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9: Memory Cognitive Neuroscience David Eagleman Jonathan Downar Chapter Outline The Many Kinds of Memory Travels in Space and Time Remembering the Future The Confabulation of Reality The Mechanisms of Memory Beyond Synaptic Plasticity The Mysteries of Memory 2 The Many Kinds of Memory Working and Long-Term Memory Implicit Memory Explicit Memory 3 Working and Long-Term Memory Working memory uses information to address a particular problem. It only lasts for a short period of time and has a limited capacity of about seven items. Working memory includes the phonological loop and the visuospatial sketchpad. 4 Working and Long-Term Memory Long-term memory stores large quantities of information for long periods of time. There are two subdivisions of long-term memory Implicit memory encodes information that is not easy to recall or describe consciously. Explicit memory can be consciously recalled. 5 Working and Long-Term Memory 6 Implicit Memory Procedural memory refers to the knowledge of how to do something. Priming describes how past experiences increase the response to a given sensory stimulus. 7 Implicit Memory 8 Implicit Memory 9 Implicit Memory In classical conditioning, an unconditioned stimulus naturally brings about an unconditioned response. A conditioned stimulus is paired with the unconditioned stimulus, so that it now brings about the response. The response to the conditioned stimulus is known as the conditioned response. 10 Implicit Memory 11 Implicit Memory In operant conditioning, rewards encourage the animal to repeat a behavior and punishment discourages the behavior. Nonassociative learning refers to longterm changes in reflex pathways. 12 Explicit Memory Episodic memories are autobiographical memories of specific events. The medial temporal lobe, particularly the hippocampus, are important for storing and recalling episodic memories. Semantic memories are memories of facts, without details of when or where you learned the fact. 13 Explicit Memory 14 Travels in Space and Time: The Hippocampus and Temporal Lobe A Map of the Medial Temporal Lobe Episodic Memory Spatial Memory Theories of Hippocampal Function Unifying the Functions of the Hippocampus 15 A Map of the Medial Temporal Lobe The anterior hippocampus is important for object recognition memory. The posterior parts are important for spatial memory. The amygdala is important for emotional memories. 16 A Map of the Medial Temporal Lobe 17 Episodic Memory The exact roles of the hippocampus in episodic memory is still being studied. Some research suggests it is necessary for encoding new memories, but not for recalling memories. Other research suggests it is necessary for both encoding and recalling memories. 18 Episodic Memory 19 Spatial Memory Place cells and grid cells in the posterior hippocampus and the adjacent entorhinal cortex build spatial cognitive maps. The Morris water maze and radial arm maze are experimental procedures that test spatial maps in rodents. 20 Spatial Memory 21 Spatial Memory 22 Theories of Hippocampal Function Several theories attempt to describe the function of the hippocampus. Declarative theory: The hippocampus is crucial for new declarative memories. Multiple-trace theory: The hippocampus is crucial for new and old declarative memories. Dual-process theory: The hippocampus is crucial for recalling the context of an event. 23 Theories of Hippocampal Function Several theories attempt to describe the function of the hippocampus. Relational theory: The hippocampus stores the relations between events. Cognitive map theory: The hippocampus originally stored maps of space. 24 Remembering the Future: Prospection and Imagination How We Imagine Future Experiences The Circuitry of Prospection and Recollection Prospection in Other Species Models of Prospection 25 How We Imagine Future Experiences Prospection refers to how we imagine future events. Lesions of the hippocampus impair both recollection and prospection. The medial temporal lobes, medial parietal and prefrontal areas, and lateral temporal and parietal lobes are important for both recollection and prospection. 26 How We Imagine Future Experiences 27 The Circuitry of Prospection and Recollection The medial prefrontal cortex connects to the temporal lobes and amygdala. It is important for tracking the value of a stimulus and for establishing long-term goals. The medial parietal lobe connects to medial temporal areas and is important for mapping. 28 The Circuitry of Prospection and Recollection The retrosplenial cortex interacts with the posterior hippocampus and is important for navigation. The temporoparietal junction and the superior temporal sulcus integrate information from various senses. The hippocampus may integrate activity in these different areas. 29 The Circuitry of Prospection and Recollection 30 Prospection in Other Species Other species appear to use prospection. Jays Rats It is difficult to design and interpret studies of prospection in other species. 31 Prospection in Other Species 32 Models of Prospection The BBB model proposes that the place cells in the hippocampus are important for all mental imagery. These cells reactivate maps of the environment and objects within the environment. Such maps allow the animal to use past experiences to meet current needs. 33 Models of Prospection 34 The Confabulation of Reality Confabulation in the Injured Brain The Anatomy of Spontaneous Confabulation Confabulation in the Normal Brain The Anatomy of a False Memory 35 Confabulation in the Injured Brain Confabulation is creating an alternate version of the past and acting as if it is completely true. Provoked confabulations occur when a person is prompted for more details than they can remember. Spontaneous confabulations occur without external cues. 36 Confabulation in the Injured Brain 37 The Anatomy of Spontaneous Confabulation In confabulation, the person fails to inhibit currently irrelevant memories. Spontaneous confabulations occur following damage to the medial orbitofrontal and prefrontal cortex. The dorsomedial thalamus or hypothalamus are sometimes damaged in patients who confabulate. 