Memory and learning 2

Question 0

where does synaptic plasticity occur?

Answer 0

found in many brain regions

mostly studied in the hippocampus

Question 1

what is synaptic plasticity ?

Answer 1

its the communication between 2 neurons - its the change in the strength of this connection
it is the flow of current between them - movement and exchange of charged particles
signals cause depolarisations causing changes to the extracellular and intracellular currents which can be measured using electrodes

Question 2

why is the hippocampus ideal for recording synaptic plasticity ?

Answer 2

because of the geometry of the neurons

in CA1 the neurons are all orientated in the same direction - all have strong connections with one another

Question 3

when was synaptic plasticity founded and how was it founded ?

Answer 3

1970
found by artificially stimulating the afferents the perferent pathway in rabbits - the stimulating electrode is inserted into the perferent pathway and the recording electrode is inserted into the DG
the resulting extracellular recordings were larger than before after a train of stimulation
this lasted weeks afterwards
the plasticity of the connection had been strengthened= long term potentiation

Question 4

what is another pathway other than the perferent pathway which is looked at in the hippocampus ?

Answer 4

the pathway between CA3 and CA1 via the schaffer collaterals
the stimulating electrode is on CA3 and the recording electrode is by the dendrites in CA1

Question 5

what are the standard protocols to induce synaptic plasticity ?

Answer 5

theta waves and 100Hz

Question 6

what does it mean by 100Hz stimulation ?

Answer 6

deliver 100 pulses at 100Hz = intense stimulation

Question 7

how do theta waves work ?

Answer 7

works at 8 Hz

Question 8

what is the conditioning stimulus in LTP protocol ?

Answer 8

brief high frequency extracellular stimulus given - 100 pulses at 100Hz = tetanus

Question 9

what response is caused by the conditioning stimulus?

Answer 9

extracellular recordings show that the post synaptic potential increases in amplitude

Question 10

what is usually used to measure LTP?

Answer 10

brain slices but whole animal preps can also be used

Question 11

how is LTD caused ?

Answer 11

its caused by a low frequency stimulation

Question 12

what is the molecular mechanism for LTP?

Answer 12

1- stimulation causes depolarisation by activation of AMPA receptors
2- tetanic stimulation causes intense depolarisation by activation of more AMPA receptors - causes the removal of magnesium block in NMDA receptors leading to their activation
3- influx of calcium ions through the NMDA receptors and this causes activation of kinases
4- kinases phosphorylate intracellular AMPA and cause more AMPA to be inserted into the membrane leading to larger responses
5- retrograde messenger may play a role

Question 13

what type of AMPA receptors are inserted into the membrane during LTP?

Answer 13

GluA2 + 3 these dont allow calcium through

Question 14

how does retrograde messengers play a role in LTP?

Answer 14

NO synthetase has domains that are linked to cAMP and NMDA receptors by PZ domain
when calcium enters the post synaptic neuron it activates NO synthetase and this causes the production of NO which diffuses into the synaptic cleft and enters the presynaptic neuron so it can control the amount of neurotransmitter released during its next stimulation

Question 15

what happens to dendrites after plasticity ?

Answer 15

their morphology changes - they expand and get bigger because they have more machinery
mushroom like dendrtes are fully formed dendrites which contain all the machinery

Question 16

explain the process of synaptic plasticity involving mice whiskers

Answer 16

this process is known as experience dependent plasticity due to sensory depletion
in mice each whisker is represented by its own barrel in the neocortex, therefore activation of a single whisker will activate a its specific barrel in the neocortex
but if you remove all whiskers apart from one for a while then if you stimulate that single whisker you can record activity in all barrels beause due to synaptic activity the repsonses has spread out in the neocortex - the system becomes more sensitive
in humans this is used to represent phantom limbs

Question 17

what regions of the brain are LTP/LTD normally found ?

Answer 17

in brain regions associated with learning

Question 18

what happens to knockout mice of GluA1 ?

Answer 18

they have impaired early LTP and impaired spatial working memory - get much slower potentiation

Question 19

what is long term non-declarative memory ?

Answer 19

procedural/implicit memory
skills and associations acquired mainly at an unconscious level
rigid memory store
commonly involved in training reflexive motor or perceptual skills- driving a car

Question 20

what are the brain regions involved in non-declarative memory ?

Answer 20

basal ganglia
amygdala- emotional memories
prefrontal cortex
sensory association cortex 
cerebellum-motor memories

Question 21

what are the 2 types of non declarative memory ?

Answer 21

non- associative - change in motor response after repeated presentation of a stimulus
associative - emotional type

Question 22

what are the divisions of non associative procedural memory ?

Answer 22

habituation- decreases in motor response

sensitisation- increase in motor response

Question 23

what are the 2 divisions of associative procedural memory ?

Answer 23

classical conditioning - change in passive motor response after learned association between 2 stimuli
instrumental or operant conditioning - change in active motor response after association between motor action and reward

Question 24

what invertebrate model was used to analyse the molecular mechanisms of habituation, sensitisation and classical conditioning ?

Answer 24

aplysia

marine sea slug

Question 25

what is the gill withdrawal reflex in aplysia ?

Answer 25

stimulus= mild tactile stimulus to siphon- blow of water
response= reflex contraction of gill
first time this happens there is a vigourous contraction of the gill but once it realises that no harm is caused by it the contraction is reduced

Question 26

how is the reflex in aplysia recorded ?

Answer 26

its a monosynaptic reflex arc

intracellular electrode is placed into the abdominal ganglion to record the synaptic activity

Question 27

how is habituation caused ?

Answer 27

caused by presynaptic modfications
- nt is released in quanta
- quantal analysis of psp showed that decreased synaptic strength results from a decrease in the number of transmitter vesicles released
there is no chnage in the sensitivity of the post synaptic receptors to nt
- means that presynaptic modulation underlies habituation in aplysia

Question 28

what is the circuitry of sensitisation of gill withdrawal in aplysia ?

Answer 28

by applying an electric shock to the tail after the water shock, increases motor responses 
neuron L29 (5HT)  makes an axo-axonic synapse with axon terminal of the sensory neuron onto th motor neuron

Question 29

what is the molecular basis for sensitisation in aplysia ?

Answer 29

1- serotonin binds to g protein linked receptor to increase cAMP
2- cAMP activates protein kinases A to phosphorylate potassium channels and decrease K current
3- action potential is prolonged and more voltage gated calcium channels open
4- increasess in the amount of intracellular calcium increases amount of nt release

Question 30

explain the example of classical conditioning

Answer 30

pavlovs dog

• conditioned stimullus was a bell
• unconditioned stimulus was food
• both stimuli given simultaneously for many trials
• conditioned stimulus then produces conditioned response of salvation

Question 31

explain the example of instrumental conditioning

Answer 31

rat learns that by pressing a lever there is a reward of food
or
rat learns to associate pressing lever when light comes on with a food reward

Question 32

explain an example of aversive emotional learning

Answer 32

rodent will drink a sweet substance
then LiCl is injected into the rodent causing nausea
24 hours later the rodent should avoid that drink
involves many brain areas including the thalamus and amygdala

pairing of a tone to a footshock
requires the lateral amygdala to central nucleus of the amygdala pathway
stimulus will automatically produce fear reaction
lesions to the central nucleus show animals that have no fear