hippocampus

Hippocampus, from Greek hippos (horse) and kampos (sea monster), is a seahorse-shaped structure in the medial temporal lobe. It belongs to the limbic system and forms the hippocampal formation, which includes the hippocampus proper, the dentate gyrus, and the subiculum, as well as connections with the entorhinal cortex. In each hemisphere, it lies along the floor of the temporal horn of the lateral ventricle and is connected to other brain regions via the fornix, the perforant pathway, and various associations with the thalamus and cortex.

Its primary role is in the consolidation of information from short-term to long-term memory and in spatial navigation. The hippocampus supports declarative memory, including episodic and semantic memory, and participates in pattern separation and pattern completion processes. It receives input from the entorhinal cortex and other polymodal areas and communicates with the cortex through the subiculum and the fornix. The hippocampal-entorhinal network is involved in rapid encoding of new experiences during learning and is modulated during sleep.

Clinical relevance and development: damage to the hippocampus impairs the formation of new memories (anterograde amnesia) while sparing older memories. It is among the first regions affected by Alzheimer’s disease and is a common focus in temporal lobe epilepsy. The dentate gyrus is notable for adult neurogenesis in many species. The hippocampus is vulnerable to hypoxic injury and thiamine deficiency (Wernicke-Korsakoff syndrome) and exhibits notable plasticity in response to experience and injury.