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Structure of the Fornix of the Brain

Structure of the Fornix of the Brain

The fornix is a C-shaped clump of fibers located in the brain. Its function is to carry signals from the hippocampus to the different parts of the brain.
Sharmistha Sarkar
Did You Know?
In Latin, 'fornix' means an arch or a span. It is a part of the brain named for its unique shape. This part has been found to relate with the recall memory, rather than the recognition memory.
The fornix is an arch-like pack of axons in the brain, which connects the hippocampus to the various parts of the limbic system. The hippocampus is an important part of the brain. There are two hippocampi; one on each side of the brain, located under the cerebral cortex. The cerebral cortex is the external layer of neural tissues of the cerebrum in humans and other mammals.

The limbic system comprises a group of structures in the brain situated on the two sides of the thalamus, below the cerebrum. The hippocampus, amygdala, anterior thalamic nuclei, fornix, mammillary body, septum, cingulate gyrus, and hippocampal gyrus come under this system. The limbic system brings about memory, instincts, sensations, and wisdom.

The fornix is essential for cognitive functioning. It is a major 'input' and 'output' passageway in the memory circuit of the brain. It is also one of the initial areas that is affected by Alzheimer's disease. Alzheimer's is a chronic disease that begins steadily and gets worse with time.
What is the Fornix?
Fornix Location
Location of the Fornix
The fornix is a cluster of fibers, or a band of white nerve fibers, also known as 'axons'. Its function is to carry signals from the hippocampus to the mammilary bodies, and then to the front region of the nuclei of thalamus. The thalamus is an extended space above the brain stem in the brain. The fornix is located beneath the corpus callosum at the base of the brain. It joins the hippocampus to the hypothalamus. The hypothalamus is situated under the thalamus on top of the brain stem.
Structure of the Fornix
Fornix Structure
Structure of the Fornix
In the hippocampus, the fornix initiates as a bunch of fibers called the 'alveus'. As the alveus move at the rear side, they accumulate at the middle to form the fimbria. Fimbria is the edge of the hippocampus. The fimbria of each hippocampus thickens as it ascends and splits off from the hippocampus. It then forms the crus or leg of each hippocampus. The two crura combine in the mid-line of the brain to form the hippocampal commissure, through which the hippocampi communicate with each other.
The hippocampal commissure is one of the significant paths of hippocampal communication. Succeeding the hippocampal commissure, the single-merged fiber bundle is called the fornix. The fornix resumes as a span structure to the anterior commissure. From the anterior commissure, the fornix divides again into three parts and goes to various regions.
  • The split prior to the anterior commissure is known as precommissural fornix. This branch connects to the septum, the ventral striatum, and the cingulate cortex.
  • Some fibers of the fornix also go through the anterior commissure to the contralateral hippocampus, the second of the two essential paths of hippocampal communication.
  • The split following the anterior commissure is known as the postcommissural fornix, which goes to the mammillary bodies of the hypothalamus and the anterior nuclei of the thalamus.
The two ways in and out of the hippocampus are the fornix and the entorhinal cortex. The anterior thalamic nuclei is joined to the cingulate cortex. The cingulate cortex is situated in the middle of the cerebral cortex in the brain. It comprises the cortex of the cingulate gyrus, which is located above the corpus callosum, and its continuation in the cingulate sulcus.

The cingulate cortex juts out to the entorhinal cortex of parahippocampal gyrus to form a loop referred to as the Papez circuit. The Papez circuit in the limbic system is involved in recollection, emotion, and behavior. The amygdala and neocortical areas are involved in emotions.
Fornix Degeneration and Memory in Distressing Brain Injury
According to post-injury magnetic resonance studies, fornix-to-brain (FBR) ratios were calculated on a group of around 30 traumatic brain injury (TBI) patients and 20 female medical controls, by taking the biggest aspect of the fornix at the level of the anterior horns and third ventricle, and ascertaining a 'fornix surface' area. The FBR was notably decreased in the TBI group than that of the medical control group. Despite these findings, the TBI did not relate properly to the neuropsychological outcome. The study indicated the possibility of fornix damage in the TBI patients. However, fornix degeneration accounts for only one of the many bestowing factors to the foundation of TBI cognitive disturbances, as fornix atrophy did not relate well to the neuropsychological outcome.
The working and physiology of the fornix in the brain is not yet very clear. However, it has been shown that surgical transection can cause memory loss in humans. Damage to it will result in problems in remembering long-term information like past happenings, but will have less effect on the ability of object recognition.