fornix

The fornix is a major fiber tract of the limbic system in the brain. It is a C-shaped bundle that carries information from the hippocampus to several diencephalic and basal forebrain structures, playing a key role in memory processing and navigation.

Anatomy and structure: The fornix originates from the fimbria and alveus of the hippocampus, where these fibers converge to form the crura (two limbs) that ascend and join to become the body of the fornix beneath the corpus callosum. From the body, the tract continues as paired columns toward the diencephalon, where it splits into two pathways around the level of the anterior commissure.

Corticopetal and corticofugal connections: The fornix contains precommissural fibers that project anterior to the anterior commissure to elements such as the septal nuclei and certain basal forebrain areas. The postcommissural fibers pass posterior to the anterior commissure and connect with the mammillary bodies; from there, the mammillothalamic tract carries signals to the anterior nuclei of the thalamus. Through the Papez circuit, these connections link the hippocampus with the thalamus and cingulate cortex, supporting memory consolidation and retrieval.

Function and clinical relevance: By conveying hippocampal output to subcortical and cortical regions, the fornix supports declarative memory and spatial navigation. Lesions or degeneration of fornicial pathways can contribute to amnestic syndromes and disorientation, and damage is sometimes seen in individuals with thalamic or mammillary body pathology.

Etymology: The name fornix derives from the Latin for “arch” or “vault,” reflecting its curved shape within the brain.