Corpus callosum is the largest C-shaped white matter structure of the brain. It refers to the biggest collection of nerve fibers, labeled as commissures in the central nervous system.
This collection of commissures is located beneath the cerebral cortex, and connects specific areas of both left and right hemispheres of the upper brain.
This brain structure is one of the most important ones in the brain since it allows the communication of both sides of the brain, i.e. it enables the relay of information among the most important brain processing centers.
Anatomy and Structure of the Corpus Callosum
The structure of the corpus callosum is fully developed in the 20th week of embryonic development. This largest white matter structure of the brain comprises of 4 parts:
- Rostrum of the corpus callosum
- Genu of the corpus callosum
- Body/trunk of the corpus callosum
- Splenium of the corpus callosum
Rostrum of the Corpus Callosum
The rostrum of the corpus callosum is the part of the bundle of neuron fibers that project behind and under the backside of the genus. It connects the orbital surfaces of the temporal lobe.
Genu of the Corpus Callosum
The bend of the front part of this brain structure is labeled as genus of the corpus callosum. It branches from the Foramen of Monro to the location where the corpus callosum is attached to the septum pellucidum, while stretching behind the fornix.
The foramen of Monro refers to a part of the ventricular system that established the connection between the third ventricle and the lateral (side) ventricle.
Body (or Trunk) of the Corpus Callosum
The central portion of the corpus callosum is called a body or trunk. The neuron fibers from the body of the corpus callosum branch to the corona radiata (the innermost cell layer) and pass through it. In this way, they hold out to the surface of both the left and right parts of the brain.
The slim part located between the body of the corpus callosum and the splenium is labeled as the isthmus of the corpus callosum.
Splenium of the Corpus Callosum
The splenium of the corpus callosum connects the back parts of the cerebral cortex. Its neuron fibers differ in size and link both the primary and the secondary visual areas, in charge of the regulation of the following processes:
- Identification of visual stimuli and signals
- Receiving information from the retina of our eyes
- Processing visual information
- Determining the field of vision and the objects within that field
- Assessment of distance, depth, and size of both the visual field and the objects within the field
- Transferring visual information to other parts of the brain
- Control and regulation of the sense of sight
- Determining colors of an object in the visual field
- Recognizing people/faces
- Reading
- Reading comprehension
Transmission of information from the primary visual cortex (the receiving center) to the visual association cortex (the interpretation center) is a single process that incorporates all the above-mentioned processes, and, as such, is one of the main functions of the occipital lobe.
Neuronal Connections of the Corpus Callosum
On both sides of the corpus callosum, the neuron fibers branch in the white matter and pass to the various parts of the cerebral cortex of the brain.
The neuron fibers that stem forward from the genus into the frontal lobe comprise the forceps anterior, while the neuron fibers that stem backward into the occipital lobe, make up the forceps posterior.
The main body of the neuron fibers is located between these two structures of the brain, comprising the tapetum. They branch sideways on either side into the temporal lobe, thus covering the central part of the lateral ventricle.
What Is the Main Function of the Corpus Callosum?
As we mentioned earlier, the main function of the corpus callosum is to facilitate communication between the cortical and the subcortical neurons of the two brain hemispheres. Similar areas of this brain structure are connected by neuron fibers that branch out to them from different areas of the corpus callosum.
Namely, the corpus callosum organizes the complex brain commands that involve bilateral tasks and relays them to the corresponding brain centers in both the left and the right hemisphere.
Due to these types of established interhemispheric connections, all the areas of the brain responsible for the processing of information, as well as the regulation and control of different processes of the body, function in a harmonious manner.
The corpus callosum also plays a crucial role in the development of the cognitive processes in the brain. By supporting the transmission of information to the hemispheres, it aids the functional coordination of the areas dedicated to the processing of the cognitive processes by supporting them to work together.
Which Are the Surrounding Brain Structures of the Corpus Callosum?
The corpus callosum is surrounded by the following structures of the brain:
- The interhemispheric fissure
- The indusium griseum
- The cingulate gyrus
- The fornix
The Interhemispheric Fissure
Also known as the medial longitudinal fissure, this term refers to a deep groove that separates the two parts of the brain, i.e. its hemispheres. It contains a part of the dura mater (a membrane that envelopes both the brain and the spinal cord on the outside), labeled as falx cerebri.
The falx cerebri is the largest fold that separates the two hemispheres of the cerebral cortex.
