Gluck & Myers; Gateway to Memory - Modeling the Hippocampus
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Gluck & Myers; Gateway to Memory 12 Subfields of the hippocampus, CA1 through CA4
Gluck & Myers; Gateway to Memory 12 Hippocampus nearby structures -- dentate gyrus, subiculum, entorhinal cortex, perirhinal cortex, parahippocampal cortex, amygdala 0
Gluck & Myers; Gateway to Memory 13 Hippocampal region refers to a subset of medial temporal structures -- hippocampus, dentate gyrus, subiculum, entorhinal cortex. 1
Gluck & Myers; Gateway to Memory 13 Fornix, a fiber pathway connecting the hippocampus to subcortical structures, is often included as part of the hippocampal region. 0
Gluck & Myers; Gateway to Memory 13 Exact functions of the hippocampal region remain a subject of contentious debate. 0
Gluck & Myers; Gateway to Memory 14 Neuroscientists now agree that the hippocampus has something to do with learning and memory, but there is little consensus about exactly what the hippocampus is doing when we learn and store new memories. 1
Gluck & Myers; Gateway to Memory 14 Much of our understanding of the hippocampal region's role in learning and memory comes from individuals who have suffered damage to the medial temporal lobes. 0
Gluck & Myers; Gateway to Memory 14 One of the most famous individuals with hippocampal region damage was a young man HM whose epileptic seizures originated in the hippocampi. Doctors removed an 8 cm segment from each of his temporal lobes, including two thirds of each hippocampus. HM's ability to acquire new memories had been devastated. 0
Gluck & Myers; Gateway to Memory 15 Although HM's intelligence, language skills, and personality are largely as they were before the surgery, he has essentially no memories for any events of the last decades of his life. 1
Gluck & Myers; Gateway to Memory 15 HM does have a reasonably normal memory for events that occurred at least two years before his surgery. 0
Gluck & Myers; Gateway to Memory 15 Although HM can participate in a conversation, a few minutes later he will have lost all memory of it. 0
Gluck & Myers; Gateway to Memory 15 H.M. cannot learn the names or faces of people who visit him regularly. 0
Gluck & Myers; Gateway to Memory 15 Even the doctors and psychologists who have worked with H.M. for over 45 years must reintroduce themselves to him each time they meet. 0
Gluck & Myers; Gateway to Memory 15 Since H.M. himself has aged sense surgery, he does not recognize his own face when he is shown a current picture of himself. 0
Gluck & Myers; Gateway to Memory 15 HM is painfully aware of his own problems and has described his life as constantly waking from a dream he can't remember. 0
Gluck & Myers; Gateway to Memory 15 HM's condition is known as anteriorgrade amnesia, the inability to form new memories. 0
Gluck & Myers; Gateway to Memory 16 Unilateral removal of a hippocampus may still be done in cases of severe epilepsy, but this usually results in a much milder memory impairment than seen in HM. 1
Gluck & Myers; Gateway to Memory 17 Transient loss or reduction of oxygen (called anoxia or hypoxia) is a frequent cause of amnesia, because hippocampal cells seem particularly sensitive to oxygen deprivation. 1
Gluck & Myers; Gateway to Memory 17 Damage to or disruption of the hippocampal region may cause anteriorgrade amnesia -- a devastating loss of new memory formation, with a relative sparing of intelligence, personality, skill learning, and old memories. 0
Gluck & Myers; Gateway to Memory 31 Classical Conditioning and the Hippocampus 14
Gluck & Myers; Gateway to Memory 32 Schematic of classical conditioning -- unconditioned stimulus (US), conditioned stimulus (CS) (diagram) 1
Gluck & Myers; Gateway to Memory 82 Representation and Generalization 50
Gluck & Myers; Gateway to Memory 82 Psychologists have long understood that a fundamental property of animal and human learning is generalization, the degree to which learning about one stimulus transfers to other stimuli. 0
Gluck & Myers; Gateway to Memory 84 Generalization is critical for applying prior experience to new situations, without requiring fresh learning about every new instance. 2
