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

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Questions and Answers

Hvad er en lobectomi, i forhold til medicinsk kirurgi?

En lobectomi er en operation, hvor en lap eller en stor del af en lap fjernes fra hjernen.

H.M. manglede hukommelse, men hans hukommelse var normal.

Hvad er H.M. også kendt som?

Henry Molaison

Hvad er årsagen til Korsakoffs syndrom?

Tilaminmangel Signup and view all the answers

Hvilken del af hjernen forbindes oftest med explicit hukommelse?

Hippocampus Signup and view all the answers

Hvad kalder man en 'hippocampal place cell'?

En celle der kun aktiveres når et dyr befinder sig i en bestemt del af et miljø Signup and view all the answers

Hvordan påvirker optogenetik, studiet af hukommelsesceller?

Optogenetik gør det muligt for forskere at aktivere eller inhibere specifikke neuroner ved at bruge lys som en trigger Signup and view all the answers

Hvad kalder man den teori der siger at hukommelse er en proces der bliver stærkere med tiden?

Hukommelseskonsolidering Signup and view all the answers

Hvad er den primære forskel mellem semantisk og episodisk hukommelse?

Semantisk hukommelse refererer til generel viden, mens episodisk hukommelse refererer til specifikke personlige oplevelser Signup and view all the answers

Hvad er infantile amnesia?

Evnen til at huske oplevelser fra den tidlige barndom er begrænset Signup and view all the answers

Hvilken tilstand betegner tab af hukommelse efter en hjerneblødning?

Posttraumatisk amnesia Signup and view all the answers

Hvilken synaptisk mekanisme er tæt forbundet med hukommelse?

Langtidspotentiering (LTP) Signup and view all the answers

Hvad er NMDA-receptoren?

En receptor der er ansvarlig for at udløse langtidspotentiering (LTP) i hjernen Signup and view all the answers

LTP forekommer kun, når der er samtidig aktivitet i både den presynaptiske og postsynaptiske neuron.

True Signup and view all the answers

Hvad er de tre faser af langtidspotentiering (LTP)?

Induktion, vedligeholdelse og udtryk Signup and view all the answers

Hvad er langtidsdepression (LTD)?

En mekanisme, der mindsker signalstyrken i de synaptiske forbindelser Signup and view all the answers

Hvad er metaplasticitet?

Den måde, hvorpå langtidspotentiering (LTP) og langtidsdepression (LTD) påvirkes af tidligere synaptisk aktivitet. Signup and view all the answers

Hvilken funktion har cerebellumet i forhold til hukommelse?

Det hjælper med at lagre sensorimotoriske færdigheder Signup and view all the answers

Hvad er en engram-celle?

En neuron der har gennemgået en permanent ændring på grund af en oplevelse Signup and view all the answers

Hvad gør engram celler?

De udløser eller undertrykker tilbagekaldelsen af den oprindelige oplevelse når de aktiveres eller inhiberes Signup and view all the answers

Study Notes

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.

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.
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.

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.

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.

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.
Emerging perspectives suggest memory consolidation is a more complex, distributed process involving multiple brain areas and potentially lasting throughout a lifetime.

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 Deficity

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.
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.

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.

Induction of LTP: Learning

The co-occurrence of presynaptic stimulation and postsynaptic depolarization is crucial for LTP induction, a characteristic fundamental for associative learning.

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.

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.

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.

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Description

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.