The hippocampus is a component of the brain recognized for its involvement in forming new memories and navigating through space. It acts to convert short-term memories into more lasting long-term ones, organizing and storing experiences for later retrieval. This structure also supports our awareness of our surroundings and helps in remembering words, making it important for learning and memory.
The Brain’s Medial Temporal Lobe
The hippocampus is located deep within the brain, specifically in the medial temporal lobe. The temporal lobes are situated on each side of the head, roughly behind the temples. Since the brain has two hemispheres, a left and a right, it also contains two hippocampi, one in each corresponding temporal lobe. Each one is an elongated structure tucked inside the parahippocampal gyrus, which is a ridge of gray matter tissue.
This location places the hippocampus inside the inferior horn of the lateral ventricle, a fluid-filled cavity within the brain. The structure itself is a curved sheet of cortex that folds into the medial surface of the temporal lobe.
The hippocampus is not uniform along its length; it is divided into a head, body, and tail. The anterior portion, or head, is connected to the amygdala, while the posterior part, the tail, extends toward the back of the brain near the corpus callosum. The anterior hippocampus is more involved in emotion and stress regulation, whereas the posterior part is associated with cognitive and spatial processing.
A Part of the Limbic System
The hippocampus is a component of the limbic system, a collection of brain structures located deep within the brain, beneath the cerebral cortex. This system is involved in behavioral and emotional responses, including motivation, hunger, and mood. The term “limbic” is derived from the Latin word for “border,” reflecting its position between the neocortex and other subcortical structures.
Its placement within this system is functionally significant. The hippocampus is situated next to the amygdala, a structure central to processing emotions like fear and pleasure. This proximity facilitates rapid communication, allowing emotional context to be attached to memories, which influences how strongly those memories are stored.
The hippocampus also works closely with the entorhinal cortex, which acts as a major hub for information. It receives information from various parts of the cerebral cortex and relays it to the hippocampus for memory formation. This network of connections allows the hippocampus to consolidate new information and retrieve existing memories effectively.
Shape and Structure
The physical appearance of the hippocampus is distinctive. Its name is derived from the Greek word “hippokampus,” which translates to “seahorse,” because its curved shape closely resembles the sea creature. This S-shaped or C-shaped structure is an elongated and convex elevation of gray matter.
Each hippocampus is about 5 centimeters in length and is composed of densely packed neurons. The anterior part, known as the pes hippocampi, is expanded and has shallow grooves. The main body of the structure is often described as having an appearance like a Swiss roll in cross-section, showing two interlocking U-shaped structures.
The structure is part of the larger hippocampal formation, which includes the dentate gyrus and the subiculum. The dentate gyrus is a layer of neurons that interlocks with the hippocampus proper. The subiculum is the area that connects the hippocampus to other parts of the brain, facilitating the flow of information for memory retrieval.