Gluck & Myers; Gateway to Memory 85 A major challenge for learning theorists has been to understand how differences in stimulus similarity affect learning and generalization behaviors. 1
Gluck & Myers; Gateway to Memory 86 Animals and people tend to assume that to stimuli that are physically similar will have similar consequences and generalize accordingly. 1
Gluck & Myers; Gateway to Memory 86 There is also a need for specificity in learning, too allowed superficially similar stimuli to be associated with different responses 0
Gluck & Myers; Gateway to Memory 86 In general, there is always a trade-off between generalization and specificity in learning. 0
Gluck & Myers; Gateway to Memory 86 The brain generally represents information using distributed representations, in which each stimulus is encoded by many different neurons and each neuron may respond to conjunctions of features that may be present in many different stimuli. 0
Gluck & Myers; Gateway to Memory 87 Distributed representation is efficient because a large number of stimuli can be processed by smaller number of neurons, each of which encodes some features of the stimuli. 1
Gluck & Myers; Gateway to Memory 87 Distributed representations have the advantage that if some of the units are lost or degraded, the remaining units may be able to provide enough information to represent the stimuli adequately. 0
Gluck & Myers; Gateway to Memory 87 The drawback of a distributed representation is that recognizing a particular stimulus may require integrating information from many different neurons that encode the stimulus features. 0
Gluck & Myers; Gateway to Memory 87 Neuroscientists have concluded that the brain most likely uses distributed representations to encode information. 0
Gluck & Myers; Gateway to Memory 87 Distributed representation uses a set of overlapping elements to encode input stimuli. 0
Gluck & Myers; Gateway to Memory 87 Nodes in the neural network are, in general, laid out topographically, meaning that nodes responding to physically similar stimuli are physically next to each other in the network. 0
Gluck & Myers; Gateway to Memory 87 The degree of overlap between the representations of two stimuli reflects their physical similarity. 0
Gluck & Myers; Gateway to Memory 111 Unsupervised Learning -- Autoassociative Networks and the Hippocampus 24
Gluck & Myers; Gateway to Memory 114 Hebbian learning is unsupervised, meaning that it does not depend on a special teaching signal. 3
Gluck & Myers; Gateway to Memory 114 Weight change is automatic in Hebb's rule and depends only on conjoint activity in pairs of nodes. 0
Gluck & Myers; Gateway to Memory 115 The ability to remember patterns is one mechanism by which the brain might store memories of past events. 1
Gluck & Myers; Gateway to Memory 115 Once a pattern has been stored, activation in any one node will produce activation in the other nodes of a pattern. 0
Gluck & Myers; Gateway to Memory 115 Even after the external input is turned off, the pattern (stored as an assembly of active nodes) remains for some time, until activation gradually dies away. In this way, superficially unrelated but temporally coincident stimuli can be bound together into a unified memory. 0
Gluck & Myers; Gateway to Memory 115 The most interesting property of an autoassociative network -- given a partial or incomplete version of the stored memory, an autoassociative network can retrieve the entire stored pattern -- this is called pattern completion. 0
Gluck & Myers; Gateway to Memory 116 A variation of a pattern completion property of an autoassociatiave network is a process of pattern recognition -- the ability to take an arbitrary input and retrieve the stored pattern that is most similar to that input. 1
Gluck & Myers; Gateway to Memory 117 The twin features of pattern completion and pattern recognition has led to many engineering applications of autoassociative networks. 1
Gluck & Myers; Gateway to Memory 117 Hippocampal Anatomy and Autoassociation 0
Gluck & Myers; Gateway to Memory 117 Most theories that have tried to map from hippocampal anatomy to behavioral function have focused on a particular subfield within the hippocampus -- field CA3. 0
