memory Flashcards
what does memory allow animals to do and explain the example of pavlov
memory allows animals to predict the future, but it isnt always predicted correctly.
pavlovs dogs had classical conditioning, the unconditioned stimulus was food and the neutral stimulus was the bell and this becomes the conditioned stimulus.
the NS predicted the future, the bell means that food will come.
the CS should coincide with or precede the US.
give the example of how flies can be classically conditioned to smells
pair a particular odor with either a shock or sugar coat the walls of the cage.
present odor A with the shock and odor B with the sugar, then present both odors and see which the fly chooses to move towards.
The fly should avoid A and go to B.
how are odors detected and then where is the info sent to
what are the kenyon cell connections like and how do they code odors
odors activate olfactory receptor neurons which will activate projection neurons and they will activate kenyon cells.
each kenyon cell receives input from many projection neurons, the kenyon cells require a lot of input to fire so they fire very rarely.
kenyon cells sample small regions in the projection neuron coding space and this turns the dense combinatorial code of PNs into a sparse selective code in the kenyon cells.
what neurons are activated when a fly experiences an odor at the same time as a reward/punishment
you will get simultaneous activation of the kenyon cell for that odor and of dopaminergic neurons for the reward/punishment.
this will result in a change in the output synapse of the kenyon cell and this will affect the behavioral response.
what is GAL4 and how is it used in the GAL4/UAS system
what is the problem with this method
is an exogenous TF from yeast.
the GAL4/UAS system allows us to artificially express arbitary transgenes in specific cells.
GAL4 is implanted into the genome next to an enhancer for a specific area of the body.
GAL4 protein will be made and it will bind to the UAS gene, this will induce the transcription of the gene next to the UAS gene.
This gene could be anything such as GFP.
this is achieved by having a mother fly with GAL4 expression and the father fly with UAS expression and so their progeny will have both and can be used
it is very hard to find specific enhancers for specific cells.
what is the split GAL4 system
it allows even greater specificity in which cells express the transgene.
GAL4 is split into its two domains, the DNA binding domain for recognizing UAS and the activation domain for recruiting transcription machinery.
you need both halves to induce transcription.
if you put a zipper domain on each of the two GAL4 domains, only where both expression domains are present will GAL4 be active, and this means that this is the only place where the transgene is expressed too.
what cells make up the mushroom body and where are they found
picture of structure
the kenyon cells make up the mushroom body and they are at the back of the brain.
there is one in each hemisphere.
how are kenyon cells axons subdivided into compartments
kenyon cell axons are subdivided into compartments by innervation of mushroom body output neurons (mbons)
mbons send info onto other parts of the brain, each one goes to a different area.
the kenyon cell axons are also subdivided into compartments by innervation of dopaminergic neurons which also all send info to a unique area
the mbon and dopaminergic compartments match, there is a 1:1 match of one of each.
what can happen when you activate mbons optogenically and how would they do this
some mbons lead to approach/avoidance behavior if they are activated optogenically.
cschrimson is expressed in specific mbons using split GAL4.
the flies are put in a behavior chamber where they can choose to be in one of four quadrants, light is shone into particular quadrants that will activate the gene with split GAL4.
this will activate the mbon and the fly will show the behaviour that the mbon encodes, if the mbon is for avoidance behaviour the fly will avoid the lit up chambers and vice versa.
how can dopaminergic neurons be used to write artificial memories
this can happen when they are activated optogencally.
a chamber is used with different odors in each quadrant, the light is shone to activate the dopaminergic neurons at the same time the flies smell the odor.
then a second odor is given when there is no dopaminergic activation.
then the flies are made to choose between the two odors.
if the dopaminergic neurons activated was for pain response, the fly will avoid this odor when it gets to choose and it will go towards the seconds odor.
this has created an artificial memory because the fly hasnt really got an bad consequences from the odor.
in what way are dopaminergic and mbons paired
what does this mean for the function of dopaminergic signalling
they are paired with a partner of the opposite valence.
a reward neuron is paired with an output neuron that drives avoidance behaviour and vice versa.
this means that dopaminergic signalling weakens the synapse between the kenyon cells and the mbons.
this means the ‘approach’ mbon neurons response will be weakened by punishment dopaminergic neurons.
this means the fly will avoid because no approach response is being made.
PICTURE
the response is decided by whichever of the neurons are not being weakened, they will give the response.
an experiment that shows that dopaminergic neurons weaken synapses
an odor was paired with optogenetic activation of a dopaminergic neuron.
it caused a depression in the mbon response to the odor because the dopaminergic neuron had weakened the synapse.
if you present the light before the odor is given, they dont show the learning.
what is spike timing dependant plasticity and how do we test for it
depends on the relevant timing of the spikes in the post and pre synaptic neuron.
if the pre spike comes before the post you will strengthen the synapse.
if the post fires before the pre it means the pre was useless in causing post firing, so the synapse isnt useful and will be weakened.
if you block firing in the post synapse using a voltage clamp so it cannot spike.
they found that spikes in the mbon are not required for plasticity because there was a decrease in the spiking of the mbon, this means it is not STDP.
what is the plasticity learning rule
it is different across all compartments.
some take longer to learn than others and this allows for different types of memories to form.
fast learned ones that are easily forgotten or slow learned ones that last longer.
what part of the brain is for correcting errors in different animals
and how do they do it
mushroom body in insects and cerebellum and the electrosensory lobe in electric fish.
the mushroom body has synaptic depression to stop the wrong behavior.
the cerebellum has climbing fibres that carry error signals for wrong motor actions
the architecture of the mushroom body and the cerebellum are very similar, the climbing fibres depress synapses too.
