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
Depiction of Ammon
Ammon’s Horn, seen
from the top of the brain
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.
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 lucidum:
receives mossy fiber input from dentate gyrus
Stratum pyramidale
Stratum oriens:
receives afferents from CA3 (ipsi & contra)
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