Gluck & Myers; Gateway to Memory 117 One primary input to CA3 comes from entorhinal cortex, carrying highly processed information about all kinds of sensory input. This pathway is called the perforant path, since its fibers physically perforate the dentate gyrus to reach CA3. 0
Gluck & Myers; Gateway to Memory 118 A secondary path from the entorhinal cortex synapses in dentate gyrus before proceeding on to CA3. The connections from dentate gyrus to CA3 are called mossy fibers, and they make sparse, large, and presumably very powerful synapses onto CA3 neurons. 1
Gluck & Myers; Gateway to Memory 118 CA3 neurons process the information and send their outputs on to hippocampal field CA1 and from there out of the hippocampus. 0
Gluck & Myers; Gateway to Memory 118 One of the most striking features of CA3 anatomy is a high degree of internal recurrency, meaning that CA3 neurons send axons not only out of CA3, but also back to synapse on other CA3 neurons. 0
Gluck & Myers; Gateway to Memory 118 Recurrency feedback is a general principle throughout the brain, but it is dramatically heightened in CA3. 0
Gluck & Myers; Gateway to Memory 118 Each CA3 pyramidal neuron in the rat may receive about 4000 synapses from entorhinal inputs but up to about 12,000 synapses from other CA3 cells. 0
Gluck & Myers; Gateway to Memory 118 Each CA3 pyramidal neuron receives inputs from about 4% of all other CA3 pyramidal neurons. 0
Gluck & Myers; Gateway to Memory 119 The 4% recurrency is orders of magnitude higher than the degree of internal recurrency that is observed elsewhere in the brain. 1
Gluck & Myers; Gateway to Memory 119 The connections between CA3 neurons are modifiable by LTP in much the same manner as Hebb proposed. 0
Gluck & Myers; Gateway to Memory 119 LTP was originally discovered by researchers studying synapses in the hippocampal region. 0
Gluck & Myers; Gateway to Memory 119 A Hippocampal model assumes that CA3 pyramidal neurons form an autoassociative network in which external inputs (from entorhinal cortex and dentate gyrus) activate a subset of CA3 neurons. Recurrent collaterals between coactive nodes are strengthened, storing the pattern. 0
Gluck & Myers; Gateway to Memory 119 Many of the basic ideas underlying the recurrent hippocampal model have withstood continuing empirical and theoretical analysis and are implicit in most modern models of hippocampus. 0
Gluck & Myers; Gateway to Memory 124 Autoassociative models of hippocampus have considerable power for describing the hippocampal regions role in episodic memory formation. 5
Gluck & Myers; Gateway to Memory 148 The hippocampal region is not the final site of memory storage as evidence by empirical data showing that old, well established memories can survive hippocampal-region damage. 24
Gluck & Myers; Gateway to Memory 149 A cerebellum model shows that stimulus inputs are processed by various primary cortical areas and then travel to the cerebellum via structure of the bonds. The cerebellum learns to map from these inputs to an output that derives a condition motor response. 1
Gluck & Myers; Gateway to Memory 149 The cerebellum model also contains an inhibitory feedback loop through the inferior olive that manages the era between the actual response (which is a prediction of unconditioned stimulus (US) arrival) and whether the US actually arrived. 0
Gluck & Myers; Gateway to Memory 165 The neurophysiological evidence currently available is remarkably consistent with the implication suggesting that hippocampal neuronal representations can and do change to reflect associations between stimuli and rewards. 16
Gluck & Myers; Gateway to Memory 175 Several prominent theories assume that the hippocampal region is involved in stimulus configuration (or chunking), whereby a set of co-occurring stimuli come to be treated as a unary whole (or configuration) that can accrue associations. 10
Gluck & Myers; Gateway to Memory 177 The hippocampal region has been implicated in contextual processing. The hippocampus has been proposed as a source for contextual tags to memories, which identify the spatial and temporal settings in which events occur. 2
