The hippocampus is a structure in the limbic system in the brain, and looks a little like an upside-down seahorse that faces towards the front of the head. Symmetrical, hippocampus anatomy is mirrored in both hemispheres of the brain. The structure is responsible for relaying information to the thalamus and has an impact on spatial awareness, memory and learning.
A part of the limbic system, the hippocampus is located deep within the brain. The hippocampus is divided into two symmetrical sides on the left and the right of the brain. It is wrapped around the thalamus, another structure in the limbic system, which is found close to the center of the brain. The structure above both the hippocampus and the thalamus is known as the corpus callosum.
The hippocampus is composed of a few key structures. Its base, which is its widest point, is called the hippocampus proper, or the cornu Ammonis, and is partially enclosed by another section of the hippocampus called the alveus. The subiculum is the part of the hippocampus that begins to thin and curve towards the top of the thalamus. Along the top of the thalamus sits the part of the hippocampus called the fimbria. The fornix is the thinnest part of the hippocampus and also the point where this structure connects to the thalamus, behind the forehead.
Electrical information is collected by the hippocampus proper. Once the information enters the hippocampus proper, it moves into another part of the hippocampus anatomy called the choroid plexus. This structure begins in the middle of the hippocampus proper and follows the spiral, through the subiculum, fimbria and the fornix all the way to the thalamus.
The fornix of the hippocampus is joined at the top as it comes over the thalamus. The two sides press together but then separate out again to connect to both the right and left lobes of the thalamus. The connection between the two sides of the fornix is known as the hippocampal commissure.
It is useful to think of hippocampus anatomy as an upside-down seahorse. Indeed, the name hippocampus comes from the Greek for horse, hippo, and sea monster, campus. The hippocampus is wide and thick at the lower region, like the head of a sea horse. As it wraps around the thalamus, it thins into the fornix, which looks similar to a seahorse's tail. Two such “seahorses” circle the thalamus because hippocampus anatomy is symmetrical.