Learning and memory 2

Question 1

Why is the Aplyisa used extensively in neuroscience?

Answer 1

because Aplysia only has around 20000 neurones so it is much easier to relate specific neurones to behaviour

Question 2

Who won a nobel prize for his work with Aplysia?

Answer 2

Eric Candel

Question 3

What forms of learning does Aplysia have?

Answer 3

non-associative and associative

Question 4

What is non-associative learning?

Answer 4

• Non-associative learning: change in animals behaviour as a function of experience with particular kinds of stimuli (no temporal relationship between stimuli and response)

• Habituation: loss of response because of repeated stimulus
• Dishabituation: recovery of innate response
• Sensitisation: response stronger than normal (e.g. if a student had experienced a real fire they are more sensitive to fire alarms)

Question 5

what is an example of associative learning?

Answer 5

Classical conditioning

Question 6

What was a non-associative learning experiment carried out with Aplysia?

Answer 6

In experiment Aplysia were kept in an aquarian with parapodium and mantle showing the gill, the movement of the gill was recorded to trace the amplification and response to a specific stimulus. The gill was then poked to elicit a response (siphon stimuli). After first stimuli there was a strong response. As poking carried on the gill response decreases. However, if a stimulus is then given a strong stimulus such as an electric shock, the response was back to normal after that (sensitisation)

Question 7

How is classical conditioning shown in Aplysia?

Answer 7

• Tail shock is unconditioned stimulus
• Siphon stimulus is conditioned stimulus
• Group 1: siphon stimulation paired with tail shock
• Group 2: 2 stimuli were unpaired
• Group 3: received tail shock alone constituting a sensitisation control
• The paired stimuli showed much greater response to CS alone, then the US did then the unpaired

Question 8

what are features of associative learning in Aplysia?

Answer 8

• No learning with backward pairing

- Optimal learning occurred only if CS preceded US by 0.5s – time influences learning

Question 9

What is key in formulating long term memory?

Answer 9

Training

Question 10

What is distributed vs massed training?

Answer 10

• Distributed training (10 trials every day for 4 days) – better than mass training
• Massed training (40 trials in one day)

Question 11

What does Aplysia show long term memory for?

Answer 11

• Aplysia shows LT memory for habituation
• Aplysia shows LT memory for sensitisation
• Aplysia shows LT memory for classical conditioning

Question 12

Give features of Aplysia’s nervous system

Answer 12

• Nervous system consists of ganglia
• Ganglia communicate through connectives
• Ganglia arranged in bilaterally symmetrical pairs
• Abdominal ganglion is unpaired
   Controls heart rate, blood circulation and respiration
   Contains primary sensory neurons, interneurons and motor neurons involved in the gill and siphon withdrawal reflex

Question 13

What does synaptic analysis show about Aplysia learning?

Answer 13

• Influx on calcium into the cell, release of neurotransmitters, EPSP
• Sensitisation input (tail shock) -> marked increase in duration of sensory AP (spike broadening
• Spike broadening induces increase in depolarisation in century neuron terminals -> increased calcium release -> increased transmitter released -> increased EPSP (presynaptic facilitation)

Question 14

What is the importance of serotonin in sensitisation and presynaptic facilitation?

Answer 14

• Induces facilitation
• Increases sensory neurone excitability
• Increased in motor neuron EPSP
• Increase in reflex amplitude

Question 15

What does biophysical analysis in the sensory neuron tell us about aplysia sensitisation?

Answer 15

• Tells us about ionic events contributing to reflex
  1. Serotonin temporarily closes potassium channel (S current) in sensory neuron
  2. Outward potassium current is slowed
  3. Repolarisation of membrane potential is slowed -> spike broadening
  4. Increase calcium influx
  5. Increase in transmitter release

Question 16

What does Molecular analysis tell us about sensitisation?

Answer 16

• cAMP acts as second messenger
• cAMP activated PKA
• Active PKA phosphorylates substrate proteins
• Serotonin increases levels of cAMP inside sensory neurons
• Injections of cAMP directly into sensory neurons causes increased transmitter release
• Injection of PKA causes increased spike broadening
• Inhibition of PKA causes decreased spike broadening

Question 17

What does mechanistic analysis of long-term memory do?

Answer 17

• Repeated serotonin or cAMP applications induces long term sensitisation:
• Persistent phosphorylation of pre-existing proteins and synthesis of new proteins ->
• Long-term increase in synaptic facilitation ->
• Long-term increase in synaptic transmission ->
• Dramatic growth of sensory neuron processes ->
• Long term memory for sensitisation

Question 18

What does synaptic facilitation require and how was this found?

Answer 18

• Synaptic facilitation requires postsynaptic protein synthesis

• Researchers isolated sensory neurone and motor neurone
• If serotonin added to the dish the size of the response increases
• If galanin (protein synthesis inhibitor) is added with serotonin initial response is not affected but long term response is (showing protein synthesis is needed)

Question 19

What are the long term sensitisation and habituation effects of neuron synapses?

Answer 19

• Long-term sensitisation: much more branching

- Long-term habituation: reduces number of neuronal projections