learning and memory 2

withdrawal reflex of aplysia

• tactile sitmulus brushes the mantle shelf or siphon

• gill and siphon are withdrawn into mantle cavity and covered by the parapoidium

  • protects respiratory apparatus

• the longer it remains contracted the more it has learnt

non associative learning

• change in behaviour as a function of experience w stimulus

• no temporal relationship

examples of non associative learning

Habituation: loss of response because of repeated stimulus

Dishabituation: partial or complete restoration of innate response

• seen with tail shock

Sensitisation: response stronger than normal

associative learning

classical conditioning

classical conditioning in aplysia

• tail shock as unconditioned stimulus

• tactile stimulus to siphon as conditioned stimulus

• intensity of reflex response inc with paired stimuli

differential classical conditioning in aplysia

• two conditioned stimuli used

  • tactile stimulus to siphon

  • tactile stimulus to the mantle

• animals responded more to paired stimulus than unpaired

forward pairing example for learning in aplysia

• siphon stimulus preceeding tail shock for optimum learning

• associative learning

• time and order is important

distribution vs massed training

• distributed produced superior retention of memory

• trials spread out over more days

memory for habituation in aplysia

• duration of response decreases after accumulative habituation

• after 3 weeks response starts recovering but still half of what it used to be at the start of the experiment

memory for sensitisation

• response is higher one day after tranining due to sensitisation

• higher response is kept for several weeks

• accumulative sensitisation

• even after 3 weeks the response is higher than the control before training

neural circuit for siphon withdrawal

• sensory neurons, interneurons, motor neurons

• 22 sensory neurons connect directly to motor neurons

• modulatory input from tail

3 forms of mechanistic analyis of short term learning

synaptic

biophysical

molecular

synaptic analysis

• sensitisation causes spike broadening so longer duration of depolarisation

• serotonin plays major role in sensitisartion and presynaptic facilitation

• increase in amplitude of response

biophysical analysis of sensitisation

• serotonin temporarily closes potassium channels current in sensory neurons

• prolongation of action potential

• enhances excitability

molecular analysis of sensitisation

• cAMP acts as a second messenger

• activates pKA

• activated pKA phosphorylates substrate proteins

• serotonin inc cAMP

long term memory mechanistic analysis

• repeated serotonin or cAMP applications leads to

  • persistent phosphorylation of preexisting proteins

  • synthesis of new proteins

  • long term increase in synaptic facilitation

  • long term inc in synaptic transmission

  • dramatic growth of sensory neuron processes

  • long term memory for sensitisation

what is required for long term synaptic facilitation

post synaptic protein synthesis

gelanine

• protein synthesis inhibitor

• would reduce long term response

long term sensitisation effects on neuron synapses

neurons have increased branching and sites

long term habituation effect on neuron synapses

neurons have less branching