Chapter 9 - Memory.docx

*Mark Twain* CHAPTER Memory ====== - What is forgotten in amnesia, and are all forms of amnesia the same? - Are memories about personal events processed in the same way as procedural memories for how to perform a physical task? - What brain systems have proved to be critical for the f...

*Mark Twain* CHAPTER Memory ====== - What is forgotten in amnesia, and are all forms of amnesia the same? - Are memories about personal events processed in the same way as procedural memories for how to perform a physical task? - What brain systems have proved to be critical for the formation of long-term memory? - Where are memories stored in the brain, and by what cellular and molecular mechanisms? **379** ### Learning and Memory, and Their Associated Anatomy 1. **Characteristic of Memory** **Conscious** **Type of Memory Time Course Capacity Awareness? Mechanism of Loss** 1. **Encoding** is the processing of incoming informa- tion and experiences, which creates *memory traces*, traditionally thought to be alterations in the synaptic strength and number of neuronal connections. (Re- search in the last few years, however, has challenged the traditional notion that synaptic strength is the mechanism behind encoding.) 2. **Storage** is the retention of memory traces. It is the result of acquisition and consolidation, and it repre- sents the permanent record of the information. 3. **Retrieval** involves accessing stored memory traces, which may aid in decision making and change behavior. We have conscious access to some but not all of the information stored in memory. TAKE-HOME MESSAGES - Learning is the process of acquiring new information, the outcome of which is memory. - Memories can be short-term or long-term. Long-term memories may be declarative, consisting of either the conscious memory for facts (semantic memory) or the conscious memory of past experiences (episodic - Learning and memory have three major stages: encoding (acquisition and consolidation), storage, and retrieval. - The medial temporal lobe memory system is made up of the hippocampus and the surrounding entorhinal cortex, perirhinal cortex, and parahippocampal cortex within the temporal lobes. ### Memory Deficits: Amnesia Brain Surgery and Memory Loss 2. Dementias TAKE-HOME MESSAGES - Anterograde (forward-going) amnesia is the loss of the ability to form new memories, as in the case of H.M. - Retrograde (backward-going) amnesia is the loss of memory for events that happened in the past. - Retrograde amnesia tends to be greatest for the most recent events---an effect known as a temporal gradient or Ribot's law. - The most common neurodegenerative cause of dementia is Alzheimer's disease. 3. ### Mechanisms of Memory Short-Term Forms of Memory 0.75 1.50 3.00 6.00 9.00 12.00 -- -- -- -- -- -- Long-Term Forms of Memory 1 2 3 4 Time **a b** know that a pattern exists. Reward Gate open Start Tone Begin Warning click turn 1 1 --1 1 --2 100 90 80 70 60 50 40 30 20 10 0 100 90 80 70 60 0 a. **b c** a. CS b. US CS US a. When a stimulus is presented that has no meaning to an animal, such as the sound of a bell (CS), there is no response (NR). b. In contrast, presentation of a meaningful stimulus like food (US) generates an unconditioned response (UR). **(c)** When the sound is paired with the food, the animal learns the association. **(d)** Later, the newly conditioned stimulus (CS) alone can elicit the response, which is now called a conditioned response (CR). TAKE-HOME MESSAGES - Memory classified by duration includes sensory memory, lasting only seconds at most; short-term memory, lasting from seconds to minutes; and long-term memory, lasting from days to years. - Working memory extends the concept of short-term memory: It contains information that can be acted on and processed, not merely maintained by rehearsal. - Long-term memory is split into two divisions defined - Declarative memory can be further broken down into episodic and semantic memory. Episodic memory involves conscious awareness of past events that we have experienced and the context in which those events occurred. Semantic memory is the world knowledge that we remember even without recollecting the specific circumstances surrounding its learning. - Procedural memory is a form of nondeclarative memory that involves the learning of various motor and cognitive skills. Other forms of nondeclarative memory include perceptual priming, conditioned responses, and non- associative learning. 4. ### The Medial Temporal [ ] Evidence From Amnesia a. The red circles in this anterior slice indicate where the hippocampus was removed bilaterally. b. This more posterior slice, however, shows that the hippocampus (circled in red) was still intact in both hemispheres! This finding stood in marked contrast to the belief that H.M. had no hippocampus---a view, based on the surgeon's report, that the scientific community had held [ c] Collateral Entorhinal  b. Nonamnesic **c** Case R.B. Neurons Evidence From Animals With Medial Temporal Lobe Lesions a. The correct response has a food reward located under it. b. The monkey is shown the correct response, which will yield a reward for the monkey. **(c)** The door is closed, and the reward is placed under a second response option. **(d)** The monkey is then shown two options and must pick the correct response (the one that does *not* match the original sample item) to get the reward. Here the monkey is pictured making an error. a. This lateral, see-through view of the left hemisphere shows the amygdala (red) and hippocampus (blue) within the temporal lobe. b. This view from the ventral surface of the same hemisphere shows the amygdala and hippocampus, and indicates the locations of the parahippocampal gyrus and the entorhinal area (consisting of Brodmann areas 28 and typically also 34, which are located in the most anterior portion of the parahippocampal gyrus). 