Gluck & Myers; Gateway to Memory 177 Context is usually defined as the set of background cues that are present during a learning experience. 0
Gluck & Myers; Gateway to Memory 177 Patients with medial temporal lobe amnesia can often acquire new information but not recall the spatial and temporal context in which it occurred. 0
Gluck & Myers; Gateway to Memory 177 The nondeclarative learning that is often preserved in amnesia tends to be acquired slowly, over many trials, and is less strongly associated with any particular context. 0
Gluck & Myers; Gateway to Memory 179 The hippocampal region has a role in maintaining information over a course of a few minutes -- this kind of memory is often called intermediate term memory (as distinct from the short-term memory that is we used to remember a telephone number by constant rehearsal or long-term memory, which can last for years). 2
Gluck & Myers; Gateway to Memory 179 Researchers have suggested that the intermediate-term memory buffer can be specifically localized within the parahippocampal region, including entorhinal, perrirhinal, and parahippocampal cortices. 0
Gluck & Myers; Gateway to Memory 179 The hippocampal region may be involved in constructing new representations that can press together stimuli that cooccur or similar in meaning; this compression could apply equally to stimuli that are superficially dissimilar, and to those that are separated in time or in space. 0
Gluck & Myers; Gateway to Memory 189 Cortico-Hippocampal Interaction and Contextual Processing 10
Gluck & Myers; Gateway to Memory 215 The hippocampal region is the culmination of a long and intricate processing chain. 26
Gluck & Myers; Gateway to Memory 215 Sensory inputs from receptors such is retinal transducers and tastebuds travel through the thalamus and into areas of cerebral cortex that are specifically devoted to processing different kinds of sensory information. 0
Gluck & Myers; Gateway to Memory 215 Information travels to higher cortical areas, which combine and integrate across sensory modalities, before finally reaching the hippocampal region. 0
Gluck & Myers; Gateway to Memory 216 This cerebral cortex is a grade sheet covering most of the mammalian brain and containing the cell bodies of neurons. The output processes of these cells, axons, form the underlying white matter that makes up much of the bulk of the brain in higher species. 1
Gluck & Myers; Gateway to Memory 216 Only mammals have six layered cortex; reptiles and birds have a simpler kind of cortex -- sometimes called paleocortex or allocortex -- with only two layers. 0
Gluck & Myers; Gateway to Memory 216 Six layered cortex is often called neocortex or isocortex, reflecting the assumption that it developed later in evolution. 0
Gluck & Myers; Gateway to Memory 216 There are a few places in the mammalian brain that are also two-layered paleocortex, and these may be evolutionary remnants from which neocortex developed. 0
Gluck & Myers; Gateway to Memory 217 Mammalian brains show a variety in size and complexity but also share many features, including the presence of six layered neocortex. The rat brain and the human brain show many of the same structures. 1
Gluck & Myers; Gateway to Memory 216 The rats olfactory system is proportionately larger than the human's, while the rats neocortex is only a fraction of the size of the human's. -1
Gluck & Myers; Gateway to Memory 218 The cortex of an adult human would measure about 1.5 ft. if spread out into a flat sheet. 2
Gluck & Myers; Gateway to Memory 218 The wrinkled appearance of the human brain reflects the fact that the cortex has to fold to fit inside the confines of the skull. 0
Gluck & Myers; Gateway to Memory 218 The rat cortex fits quite comfortably inside the rats skull without wrinkles. 0
Gluck & Myers; Gateway to Memory 218 For each sensory modality, the first cortical processing occurs in a specific region -- primary visual cortex (V1) for vision, primary audio cortex (A1) for sounds, etc. 0
Gluck & Myers; Gateway to Memory 218 Primary sensory cortex is organized topographically. Each region of cortex responds preferentially to a particular type of stimulus, and neighboring cortical regions respond to similar stimuli.
