupid connections being broken)

Undesirable links broken, the irrelevant eliminated

Not just random, a function & purpose

Question 25

Neural networks

Answer 25

Theoretical influence Network of cells linked together= 1 event Distributed, robust & superimposed (some nerve cells might encode different things) Different stimuli activates different cells, pattern of activation= experience When such networks become overloaded, distant associations activated, responses from weak stimuli (want strong stimuli activating its representation)

Question 26

Reverse learning- how to fix an overloaded network

Answer 26

How to eliminate the parasitic connection 1) switch off external input 2) bombard with random signals 3) weaken any association that fires

Question 27

Brain stem mechanisms

Answer 27

Random firing in brain stem effects cortex PGO waves first sign of REM sleep in animals Weak signals activated are experienced in dream- want to break these links so brain isn’t overloaded (ensures appropriate connections) PGO waves send weak signals If weak signal can activate a memory, that link must be broken Reverse learning is this process that weakens the links Dreams are the experience of the activation of memories by weak random input If they were important, you’d remember them Dream for 1.5-2 hrs every night & little remembered During dreaming we get rid of memories we don’t need- dream in order to forget

Question 28

Synaptic homoeostasis hypothesis

Answer 28

You get a glimpse at the neural free for all in dreams Tonnoni (2013) Fruit flies- control flies left in boring 1 fly per tube, experimental flies unleaded for 12 hrs to a fly mall with hundreds of other flies Number of connections fell back to normal levels after sleep, showing correlating cycle of neuronal connections after waking activities & declines after sleep Rapidly create dendrites (connections) throughout the day, simplified during sleep (get rid of irrelevant stuff)

Question 29

Activation- synthesis

Answer 29

Hobson & McCarley (1977) Random signals sent from brain stem to visual cortex & other areas Memories, emotions etc are randomly activated External signals attenuated Internal signals relatively strong Hypothesis- cortex tries to make sense of input, that is experienced as dreaming

Question 30

Brain stem activity- the signal starts

Answer 30

PGO waves Brain getting input it needs to make sense of

Question 31

The input to be understood

Answer 31

Brain is living in virtual reality world, constructing it Analogous to a Rorscach ink blob- brain makes sense of things with no meaning Dream seems real as same neural structures used that create your reality when awake

Question 32

AIM model

Answer 32

Extension of activation-synthesis theory Accommodates all conscious states, including the dream state

Question 33

Activation element of AIM

Answer 33

Activation- low= no consciousness, high= consciousness In REM sleep activation is high, in NREM activation is low

Question 34

Physiological mechanism

Answer 34

A brain stem mechanism Reticular activating system Long axons to many parts of the brain Neuromodulators- widespread effects

Question 35

Internal element of AIM

Answer 35

Where does input come from? External- when awake Internal- REM & NREM sleep Random brain stem signals to many cortical areas (see & hear) & limbic areas (emotions)

Question 36

External attenuation

Answer 36

Shell of the thalamus (reticular nucleus)

Question 37

Modulation element of AIM

Answer 37

Neuro-modulators balance shifts Awake & NREM- acetylcholine (inhibited) REM- acetylcholine released

Question 38

Key neurotransmitter systems

Answer 38

Serotoninergic- raphe nuclei Noradrenergic- locus coerulus Acetylcholinergic- dorsal brainstem (peribrachial area)

Question 39

Shift in neurotransmitter balance

Answer 39

Relative balance of neurotransmitters change during sleep Activated limbic structures, deactivated dorsolateral prefrontal lobe structures, can’t judge, remember, plan, reason etc Deactivated posterior cingulated- poor episodic memory

Question 40

Dream features accounted for

Answer 40

Dreams seem very real (sensory character) Planning & memory is weak e.g. why are you there, what you are trying to do Often a strong, typically negative tone