Hippocampal formation

Hippocampal formation
The hippocampal formation, as drawn by Santiago Ramon y Cajal: DG: dentate gyrus. Sub: subiculum. EC: entorhinal cortex. CA1-CA3: hippocampus proper
Details
Part of	Temporal lobe
Identifiers
NeuroLex ID	Hippocampal formation
Anatomical terms of neuroanatomy []

The hippocampal formation is a compound structure in the medial temporal lobe of the brain. There is no consensus concerning which brain regions are encompassed by the term, with some authors defining it as the dentate gyrus, the hippocampus proper and the subiculum; and others including also the presubiculum, parasubiculum, and entorhinal cortex. The hippocampal formation is thought to play a role in memory, spatial navigation and control of attention. The neural layout and pathways within the hippocampal formation are very similar in all mammals.

During the nineteenth and early twentieth centuries, based largely on the observation that, between species, the size of the olfactory bulb varies with the size of the parahippocampal gyrus, the hippocampal formation was thought to be part of the olfactory system.

In 1937 Papez theorized that a circuit including the hippocampal formation constitutes the neural substrate of emotional behavior, and Klüver and Bucy reported that, in monkeys, surgical removal of the hippocampal formation and the amygdaloid complex has a profound effect on emotional responses. As a consequence of these publications, the idea that the hippocampal formation is entirely dedicated to olfaction began to recede. (Today there is little support for the idea that the hippocampal formation is directly involved in emotion.)

In an influential 1947 review, Alf Brodal pointed out that mammal species thought to have no sense of smell nevertheless have fully intact hippocampal formations, that removal of the hippocampal formation did not affect the ability of dogs to perform tasks dependent on olfaction, and that no fibers were actually known that carry information directly from the olfactory bulb to any part of the hippocampal formation. Though massive direct input from the olfactory bulb to the entorhinal cortex has subsequently been found, the current view is that the hippocampal formation is not an integral part of the olfactory system.