Kapitel 11: Casen om H.M. og hukommelses forskning

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Chapter Overview and Learning Objectives

• LO 11.1: Describe five specific memory tests used to assess H.M.'s anterograde amnesia.
• LO 11.2: Describe three major scientific contributions of H.M.'s case.
• LO 11.3: Discuss research on medial temporal lobe amnesias and its implications for learning and memory.
• LO 11.4: Describe the difference between semantic and episodic memories.
• LO 11.5: Discuss two pieces of evidence supporting the idea that selective hippocampal dysfunction can cause medial temporal lobe amnesia.

Amnesic Effects of Bilateral Medial Temporal Lobectomy

• H.M.'s surgery, a bilateral medial temporal lobectomy, was aimed at controlling severe epilepsy.
• This procedure significantly affected his ability to form new long-term memories (anterograde amnesia) while leaving his pre-existing memories largely intact (retrograde amnesia, limited).
• H.M.'s case revolutionized memory research.

The Case of H.M., the Man Who Changed Studying Memory

• During 11 years pre-surgery, H.M. experienced seizures, despite medication.
• He underwent bilateral medial temporal lobectomy, removing medial portions of both temporal lobes (hippocampus, amygdala, and adjacent cortex).
• H.M.'s surgery was initially a success in reducing seizure frequency.
• Post-surgery, H.M. exhibited significant anterograde amnesia.

Formal Assessment of H.M.'s Anterograde Amnesia: Discovery of Unconscious Memories

• Digit-Span + 1 Test: H.M. had difficulty forming new long-term verbal memories, demonstrated by his poor performance on this test.
• Block-Tapping Test: H.M. showed difficulties with forming new procedural memories, as indicated by his inability to perform complex sequences on this test.
• Mirror-Drawing Test: H.M. unconsciously retained and improved on this nonsensorimotor test of memory over time.
• Incomplete-Pictures Test: H.M.'s performance improvements on this test demonstrated a type of implicit memory storage unaffected by his anterograde deficit.
• Pavlovian conditioning showed H.M. could learn tasks like eye-blink conditioning, though slower, with retention and no conscious recollection of the training.

Three Major Scientific Contributions of H.M.'s Case

• Challenged the view of memory as a diffuse brain function.
• Highlighted medial temporal lobes' crucial role in forming certain long-term memories.
• Illustrated the distinction between conscious (explicit) and unconscious (implicit) memory.

Medial Temporal Lobe Amnesia

• Research on medial temporal lobe amnesia demonstrated different memory types (explicit and implicit) and their different vulnerabilities.
• Tests like repetition priming tests assess implicit memory.
• H.M.'s case illustrated that formation of certain kinds of long-term memories can be impaired without causing deficits in short-term, or remote memories.
• Existence of implicit and explicit systems raises questions such as the advantages of having a conscious system.
• Research suggests explicit memory enables flexible use of information.

Semantic and Episodic Memories

• Explicit memories include semantic memories (general knowledge) and episodic memories (personal experiences).
• People with medial temporal lobe amnesia often struggle more with episodic memory than semantic memory.
• Endel Tulving described episodic memory as autobiographical, likened to mentally time traveling into one's past.
• Some patients like K.C. display a marked inability to recall any personal events, despite his general intelligence and good factual/semantic knowledge, suggesting spared retrieval from one memory system, but impaired retrieval from the other.
• It is difficult to spot these deficits, neuropsychologists usually have no way of knowing true events.

Effects of Global Cerebral Ischemia on the Hippocampus and Memory

• Global cerebral ischemia patients exhibited episodic amnesia.
• It is difficult to rule out other cerebral dysfunction.

Amnesia After Traumatic Brain Injury: Evidence for Consolidation

• Closed-head traumatic brain injuries frequently cause post-traumatic amnesia, featuring retrograde (loss of old memories) and anterograde (loss of new memories) amnesia.
• The duration of confusion and retrograde amnesia is typically longer than the coma itself, and more severe traumas lead to more extensive deficits.
• Islands of memory may survive.

Gradients of Retrograde Amnesia and Memory Consolidation

• Retrograde amnesia following traumatic brain injury often shows a gradient, with recent memories more susceptible to disruption than older ones.
• This gradient supports the classic theory that memory consolidation involves a gradual process of transferring memories into more stable long-term storage.
• Electroconvulsive shock (ECS) seemed to indicate a period over which retrograde amnesia was produced.
• The standard consolidation theory accounts for the disproportionate disruption of recent memories following medial temporal lobectomy.
• Emerging perspectives suggest memory consolidation is a more complex, distributed process involving multiple brain areas and potentially lasting throughout a lifetime.
• Reconsolidation involves memories retrieved shifting, where memories are labile and susceptible to the same treatments and effects applied during the consolidation period.

