CA3

CA3, or Cornu Ammonis area 3, is a subregion of the hippocampus located in the medial temporal lobe. It is one of the four main sectors (CA1–CA4) that form the hippocampal circuitry and is composed predominantly of pyramidal neurons organized in a trilaminar arrangement within the hippocampal formation.

Anatomy and connections: CA3 receives major excitatory input from the dentate gyrus through mossy fiber synapses as part of the trisynaptic circuit. It also obtains input from the entorhinal cortex and other hippocampal regions. The principal output of CA3 is to the CA1 region via the Schaffer collateral pathway, but CA3 neurons also form extensive recurrent collateral connections with each other, giving CA3 a highly interconnected, autoassociative network.

Function: Through its recurrent network, CA3 is thought to support pattern completion and rapid encoding of associative memories. The combination of dense recurrent excitation and feedforward input enables CA3 to retrieve full memory representations from partial cues. CA3 activity participates in various hippocampal oscillations, including theta rhythms during navigation and sharp-wave ripples during memory consolidation in sleep and rest.

Clinical significance: CA3 is implicated in temporal lobe functions and is a region of interest in neurological conditions such as temporal lobe epilepsy, where network excitability can contribute to seizure activity. It is also studied in aging and neurodegenerative disease contexts for its role in memory processing and hippocampal dysfunction.

Overall, CA3 is a central hub within the hippocampus, balancing input integration with an extensive recurrent network to support memory encoding and retrieval.