The Indusium Griseum
This term denotes a thin membranous layer of gray matter, i.e. a cellular component of the supra-callosal gyrus of the cerebral cortex. The indusium griseum is located over the dorsal surface of the corpus callosum.
The Cingulate Gyrus
This is the gyrus located in the middle of each of the hemispheres of the brain. As an important part of the limbic system, the cingulate gyrus supports the regulation of both pain and emotions.
In addition, the cingulate gyrus is involved in the regulation of voluntary motor movement and behavior.
The Fornix
The fornix is one of the three brain commissures, i.e. an arch-shaped bundle of white matter neuronal fibers. It connects two identical parts across the left and right hemispheres of the brain, as well as different structures with the same function.
Located under the corpus callosum, the fornix serves as the primary output of information to the hippocampus. Namely, the sensory signals which the brain receives from the sensory organs create a chemical or electrical response in the hippocampus (the part of the brain in charge of the memory processes).
From here, the fornix aids the transmission of information to the septal nuclei (responsible for the formation of feelings of pleasure) where they are processed and translated into the corresponding behavior, reaction, or emotion.
What Happens When the Corpus Callosum Is Dysphunctional or Damaged?
When there is a lesion or damage to the corpus callosum, it results in numerous medical conditions, neurological diseases, and disorders.
This affects the communication between the two brain hemispheres which, in turn, causes cognitive disorders in learning, memory, thinking, as well as impaired executive functions.
One of the disorders that result from a dysfunctional or damaged corpus callosum is agenesis.
Agenesis of the Corpus Callosum
Agenesis of the corpus callosum is a rare congenital disorder. The partial development or complete absence of this part of the brain is a typical sign of it.
Depending on their nature, the symptoms of agenesis can be divided into 4 groups:
- Physical symptoms (impairment of vision, seizures, abnormal facial and head features, sleeping problems);
- Cognitive symptoms (problem-solving difficulties, lack of ability to understand emotions, difficulty in reading facial expressions or tone of voice, inability to understand sarcasm or slang expressions);
- Developmental symptoms (delays in speech and language acquisition, poor coordination of movements);
- Social and behavioral symptoms (social immaturity, difficulty in maintaining attention, lack of fear).
The agenesis of the corpus callosum can sometimes lead to other abnormalities of the brain.
The list includes the following:
- Hydrocephalus, or accumulation of fluid in the skull
- Arnold-Chiari malformation
- Deep clefts in brain tissue
- Failure of the forebrain to divide into lobes
- Disorders of neural migration
In addition, there are also some syndromes that can lead to the occurrence of this disorder. Those are:
- Aicardi syndrome – A rare genetic malformation of the brain where the corpus callosum is not completely developed or it’s completely absent from the brain. It appears almost exclusively in the female population.
- Andermann syndrome – This is a neurological disorder that damages the nerves that are used for the motor movement of the muscles, as well as the nerves that relay the sensory information. The symptoms of the Andermann syndrome include a hole or gap in one of the structures of the eye, abnormally small eyes, an unusually small head, hand deformities, intellectual disabilities, developmental delays, difficulty eating, diarrhea.
- Shapiro syndrome – A rare neurological disease with characteristic excessive sweating and hypothermia as a result of the agenesis of the corpus callosum.
- Acrocallosal syndrome – A rare mental retardation syndrome caused by an abnormality of the brain, i.e. agenesis. Typical for this syndrome is the development of extra fingers on the hands and toes on the feet, as well as severe impairment of the cognitive abilities of the affected individual.
Fun Facts
Did you know?
- The name of this brain structure has Latin origin, meaning ‘tough body’.
- The corpus callosum is the largest white matter structure, comprising more than 200 million axonal projections.
- One in 4000 infants is born without a corpus callosum. This results in brain malformations leading to impaired cognitive functions as well as behavioral aberrations.
- Using the non-dominant hand helps with the strengthening of the corpus callosum functions, i.e. supports the connections between the two hemispheres of the brain.
- The corpus callosum is fully developed by the age of 12.
- The word ‘splenium’ comes from the Greek language and translates to bandage.
- Damage to the fornix is primarily related to memory loss. Anterograde amnesia is one of the most common diseases which occur due to the dysfunctionality of the fornix. It’s an inability of the affected individual to create new memories.
- The fornix does not have a specific function in the brain but is nonetheless one of the most active ‘assistants’ to the other parts of the brain.
- Musicians and left-handed individuals have a larger frontal part of the corpus callosum.
- The primary visual cortex is the area of the brain which is responsible for our recognition of patterns.