questions of learning and memory Flashcards
how do third order neurones respond selectively to odours
sample second order neurones and respond
what are kenyon cells
- in mushroom body
- each cell only responds to few odours
- receive input from multiple projection neurons and require multiple simultaneous inputs to fire (thus fire very selectively)
- sample small regions in PN “coding space”
recieve dopaminergic transmission and edit behavioural output
how is the dense combinational code turned into a sparse selective code for odour recognition
kenyon cells receive input from multiple projection neurons and require multiple simultaneous inputs to fire selectively
what is the GAL4/UAS system
- binary expression system
- allows us to artificially express arbitrary transgenes in specific cells
what is GAL4
yeast transcription factor
- insert into genome and control under enhancer which puts GAL4 into certain cells of body → cellular specificity
- TF binds to DNA sequence = upstream activating sequence → recruits TF to initiate transcription downstream of UAS
what happens if you split the GAL4 system
split into 2 separate proteins
1 half = DNA binding domain = binds to uas
1 half = activation domain = recruits tf
only in overlap where both halves of GAL4 expression = zip together and express UAS transgene
what is the mushroom body
- structure in fly brain = olfactory activity
- forms circuit for associative memory
- encode dopaminergic neurones = form different compartments of axonal lobe
- based on punishment = less = approach, more = avoid
how are kenyon cells organised in mushroom body
- cell axons are subdivided into compartments by innervation of mushroom body output neurons (MBONs)
what are MBONS
mushroom body output neurons
determines value = good or bad experience
Some MBONs lead to approach/avoidance behaviour when activated optogenetically
activation/deactivation leads to approach and avoidance behaviour
role of DANS
dopamine activated neurones
can entrain aversive or appetitive memory
what order are response and conditioned stimulus in for correct conditioning
odour -> punishment = avoid
punishment -> odour = relief = approach
how do flies know whether CS or response comes first
- electrically stim kenyon cells
- recording MBON
- artificially stim dopa neurone using art receptor + ligand
- measure response of MBON to kenyon cell = measures synaptic strength
which type of cells in MB are linked to odour detection
kenyon
which type of cells in MB are linked to reward detection
DANS
what happens when kenyon cells and DANS are activated at same time
activation at same time = synaptic depression
difference between dopr1 and dopr2
- signal through different gpcr pathways
- 1 = Gs → AC → cAMP
- 2 = Gq → PLC → IP3 → Ca2+ release
how is ER Ca release sensitive to order?
- IP3 receptor = sensitive to Ca
- Ca = signal for when kenyon cell is active
- IP3 → Ca = open
- Ca → IP3 = not open
- 2 possible binding sites for Ca
- if no ip3 = only red binding site available = locks receptor into conformation
- no ca = green is open → channel opens
what happens if ca binds to ER channel first
ca → locks → no ip3
what happens if ip3 binds to ER channel first
ip3 → ca binds → open
do we have similar odour detection structure as drosophila
- similar structure in cerebellum
- mossy fibres → more neurones (granule) → purkinje cells
- synapse between gran and purkinje fibres is modified by climbing fibres
what carries error signals
climbing fibres modify sinapse between granular and purkinje fibres
