Lecture 14 & 15: McDearmid

Question 1

Define learning:

Answer 1

A change in behaviour as a result of experience with a specific stimuli. - Allows for appropriate behavioural responses to a stimulus.

Question 2

Define memory:

Answer 2

Storage and the ability to recall experiences

Question 3

Why use aplysia californica to study learning and memory?

Answer 3

Simple model, Easy to observe response, easy to experiment on

Question 4

Why is aplysia californica a simple model

Answer 4

Only 2x10^4 cells in nervous system (reductionist) Cells are up to 1mm (very large) Many cells are identifiable and invariant as unique individuals.

Question 5

Why is aplysia californica easy to observe and measure responses

Answer 5

Respiratory appartus (gill, siphon) has distinct withdrawal response- withdraws into mantle cavity for protection when exposed to tactile stimulation

Question 6

Why is aplysia californica easy to experiment on?

Answer 6

Place on top of a photocell (photocell under gill) When gill is withdrawn light can pass through –> measurement of withdrawal

Question 7

What is non-associative learning?

Answer 7

A change in response strength due to prolonged exposure to a stimulus?

Question 8

What are examples of non-associative learning?

Answer 8

Habituation: experience leasd to decreased response strength (repeat innocous stimulus) Dishabituation: restoration of a habituated response due to a novel stimulus Sensitisation: increase in strength of a response following a strong novel stimulus

Question 9

How does the gill siphon withdrawal reflex habituate?

Answer 9

Gentle tactile stimulation to the siphon every 90 secs –> decreased withdrawal INSERT DIAGRAM

Question 10

How does the gill siphon withdrawal reflex display dishabituation?

Answer 10

Novel stimulus (shock) applied to the tail following habituation to tactile stimulus) –> increased withdrawal

Question 11

What is associative learning?

Answer 11

Classical conditioning: Present a conditioned stimulus (siphon stimulation) and pair this with an unconditioned stimulus (tail shock) Measure response of unconditioned stimulus alone

Question 12

How has associative learning been tested with aplysia californica?

Answer 12

Pair siphon stimulation with tail shock –> measure response to tail shock alone Unpaired CS and US –> measure response Apply tail shock –> measure response

Question 13

What are the results of associative learning experiments on aplysia californica?

Answer 13

Insert diagram - Paired response is the strongest —> increased strength response is retained for roughly 4 days due to memory?

Question 14

How do the intervals between the stimuli affect results?

Answer 14

The unconditioned stimuli will not be associated with the conditioned stimulus if it is applied before or if it is over 2 seconds after. The interval which provokes the strongest learning response is 0.5s

Question 15

Define short term memory:

Answer 15

temporary storage of information relating to an event that has just occured

Question 16

Define long term memory:

Answer 16

storage of information that relates to an event that has not recently occurred

Question 17

What does memory duration depend on?

Answer 17

Training period duration - 5 day training period: day 2 = reduced response, strong habituation by day 4, still habituated at day 12, forgotten by day 26. –> increase training period duration –> increased memory (long-term memory)

Question 18

What is the cellular basis of the gill-siphon withdrawal mechanism.

Answer 18

Monosynaptic connections between sensory and motoneurons. - Glutamatergic synapses (excitatory) —> easy to monitor changes

Question 19

How do you record post-synaptic gill responses to siphon stimulation on a cellular basis.

Answer 19

Question 20

How does short term memory work in aplysia californica?

Answer 20

Habituation: homosynaptic - Narrowing of pre-synaptic spike –> decreased glutamate release –> decreased EPSP Sensitisation: -increased activity: increased Ca2+ –> increased glutamate release –> increased EPSP

Question 21

What causes sensitisation?

Answer 21

Sensory neurons receive input from serotoninergic neurons which are innervated by tail sensory neurons. - serotonin binds to GPCRs

Question 22

Why does serotonin cause sensitisation

Answer 22

Serotonin is a neuromodulator –> activates signalling

Question 23

What evidence is there for the affect of serotonin?

Answer 23

Stimulate serotoninergic neurons –> release of serotonin –> sensitisation –> increased strength of synapse Apply serotonin directly –> sensitisation. Insert digram

Question 24

What are the effects of serotonin?

Answer 24

Depression of K+ channel conductance, reducing the speed of repolarisation –> increased duration for Ca2+ influx –> spike broadening

Question 25

What is the biochemical pathway for serotonin action?

Answer 25

serotonin binds to G-proetin coupled serotonin receptors on sensory neurons –> adenylyl cyclase activation –> increased cAMP production –> activates pKA –> phosphorylation of potassium channels –> reduced potassium conductance

Question 26

Comparing the chemical effects of habituated and sensitised responses.

Answer 26

Question 27

How does long term memory (sensitisation) work in aplysia californica?

Answer 27

serotoninergic activation of cAMP signalling –> duration and extent of activation is the difference between long and short-term memory. Longer duration activation –> longer duration memory

Question 28

What causes long term memory in aplysia californica?

Answer 28

Requires more powerful / repeated activation Leads to the expression of genes –> synthesis of new proteins.

Question 29

What is the biochemical basis for long-term memory in aplysia californica?

Answer 29

Changes in neuronal morphology: new synapses are formed (increased number and branches) cAMP builds up –> translocation of PKA to the nucleus –> phosphorylation of CREB1 (TF for intermediate early genes) –> transcription of genes –> transcription factors for late responsive genes –> expression of genes that encode proteins required for nascent synapse formation

Question 30

Why does associative learning produce a heightened response?

Answer 30

Increased synaptic transmission (sharp electrode exp) - adenylyl cyclase is calcium sensitive, action potentials —> Ca2+ influx –> adenylyl cyclase priming –> calmodulin binds to adenylyl cyclase –> increased response

Question 31

What relevance does this have to humans?

Answer 31

Procedular memory ( unconscious- perceptual and motor skills)

Explicit memory (conscious: fact/event recall)

Spatial memory in hippocampus

• long term potentiation