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Excitable Cells - Lecture 19 (24/04/2018)
Learning and Memory II
Long-term potentiation (LTP) is a model system for studying synaptic plasticity and the neural basis of learning and memory with links to behaviour.
LTP aligns with Donald Hebb's hypothesis that "neurons that fire together wire together", so neurones connect synaptically and consistently fire at the same time become strengthened together. It aligns as LTP is a neural correlate for a change in synaptic strength during learning.
Learning in Invertebrates
For simple models for access to the nervous system and understand changes in neural function, invertebrates are used.
These include 2 main classic models:
Caenorhabditis elegans (nematode worm with 302 neurons).
Drosophila melanogaster (fruit fly).
For example, the drosophila can link odours to particular scenarios through olfactory associative conditioning.
To study this learning mutants can be produced and screen them for that they have disrupted in terms of its function. If you look deeper and observe the genome, in many cases the mutated genes are linked to the cAMP signalling cascade within cellls.
For example, a drosophila mutant has shown deficits in olfactory associative conditioning due to a mutation in the cAMP phosphodiesterase gene.
Aplysia californica - The Sea Hare
This is a sea slug that can grow to a large size and is native to the sea floor, and can learn through non-associative and associative conditioning.
The Gill withdrawal reflex was studied by Eric Kandel.
It is when the muscles at the base of the gill contract in response to a touch stimulus and the gill withdraws as a protective measure, in a reflex action.
This showed 2 methods of non-associative learning: habituation, sensitisation as well as classical conditioning.
This nervous system has been studied extensively. It consists of a ring of ganglia in the head with 2 more distant ganglia called distance ganglia.
Eric Kandel won the Nobel prize in 2000 for the synaptic plasticity of the sea hare, and he has been able to identify specific synapses in the brain that are plastic and change as the animal learns, providing the foundations of study in other animals, including mammals.
The experiment involved squirting a water jet to get a mechanical stimulus and recording the amount that the area of the gill decreased.
The experiment showed habituation, as the response decreased over time as shown in this graph.
This is so energy isn't spent through responses on non-threatening stimuli.
Kandel used simple physiological techniques to find the sensory and motor neurones that controlled the cell.
He could show that these were directly connected via a synapse by stimulating the presynaptic neurone in order to record the measurements on the post synaptic neurone.
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