There is an important structure made up of white matter that connects different regions of the brain. It is the so-called fornix whose functions are essential for proper cognitive functioning. Today we will talk about the anatomy, functions and problems that damage can cause in this interesting structure of the brain.
The fornix is a C-shaped structure that originates in the hippocampus, extending from there to the front of the brain, arching around the hypothalamus. The word fornix means "arch" in Latin and for a long time, through the discoveries of the neuroanatomist James Papel, it was affirmed that the fornix was part of the Papez circuit, a set of brain regions that according to the scientist constituted the "anatomical basis of emotions ".
The circuit of Papez consisted of the hippocampus, the anterior nucleus of the thalamus, the cingulate gyrus, the parahippocampal gyrus, and the mammillary bodies. The fornix was the connector of the structures of this circuit and its participation was and continues to be essential. Later, the Papez circuit gave rise to what is now known as the limbic system, whose functions are so broad that they range from emotional processing to movement.
The fornix is made up of white matter, a substance made up of myelinated nerve fibers or axons of neurons, which is also found in very important structures of the brain such as the cerebellum, the thalamus or the hypothalamus. The fornix is located in the telencephalon, in the middle of both cerebral hemispheres. Its structure is divided into several areas where we can find the body, two anterior projections and two posterior projections, hence it is usually also known as the “four-pillar vault”. These anterior columns connect with the mammillary bodies, while the posterior columns connect with the tonsil bodies..
In addition, the fornix connects with the structures that are part of both the limbic system and the cerebral cortex, with structures such as the hippocampus, the thalamus or the Brodmann area, located in the frontal lobe, being connected. That is why it acts as a connector that allows the proper functioning of the brain as a whole..
The clearest function of the fornix is to connect the different structures allowing the transmission of information, being an essential communicator in the brain. Without a normal preservation of this structure, cognitive functioning would be impaired.
The fornix acts as the main outlet for the hippocampus, a key structure for memory formation. That is why the fornix is commonly associated with the participation of the memory consolidation process, in fact, when damage occurs in this structure, problems are usually triggered in this cognitive process.
Although it is rare that it happens, there are cases in which there is a congenital absence of this fibrous structure. This is the case of holoprosencephaly, a brain malformation in which there is a deficient division of the forebrain. There are also problems that can affect the fornix such as tumors, herpes simplex or multiple sclerosis, giving rise to different problems in this structure..
When fornix damage occurs, there are mainly declarative memory deficits, the type of memory that allows us to voluntarily recall events or events, such as when we remember an important moment in our lives. Among the problems in declarative memory, it is specifically episodic memory that damage to the fornix can affect the most. In this type of memory, an autobiographical record is given through which we can remember specific events that are part of our history.
In addition, problems in this structure are associated with a type of amnesia known as anterograde amnesia, a loss of memory that prevents us from forming new memories and learning, even though our past memory remains intact..
During Alzheimer's disease specifically, neurodegeneration of this structure occurs, which is usually associated with the cognitive deterioration that this disease produces in those affected. This degeneration usually occurs early in the disease and can indicate and predict its subsequent development, preceding degeneration of the hippocampus, a region whose degeneration is significantly associated with the cognitive symptoms of this disease..