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Memory Part 4

Table of Contents

Patient H.M. (Hippocampus Damage)

  • Henry Molaison (H.M.) had a bilateral medial-temporal lobe resection, which is the removal of the hippocampus and nearby structures.
    • His seizures stopped, but there was evidence of amnesia and difficulty forming new memories.
  • Anterograde Amnesia: The failure to form new memories for anything that happens after the time of brain damage, which is an issue with the encoding stage of memory consolidation.
    • All declarative memories after the time of the injury are impaired.
  • Retrograde Amnesia: The difficulty of retrieving memories that happened before the injury of the hippocampus.
    • There is a gradient in this, with things that happened closer to the injury being harder to remember and things that happened a little earlier being easier to remember.
  • Patients with hippocampal damage have issues with imagining the future, as that involves taking existing memories and combining them in new ways.

Serial Position Curves in Amnesia Patients

In examining recall abilities of amnesia patients, serial position curves offer insightful information, particularly in understanding how amnesia affects different types of memory:

  • Recency Effect Preservation: Amnesia patients typically show no difficulty with the recency effect in serial position curves. This indicates that their working memory, responsible for holding recent information, is largely intact.
  • Primacy Effect Impairment: These patients often struggle with recalling earlier items in a list, which is reflected in a diminished primacy effect. This suggests impairments in transferring information into long-term memory.
  • Hippocampal Damage Variability: This variation is often correlated with the degree of damage to the hippocampus, a crucial area for long-term memory formation.
    • Patients with less hippocampal damage may exhibit a less pronounced decline in the primacy effect, while those with more extensive damage typically show greater impairments.

Single/Double Dissociations

  • Patient H.M. could learn new skills, meaning that their procedural memory was fine, which does not depend on the hippocampus.
    • Isolating the procedural memory showed it was unaffected by hippocampus lesions.

Hippocampus Function Summary

  • Aids in the formation of new declarative memories, both episodic and semantic.
    • Facilitates the binding of different event details into coherent episodic memory.
  • Also plays a role in indexing the relationship between event elements contributing to the recollection of episodic memories, which is not typically involved in semantic memory retrieval.
    • Episodic memories become gradually consolidated in the cortex and depend less on the hippocampal indexing.

Memory Precision

  • Critical Lures: These are stimuli that lead individuals to falsely recall or recognize elements that were not part of an original event. This phenomenon highlights the fallibility and suggestibility of memory.
  • Reliance on Schemas: When recalling memories, people often rely on schemas – their knowledge and expectations of what typically occurs in certain situations, events, or locations.

Schema

  • A schema represents a mental framework or set of preconceived ideas that helps individuals organize and interpret information.
  • Schemas can lead to intrusions in memory, where elements from one episodic memory blend into another. This often happens due to connections between semantically related memories, akin to a network or graph.

Memory Reconstruction

  • Memory is not a passive retrieval of past events but a dynamic reconstructive process.
    • When we recall an event, we reconstruct it, often filling in gaps with current knowledge, beliefs, or expectations.
  • Retrieving a memory involves similar brain mechanisms as imagining a future event, suggesting a shared neural substrate for remembering the past and envisioning the future.

Misinformation Effects

  • The way we hear information can influence what we remember, and we can even create memories that do not exist if they are plausible in the context of the situation we are in.
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