Modern Questions in Learning and Memory Flashcards
How does classical conditioning work? (3)
- Unconditioned stimulus causes an unconditioned response
- Present a conditioned stimulus before the unconditioned stimulus to associate the two
- The conditioned stimulus on its own then causes the response to the unconditioned stimulus = the conditioned response
How is classical conditioning done in flies? (3)
- Present odour A and B to the flies
- Associate odour A with an electric shock
- Give the flies a choice between the two odours, the flies avoid odour A and choose odour B
Which cells are in the Mushroom body?
Kenyon cells
How do drosophila respond sparsely to odours? (3)
- Each Kenyon cell requires multiple simultaneous inputs from projection neurons to reach threshold
- This converts a dense combinatorial code in the projection neurons into a sparse selective code in the Kenyon cells
- Each Kenyon cell responds to a specific combination of odours = selectivity
How is reward/punishment associated with odour in drosophila? (2)
- Dopaminergic neurons respond to reward/punishment and modify the output of the Kenyon cells
- This leads to a behaviour associated with the odour
How does the GAL4/UAS system work? (3)
- GAL4 is a transcription factor from yeast
- Insert GAL4 into the genome under the control of a promoter which drives expression of GAL4 in specific cells
- GAL4 binds to UAS and causes transcription of whatever is downstream of UAS e.g. GFP etc.
What is the UAS?
Upstream activating sequence
What is the split-GAL4 system? (3)
- Split the GAL4 gene into the DNA binding domain and the activation domain, put each one under a different promotor
- Very specific subsection of cells in which both promoters will be active so both halves of the GAL4 protein are made, zip together and cause expression of the UAS-transgene
- Allows for greater specificity
Which part of the brain in drosophila is responsible for olfactory memory?
Mushroom body
What is the structure of the mushroom body? (3)
- Kenyon cells have their dendrites in the calyx
- Kenyon cells send axons down the peduncle
- The axons split to form the vertical lobe and horizontal lobe
What are MBONs? (3)
- Mushroom body output neurons
- Receive input from the Kenyon cells
- Encode value (good/bad experience) and lead to approach/avoidance behaviour
What are DANs?
Dopaminergic neurons
How does olfactory learning occur in the mushroom body? (3)
- Reward DAN axons innervate the same section of the mushroom body as the avoidance MBON dendrites
- Punishment DAN axons innervate the same section of the mushroom body as the approach MBON dendrites
- Learning occurs by the DANs weakening the synapse between the Kenyon cell and the avoid or approach MBON
How does the order of reward/punishment and odour change the behavioural response of the flies? (4)
- Flies learn to approach an odour if it is presented after a punishment
- Flies learn to avoid an odour if it is presented before a punishment
- Flies learn to approach an odour if it is presented before a reward
- Flies learn to avoid an odour if it is presented after a reward
What mechanism allows for plasticity in olfactory learning in drosophila?
DAN activity coinciding with Kenyon cell activity onto an MBON
What are the 2 types of dopamine receptor on Kenyon cells in drosophila?
DopR1 and DopR2
What kind of receptors are DopR1 and DopR2?
G protein coupled receptors
Which G protein is DopR1 coupled to:
Gs
Which G protein is DopR2 coupled to:
Gq
What happens when DopR1 is activated? (2)
- Adenylyl cyclase is activated which produces cAMP
- Leads to acquisition of memory
What happens when DopR2 is activated? (3)
- PLC is activated which makes IP3 and DAG
- IP3 causes release of Ca2+ from the endoplasmic reticulum
- Leads to forgetting
What is the equivalent of adenylyl cyclase in drosophila?
Rutabaga
How do the different dopamine receptors respond to different orders of odour and reward? (3)
- When reward happens before odour, DopR1 and DopR2 pathways are both active but DopR2 outweighs DopR1, causing synaptic potentiation i.e. backward learning
- When reward happens after odour, DopR2 is inactive so the DopR1 pathway causes synaptic depression i.e. forward learning
- Learning occurs by DANs weakening the synapse
What is EPAC?
Sensor for cAMP