Have you ever wondered how the brain communicates internally and with the rest of the body? What methods of communication does the brain apply, and how does it tell your body it needs sleep or coffee? Have you ever heard of the term corpus callosum?
The corpus callosum connects the right and left hemispheres in the center. It contains more than 200 million myelinated axons. The corpus callosum is critical in body functions that require both hemispheres to work together to perform a task.
Because the left brain controls the movement of the right side of the body and vice versa, it is easy to understand the importance of the corpus callosum in effectively transmitting communication between the two hemispheres.
Function Of The Corpus Callosum
Both brain hemispheres need to communicate in all day-to-day activities such as movement of the arms and legs and while talking, walking, typing, dancing, and driving. Both hemispheres are responsible for processing language information and speech.
The corpus callosum does this complex and lighting fast processing of information without the need for the person to give it any thought. The corpus callosum is the information super highway that connects the left and right hemispheres.
The 200 to 300 million axons are made up of white matter fiber tracts. These fibers in the corpus callosum are called commissural fibers, and they are involved in the following functions -
- Vision
- Eye movement
- Tactile function and localization
- Left and right hemisphere communication
- Maintaining the balance between attention and arousal
- Communication between left and right hemispheres
The anterior and posterior corpus callosum has different regions or sections that are identified as follows –
- The rostrum – connects the right and left frontal lobes
- The genu – connects the right and left frontal lobes
- The body – connects the temporal lobe and occipital lobe hemispheres
- The splenium – connects the temporal lobe and occipital lobe hemispheres
The Corpus Callosum And Vision
The left and right hemispheres separately process images by combining them and creating a full image. The corpus callosum is vital in how we perceive images in our field of vision.
The corpus callosum helps the brain identify and recognize objects we see by connecting the brain's language centers with the visual cortex. It also transfers any tactile information between the left and right brain hemispheres.
How Big Is The Corpus Callosum?
The corpus callosum is shaped like an elongated C and measures between 8 and 10 cm long and around 3.2 cm wide. A slight difference in length between male and female subjects is observed through an MRI scan.
The male corpus callosum is a few cm longer and wider than the female and is easily distinguished when observed on an MRI or CAT scan.
When Does The Corpus Callosum Start Forming?
During pregnancy, some parts of the fetus develop earlier than others. The brain starts forming during the first three weeks, and the corpus callosum forms between the 3rd and 4th months of gestation.
The corpus callosum develops with a child until it reaches full development at the age of 12, whereafter it remains the same for the rest of the person's natural life.
The Anatomy Of The Corpus Callosum
The anatomy of the corpus callosum is not complicated, and it is divided into four parts that connect the two brain hemispheres. The four parts are –
- The rostrum
- The genu
- The trunk or body
- The splenium
The rostrum connects the frontal lobe orbital surfaces. It is continuous with the lamina terminalis.
The genu connects the lateral and medial frontal lobe surfaces. The genu is the arched or bent area of the anterior corpus callosum, and the forceps minor projects fibers via a tract connecting them.
The elongated central area is the body. The body's fibers reach the surfaces of both hemispheres and wind through the corona radiata.
Where the corpus callosum tapers to the back or posterior section, it becomes the splenium. The occipital lobes are connected by the forceps of major fibers protruding from the splenium.
White matter fibers that protrude only from the body and splenium are known as the tapetum and run the length of the temporal and occipital horns of the lateral ventricle.
These fibers are not found in the forceps major and are divided into two types of connections, heterotopic and homotopic.
- Heterotopic connections – Only connect the brain's dissimilar right and left sides.
- Homotopic connections – Only connect the brain's similar right and left sides.
What Are Common Disorders Of The Corpus Callosum?
Agenesis, or ACC, is one of the rarest disorders of the corpus callosum. This congenital disorder occurs in children that are born without a corpus callosum or born with one that is severely damaged.
This condition currently affects only 0.5% of children, or 1 in 3000, and can be the result of several factors such as –
- Fetal alcohol syndrome – the mother abused alcohol during pregnancy
- Genetic predisposition or recessive gene in one parent carrying the vector gene
- Aicardi Syndrome
- Andermann Syndrome
- Rubella infection in the mother
- Other toxic metabolic conditions such as poisoning
- Drug abuse by the mother while pregnant
- A brain cyst
- Injury or trauma to the fetus in the first trimester, such as an MVA.
If one parent carries a vector gene that can cause a genetic disorder of the corpus callosum, the chances are slim that it will carry over to the child; however, should both parents carry the recessive gene, the chances of the child having a defective corpus callosum climbs to 25%.
That child then carries a 50% risk of being a recessive gene carrier as well and possibly passing it on to their future children, and it seems to affect both male and female fetuses equally.
In the past, there were no tests to accurately determine congenital defects of the corpus callosum, such as the MRI or CAT scans used in modern medicine resulting in many babies with agenesis that may have gone undetected and misdiagnosed for decades.
What Happens If You Are Born Without A Corpus Callosum?
Babies that are born without a corpus callosum may face many challenges in development and reaching certain milestones. Being born without a corpus callosum does not mean the baby will not survive; however, it may be severely disabled or be a high-functioning person.
