Lecture 5 Flashcards
What is learning?
Strengthening of responses or formation of new responses to stimuli due to repetition or practice
What is non-declarative or implicit learning and memory?
Knowledge about how to perform something
Implicit learning and memory can be associative or non-associative
What is memory?
Storage and retrieval of knowledge gained through learning
What are the two forms of non-associative learning and memory
Habituation - Decrease in response to a benign stimulus through repeated presentation of the stimulus
Sensitisation - Enhanced response to multiple different stimuli after presentation with a noxious or intense stimulus
What is declarative or explicit learning and memory?
knowledge about facts or their meaning
Associative learning and memory
- Association between two stimuli learned
Classical conditioning: Pavlov’s paradigm
Food is unconditioned stimulus
Bell is conditioned stimulus
When bell us paired with food, the bell becomes able to elicit salivation, and is now the conditioned response
What do invertebrate neuromodulation studies indicate?
Forms of implicit memory involve experience-dependent modulation of synaptic strength and structure.
Short term memory
Lasts minutes
Involves covalent modifications of pre-existing proteins at synapse by kinases
Intermediate term memory
Last minutes
New protein synthesis (not mRNA synthesis)
Long term memory
Last days, weeks, or longer
Requires CREB-mediated gene expression
Also requires new mRNA and protein synthesis
Neuromodulation in Aplysia
Natural predator is spiny lobster
Respond to attack by closing gill and syphon, ejects ink containing chemicals that confuse and repel lobsters - behaviour controlled by simple reflex circuit
Following an attack, sea snail sensitized to future attacks
Sensitization to attack involves modulation of synapses at sensory neurons
Aplysia nervous system
20,000 large, identifiable nerve cells
Individual neurons identified and electrical activity recorded
Neural circuits controlling behaviour have been identified
Behaviour most extensively studied is gill and syphon-withdrawal reflex
Tacticle stimulus on siphon activates sensory neuron 1
Cellular mechanisms of short and intermediate term memory formation in Aplysia
- Serotonin released in vivo or applied to cultured neurons - binds to cell surface receptors of sensory neurons
- Binding activates adenyl cyclase - Promotes cAMP production
- Increased cAMP leads to shirt term sensitisation - Increased synaptic strength of sensory to motor neuron connection (short term facilitation)
- Short term facilitation is partially due to enhanced glutamate release
- Short term facilitation accompanied by an increase in neuron excitability due to certain K+ channel depression
- Changes in cAMP and Ca levels regulate activity of kinases and phosphatases - Controls duration and strength of synpatic efficiency changes
What molecules are involved in short and intermediate-term synaptic plasticity in Aplysia
Presynaptic PKA
Presynaptic calcium and CamKII
Presynaptic PKA
Postsynaptic calcium and CamKII
Recruitment of pre- and possibly postsynaptic molecules to new sites
Results in enhanced neurotransmitter release from sensory neurons
Cellular mechanism in long-term memory formation in Aplysia
- Neurotransmitter release and short-term strengthening of synaptic connections
- Equilibrium between kinase and phosphatase activities at synapse
- Retrograde transport from synapse to nucleus
- Activation of nuclear transcription factors
- Activity-dependent induction of gene expression
Cellular mechanisms of long-term memory formation in Aplysia
chromatin alteration and epigenetic changes in gene expression
synaptic capture of newly synthesized gene products
local protein synthesis at active synapses
synaptic growth and the formation of new synapses
activation of pre-existing silent synapses
The location of these events moves from the synapse to the nucleus and then back to the synapse.
Classical (associative) olfactory learning and memory in Drosophila
- Learning contingency between odor and an aversive or appetitive stimulus
- Requires activity of molecules that can integrate 2 types of sensory information
- Form of adenyl cyclase performs integration function in mushroom body neurons of fly brain
- Dopaminergic neurons carry info about aversive stimuli and octopaminergic neurons about appetitive stimuli to MB neurons
- GABAergic neurons control ability to learn via inhibitory inputs
