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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 glutamate receptor that controls a calcium channel that is normally blocked by Mg2+ 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 the NAC might also be involved in stress Functions of the Reinforcement System: must serve to (1) detect the presence of a reinforcing stimulus and (2) strengthening the connections between the neurons that detect the discriminative stimulus and the neurons that produce the instrumental response - Detecting: the reinforcement depends on both the stimulus and the state of the animal i.e. a hungry animal will get reinforcement with food present. o Activated by unexpected reinforcing stimuli o Sometimes novelty in itself can activate dopaminergic neurons and facilitate LTP and learning o Anticipation also can increase activation of the VTA when it is activated Prefrontal cortex involved: it could turn on the reinforcement mechanism when it determines that the ongoing behavior is bringing the organism near its goal aka that its strategy is working. Also thinking and planning can bring reinforcement too. The prefrontal cortex is also a target of dopamine neurons as well a source of their control. - Strengthening: Instrumental conditioning involves a discriminative stimulus, a response, and a reinforcing stimulus. The discriminative stimulus activates weak synapses on motor neurons responsible for movement, then the response activates strong synapse and then the reinforcing stimulus if present triggers the stimulation of a NT or neuromodulator throughout the region in which the synaptic change takes place and this is what is needed to strengthen the weak synapses of the discriminative stimulus and that’s what you need dopamine for LTP Relational Learning More complex learning, also more common because involves memories related to other memories. Like seeing a photograph of a friend makes you remember their name, times you’ve had together, where they’re from, etc. Relational learning includes the establishment and retrieval of memories of events, episodes, and places. Human Anterograde Amnesia At first glance appears to be the inability to learn new information following an event. - later see that basic abilities of perceptual learning, stimulus-response learning, and motor learning are still intact but not relational learning. Can be caused by damage to the temporal lobes Scoville and Milner showed that bilateral removal of the medial temporal lobe produced a memory impairment in humans that was identical to that of Korsakoff’s syndrome o Conclusions of study of H.M. : (1) the hippocampus is not the location of long-term memories, nor is it necessary for the retrieval of long term memories. (2) the hippocampus is not the location of immediate (short-term) memories. (3) the hippocampus is involved in converting immediate (short-term) memories into long-term memories Retrograde amnesia: the inability to remember events that happened before the brain damage occurred. Often people with anterograde amnesia also have a small aspect of retrograde amnesia too. Korsakoff’s syndrome: permanent anterograde amnesia caused by brain damage resulting from chronic alcoholism or malnutrition - can remember old memories, can’t form new ones - can converse normally and remember events that happened long before their brain damage but not after Consolidation: the process by which short-term memories are converted to long-term memories - short-term memories: limited amount of storing of information temporarily - long-term memories: unlimited amount of information permanently Spared Learning Abilities People with memory deficits can perform the other three types of learning. - patients were able to perform better and better on a recognition test even though they don’t remember ever doing the test before - patients can acquire stimulus-response learning too, like a classically conditioned eye blink response without memory of the learning itself - can also learn motor learning but not know what they’re doing even while they’re doing it Declarative and Nondeclarative Memories Amnesic patients lack declarative memories aka they can not say they have memory of things but still have Nondeclarative memories Declarative memories can be verbally expressed, such as a memory for events in a person’s past - amnesic patients seem unable to form this type - involve facts and experiences Nondeclarative memories have formation that does not depend on the hippocampal formation. It is a collective term for perceptual, stimulus-response, and motor memory - appear to operate automatically aka they don’t require deliberate attempts on the learner to memorize something - don’t involve facts or experiences - they are implicit memories - involve basal ganglia Anatomy of Anterograde Amnesia One clear fact: damage to the hippocampal formation (dentate gyrus, CA fields, hippocampus itself, and the subiculum + subregions) or to regions of brain that supply its input/receive its outputs causes anterograde amnesia Most important input to hippocampal formation is the entorhinal cortex - receives its input from amygdala, various regions of the limbic cortex, and all association regions of the neocortex either directly or via two adjacent regions of the limbic cortex: the perirhinal cortex and the parahippocampal cortex o Perirhinal cortex receives information from the ventral stream and the parahippocampal from the dorsal stream o collectively these 3 regions constitute the limbic cortex of the medial temporal lobe Also receives input from the subcortical regions via the fornix - these select and modulate the functions of the hippocampal formation - fornix carries dopaminergic axons from the VTA, noradrenergic axons from the locus coeruleus, serotonergic axons from the raphe nuclei, and acetylcholinergic axons from the medial septum - also fornix connects hippocampal formation with the mammillary bodies o Most prominent brain damage in Korsakoff’s syndrome and presumably the cause of the anterograde amnesia is degeneration of the mammillary bodies Primary outcome from hippocampal system comes mainly from field CA1 and the subiculum - this is often relayed back through the entorhinal, perirhinal, and the parahippocampal cortex to the same regions of the association cortex that provides inputs Periods of anoxia can cause damage to the CA1 field and this causes anterograde amnesia. - these cells are more vulnerable to anoxia because they have a lot of NMDA receptors o lack of oxygen, seizures, metabolic disturbances, or hypoglycemia causes glutamatergic terminal buttons to release glutamate at abnormally high levels which then stimulate the receptors which permit lots of calcium into the cell and then the calcium starts