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Gluck & Myers; Gateway to Memory 218 Primary sensory cortex (S1) is a thin strip of cortex running down each side of the brain in humans. 0
Gluck & Myers; Gateway to Memory 219 Primary audio cortex (A1) lies near the top of the temporal lobe in humans and is organized as a topographic map. 1
Gluck & Myers; Gateway to Memory 219 Adjoining areas of the A1 respond to similar tone frequencies in an orderly fashion. 0
Gluck & Myers; Gateway to Memory 219 The topographic organization of primary sensory cortex seems to be a consistent feature across modalities and across mammalian species. 0
Gluck & Myers; Gateway to Memory 220 The output from primary sensory cortex goes to higher-order cortical areas, where the obvious topographic ordering may be lost, or else information may be coded in a topographic manner that researchers don't yet understand. 1
Gluck & Myers; Gateway to Memory 223 An unsupervised learning system does not learn to produce any predefined desired output. Instead, the network discovers underlying regularities -- statistically significant features -- of the input it is given. 3
Gluck & Myers; Gateway to Memory 223 Unsupervised learning systems are also called self-organizing networks, since they do not depend on an external reinforcement. 0
Gluck & Myers; Gateway to Memory 223 Autoassociative networks are one kind of unsupervised network. 0
Gluck & Myers; Gateway to Memory 223 Another class of unsupervised network is a competitive network, meaning that the nodes of the network compete with one another for the 'right' to respond to stimuli. 0
Gluck & Myers; Gateway to Memory 225 A network may be termed a self-organizing feature map if it forms a topographic representation based on some features of the input. 2
Gluck & Myers; Gateway to Memory 227 Self Organizing Feature Maps -- computer algorithms to discover underlying order in a large database. 2
Gluck & Myers; Gateway to Memory 228 Speech Processing -- a continuous stream of speech is recognized as a pattern of phonemes, and eventually resulting in translated typewritten text. 1
Gluck & Myers; Gateway to Memory 232 There exists a few places in the brain where the cortex begins to change, gradually becoming two-layer paleocortex similar to reptile cortex. 4
Gluck & Myers; Gateway to Memory 232 Olfactory cortex is two-layer paleocortex. 0
Gluck & Myers; Gateway to Memory 232 The hippocampus is a two-layered sheet of paleocortex, although it is folded-in on itself to create its characteristic "C" shape. 0
Gluck & Myers; Gateway to Memory 232 One theory is that hippocampus and paleocortex are remnants of the primitive brain from which more complex neocortex evolved. 0
Gluck & Myers; Gateway to Memory 232 The relatively simple organization of paleocortex suggests that it is a logical place to begin exploring how cortical anatomy could give rise to computational function. 0
Gluck & Myers; Gateway to Memory 233 Although human olfactory cortex is relatively small, the olfactory cortex of most mammals is much larger, reflecting the importance of odor information to those species. 1
Gluck & Myers; Gateway to Memory 233 Dogs have almost 50 times as many olfactory neurons as humans. 0
Gluck & Myers; Gateway to Memory 233 Olfaction begins with a thin sheet of olfactory receptor cells, high up in the nasal cavity, called the olfactory epithelium. 0
Gluck & Myers; Gateway to Memory 237 The hippocampal region can form new stimulus representations that compress redundant information while differentiating predictive information. 4
Gluck & Myers; Gateway to Memory 237 The hippocampus receives highly processed, multimodal information from a whole range of stimulus modalities. 0
Gluck & Myers; Gateway to Memory 260 Entorhinal cortex is intermediate in structure between six-layered neocortex and two-layered paleocortex. 23
Gluck & Myers; Gateway to Memory 260 From entorhinal cortex, axons project to the dentate gyrus and hippocampus. 0
Gluck & Myers; Gateway to Memory 260 The tract from entorhinal cortex to dentate gyrus is known as the perforant path, because these fibers traveled through (perforate) the subiculum to reach their destination. 0
Gluck & Myers; Gateway to Memory 261 From dentate gyrus, axons traveled to the hippocampal subfields CA3, which also receives a direct projection from entorhinal cortex. 1
