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The Hippocampus

In this episode, we discussed an enigmatic region in the brain thought to be responsible for memory formation, the hippocampus. We covered some major theories for how the hippocampus performs computations to support its significant functions.


Where is the hippocampus?

Hippocampus in blue, located in the medial temporal lobe. We have two hippocampi on either side of the brain. (image from https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored)


Where the hippocampus got its name:

Hippocampus is the greek word for seahorse (image from https://commons.wikimedia.org/wiki)


What is the hippocampus' primary function?


The hippocampal memory indexing theory (Teyler & DiScenna, 1986)


The hippocampus as a cognitive map (O’Keefe & Nadel, 1978)


The cognitive map in humans (Epstein et al., 2017)


Time (and Space) in the Hippocampus (Howard Eichenbaum, 2017) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5565219/


How does the hippocampus work?


The classical hippocampal circuit:

Inputs from all over tha brain are sent to the entorhinal cortex (EC), specifically layer II and III. From there they project primarily to the dentate gyrus (DG). Dentate gyrus neurons send inputs to neurons in the CA3 region, which send inputs to neurons in the CA1 region, which projects inputs back to the entorhinal cortex, specifically layer V/VI. The is known as the trisynaptic hippocampal circuit, made up of the three primary connections (EC-DG, DG-CA3, CA3-CA1) (image from https://sites.lsa.umich.edu/diba-lab/neural-circuits-of-the-hippocampus/)


Edmund Rolls theory of hippocampal computation:


The mechanisms for pattern completion and pattern separation in the hippocampus (Edmund Rolls, 2013):





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