38 The Anatomy of Spontaneous Confabulation 39 The Anatomy of Spontaneous Confabulation 40 Confabulation in the Normal Brain Memory errors are common, even in uninjured brains. Schacter’s Sins of Memory Misattribution: When we attribute a memory to the wrong source. Suggestibility: False memories are implanted by information we hear after the event. Bias: Our current knowledge distorts what we recall about the past. 41 The Anatomy of a False Memory There are difference in the patterns of brain activity associated with true versus false memories. These areas include the hippocampus, parahippocampal cortex, and medial and lateral prefrontal cortex. There was a failure to inhibit the misinforming memory. 42 The Anatomy of a False Memory 43 The Mechanisms of Memory General Mechanisms of Learning and Memory Memory as Synaptic Change Long-Term Potentiation and Depression of Synaptic Connections The NMDA Receptor Consolidation and Reconsolidation Associative Neural Networks 44 General Mechanisms of Learning and Memory Memory involves widespread activity in the brain. There are general principles of plasticity that apply to all regions, All models of memory include changing the strength of the synaptic connection based on previous activity. 45 Memory as Synaptic Change Donald Hebb hypothesized about experience-dependent plasticity. If cell A repeatedly stimulates cell B, then the connection between A and B is strengthened. 46 Memory as Synaptic Change 47 Long-Term Potentiation and Depression Long-term potentiation (LTP) was the first demonstration of the experiencedependent plasticity proposed by Hebb. LTP was first described in 1973, about 25 years after it was proposed by Hebb. 48 Long-Term Potentiation and Depression 49 The NMDA Receptor This type of ionotropic glutamate receptor is important for early stages of LTP. This receptor is not active under normal conditions, because the channel is blocked by a magnesium ion. If the cell is repeatedly depolarized, the change in membrane voltage causes the magnesium ion leave the channel. 50 The NMDA Receptor The NMDA receptor allows cations, including calcium, to enter the cell. The calcium activates secondarymessenger systems, promoting learningrelated changes within the cell. This receptor acts as a coincidence detector. LTP is specific to a particular synapse. 51 The NMDA Receptor 52 The NMDA Receptor Long-term depression occurs when there is no response of the post-synaptic cell to repeated input. Short-term potentiation and depression also occur. 53 Consolidation and Reconsolidation Consolidation is moving memories from short-term to long-term storage. Consolidation occurs in the hippocampus. Once they have been recalled, memories need to be reconsolidated into long-term memory. Memories are vulnerable to editing or loss during reconsolidation. 54 Consolidation and Reconsolidation 55 Associative Neural Networks Learning can be simulated on artificial neural networks. Small changes in how the network is connected result in changes to the output of the network. 56 Associative Neural Networks 57 Beyond Synaptic Plasticity: The Frontiers of Memory Mechanisms Whole Neurons as a Substrate for Memory? New Neurons for New Memories Spines: Another Structural Basis for Memory? Looking inside the Cell: Memory in Chemical Reactions Epigenetics: Making a Single Genome Play Different Tunes 58 Whole Neurons as a Substrate for Memory? Although research has focused on synaptic changes, memory could use a different process within the cell. The birth of new neurons (neurogenesis) in the hippocampus could be important for storing information. Thousands of new neurons are formed in the hippocampus every day. 59 Whole Neurons as a Substrate for Memory? 60 New Neurons for New Memories Younger neurons have greater plasticity, so may be important for forming new connections. New cells may provide a framework for establishing connections among existing neurons. 61 Spines: Another Structural Basis for Memory? Dendritic spines grow and change shape in a matter of hours in young animals. These spines become less plastic and more stabile in adults. The spines may be important for memory storage. 62 Spines: Another Structural Basis for Memory? 63 Looking inside the Cell: Memory in Chemical Reactions Chemical reactions within the cell may store memories. This may involve some biochemical process, such as activating an enzyme. CaMKII and CPEB are proteins thought to be important for memory and learning. 64 Looking inside the Cell: Memory in Chemical Reactions 65 Looking inside the Cell: Memory in Chemical Reactions 66 Epigenetics: Making a Single Genome Play Different Tunes Epigenetics describe changes to the structure (not nucleotide sequence) of DNA and the nuclear proteins. Adding methyl groups to DNA can block transcription. Adding acetyl groups to histone proteins can facilitate transcription. Epigenetic modifications are heritable. 67 Epigenetics: Making a Single Genome Play Different Tunes 68 The Mysteries of Memory Are the Roles of LTP and LTD Overstated? The Timing of Spikes The Limitations of Neural Networks Neural Networks: Solving the Wrong Problem? Remembering Relationships, Not Features The Future of Memory Research 69 Are the Roles of LTP and LTD Overstated? Research supports that LTP and LTD are necessary for memory formation. Research does not support that these processes provide the full explanation. 70 The Timing of Spikes The roles of the timing of action potentials has not been addressed by current models of memory. The order of activity (pre-synaptic activity, then post-synaptic activity) matters greatly in memory formation. 71 The Timing of Spikes 72 The Limitations of Neural Networks Information must be relevant to be learned, but artificial neural networks cannot distinguish relevant from irrelevant. Relevance may be encoded by using neuromodulators to turn plasticity at the synapse on or off. 73 The Limitations of Neural Networks 74 Neural Networks: Solving the Wrong Problem? Neural networks can extract the identity of the object without seeing the whole thing. Brains encode information differently, encoding the relation between different stimuli. 75 Remembering Relationships, Not Features Human memory shows invariance, meaning the details of size, lighting, position, etc. do not matter. This supports the idea that we learn the relations between things, not just learn them on a pixel-by-pixel basis. 76 Remembering Relationships, Not Features 77