Study Notes on Declarative Memory and the Hippocampus

Declarative memories are those that can be consciously recalled and declared as facts about events.
Includes episodic memories, which are personal experiences, such as remembering what one had for breakfast.

An episodic memory is the "episode of your life"; personal, subjective, and falls under conscious memory.
Comparison to procedural or habit-based memories, which are non-declarative and involve unconscious recall.

Carl Leslie's search for the "engram" (the physical trace of a memory in the brain).
- Leslie was known for attempting to locate specific memories in specific parts of the brain, particularly in the cortex.
- Used rodent mazes to conduct experiments, correlating memory performance with lesions in the rodent cortex.
- Found that memory (the engram) was distributed throughout the cortex, not located in a specific area.
- More cortical damage correlated with more errors in memory tasks.

Donald Hebb expanded on Leslie's theories.
- Proposed that rather than a specific location, memories are formed by various neurons communicating in assemblies.
- For example, seeing a stimulus like a circle activates a series of interconnected neurons.
- This underscores the principle that "cells that fire together wire together"; strengthen connections through repeated activation.

The notion that neurons reinforcing each other through activation leads to formation of a robust engram.
Activation of a few neurons can reactivate the entire memory, highlighting that memories are not isolated to single neurons.
Mention of practical cues used for memory recall, such as alphabet sequencing to recall a person's name.

Focus on the hippocampus and temporal lobes.
- The hippocampus is crucial for memory formation, particularly episodic memories.
- Temporal lobe exploration revealed correlations with sensory experiences and episodic memories through procedures involving patient interactions, often those suffering from epilepsy.

Penfield performed surgeries on epilepsy patients, leading to discoveries of episodic memory activation via brain stimulation.
- Findings suggested that stimulating parts of the temporal lobe prompted individuals to recall personal memories or sensations like music.
- Observed that some memories recalled under direct stimulation were also marked by inconsistencies, raising questions about the authenticity of these memories.

The hippocampus integrates various sensory information crucial for long-term memory consolidation.
- Patients with lesions affecting the hippocampus, like Henry Molaison (H.M.), exhibit extremities such as anterograde and retrograde amnesia.
- Anterograde amnesia: inability to form new memories post-injury.
- Retrograde amnesia: loss of memories formed before the injury, particularly recent ones.
- The patient’s procedural memory remained intact despite the inability to create new declarative memories.

Introduction of tasks like the mirror tracing task to differentiate between procedural and declarative memory.
- Participants must perform tasks without direct sight, reinforcing that procedural tasks can exist independently of episodic memories.

Discussion of medial temporal lobe lesions in primates and implications for working versus long-term memory.
- Short-term or working memory remains intact in the presence of medial temporal lobe lesions for brief delays (8-10 seconds).
- Long delays result in substantial degradation of performance, reflecting memory consolidation issues.

The hippocampus plays a critical role in spatial navigation and memory, evidenced through tasks like the radial arm maze.
- Rodents can navigate efficiently across various arms of the maze to locate food with memory cues.

Description of the Morris Water Maze as a spatial learning tool.
- Training protocols for rodents involved directing them to a hidden platform, assessing their ability to remember and navigate toward it.
- Trials consist of different starting positions to observe memory and navigation efficiency over multiple trials.

Consolidation: Process of converting short-term memories into long-term storage, significantly involving the hippocampus.
Reconsolidation: Recalling memories makes them fragile, necessitating re-storing them, influencing the stability of the memory.
- Address how emotional factors moderate memory retention—high-stress situations can impair or enhance recollection, as seen with involvement of the amygdala in emotional memories.

Memory is not isolated to specific areas; rather, it is distributed across regions of the brain, highlighting the complexity of neural interconnectedness in memory functions.