1. Introduction to the Hippocampus The hippocampus is the most important (i.e., most obvious and interesting looking) structure in the limbic system, a collection of brain structures located on the inner border of the neocortex that process olfactory information, regulate emotion and encode memory.

2. Why “Hippocampus”? The basis for the name is unclear, but human hippocampus bears a resemblance to a seahorse.

3. More Nomenclature The hippocampus is also called Ammon’s Horn (cornu ammonis), after the Egyptian god Ammon (Amun) Ra, who was often depicted with ram’s horns. Depiction of AmmonAmmon’s Horn, seen from the top of the brain

4. Hippocampus: Rodent versus Man The volume of the human hippocampus is about 100 times larger than a rat’s, and about 10 times larger than a monkey’s.

5. Structure of the Hippocampus Basic structure preserved across species Hippocampal formation consists of two regions: –Dentate gyrus –Hippocampus proper

6. Subdivisions of the Hippocampus: the CA (Cornus Ammonis) Fields

7. Two Types of Principle Cells Hippocampal Pyramidal Neuron Dentate Granule Cell

8. Structure of the Dentate Gyrus Stratum moleculare: Outer 2/3 receives input from entorhinal cortex Inner 1/3 receives input from CA3 Stratum granulosum Dentate hilus

9. Structure of CA3 sl-m Stratum lacunosum-moleculare: receives afferents from entorhinal cortex Stratum radiatum: receives afferents from CA3 (ipsi & contra) Stratum pyramidale Stratum oriens: receives afferents from CA3 (ipsi & contra) Stratum lucidum: receives mossy fiber input from dentate gyrus

10. Structure of CA1 Stratum lacunosum-moleculare: receives afferents from entorhinal cortex Stratum radiatum: receives afferents from CA3 (ipsi & contra) Stratum pyramidale Stratum oriens: receives afferents from CA3 (ipsi & contra)

11. Basic Hippocampal Connections

12. Modulatory Inputs to Hippocampus AttentionMoodRewardNovelty

13. Hippocampal Output Originally proposed to play a role in control of emotion; likely also involve in memory storage :