Anatomy of the hippocampal formation.

The hippocampus is one of several brain regions that together comprise the hippocampal formation. The hippocampal formation is a prominent C-shaped structure bulging in the floor of the temporal horn of the lateral ventricle. The hippocampus proper consists of three major subfields (CA1-CA3). The other regions that together comprise the hippocampal formation consist of the dentate gyrus, the subicular complex, and the entorhinal cortex. Based on its extrinsic connectivity, the hippocampal formation receives a vast amount of highly processed multimodal sensory information that is funneled into the hippocampal formation mainly by the entorhinal cortex. The entorhinal cortex is connected to associational neocortical areas in a reciprocal manner. Extensive hippocampal integration of sensory information is established by a largely unidirectional chain of intrinsic hippocampal projections. Our current knowledge on hippocampal connectivity and function is largely based on studies of rodents and monkeys. It still remains to be determined to which extent such neuroanatomical data of experimental animals is applicable to the human hippocampal formation.