Hippocampus

The hippocampus has been used for many years to study synaptic plasticity. It is well known as being critical for memory. If the hippocampus is damaged, new declarative memories cannot formed. But it also critical for spatial learning, awareness, and navigation. For example, the rat hippocampus has been used to "bio-inspire" the RatSLAM software for robots: Milford, Robot Navigation from Nature Simultaneous Localisation, Mapping, and Path Planning Based on Hippocampal Models, 2008.

This structure is popular. It is "experimentally accessible" (to some techniques), and it is well suited to the study of synaptic plasticity due to its laminar organisation, the circuitry (connectivity between neurons) remains intact when brain slices are made.

Its cross-section has a very defined laminar structure; layers are visible where rows of pyramidal cells are arranged. In general, the connections within the hippocampus are uni-directional. They form well-characterised closed loops that start in the adjacent entorhinal cortex.

The different cell layers and sections are defined connections. The main pyramidal cell layers are the CA1-4 regions (principally CA1 and CA3), and the dentate gyrus.

Diagram below represents a slice of rodent hippocampus. It shows the major regions, excitatory pathways, and synaptic connections. Long-term potentiation has been observed at each of the three synaptic connections shown here.

Image: Purves et al, 2001.