Fornix

The fornix (meaning "arch" in Latin) is a C-shaped bundle of nerve fibers in the brain that acts as the major output tract of the hippocampus.

The fornix also carries some afferent fibers to the hippocampus from structures in the diencephalon and basal forebrain.

The fornix is part of the limbic system.

While its exact function and importance in the physiology of the brain are still not entirely clear, it has been demonstrated in humans that surgical transection – the cutting of the fornix along its body – can cause memory loss.

There is some debate over what type of memory is affected by this damage, but it has been found to most closely correlate with recall memory rather than recognition memory.

This means that damage to the fornix can cause difficulty in recalling long-term information such as details of past events, but it has little effect on the ability to recognize objects or familiar situations.

STRUCTURE

The fibers begin in the hippocampus on each side of the brain as fimbriae; the separate left and right sides are each called the crus of the fornix (plural crura).

The bundles of fibers come together in the midline of the brain, forming the body of the fornix.

The lower edge of the septum pellucidum (the membrane that separates the lateral ventricles) is attached to the upper face of the fornix body.

The body of the fornix travels anteriorly and divides again near the anterior commissure.

The left and right parts separate, but there is also an anterior/posterior divergence.

• The posterior fibers (called the postcommissural fornix) of each side continue through the hypothalamus to the mammillary bodies; then to the anterior nuclei of thalamus.
• The anterior fibers (precommissural fornix) end at the septal nuclei of the basal forebrain and nucleus accumbens of each half of the brain.