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Chapter 13

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PSYC 211
Yogita Chudasama

Chapter 13: Learning and Memory Notes taken by: Ashley Brown Contact for mistakes: [email protected] Tbh these notes might suck (esp. near the end I got way bored), some parts might be word for word from the book but I felt that since I used like soley the notes from the other chapters I might as well contribute something. Best of luck to all and hope these help The Nature of Learning: Learning: the process by which experiences change our nervous system and therefore our behavior Memory are these changes in our nervous system; alterations in neural circuits that participate in perceiving, performing, thinking, and planning Four types of learning 1. Perceptual Learning: learning to recognize a particular stimulus that has been perceived before - Primary function: the ability to identify and categorize objects and situations - Each sensory system is capable of perceptual learning - Accomplished primarily by changes in the sensory association cortex 2. Stimulus-response learning: learning to automatically make a particular response in the presence of a particular stimulus - Involves establishing connections between circuits involved in perception and in movement - Can be either an automatic response like a defensive reflex or a complicated sequence of movements - Two major categories: o Classical conditioning: a learning procedure in which an unimportant stimulus acquires the properties of an important one. This is done by taking a stimulus that normally has no meaning (this is the conditioned stimulus - CS) and following it by a stimulus (called the unconditioned stimulus - US) that has a defensive or reflexive response (called the unconditioned response – UR). Eventually the CS will be able to evoke the response too, which is then called the conditioned response, CR  Can be explained the Hebb Rule: a hypothesis proposed by Donald Hebb that the cellular Basis of learning involves strengthening of a synapse that is repeatedly active when the postsynaptic neuron fires  An association between 2 stimuli o Instrumental conditioning: Also called operant conditioning. It is a learning procedure whereby the effects of a particular behavior in a particular situation increase (reinforce) or decrease (punish) the probability of the behavior  Involves behaviors that have been learned (as opposed to automatic like in classical)  An association between a response and a stimulus  Strengthens the connections involved in perception and those involved in movement  More flexible than classical; makes it so things can adjust its behavior according to the consequences of that behavior  When followed by a favorable consequence or a reinforcing stimulus the behavior will be repeated more often  When followed by an unfavorable consequence or a punishing stimulus it will occur less frequently 3. Motor learning: Learning to make a new response. A component of stimulus response learning 4. Relational learning: involves learning the relationships among individual stimuli - Connections between different areas of the association cortex such as interconnections between different sensory association cortexes - Spatial learning is a type because you have to recognize objects, the learn the relative locations with respect to others - Episodic learning: learning the sequences of events that we witness is another type of relational learning because we have to keep track of/remember the events themselves and then recognize the order that they occur in Synaptic Plasticity: Long-Term Potentiation Learning involves synaptic plasticity or changes in the structure or biochemistry of synapses that alter their effects on postsynaptic neurons Induction of Long-Term Potentiation: Long-term potentiation (LTP): a long-term increase in the excitability of a neuron to a particular synaptic input caused by repeated high-frequency activity of that input - Can cause the long-term strengthening of the synapses between two neurons as seen in Hebb’s rule o Associative long-term potentiation: a long-term potentiation in which concurrent stimulation of weak and strong synapses to a given neuron strengthens the weak ones - Inducing LTP: o place a stimulating electrode among the axons in the perforant path and a recording electrode near the granule cells of the dentate gyrus o A pulse of electrical is delivered which produces a population EPSP, or an evoked potential that represents the EPSPs of a population of neurons, that is recorded in the dentate gyrus. This is the “before” after you stimulate the perforant path with high intensity with high frequency stimulation we induce LTP Hippocampal formation: a forebrain structure of the temporal lobe, constituting an important part of the limbic system; includes the hippocampus proper (Ammon’s horn), dentate gyrus, and subiculum - Neurons of the dentate gyrus send axons to the CA3 field and then form synapses with the dendrites of pyramidal cells o One branch of the axons from the CA3 pyramidal cells travel through the fornix to reach areas of the basal forebrain o Another branch synapse with the pyramidal cells of the CA1 field  These cells provide the main output of the hippocampus to the subiculum, entorhinal cortex, and basal forebrain - Granule cells of the dentate gyrus receive info from the entorhinal cortex via the perforant path. The entorhinal cortex channels all the major neocortical inputs and outputs Role of NMDA Receptors: Experiments showed that synaptic strengthening occurs when molecules of NT bing with postsynaptic receptors located in a dendritic spine that is already depolarized. - shows the LTP requires (1) activation of synapses and (2) depolarization of the post synaptic neuron - Can be explained by the NMDA receptor which is a specialized ionotropic glu2+mate receptor that controls a calcium channel that is normally blocked by Mg ions but when its depolarized its not blocked o AP5 is a drug that blocks NMDA receptors and therefore blocks the establishment of LTPs  this shows that the activation of NMDA receptors is necessary for the first step in the processes of events that establishes LTP aka entry of calcium into the dendritic spines o the properties of the NMDA receptor account for both the existence of LTP and for its associative nature Dendrites in some types of pyramidal cells can produce action potentials called dendritic spikes. They have a high threshold of excitement - these spikes are necessary for LTP Mechanisms of Synaptic Plasticity Strengthening