100 90 80 70 60 50 0 TAKE-HOME MESSAGES - The hippocampus is critical for the formation of long- term memory, and the cortex surrounding the hippocam- pus is critical for normal hippocampal memory function. - Evidence from humans and animals with brain damage suggests a degree of independence of procedural mem- ory, perceptual priming, conditioning, and nonassociative learning from the medial temporal lobe memory system. - Neurons that activate when rats are in a particular place and facing a particular direction have been identified in the hippocampus and are called place cells. They provide evidence that the hippocampus has cells that encode contextual information. - Damage to the temporal lobe outside of the hippocam- pus can produce the loss of semantic memory, even while the ability to acquire new episodic memories remains intact. 5. ### Distinguishing Human Memory Systems With Imaging Recollection and Recognition: Two Systems  0.4 0.3 0.2 0.1 0 --0.1 --0.2 --0.3 0.4 0.3 0.2 0.1 0 --0.1 --0.2 --0.3 a. Horizontal sections through the brain at the level of the inferior (left panel), middle (center panel), and superior (right panel) hippocampus. The red outline of the region of interest in the left hippocam- pus is based on anatomical landmarks. **(b)** Hemodynamic responses from event-related fMRI measures taken during the retrieval of previously studied words. The hippocampus was activated by correctly recollected words (solid red line) but not by words that the participants had previously seen but could not recollect, indicating that the words merely seemed familiar (solid black line). No hippocampal activ- ity occurred for words that were correctly identified as new (not seen previously; dashed red line) or for errors in which the participant did not remember the words (dashed black line), despite having seen them previously. a. Experimental design 850 ms b. Behavioral results 50 40 30 20 10 Definitely new Definitely old Recognition confidence 0.2  0 −0.2 −0.4 −0.6 −0.8 −1.0 1.0 0.8 0.6 0.4 0.2 0.0 Long-Term Memory Storage and Retrieval 0.4  Encoding, Retrieval, and the Frontal Cortex a. Regions showing greater activation for true compared to false remembering (primary b. Regions showing greater activation for false memories (medial superior prefrontal cortex and inferior parietal cortex). a. Words activate left frontal cortex during encoding. b. Nameable objects activate both left and right frontal cortex during encoding. **(c)** Encoding of faces activates primarily right frontal cortex. Retrieval and the Parietal Cortex a. The perirhinal cortex (PRC), parahippocampal cortex (PHC), and retrosplenial cortex (RSC) regions are shown. **(b)** Functional connectivity profiles of the PRC (top) and PHC (bottom), showing regions that were significantly correlated with the PRC and PHC during resting-state scans. Resting-state fMRI scans evaluate covariations in spontaneous fluctuations in the BOLD signal across the brain while the partici- pant performs no task, and they are taken as evidence of intrinsic functional connectivity between brain regions that covary. The PRC was found to be functionally connected to ventral temporopolar cortex (vTPC), where higher-order visual areas are located. In contrast, the PHC is functionally connected to the dorsal temporopolar cortex (dTPC), the retrosplenial cortex (RSC), the posterior cingulate cortex (PCC), the precuneus (PC), the medial prefrontal cortex (MPFC), and the angular gyrus (AG). a. Memory-orienting patterns Hits Correct rejections b. Unexpected novelty response TAKE-HOME MESSAGES - Functional MRI evidence suggests that the hippocampus is involved in encoding and retrieval for episodic memo- ries that are recollected. Areas outside the hippocam- pus, especially the perirhinal cortex, support recognition based on familiarity. - Different types of information may be retained in partially or wholly distinct memory systems. - The PHC and RSC have anatomical and functional con- nectivity patterns that are similar to each other and are very different from the PRC. The RSC, located in the parietal lobe, appears also to be crucial for memory. - Both the IFC and the parietal lobe are involved in retriev- ing memories, but their roles have not been clearly defined. 6. ### Memory Consolidation \ Consolidation and the Hippocampus Retrograde amnesia 9.6 Memory Consolidation \| **417** Sleep and Memory Consolidation Stress and Memory Consolidation \ TAKE-HOME MESSAGES - Two prominent theories of long-term memory consoli- dation are the standard consolidation theory and the multiple trace theory. - Sleep supports memory consolidation, perhaps when hippocampal neurons replay patterns of firing that were experienced during learning. - Stress affects episodic memory consolidation when high levels of cortisol influence hippocampal function. #### Summary #### Key Terms #### Think About It 1. Compare and contrast the different forms of memory in terms of their time course. Does the fact that some memories last seconds while others last a lifetime nec- essarily imply that different neural systems mediate the two forms of memory? 2. Patient H.M. and others with damage to the medial temporal lobe develop amnesia. What form of amnesia do they develop? For example, is it like the amnesia most often shown in Hollywood movies? What infor- mation can these amnesic patients retain, what can they learn, and what do the answers to these questions tell us about how memories are encoded in the brain? 3. Can you ride a bike? Do you remember learning to ride it? Can you describe to others the principles of riding 4. Describe the subdivisions of the medial temporal lobe and how they contribute to long-term memory. Con- sider both encoding and retrieval. 5. Relate models of long-term potentiation (LTP) to changing weights in connectionist networks. What constraints do cognitive neuroscience findings place on connectionist models of memory? #### Suggested Reading  **425**