GSU NEUR 3000 - NEUR 3000 - Chapter 25 (39 pages)

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NEUR 3000 - Chapter 25



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NEUR 3000 - Chapter 25

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Pages:
39
School:
Georgia State University
Course:
Neur 3000 - Hon Principles of Neuroscience
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MOLECULAR MECHANISMS OF LEARNING AND NEUR 3000 Dr Joseph J Normandin NEUROBIOLOGY OF MEMORY The neurobiology of memory attempts to understand where and how different types of information are stored We have seen some examples of where being explored The how has also been explored Hebb suggested that memory results from synaptic modification Cell assemblies have strengthened connections Invertebrate models Aplysia californica Vertebrate models rodents PROCEDURAL MEMORY Procedural memory is amenable to investigation as it does not depend on a model telling us what it remembers These memories are fairly simple and can be formed along reflex arcs that link sensation with motor output Molecular mechanisms may underscore principles that apply to all types of memory formation We can divide procedural memory into two categories Nonassociative learning Associative learning PROCEDURAL MEMORY Nonassociative learning A change in behavioral response that occurs over time as a result of a single type of stimulus Habituation Learning to ignore a stimulus that lacks meaning You don t feel the clothes on your back even though they are stimulating touch sensory neurons Sensitization Learning to intensify your response to a stimuli even those stimuli that were previously benign You hear a loud bang outside Just after your roommate knocks on your door and it causes you to jump out of your seat PROCEDURAL MEMORY PROCEDURAL MEMORY Associative learning Forming an association between two previously unrelated events Classical conditioning Associate a stimulus that evokes a response with another stimulus that does not normally provoke that response unconditional stimulus US evokes a unconditional response UR conditional stimulus CS requires conditioning training to produce a conditioned learned response CR PROCEDURAL MEMORY The dog has learned that bell predicts meat PROCEDURAL MEMORY Associative learning Instrumental conditioning operant conditioning Learn to associate a response with a meaningful stimulus INVERTEBRATE MODELS OF LEARNING California sea slug or sea hare Aplysia californica http www youtube com watch v ugD4s7mHSsA INVERTEBRATE MODELS OF LEARNING California sea slug or sea hare Aplysia californica NONASSOCIATIVE LEARNING Habituation of the gillwithdrawal reflex Repeated stimulation of the siphon with a poke will result in decreased gill withdrawal over time A sensory neuron from the skin in the siphon projects to motor neurons in the abdominal ganglion One of those motor neurons is called L7 L7 projects to the muscle of the gill Where could the memory of habituation be located NONASSOCIATIVE LEARNING Habituation of the gill withdrawal reflex After habituation there is less neurotransmitter released from the sensory neuron Ca2 activation of synaptic vesicles becomes increasingly less effective following habituation How this happens is unknown NONASSOCIATIVE LEARNING Sensitization of the gill withdrawal reflex A poke on the aplysia siphon will result in a small gill withdrawal Applying a shock to the head of the aplysia will result in a large gill withdrawal Subsequent pokes not shocks to the siphon result in a large gill withdrawal reflex L29 is sensitive to the head shock and forms a synapse with the axon of the sensory neuron This enhances the release of NT from the sensory neuron when an action potential makes its way down from a siphon poke NONASSOCIATIVE LEARNING ASSOCIATIVE LEARNING Aplysia can also be classically conditioned US shock to the tail UR large gill withdrawal reflex CS slight poke to siphon that normally produces almost no gill withdrawal After conditioning a slight poke CS resulted in a large gill withdrawal reflex CR CS must precede the US by 0 5sec ASSOCIATIVE LEARNING ASSOCIATIVE LEARNING Aplysia can also be classically conditioned Remember that L29 activates 5 HT metabotropic receptors in the terminal of the sensory neuron that produced sensitization Now this is happening at the same time as an AP hits the sensory neuron terminal ASSOCIATIVE LEARNING VERTEBRATE MODELS OF LEARNING AND MEMORY Synaptic plasticity the ability of synapses to change as a function of experience in widespread throughout the CNS Recall that the hippocampus is one part of the network involved in declarative memory Studies in the rodent hippocampus have provided a model of plasticity mechanisms that can be generalized to other brain regions and animals SYNAPTIC PLASTICITY IN THE HIPPOCAMPUS Long term potentiation LTP long lasting enhancement in the strength of a previously stimulated synapse Long term depression LTD long lasting reduction in the strength of a previously stimulated synapse Stimulation of particular pathways in the hippocampus can produce LTP or LTD plasticity LTP and LTD interact to form associations LTP and those associations can be modified by new inputs LTD A network of cells produces a pattern of synaptic change that is learning SYNAPTIC PLASTICITY IN THE HIPPOCAMPUS The hippocampus is located in the medial temporal lobes on either side of the brain The hippocampus exhibits well organized layers of cells Two sheets of cells folded in on one another One sheet is the dentate gyrus The other is Ammon s horn and is divided into different section Cornu ammonis 1 3 CA1 CA2 CA3 Entorhinal cortex provides input to the hippocampus via the perforant path to the dentate gyrus Dentate gyrus cells project to CA3 CA3 cells project to CA1 via Schaffer collaterals and to other structures via collaterals through the fornix LTP LTD are studied at the CA3 CA1 synapse SYNAPTIC PLASTICITY IN THE HIPPOCAMPUS SYNAPTIC PLASTICITY IN THE HIPPOCAMPUS LTP in the hippocampus long lasting enhancement in the strength of a previously stimulated synapse Stimulation is applied to CA3 axons every minute for 1530 min and EPSPs are recorded in CA1 neurons Baseline Strong rapid tetanic stimulation is applied to CA3 axons 100hz 0 5 1 sec Subsequent stimulation of the same pathway where you applied tetanus results in an EPSP well above baseline that lasts for a long time LTP If you stimulate a pathway nearby where tetanus had not been applied you see a baseline EPSP SYNAPTIC PLASTICITY IN THE HIPPOCAMPUS SYNAPTIC PLASTICITY IN THE HIPPOCAMPUS LTP in the hippocampus The resulting LTP can last for weeks and perhaps is even permanent The stimulation we quoted is quite substantial but other experiments have shown that stimulation that is similar to what naturally occurs can produce LTP Further analysis indicated the


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