Where are the hippocampal fields (CA1–CA4 and the subiculum)?
The hippocampal fields are the strips of the hippocampus’s curled band of cortex, the cornu Ammonis, named CA1 to CA4, plus the subiculum beyond CA1; they lie inside the hippocampus, deep in each temporal lobe. Signals run dentate gyrus to CA3 to CA1 to the subiculum. [1][2]
The 3D brain needs JavaScript. The text below still says where the hippocampal fields are and what they do.
Opens cut by a front (coronal) slice through the hippocampus, which holds the hippocampal fields. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Not a separate shape in this atlas; lit: the part that holds it. Lit: the whole hippocampus, on both sides. The CA fields and the subiculum are strips of cortex inside the hippocampal formation; BodyParts3D draws the hippocampus as one shape and has none for them, so the whole hippocampus is lit and nothing is drawn at a guessed point. [1][2]
Lit here: the hippocampus, the part that holds the hippocampal fields — see it on its own page.
The cornu Ammonis is divided into the fields CA1, CA2, CA3 and CA4, all filled with densely packed pyramidal cells like those of the neocortex. [1]
CA4 is in fact the deep, polymorphic layer, the hilus, of the dentate gyrus, so it is often left out of the list. [1][2]
After CA1 comes the subiculum, the lowest part of the hippocampal formation; it lies between CA1 and the entorhinal cortex, where the hippocampus gives way to the cortex proper. [1][3]
The subiculum is itself a set of related strips: the prosubiculum, presubiculum, postsubiculum and parasubiculum. [3]
What it does
They are the stations of the trisynaptic circuit: the perforant path from the entorhinal cortex reaches the granule cells of the dentate gyrus (first synapse), mossy fibres run on to CA3 (second), and the Schaffer collaterals from CA3 reach CA1 (third). [1][2]
CA1 is the main exit: it projects to the subiculum and along the hippocampus’s other output paths. Place cells, which fire when an animal is in one spot, are recorded from its pyramidal layer, for example in rats. [1][2]
The subiculum is the final stage of the pathway and the main output of the hippocampus proper; its parasubiculum holds grid cells and its postsubiculum head-direction cells. [1][3]
A major output of the hippocampus runs through the fornix to the lateral septal area. [2]
Other names
CA stands for cornu Ammonis, Ammon’s horn, after the ancient Egyptian god often shown with a ram’s head; the term survives in the names CA1 to CA4. [2]
Karl Friedrich Burdach named the subiculum (“subiculum cornu ammonis”); Latin subiculum means support. [3]
Size
The model has no shape for the hippocampal fields itself, so it is not measured here. The left hippocampus that holds it measures about 43 mm front to back, 22 mm top to bottom and 20 mm side to side on this model (the box it fits in, not its volume). [4]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.