Gluck & Myers; Gateway to Memory 261 The combination of strong dentate and weaker entorhinal projections to CA3, together with high recurrency among CA3 neurons, suggests that CA3 might function as an autoassociator. 0
Gluck & Myers; Gateway to Memory 261 Information projects from CA3 to hippocampal field CA1, through the subiculum, back through the deep layers of entorhinal cortex, and finally back to the same cortical areas that gave rise to the information in the first place. 0
Gluck & Myers; Gateway to Memory 261 The unidirectional flow from entorhinal cortex through dentate gyrus, hippocampus, subiculum back to entorhinal cortex is a primary feature of the circuitry. 0
Gluck & Myers; Gateway to Memory 265 Hippocampal field CA3 has received extensive study because of its physical resemblance to an autoassociative network. 4
Gluck & Myers; Gateway to Memory 265 Entorhinal cortex has begun to receive attention from researchers: (1) because of its similarity to neocortex and (2) because of suggestions that many behaviors that were previously thought to depend on the hippocampus may actually be mediated by the entorhinal cortex. 0
Gluck & Myers; Gateway to Memory 266 Entorhinal cortex represents the highest stage of cortical processing, in which all sensory information converges. 1
Gluck & Myers; Gateway to Memory 266 Entorhinal cortex would be a logical place to perform clustering among stimuli in different modalities, or among the multimodal features of a single stimulus. 0
Gluck & Myers; Gateway to Memory 266 Superficial layers of entorhinal cortex received highly processed, multimodal stimulus inputs. 0
Gluck & Myers; Gateway to Memory 266 Entorhinal cells are grouped together into clusters; within each cluster, cells compete to respond to the input. 0
Gluck & Myers; Gateway to Memory 266 Cells that when the competition undergo plasticity, making them more likely to respond to similar inputs in the future. 0
Gluck & Myers; Gateway to Memory 266 Losing cells also undergo plasticity, making them less likely to respond to similar inputs. 0
Gluck & Myers; Gateway to Memory 266 Losing cells in the competition become more likely to win the competition in response to very different inputs. 0
Gluck & Myers; Gateway to Memory 266 The entorhinal network model performs unsupervised clustering of its inputs. 0
Gluck & Myers; Gateway to Memory 282 In the same way that entorhinal cortex may perform representational compression, there is emerging evidence that dentate gyrus may perform representational differentiation. 16
Gluck & Myers; Gateway to Memory 282 The entorhinal cortex and dentate gyrus together may perform most or all of the representational processing that has been assumed to take place in a hippocampal region. 0
Gluck & Myers; Gateway to Memory 282 Other hippocampal region areas, such as CA3 and CA1, may be more involved in short-term storage of information and overseeing its eventual consolidation to cerebral cortex. 0
Gluck & Myers; Gateway to Memory 287 Schematic of sensory information flow through cortical areas as envisioned by Edmund Rolls (diagram) 5
Gluck & Myers; Gateway to Memory 287 Anatomical pathway by which hippocampal region processing can influence cortical areas. 0
Gluck & Myers; Gateway to Memory 287 Edmund Rolls has developed a theory of how feedback projections could allow representations developed in hippocampus to drive cortical storage. 0
Gluck & Myers; Gateway to Memory 287 Pyramidal neurons in an area of cortex receive feedforward projections carrying sensory information from earlier cortical areas and also feedback projections from the later cortical areas. 0
Gluck & Myers; Gateway to Memory 287 For entorhinal cortex, feedforward inputs detail the highly processed, multimodal features of current input, while feedback inputs carry information about the hippocampal region's representation of this information. 0
Gluck & Myers; Gateway to Memory 289 Feedback from the hippocampal region is assumed to sparsify the pattern. 2
Gluck & Myers; Gateway to Memory 289 Under the assumption that the cortex performs competitive learning, strongly activated winning neurons undergo plasticity -- strengthening the weights from active inputs -- while the remaining neurons undergo weight decreases. 0
Gluck & Myers; Gateway to Memory 290 One problem and theorizing about hippocampal region function has always been an understanding have very specific activation patterns (e.g. episodic memories) encoded in hippocampus could be transferred to cortical storage. 1
