Lecture 5 revision Flashcards
What is learning and memory
Learning - Strengthening of responses or formation of new responses to stimuli due to repetition or practice
Memory - Storage and retrieval of knowledge gained through learning
What are the different types of learning and memory
Declarative or explicit - knowledge about fact and their meaning
Non-declarative or implicit - knowledge about how to perform something (recalled unconsciously)
Implicit learning can be associative or non-associative
Non-associative learning and memory
Habituation - decrease in response to benign stimulus through repeated presentation of stimulus.
Sensitisation - Enhanced response to multiple different stimuli after presentation with noxious/intense stimulus.
Associative Learning and memory
Association between two stimuli is learnt
Classical conditioning: in Pavlov’s paradigm the food, which elicits a salivation response is the unconditioned stimulus, and the bell is the conditioned stimulus.
When bell is repeatedly paired with food the bell becomes able to elicit salivation, now called the conditional response
What have invertebrate studies shown about implicit memory?
experience modulates synaptic strength and structure
Short term memory - Lasts minutes and involves covalent modifications of pre-existing proteins at kinase synapses
Intermediate memory - Last hours and involves new protein synthesis (not mRNA)
Long term memory - Lasts days, weeks, or more and requires CREB-mediated gene expression, and new mRNA/protein synthesis
Neuromodulation in Aplysia
- Natural predator of sea snail is spiny lobster.
- Sea snails therefore close gill and syphon, and eject ink that repels and confuses lobster by a simple reflex circuit
- Following an attack, sea snails sensitized to future attacks by sensory neuron synapse modulation.
Aplysia nervous system
- 20,000 large identifiable nerve cells
- Individual neurons identified and electrical activity recorded
- Neural circuits controlling behaviour have been defined
- Behaviour most extensively studied in gill and syphon-withdraw reflex
Short term memory mechanisms
- Serotonin released in vivo or applied to cultured neurons where binds cell surface receptors of sensory neurons
- Activates adenyl cyclase and cAMP produced
- Increased cAMP causes short term sensitisation - increase in synaptic strength of sensory to motor neuron connection - short term facilitation partially due to glutamate release by sensory neuron
- Increased sensory neuron excitability due to depression of potassium channels
- cAMP and Ca level changes regulate kinase and phosphatase activity to control synaptic efficiency changes (duration and length)
What does short and intermediate term synaptic plasticity involve
Different combinations of pre- and postsynaptic molecules including:
Presynaptic PKA
Presynaptic calcium and CamKII
Presynaptic PKC
Post synaptic calcium and CamKII
Recruitment of ore and possibly postsynaptic molecules to new sites
Enhanced neurotransmitter release from sensory neurons
Cellular mechanisms of long-term memory formation in Aplysia
Long-term synaptic plasticity involves:
- Neurotransmitter release and short-term strengthening of synaptic connections
- Equilibrium between kinase and phosphatase activities at synapse
- Retrograde transport from synapse to nucleus
- Transcription factor activation
- Activity-dependent induction of gene expression
Classical olfactory learning and memory
- Learn contingency between an odor (CS) and aversive/appetitive stimulus (US)
- Conditioning requires activity of molecules that can integrate the two sets of sensory info
- AC performs integration in mushroom body neurons of fly
- Dopaminergic neurons carry info about avsersive stimuli and octopamiergic neurons about appetitive stimuli to MB neurons
GABAergic neurons control ability to learn via inhibitory inputs.
