Lecture 14 & 15: McDearmid Flashcards
Define learning:
A change in behaviour as a result of experience with a specific stimuli. - Allows for appropriate behavioural responses to a stimulus.
Define memory:
Storage and the ability to recall experiences
Why use aplysia californica to study learning and memory?
Simple model, Easy to observe response, easy to experiment on
Why is aplysia californica a simple model
Only 2x10^4 cells in nervous system (reductionist) Cells are up to 1mm (very large) Many cells are identifiable and invariant as unique individuals.
Why is aplysia californica easy to observe and measure responses
Respiratory appartus (gill, siphon) has distinct withdrawal response- withdraws into mantle cavity for protection when exposed to tactile stimulation
Why is aplysia californica easy to experiment on?
Place on top of a photocell (photocell under gill) When gill is withdrawn light can pass through –> measurement of withdrawal
What is non-associative learning?
A change in response strength due to prolonged exposure to a stimulus?
What are examples of non-associative learning?
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
How does the gill siphon withdrawal reflex habituate?
Gentle tactile stimulation to the siphon every 90 secs –> decreased withdrawal INSERT DIAGRAM
How does the gill siphon withdrawal reflex display dishabituation?
Novel stimulus (shock) applied to the tail following habituation to tactile stimulus) –> increased withdrawal
What is associative learning?
Classical conditioning: Present a conditioned stimulus (siphon stimulation) and pair this with an unconditioned stimulus (tail shock) Measure response of unconditioned stimulus alone
How has associative learning been tested with aplysia californica?
Pair siphon stimulation with tail shock –> measure response to tail shock alone Unpaired CS and US –> measure response Apply tail shock –> measure response
What are the results of associative learning experiments on aplysia californica?
Insert diagram - Paired response is the strongest —> increased strength response is retained for roughly 4 days due to memory?
How do the intervals between the stimuli affect results?
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
Define short term memory:
temporary storage of information relating to an event that has just occured
Define long term memory:
storage of information that relates to an event that has not recently occurred
What does memory duration depend on?
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)
What is the cellular basis of the gill-siphon withdrawal mechanism.
Monosynaptic connections between sensory and motoneurons. - Glutamatergic synapses (excitatory) —> easy to monitor changes
How do you record post-synaptic gill responses to siphon stimulation on a cellular basis.
How does short term memory work in aplysia californica?
Habituation: homosynaptic - Narrowing of pre-synaptic spike –> decreased glutamate release –> decreased EPSP Sensitisation: -increased activity: increased Ca2+ –> increased glutamate release –> increased EPSP
What causes sensitisation?
Sensory neurons receive input from serotoninergic neurons which are innervated by tail sensory neurons. - serotonin binds to GPCRs
Why does serotonin cause sensitisation
Serotonin is a neuromodulator –> activates signalling
What evidence is there for the affect of serotonin?
Stimulate serotoninergic neurons –> release of serotonin –> sensitisation –> increased strength of synapse Apply serotonin directly –> sensitisation. Insert digram
What are the effects of serotonin?
Depression of K+ channel conductance, reducing the speed of repolarisation –> increased duration for Ca2+ influx –> spike broadening
What is the biochemical pathway for serotonin action?
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
Comparing the chemical effects of habituated and sensitised responses.
How does long term memory (sensitisation) work in aplysia californica?
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
What causes long term memory in aplysia californica?
Requires more powerful / repeated activation Leads to the expression of genes –> synthesis of new proteins.
What is the biochemical basis for long-term memory in aplysia californica?
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
Why does associative learning produce a heightened response?
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
What relevance does this have to humans?
Procedular memory ( unconscious- perceptual and motor skills)
Explicit memory (conscious: fact/event recall)
Spatial memory in hippocampus
- long term potentiation
