introduction to the hippocampus the hippocampus is the most important (i.e., most obvious and...

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 Ammon Ammon’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 CellsHippocampal 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

Attention Mood Reward Novelty

Hippocampal Output

Originally proposed to play a role in control of emotion; likely also involve in memory storage

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