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.
Why “Hippocampus”? The basis for the name is unclear, but human hippocampus bears a resemblance to a seahorse.
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
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.
Structure of the Hippocampus Basic structure preserved across species Hippocampal formation consists of two regions: –Dentate gyrus –Hippocampus proper
Subdivisions of the Hippocampus: the CA (Cornus Ammonis) Fields
Two Types of Principle Cells Hippocampal Pyramidal Neuron Dentate Granule Cell
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
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
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)
Basic Hippocampal Connections
Modulatory Inputs to Hippocampus AttentionMoodRewardNovelty
Hippocampal Output Originally proposed to play a role in control of emotion; likely also involve in memory storage :