subiculum

The subiculum is a component of the hippocampal formation located in the medial temporal lobe. It forms the transitional region between the hippocampus proper and the entorhinal cortex and serves as the principal output stage of the hippocampus, channeling processed information to broader brain networks.

Anatomically, the human subiculum is often described as comprising the presubiculum, subiculum proper, and parasubiculum, aligned along the longitudinal axis of the hippocampal formation. It has a distinctive laminar organization with a pyramidal cell layer that gives rise to a variety of efferent projections. The subiculum receives input from the CA1 region of the hippocampus and from the entorhinal cortex, integrating hippocampal processing with cortical and subcortical circuits.

Major outputs arise via the fornix to subcortical targets such as the mammillary bodies, septal nuclei, nucleus accumbens, and ventral tegmental area. The subiculum also projects directly back to the entorhinal cortex (the back projection) and to other cortical and thalamic regions, contributing to the broader hippocampal network. The bidirectional connections with the entorhinal cortex and other limbic structures position the subiculum as a key conduit for information flow within the hippocampal system.

Functions attributed to the subiculum include its role as the main hippocampal output pathway, supporting memory consolidation, spatial navigation, and contextual processing. Subicular neurons exhibit spatially selective and time-related coding and participate in theta rhythms associated with movement and learning.

Clinical relevance includes involvement in mesial temporal lobe epilepsy and neurodegenerative conditions such as Alzheimer's disease, where subicular damage can contribute to episodic memory impairment. See also hippocampal formation, fornix, and entorhinal cortex.