destroying neurons Role of the Hippocampal Formation in Consolidation of Declarative Memories So it goes like this - hippocampus receives information about whats going on from sensory and motor association cortex and some subcortical regions like basal ganglia and amygdala - processes this information - through its efferent (out of ) connections with these regions, modifies the memories that are being consolidated there, linking them together in ways that will permit us to remember the relationships amount the elements of the memories This means declarative memories should activate the hippocampal formation, and they do. - pictorial or spatial information activates the right hippocampal formation - activation of the left hippocampal formation is related to a person’s ability to remember a list of words In anterograde amnesia the accompanying retrograde amnesia duration is related to the amount of damage tot eh medial temporal lobe - damage to limited to the hippocampus results in retrograde amnesia lasting a few years - additional damage to the entorhinal cortex produces a retrograde amnesia of one to two decades - with hippocampus and much of the medial temporal lobe damage results in retrograde amnesia that spares only memory acquired in early life such as those acquired in childhood In a recognition study at first the hippocampal formation was active with memory but as the task went on the prefrontal cortex started showing activation with the memory. So they were transferred. Episodic and Semantic Memories Distinct forms of declarative memories - episodic memories involve context and they include information about when and under what conditions a particular episode occurred and the order in which the episode took place. Specific to a particular time and place because a given episode only occurs once o must be learned all at once - semantic memories involve facts but don’t include information about the context the facts were learned. Aka they are less specific. o Acquired gradually over time Acquisition of both types require the participation of the hippocampus Episodic memories which are an integrated sequence of perceptual memories are located in the sensory association cortex because that’s were perceptual memories are located. Semantic dementia is a degenerative neurological disorder in which loss of semantic memories occur from progressive degeneration of the neocortex of the lateral temporal lobes - episodic memory retained - difficulty naming pictures of objects, understanding the meaning of words, but have no problem such as naming 6 digit numbers and matching large numbers according to their approximate size Spatial Memory Bilateral medial temporal lobe lesions produce the most profound impairment in spatial memory but significant deficits can be produced by damage that is limited to the right hemisphere. Right hippocampal formation becomes active when a person is remembering a navigational task Taxi drivers have larger right posterior hippocampi The dorsal hippocampus of rats contains place cells which are neurons that are directly involved in navigation of space. Hippocampus used in spatial strategy and caudate nucleus used in response strategy. Relational Learning in Laboratory Animals Spatial perception and learning used Morris water maze - requires relational learning because they need to navigate around the maze by getting their bearing from relative locations of stimuli located outside the maze (windows, doors, etc). - can also be used for nonrelational stimulus response learning because if they are released at the same place each time they learn swimming a certain direction leads them to safety - rats with hippocampal lesions can learn the stimulus response method but can’t find the platform if they are released in different spots because they can’t read spatial clues Place Cells in the Hippocampal Formation When animals move around the environment, they have these pyramidal cells that fire/become active when the animal is in particular places in an environment called spatial receptive fields. These cells are called place cells and they are most typically found in the hippocampal formation. - spatial receptive fields are not encoding to a particular location but rather the information is represented by particular patterns of activity in circuits of large numbers of neurons within the hippocampal formation - firing of place cells represent where an animal “thinks” it is Hippocampus receives its spatial information from the parietal lobes through the entorhinal cortex. Neurons in entorhinal cortex also have spatial receptor fields they just aren’t as clear cut as those of the hippocampal pyramidal cells Pyramidal cells in CA1 encode both the current location and the intended direction Role of the Hippocampal Formation in Memory Consolidation Confirmed that the hippocampus is involved in consolidation of spatial memories for a limited time and the result of this activity is to help establish the memories in the cerebral cortex Slow wave sleep facilitates the consolidation of declarative memories in human subjects while REM sleep facilitates the consolidation of Nondeclarative memories Reconsolidation of Memories The modification of long-term memories involves reconsolidation which is a process of consolidation of memory that occurs subsequent to the original consolidation that can be triggered by a reminder of the original stimulus. - involves LTP all the stuff about Anisomycin we learned in the revision conference led to the conclusion that when synaptic plasticity is prevented, reconsolidation cannot occur so it requires LTP - when reconsolidating a memory it can be altered or attached new information and can even be erased or be made inaccessible if there is something that interferes with reconsolidation Role of Long-Term Potentiation in Memory Experiment shows that the participation in hippocampal formation in learning involves LTP Role of Hippocampal Neurogenesis in Consolidation New neurons form connections with other neurons in the dentate gyrus and with neurons in field CA3 (??? I don’t think I grasp this section [p. 482 – 483] much I recommend reading it. Or b.s.ing if a question is actually asked…) Training rats with stimulus-response learning had no response to neurogenesis but ones that involve relational learning saw an increase in fos protein in newly formed dentate gyrus neurons that shows that those neurons had been activated by the experience It was found that it was easier to establish associative LTP in newly formed neurons than in older neurons. - Neurogenesis could be a mechanism that facilitates synaptic plasticity by providing an available pool of neurons that can make new memories This all takes a long time so enhanced neurogenesis is only a benefit for long-term basis.