Gluck & Myers; Gateway to Memory 290 In Rolls' model, the hippocampus doesn't know where to project information; it simply projects everywhere, and storage occurs automatically wherever conjoint feedforward and feedback projections converge. 0
Gluck & Myers; Gateway to Memory 290 Teaching inputs require very specific anatomical properties that appear to exist in only a few places in the brain (e.g. the mossy fiber connections from dentate gyrus to CA3 and climbing fiber inputs to cerebellum). 0
Gluck & Myers; Gateway to Memory 291 The Rolls' model requires no more than the ubiquitous Hebbian-like learning in which plasticity occurs to strengthen the connections between any two coactive inputs. 1
Gluck & Myers; Gateway to Memory 291 Neurobiological mechanisms for Hebbian learning have been observed in the superficial layers of cerebral cortex. 0
Gluck & Myers; Gateway to Memory 291 Subcortical inputs might modulate memory storage for especially significant events. 0
Gluck & Myers; Gateway to Memory 293 The cortico-hippocampal model assumes that the entorhinal cortex compresses stimulus representations. 2
Gluck & Myers; Gateway to Memory 302 The entorhinal cortex within the hippocampal region has a form intermediate between six-layered neocortex and two-layered allocortex. 9
Gluck & Myers; Gateway to Memory 302 Entorhinal cortex receives highly processed, multimodal sensory input and projects to the hippocampus. In turn, hippocampal outputs project to entorhinal cortex and from there back to cortical areas where they arose. 0
Gluck & Myers; Gateway to Memory 302 A simple entorhinal model -- clusters of nodes compete to respond to inputs; representations of similar and co-occurring (redundant) inputs are compressed. 0
Gluck & Myers; Gateway to Memory 302 Other models have suggested that the entorhinal cortex is involved in stimulus configuration, and the back projections from hippocampus to entorhinal cortex and beyond provide a possible substrate for memory consolidation. 0
Gluck & Myers; Gateway to Memory 303 Eichenbaum has suggested that the entorhinal cortex is an intermediate-term buffer, with the ability to configure representations of items that occur with slight temporal displacement. 1
Gluck & Myers; Gateway to Memory 307 An excitatory neurotransmitter increases the probability that the postsynaptic neuron will become active, and an inhibitory neurotransmitter decreases this probability. 4
Gluck & Myers; Gateway to Memory 307 Whereas neurotransmitters carry messages between neurons, neuromodulators affect how those messages are processed. 0
Gluck & Myers; Gateway to Memory 308 Acetylcholine (ACh) and Memory Function 1
Gluck & Myers; Gateway to Memory 308 Schematic of some important cholinergic projections in the brain. (diagram) 0
Gluck & Myers; Gateway to Memory 311 Many computational models assume that hippocampal field CA3 functions as autoassociator. 3
Gluck & Myers; Gateway to Memory 311 In the autoassociator, a pattern of input activations is stored in the CA3 network by strengthening connections between pairs of nodes that are simultaneously active. 0
Gluck & Myers; Gateway to Memory 311 When a partial or distorted version of the stored pattern is presented as input to the autoassociator, this activates the corresponding subset of the nodes in the stored pattern, and from these nodes, activity will spread to the remaining nodes, retrieving the rest of the pattern. 0
Gluck & Myers; Gateway to Memory 315 When cholinergic input is present, the hippocampus can store new patterns; when ACh is absent, the hippocampus can retrieve patterns that were previously stored. 4
Gluck & Myers; Gateway to Memory 315 An assumption is that acetylcholine levels should be high during learning and low thereafter. 0
Gluck & Myers; Gateway to Memory 315 New information is stored in the presence of acetylcholine. 0
Gluck & Myers; Gateway to Memory 317 Acetylcholine is not needed for recalling information. 2
Gluck & Myers; Gateway to Memory 318 When ACh is high, the hippocampus tends to store new information; when ACh is low, the hippocampus tends to retrieve previously stored information. 1
Gluck & Myers; Gateway to Memory 334 Cholinergic projection from medial septum to the hippocampus and how it can modulate hippocampal learning rates. 16
Gluck & Myers; Gateway to Memory 334 Acetylcholine functions as a neuromodulator in cortex, as well as in the hippocampus. 0
