Regions described in the hippocampus are the head, body, and tail, and other hippocampal subfields include the dentate gyrus, the presubiculum, and the subiculum.

There are also inputs from the medial septum and from the diagonal band of Broca which terminate in the stratum radiatum, along with commisural connections from the other side of the hippocampus.

[3][4] The pyramidal cells in CA3 send some axons back to the dentate gyrus hilus, but they mostly project to regions CA2 and CA1 via the Schaffer collaterals.

Both the recurrent connections and the Schaffer collaterals terminate preferentially in the septal area in a dorsal direction from the originating cells.

CA3 uniquely, has pyramidal cell axon collaterals that ramify extensively with local regions and make excitatory contacts with them.

Slow oscillatory rhythms (theta-band; 3–8 Hz) are cholinergically driven patterns that depend on coupling of interneurons and pyramidal cell axons via gap junctions, as well as glutaminergic (excitatory) and GABAergic (inhibitory) synapses.

[10] This mechanism is based on the synapses of the CA3 recurrent axon corraterals on the dendrites of the CA3 population [11] that form a complete matrix of connections.

[13] The same author thus concluded that the term CA4 should be abandoned and that the zone should be regarded as the polymorphic layer of the dentate gyrus[13] (the area dentata of Blackstad (1956)).

[14] The neurons in the polymorphic layer, including mossy cells and GABAergic interneurons, primarily receive inputs from the granule cells in the dentate gyrus in the form of mossy fibers and project to the inner molecular layer of the dentate gyrus via the associational/commissural projection.