ch 25

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Janelle Leboutillier

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Chapter 25 Neuroscience Notes  Procedural memory involves learning a motor response (procedure) in reaction to a sensory input. It includes: 1. Non-Associative Learning: there are two types of responses  Habituation: learning to ignore a stimulus that lacks meaning. So repeated presentation of the same stimulus produces a progressively smaller response  Sensitization: learning to intensify your response to stimuli, even ones that previously evoked little or no reaction 2. Associative Learning: this involves forming associations between events  Classical conditioning (involves stimulus): remember Ivan Pavlov’s dogs; this involves the unconditional stimulus (meat) and conditional stimulus (tone). Conditioning occurs when a conditioned response (CR) is learnt via close association of CS and US. The CS has to be presented slightly before or simultaneously with the US to work.  Instrumental conditioning (involves behaviour): an individual learns to associate a response, a motor act, with a meaningful stimulus, typically a reward such as food. Think of a lever pressing rat in this case. So in summary, instrumental conditioning involves the subject learning a particular behaviour is associated with a particular consequence  Why are invertebrate models of learning used?  Small nervous systems: few thousand to less than 10 million times than humans  Large neurons  Identifiable neurons  Simple genetics  Non-associative learning in Aplypsia  If a jet of water is squirted onto its siphon, the gill will retract. This is called the gill- withdrawal reflex. Overtime, the Aplypsia will habituate to this  Habituation of Aplysia  The motor neuron that receives input from the siphon sensory neuron is called L7, and this neuron innervates muscles that cause the gill-withdrawal reflex  Where does the habituation occur? Habituation occurs @ the presynaptic side of the sensory-motor synapse. So the sensory neuron side. Look @ figure 25.6 page 766  After habituation, there are less quanta containing neurotransmitter released. This occurs because the presynaptic sensory neuron becomes less effective to Calcium entry, resulting in less trigger release of NT.  Sensitization of Aplysia  Applying brief electric shock causes sensitization in Aplysia  How does increased sensitization occur? A third neuron, L29, is activated by the shock, and makes a synapse on the axon terminal of the sensory neuron  L29 releases serotonin, which sensitizes the sensory axon terminal so that it lets in more Calcium in order to release more quanta packets  The sensory receptor on the sensory axon terminal is a G-protein-coupled receptor. It causes the release of an intracellular second messenger, cyclic AMP (cAMP) produced by adenylyl cyclase, which then activates protein kinase A (remember kinases phosphorylate proteins).  Protein kinase A then phosphorylates a potassium channel resulting in it’s closure. This leads to a prolonging of presynaptic action potential, meaning more quanta are released resulting in sensitization  Look @ figure 25.9 page 768  Associative learning in Aplypsia is summarized well in lecture notes  Long Term Potentiation (LTP): long lasting enhancement of stimulated synapses. After potentiation, a previous stimuli could now evoke a larger response  Anatomy of the hippocampus: it contains the dentate gyrus and Ammon’s horn  Our
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