Hippocampus — Function, Location & Quiz
The hippocampus is not a permanent filing cabinet for every memory. It binds the elements of new declarative experiences, supports spatial maps and helps consolidate information toward neocortex, while procedural learning can proceed through other systems.
That separation is the lesson of patient H.M.: after bilateral medial temporal surgery, new episodic learning was devastated but mirror-tracing skill could still improve. Clinically, the hippocampus also matters because it is vulnerable early in Alzheimer’s disease, temporal lobe epilepsy and hypoxic injury.
Test this anatomy in the Brain Regions Quiz or open the interactive 3D brain model.
Location and anatomical map
Memory formation, spatial navigation, learning, consolidation.
Atlas category: subcortical. Brodmann areas or landmark: Not a Brodmann area (allocortex, 3-layer).
Functions
- Declarative memory formation — episodic and semantic
- Spatial navigation and cognitive mapping
- Memory consolidation — transferring to neocortex during sleep
- Pattern separation (dentate gyrus) and pattern completion (CA3)
- Contextual memory — binding what/where/when
Pathways and connections
- Entorhinal cortex → Dentate gyrus → CA3 → CA1 (trisynaptic circuit)
- CA1 → Subiculum → Entorhinal cortex (output loop)
- Hippocampus ↔ PFC (memory retrieval, planning)
- Hippocampus → Fornix → Mammillary bodies → Anterior thalamus (Papez circuit)
Clinical relevance
- Patient HM (Henry Molaison) — bilateral MTL resection → severe anterograde amnesia
- HM could still learn procedural skills (mirror tracing) — proving multiple memory systems
- Alzheimer's disease: hippocampus is one of the first structures to atrophy
- Transient global amnesia — temporary hippocampal dysfunction
- Epilepsy: hippocampal sclerosis is the most common cause of temporal lobe epilepsy
Key facts
- Place cells (O'Keefe, Nobel 2014): fire when animal is at a specific location
- Grid cells (Moser & Moser, Nobel 2014): hexagonal spatial firing in entorhinal cortex
- LTP (Long-Term Potentiation) first described in hippocampus (Bliss & Lømo, 1973)
- Adult neurogenesis occurs in dentate gyrus — one of only two known sites
- London taxi drivers (Maguire): larger posterior hippocampi correlating with navigation experience
- Sharp-wave ripples during sleep replay waking sequences (memory consolidation)
Exam tip
HM = the most important patient in memory research. Know: anterograde amnesia, preserved procedural memory, intact STM. Trisynaptic circuit: EC → DG → CA3 → CA1.
Common questions
What is the main function of the hippocampus?
It is essential for forming new declarative memories, binding contextual details, spatial navigation and consolidation of memories into distributed cortical networks.
Where is the hippocampus located?
It is a curved medial temporal lobe structure on each side of the brain, connected to cortex chiefly through the entorhinal region.
What did patient H.M. teach us?
His severe anterograde amnesia after bilateral medial temporal resection showed that the hippocampal system is critical for new declarative memory, while preserved mirror tracing demonstrated a separate procedural memory system.