Gluck & Myers; Gateway to Memory 334 Dopamine modulation in predicting reward, and norepinephrine in modulating sensitivity to behavioral context. 0
Gluck & Myers; Gateway to Memory 335 Theta rhythm, a phenomenon in which large numbers of hippocampal neurons begin to fire in synchronous bursts, approximately 4 to 8 times a second. 1
Gluck & Myers; Gateway to Memory 335 Although the firing of any one neuron results in a minuscule electric charge, the synchronized activity of many thousands of neurons causes an electric charge large enough to be detected through the scalp. 0
Gluck & Myers; Gateway to Memory 335 In a rat, theta rhythm typically occurs during exploratory behaviors, such as walking, rearing, and sniffing. 0
Gluck & Myers; Gateway to Memory 335 Non-synchronized firing occurs during consummatory behaviors, when the animal is sitting quietly and eating, drinking, or grooming. 0
Gluck & Myers; Gateway to Memory 335 Theta rhythm (diagram) 0
Gluck & Myers; Gateway to Memory 336 Theory proposes that theta rhythm occurs during exploration and other learning behaviors when new information is bombarding the brain and is being temporarily stored in the hippocampus. 1
Gluck & Myers; Gateway to Memory 336 Theta rhythm serves the purpose of rhythmically silencing the hippocampus, breaking a steady stream of inputs into manageable 200 ms packets of information. 0
Gluck & Myers; Gateway to Memory 336 Once exploration stops, there is time for the brain to "catch its breath" and analyze the information. 0
Gluck & Myers; Gateway to Memory 337 If ACh modulates information storage in hippocampus, it might have a similar function in cortex. 1
Gluck & Myers; Gateway to Memory 338 Understanding cholinergic modulation of brain function is important with respect to understanding our normal learning and memory occur. 1
Gluck & Myers; Gateway to Memory 338 One of the most common sites of cerebral aneurysm is the anterior communicating artery. The resulting syndrome has three basic components: (1) anteriorgrade amnesia, (2) personality changes (such as loss of self-control, unpredictable aggression, or apathy), and (3) confabulation, or the spontaneous production of false memories. 0
Gluck & Myers; Gateway to Memory 339 Confabulation should be distinguished from lying; confabulators are genuinely unaware that their memories are inaccurate. 1
Gluck & Myers; Gateway to Memory 341 One anatomical hallmark of Alzheimer's disease is the dysfunction and death of basal forebrain neurons, leading to cholinergic depletion throughout the brain. 2
Gluck & Myers; Gateway to Memory 341 Other neuromodulators, including dopamine, norepinephrine, and serotonin, are also reduced in Alzheimer's disease, but the cortical cholinergic systems seem to be affected earlier and to a greater extent. 0
Gluck & Myers; Gateway to Memory 342 Various neuromodulators, including acetylcholine (ACh), alter how neurons transmit messages, without altering the content of the message. 1
Gluck & Myers; Gateway to Memory 342 The major cholinergic input to the hippocampus is the medial septum in the basal forebrain. 0
Gluck & Myers; Gateway to Memory 345 The hippocampus interacts with other brain regions that are its partners in learning and memory, including the entorhinal cortex, the basal forebrain, the cerebellum, and the primary sensory and motor cortices. 3
Gluck & Myers; Gateway to Memory 346 Individuals would've medial temporal lobe epilepsy generally report memory and paramedics even before surgery, and this is at least partially due to his sclerosis (scarring) and the hippocampus as a result of repeated seizures. 1
Gluck & Myers; Gateway to Memory 347 Studies of the simplest forms of animal learning may assist us toward understanding more complex aspects of learning and memory in humans. 1
Gluck & Myers; Gateway to Memory 350 Computational models have assisted our understanding of the neural bases of learning and memory. 3
Gluck & Myers; Gateway to Memory 350 Covering a range of models from a variety of researchers, makes it possible for different models to capture different aspects of anatomy and physiology and different kinds of behavior, and in many cases these models complement each other. 0
Gluck & Myers; Gateway to Memory 350 Informative models should raise as many new questions as they answer old ones. 0
Gluck & Myers; Gateway to Memory