of an individual synapse appears to be accomplished by inserting more AMPA receptors, an ionotropic glutamate receptor that controls a sodium channel and when open produces EPSPs, into the postsynaptic membrane of the dendritic spine - After LTP the AMPA receptors of CA1 cells move from the dendritic spine through the synapse to the membrane of the postsynaptic neuron o This movement is caused by a calcium dependent enzyme called CaM-KII (type 2 calcium-calmodulin kinase)  The enzyme becomes concentrated in the postsynaptic density (a band inside the postsynaptic membrane that contains proteins, receptors and all that good stuff) It has also been suggested that LTP changes the synaptic structure and causes production of new synapses. - thin dendritic spines become fatter, mushroom shaped spines - also new dendrites can grow that then form connections with nearby axons Some research also indicates that PRESYNATIC changes can occur as well such as an increase in the amount of glutamate released by the terminal button - This could be because nitric oxide can communicate messages from one cell to another. Several studies show that NO could be a retrograde messenger involved in LTP Long lasting LTP requires protein synthesis. Three types of LTP: - LTP1 involves almost immediate changes in synaptic strength caused by insertion of AMPA receptors. Last for an hour or 2. - LTP2 a local protein synthesis that is made possible because dendrites contain mRNA that can be translated into proteins/enzymes - LTP3 is the more durable type of LTP that involes production of mRNA in the nucleus that is then transported to the dendrites where protein synthesis then takes place. Requires dopamine. LTP initiates 2 processes: - the production of plasticity-related proteins through normal synthesis of mRNA in the nucleus - the production of a chemical “tag” in the dendritic spines where LTP has taken place SUMMARY OF LTP: Terminal button releases glutamate which binds to the NMDA receptor Ca2+ enter postsynaptic cell if membrane is depolarised (via NMDA receptors) CA2+ activate CAM-KII CAM-KII facilitates the insertion of AMPA receptors into postsynaptic density LTP causes structural changes (e.g., dendritic growth) Long lasting LTP requires protein synthesis Other Forms of Long-Term Potentiation In field CA3 of the hippocampal formation LTP appears to involve only presynaptic changes Perceptual Learning Learning is what enables us to adapt to our environment and respond to change. Perceptual ability involves learning to recognize things, not what to do when they’re there. - can involve learning to recognize entirely new stimuli - also involved with recognizing changes or variations in familiar stimuli Learning to Recognize Stimuli Visual info pathway: LGN of thalamus  primary visual cortex (first level of analysis) extrastriate cortex  (analysis of particular attributes of a visual scene like form, color, movement)  next level of visual association which is either the ventral (object recognition or “what”) stream or dorsal (perception of location or “where”) stream Perceptual learning involves changes in synaptic connections in the visual association cortex Perceptual Short-Term Memory Short-term memory is the memory of a stimulus or an event that last for short while usually just a few seconds Recognition of a stimulus is when sensory activates an established set of neural circuits. Short term memory of a stimulus involves the activity of these circuits that continues after the stimulus disappears. Like for visual you can see this with continuous activation of the fusiform face area to remember someone is still there after recognizing them Delayed matching-to-sample task requires the subject to indicate which of several stimuli has just been perceived. It is used to experiment with short-term memory. Perceptual short-term memories often involve other brain regions than just the sensory association cortexes. - prefrontal cortex: plays a role to manipulate and organize to-be-remembered information, devise strategies for retrieval, and also to monitor the outcome - dorsolateral prefrontal cortex involved when reordering words, and later people were more likely to remember from reordering than rehearsing Classical Conditioning The amygdala is involved in classically conditioned emotional responses. - More firing in the lateral nucleus of amygdala corresponded with a larger magnitude of a conditioned emotional response - Involves LTP  LTP in the lateral amygdala, mediated by NMDA receptors, plays a critical role in the establishment of conditioned emotional responses Instrumental Conditioning Basal Ganglia Instrumental conditioning entails the strengthening of connections between neural circuits that detect a particular stimulus and neural circuits that produce a response so they begin in regions of sensory association cortexes and end in the motor association cortex of the frontal lobe Two major pathways between the sensory association cortex and motor association cortex: - Direct transcortical connections: connections from one area of the cerebral cortex to another o Together with the hippocampal formation, theses are involved in the acquisition of episodic memories (complex perceptual memories of sequences of events) o Involved in the acquisition of complex behaviors that involve deliberation or instruction - Connections via the basal ganglia and thalamus As behaviors become automatic and routine they are “transferred” to the basal ganglia Reinforcement When good things happen reinforcement mechanisms in the brain become active and the establishment of synaptic changes is facilitated. Neural Circuits Involved in Reinforcement: Axons of dopaminergic cells project to areas of the brain through three major pathways - Nigrostriatal pathway connects substantia nigra with the striatum: involved in movement - Mesocortical pathway connects the ventral tegmental area (VTA) (which is a group of dopaminergic neurons in the ventral midbrain that plays a critical role in reinforcement) to the cerebral cortex: its involved in cognition, motivation, and emotion - Mesolimbic pathway connects the VTA to the nucleus accumbens (NAC) which is a nucleus of the basal forebrain near the septum and is involved in reward and desire also in attention and reinforcement o Neurons in the NAC project to the ventral part of the basal ganglia The bundle of axons that carry the information from the VTA to the NAC is called the medial forebrain bundle (MFB) Also shown that dopaminergic neurons projecting to
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