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The hippocampus is one of the most important structures of the human brain, deeply embedded within the medial temporal lobe. It forms an essential part of the limbic system, the network of brain structures that regulates emotions, learning, and memory. The name “hippocampus” is derived from Greek, where hippos means horse and kampos means sea monster. Early anatomists noticed that its curved shape resembled a seahorse, and the name has remained in scientific use ever since.

Although small in size compared to the overall brain, the hippocampus has an immense role in human cognition. It is best known for its contribution to the processes of memory formation and spatial navigation. Whenever we learn something new, such as a fact, a personal experience, or even the route to a new place, the hippocampus becomes actively involved in encoding this information. Without it, humans would not be able to convert fleeting short-term memories into stable long-term memories, making meaningful learning nearly impossible.

The hippocampus is also a highly conserved structure across different species, from humans to other mammals, which highlights its evolutionary importance. This similarity allows researchers to study animal models to better understand how memory and learning work in the human brain.

Functionally, the hippocampus acts as a kind of bridge between perception and memory. It does not serve as a permanent storage area for all memories, but rather organizes, processes, and transfers them to other cortical regions for long-term storage. In this way, it ensures that experiences are not lost but preserved for future recall.

Structure of Hippocampus

The hippocampus is a curved, elongated structure located deep within the medial temporal lobe of the brain, one in each hemisphere. Although small in size, it has a very complex internal organization. Its shape is often compared to that of a seahorse, which is why early anatomists named it “hippocampus.” Structurally, it forms a major part of the hippocampal formation, which includes three closely related regions: the hippocampus proper or cornu ammonis, the dentate gyrus, and the subiculum.

The dentate gyrus is positioned along the edge of the hippocampus and serves as the main entry point for incoming signals. It contains densely packed granule cells, which are small neurons that receive excitatory inputs from the entorhinal cortex through a pathway known as the perforant path. The dentate gyrus plays an important role in neurogenesis, as new granule cells continue to form here even in adulthood, something that is rare in most other parts of the brain. Structurally, it is C-shaped and curves around the hippocampal regions, making it an essential component of the processing loop.

The hippocampus proper, also known as cornu ammonis, is subdivided into four regions called CA1, CA2, CA3, and CA4. Each of these areas contains pyramidal cells, which are excitatory neurons with a characteristic triangular shape. CA1 is the largest and serves as a major output region, transmitting processed information to other brain areas. It is highly sensitive to oxygen deprivation and damage. CA2, although small, has a unique set of connections and is associated with certain forms of social memory. CA3 receives direct inputs from the dentate gyrus through mossy fiber connections and is crucial for pattern completion, which allows a person to recall a full memory from partial cues. CA4 lies within the hilus of the dentate gyrus and forms a relay between the granule cells of the dentate gyrus and other CA regions.

Adjacent to CA1 lies the subiculum, which acts as the principal output structure of the hippocampus. It sends information to the entorhinal cortex, the amygdala, the prefrontal cortex, and several other brain regions. The subiculum also consists of pyramidal cells and plays a vital role in relaying processed signals from the hippocampus to the rest of the brain.

One of the defining structural features of the hippocampus is its highly organized flow of information known as the trisynaptic circuit. In this circuit, signals enter from the entorhinal cortex into the dentate gyrus, pass from the dentate gyrus to CA3, then from CA3 to CA1, and finally from CA1 to the subiculum. This sequential arrangement ensures that information is carefully processed, refined, and integrated before being sent to other cortical regions for long-term storage.

At the cellular level, the hippocampus mainly contains two types of excitatory neurons: granule cells in the dentate gyrus and pyramidal cells in the CA regions and subiculum. These neurons are supported by inhibitory interneurons that regulate and balance their activity, preventing excessive excitation that could disrupt normal processing.

The hippocampus is also richly interconnected with other brain areas. Its primary input comes from the entorhinal cortex, which gathers information from sensory and association areas of the cerebral cortex. The processed signals are then returned to the neocortex and also sent to subcortical structures. This constant exchange of information emphasizes the hippocampus as a central hub for learning, memory, and spatial navigation.

Functions of Hippocampus

The hippocampus is best known for its essential role in learning and memory. It acts as a central hub where experiences are transformed into stored knowledge that can be recalled later. One of its most important functions is the conversion of short-term memory into long-term memory. Without the hippocampus, information received through the senses would quickly fade and never become part of lasting memory. For example, remembering a conversation, a classroom lecture, or an important life event requires the hippocampus to process and consolidate that information before transferring it to different areas of the cerebral cortex for permanent storage.

Another major function of the hippocampus is spatial memory and navigation. This refers to the ability to understand and remember spatial relationships in the environment. It allows a person to remember routes, directions, and the layout of familiar places. Specialized neurons within the hippocampus, known as place cells, become active when a person is in a specific location. These cells collectively form a kind of internal map, which explains why damage to the hippocampus often leads to disorientation and difficulty in navigating even familiar surroundings.

The hippocampus also contributes significantly to learning processes. When individuals encounter new information or experiences, the hippocampus compares them with past knowledge, helps detect similarities or differences, and creates associations that make new learning meaningful. This associative learning ensures that memories are not stored as isolated fragments but are connected with broader networks of knowledge.

Emotional regulation is another important function of the hippocampus. Although the amygdala is the primary center for emotions, the hippocampus works closely with it to link memories with emotional experiences. Events that are emotionally charged, whether positive or negative, are remembered more vividly because of this cooperation. For example, a person may clearly remember details of a joyful celebration or a traumatic event due to the combined activity of the hippocampus and amygdala.

The hippocampus is also involved in the process of imagination and future planning. By drawing on stored memories, it allows individuals to construct possible future scenarios, make decisions, and plan actions. This function highlights that the hippocampus is not only a memory storage assistant but also an active participant in guiding behavior and thought.