White matter
Fornix
Also called Fornix cerebri
The arching cable that carries the hippocampus's messages out.
The fornix is a curved bundle of nerve fibers, like a cable, that arches up and over the thalamus. It carries signals out of the hippocampus to the mammillary bodies and other deep areas, and brings some signals back in. It is a key link in the brain's memory network. Damage to it can cause memory problems similar to damage to the hippocampus itself.
Where it is
Deep in the middle of the brain, just under the corpus callosum. It starts at the back of each hippocampus, rises and sweeps forward over the thalamus, where the left and right sides come together, then curves down toward the mammillary bodies.
What it does
Carrying memory signals
It is the hippocampus's main output cable, sending its messages to the mammillary bodies and other deep areas.
Two-way traffic
It also brings signals into the hippocampus, including fibers that release acetylcholine, a messenger that helps with attention and learning.
Joining the memory loop
It is one link in the Papez circuit, a loop that runs from the hippocampus to the mammillary bodies, the thalamus, the cingulate cortex and back.
Linking left and right
Where the two sides meet, some fibers cross over, letting the two hippocampi share information.
Think of it as a curved highway overpass that carries traffic from the memory center to the rest of the city.
Works with
- HippocampusIt begins at the hippocampus and carries much of its output.
- SubiculumMany of its fibers start in the subiculum, the hippocampus's main exit.
- Mammillary bodiesIts main destination is the mammillary bodies, a key relay on the memory loop.
- Anterior nucleus of the thalamusSome of its fibers go straight to the anterior nucleus of the thalamus.
- AcetylcholineIt carries acetylcholine-releasing fibers into the hippocampus from the septum, a small area near the front of the brain, helping to set the hippocampus's rhythm and learning mode.
When it goes wrong
Memory loss
Damage to the fornix, for example during surgery to remove a nearby cyst, can make it hard to form new memories.
Alzheimer's research
Brain scans can show changes in the fornix early in Alzheimer's disease, and electrical stimulation of it has been tested as an experimental treatment.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- The left and right fornix run side by side for part of their length and share some crossing fibers, a small bridge that links the two hippocampi.
- Its arching shape follows the curve the brain grew in before birth, the same curve seen in the lateral ventricles and the caudate nucleus.
Where the name comes from
Latin for "arch" or "vault", describing how it curves up and over like the arch of a doorway.
Learn it in a lesson
- MemoryThe hippocampus and its circuit. A short guided lesson in 3D.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the fornix?
Show the answer
Carrying memory signals. It is the hippocampus's main output cable, sending its messages to the mammillary bodies and other deep areas.
Carrying memory signals. It is the hippocampus's main output cable, sending its messages to the mammillary bodies and other deep areas.
The fornix is part of which larger structure?
Show the answer
Limbic system. It belongs to the limbic system.
Limbic system. It belongs to the limbic system.
Which part fits this description? "Like a curved highway overpass that carries traffic from the memory center to the rest of the city."
Show the answer
Fornix. It is the fornix. The arching cable that carries the hippocampus's messages out.
Fornix. It is the fornix. The arching cable that carries the hippocampus's messages out.
These parts now come back in your daily review, just before you would forget them.
Practice it and its neighbors in 3DSources
- Fornix (brain), Radiopaedia
- The Anatomy of the Hippocampus, Cerebral Ischemia (Exon Publications), NCBI Bookshelf
- Neuroanatomy, Mammillary Bodies, StatPearls, NCBI Bookshelf
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Explore the fornix in 3D
Turn it around, zoom inside and see how it connects to the rest of the brain, then test yourself with quick quizzes.
Open it in 3D