Amnesias of Korsakoff's Syndrome and Alzheimer's Disease

• Korsakoff's syndrome typically seen in individuals with high alcohol consumption, associated with thiamine deficiency.
• Alzheimer's is another major cause of amnesia, begins as a mild deterioration of memory, ultimately affecting the ability to have simple memories.

Animal Models of Object Recognition Amnesia

• Delayed Nonmatching-to-Sample Test (Monkeys & Rats): Using this test, scientists found that medial temporal lobe lesions in primates and rodents significantly impair object recognition memory.

Neuroanatomical Basis of the Object-Recognition Deficit

• Challenges the emphasis on hipocampus role.
• Lesions to the medial temporal cortex in rodents and monkeys consistently result in more severe object-recognition deficits compared to hippocampal lesions alone, challenging the earlier emphasis on hippocampus.
• Cerebral ischemia primarily damages CA1 hippocampal pyramidal cells, but extensive damage to the cortex is also implicated in many cases.

Neurons of the Medial Temporal Lobes and Memory

• Place Cells: Hippocampal neurons that fire only when a subject is in a particular location; this activity adapts to new environments.
• Grid Cells: Entorhinal neurons with a repeating grid pattern of evenly spaced place fields tiling the environment.
• Activity of place cells indicates where the subject thinks it its, regardless of where they actually are.
• The relationship between grid cells and place cells is complex and not fully understood, but a major pathway between entorhinal cortex and hippocampus implies grid cells play a crucial, although not necessarily exclusive, role. Hippocampus has role learning about social organization.

Jennifer Aniston Neurons: Concept Cells

• There are distinct neuron types in the temporal lobes, concept cells.
• Concept cells are found in the hippocampus are more selective than other medial parts.

Cellular Mechanisms of Learning and Memory: Long-Term Potentiation

• Long-term potentiation (LTP): A long-lasting increase in synaptic strength following high-frequency stimulation; a key cellular mechanism for learning and memory.
• LTP involves the NMDA receptor, which requires both glutamate binding and postsynaptic depolarization for calcium influx, triggering LTP-inducing molecular changes.
• Hebbian synapse has activity that occurs and strengthens synapses.

Induction of LTP: Learning

• The NMDA receptor does not initially respond unless two events happen, glutamate binding and postsynaptic depolarization.
• The co-occurrence of presynaptic stimulation and postsynaptic depolarization is crucial for LTP induction, a characteristic fundamental for associative learning.
• NMDA mediated LTP is not the only type of LTP.

Maintenance and Expression of LTP: Storage and Recall

• LTP maintenance involves structural changes, including alterations in spine morphology, influenced by protein synthesis and possibly epigenetic mechanisms.
• Maintenance is related to specific synapses on a post synaptic neuron. LTP involves transcriptional factors intracellular.

Variability of LTP

• Long-term depression (LTD) is the opposite of LTP, representing a weakening of synaptic strength, influenced by low-frequency stimulation.
• Metaplasticity describes how previous synaptic activity influences the induction of LTP or LTD, complicating predictions.

Nonsynaptic Mechanisms of Learning and Memory

• There are neuroplastic changes that are non synaptic.
• Neuroplastic changes can occur outside synapse.

Infantile Amnesia

• Infantile amnesia is the inability to recall explicit memories from early childhood.
• Research suggests that implicit memories retained.

Smart Drugs: Do They Work?

• Nootropics, or "smart drugs" that aim to improve memory, are commonly touted but often have limited scientific support for efficacy, with research often low quality and poorly controlled.

Posttraumatic Amnesia and Episodic Memory

• Posttraumatic amnesia, following a head injury, involves loss of memories preceding the concussion.
• Cases like R.M.’s highlight the potential dissociation between episodic memory (personal events) and other memory types, revealing complexities of memory function beyond simple storage.

Themes Revisited

• Biopsychology of memory highlights neuroplasticity, highlighting the changes in brain structure and function supporting memory.
• Clinical implications arise from understanding memory disorders.
• Animal models provide valuable research possibilities. Thinking creatively suggests more unconventional ways to help those with conditions.

Udforsk H.M.'s bane med anterograd amnesi og de betydelige videnskabelige bidrag fra hans sag. Denne quiz dækker hukommelsestests, forskningen om medial temporallap amnesier, samt forskellene mellem semantisk og episodisk hukommelse. Deltag for at lære om, hvordan H.M. revolutionerede hukommelsesforskning.