Lecture Notes: The Hippocampus and Memory

Introduction

• The hippocampus is a crucial brain region for memory retrieval.
• There is much debate surrounding its precise functions and memory storage.

Location of the Hippocampus

• The hippocampus is located deep within the temporal lobe of the brain.
• Each hemisphere has one hippocampus, one in the left and one in the right medial temporal lobe.
• It is part of the limbic system, which is responsible for emotions, memories, and drives.

Limbic System Components

• Key structures of the limbic system include:
  • Hippocampus - Memory
  • Amygdala - Emotional memories
  • Hypothalamus - Controls endocrine and autonomic functions
  • Thalamus - Additional functions within the limbic system

Types of Amnesia

• Anterograde Amnesia:

  • Inability to form new memories after an injury.
  • Example: Henry Molaison (H.M.) could not form new episodic memories after his medial temporal lobes were removed.

• Retrograde Amnesia:

  • Inability to recall old memories prior to the event or injury.
  • Often affects memories from weeks or months leading up to the injury.

Major Functions of the Hippocampus

1. Formation of New Memories

   • Involves explicit or declarative memory, which requires conscious recall.
   • Two types:
     • Episodic Memories: Personal life experiences.
     • Semantic Memories: General knowledge about the world.

2. Memory Consolidation

   • The process of transferring short-term memories into long-term memories.
   • Involves strengthening neural connections through repeated recall and practice (Long-Term Potentiation - LTP).

3. Spatial Navigation

   • Awareness of the environment and ability to create a cognitive map.
   • Research shows the hippocampus is involved in navigating spaces, demonstrated by studies on place cells in rats.

Example Scenario: Formation of Memory

• During a date, sensory information is collected (e.g., sounds, sights, smells) which is then processed by the hippocampus to form a cohesive memory.
• The hippocampus encodes the sensory information into a unique memory.

Conclusion

• The hippocampus is essential for memory formation, consolidation, and spatial navigation.
• It acts like a mental time machine, allowing us to relive past experiences.
• The term "hippocampus" derives from the Greek word for seahorse, reflecting its shape.