hippokampuksen

The hippocampus is a seahorse-shaped structure in the medial temporal lobe and a core component of the limbic system. In humans, it forms part of the hippocampal formation, which includes the hippocampus proper (cornu ammonis CA1–CA4), the dentate gyrus, and the subiculum, interlinked with the entorhinal cortex and other limbic regions.

The hippocampus is essential for the formation of new declarative memories (especially episodic memory) and plays a key role in spatial navigation and relational memory. It supports memory consolidation, transferring temporary representations from the entorhinal cortex to long-term storage during sleep. Place cells in the hippocampus encode specific locations, contributing to a cognitive map of the environment.

Connectivity and circuitry: The hippocampus receives input from the entorhinal cortex via the perforant path and participates in the trisynaptic circuit through the dentate gyrus and CA3 to CA1, before sending output via the subiculum to the fornix and onward to mammillary bodies, thalamus, and back to cortex. It interacts with the amygdala to assign emotional salience to memories and communicates with other cortical and limbic areas to integrate memory with perception and behavior.

Clinical relevance: Bilateral hippocampal damage produces severe anterograde amnesia, as illustrated by cases such as patient H.M., and is involved in various forms of temporal lobe epilepsy and Alzheimer’s disease, which often show early hippocampal atrophy and sclerosis.

Development and neurobiology: The dentate gyrus supports continued neurogenesis into adulthood in many species, and hippocampal function is influenced by stress, aging, and overall brain development, with activity patterns adapting across life stages.