Disabilities that may occur as a result of being born without a corpus callosum are –
- Deafness
- Blindness
- Motor and movement disabilities – the baby may never walk
- Spatial – the baby may never learn to speak
- The baby may develop seizures.
- Distorted facial or cranial features
- Body or limb spasms
On the other spectrum of babies born with agenesis, some individuals end up being high-functioning. High-functioning means –
- High IQ – disproportionate to the condition
- Strong verbal skills
- In-tact vision
- Some social skills
- Special abilities in one area, such as art or mathematics
Having a disorder of the corpus callosum is not classified as a disease. It is rather known as a congenital defect that causes other afflictions. It is possible to live a relatively normal life with agenesis of the corpus callosum.
In disorders that cause seizures or spasms, medication is prescribed to assist the individual in daily tasks.
How Does The Brain Communicate Without The Corpus Callosum?
As established, the corpus callosum is crucial in the communication between the left and right hemispheres, so how will the brain be able to carry information back and forth without it effectively?
It has been established that the brain resting-state activity in people with agenesis and those with a normally functioning brain are similar. This means that a brain with agenesis can effectively rewire itself and reestablish a communication pathway.
How the brain can perform this task of rewiring to compensate for the missing corpus callosum is not known but well documented by several neurological studies.
What Other Conditions Are Caused By Agenesis Of The Corpus Callosum?
Agenesis of the corpus callosum causes several other conditions or abnormalities, and some of the most well-known are –
- Arnold – Chiari malformation
- Neural migration disorders
- The forebrain fails to divide into lobes
- Hydrocephalus – excess fluid that builds up between the skull and the brain, causing the head to swell grotesquely
- Deep and prominent clefts in the tissue of the brain
There are several other syndromes associated with agenesis of the corpus callosum, and they are as follows –
- Shapiro Syndrome – An extremely rare condition of adult-onset agenesis, paroxysmal hypothermia, and hyperhidrosis.
- Menkes Syndrome – A rare condition affecting the copper levels in the body, resulting in underweight patients with kinked, sparse hair and a deteriorating nervous system.
- Andermann Syndrome – A condition where the nerves used for movement and muscle sensation are damaged, causing neuropathy.
- Mowat-Wilson Syndrome – Recognized by the distinctive facial features it causes. It affects many areas of the body.
- FG Syndrome Type 1 – An X-linked or male-exclusive condition that causes poor muscle tone, chronic constipation, and intellectual disability.
- Aicardi Syndrome – An X-linked syndrome that causes fatality in males. Presents with facial deformities, spasms, and seizures.
- Acrocallosal Syndrome – A syndrome that presents with polydactylism - extra toes and fingers - and deformed facial features.
- Rarely with Spina Bifida – Spina Bifida is when the spine is left exposed in the lower back. Usually, there is a large hole in the body where the spinal cord can be seen through a thin membrane, as it did not fuse in the womb.
What Are Common Signs And Symptoms Of Agenesis?
Within the first 24 months of an infant's development, there will be clear signs and symptoms that point to agenesis of the corpus callosum. The symptoms may not be severe and mimic other diseases, so a thorough clinical investigation is crucial.
Some of the early onset symptoms may be as follows –
- Hearing disorders
- Epileptic type seizures
- Unusual movements of the limbs
- Slow in reaching developmental milestones
- Blindness
Seizures are always connected to brain dysfunction and are typically the first sign and symptom of possible agenesis. Some seizures do not present as violet fits and may look like the infant or child is "stuck staring" into the distance.
One way to eliminate or accurately diagnose agenesis is by performing an MRI or Magnetic Resonance Imaging scan of the brain. The MRI can deliver detailed images of the internal organs and the brain.
Without an MRI, agenesis of the corpus callosum can remain undetected for several years, leading to wrong diagnoses and treatment. The sooner it is identified, the sooner proper treatment protocols can be implemented.
Which Other Tests Can Be Performed To Diagnose Agenesis?
Apart from the highly advanced MRI scan, other tests can be performed to help with an accurate diagnosis of agenesis or malformations of the corpus callosum.
- Ultrasound or Doppler tests – usually done prenatally
- CT (computerized tomography) scan of the brain
- CAT scan
Corpus callosum deformities or agenesis in infants can be identified by paying attention to the following physical signs –
- Difficulty in feeding or nursing
- Bulging eyes, facial deformities, or abnormal jaw and head
- Low and underdeveloped muscle tone
- A chronic state of constipation
- High pain tolerance
- Problems sleeping or constant disturbances in sleeping patterns
- Epileptic fits or seizures
- Hearing impaired
Besides the physical presentation of disorders of the corpus callosum, the following cognitive signs can be an identifying factor –
- Inability to complete tasks
- Inability to problem-solve
- Struggles to understand sarcasm or takes everything literally
- Has no problem lying because they believe their lie to be a truth
- Struggles to read and interpret facial expressions
- Lacks the ability to assess danger or risk
- Does not toilet train in line with developmental milestone guides
- Struggles to socially function – Cannot understand social cues, lacks self-awareness, and is immature.
- Poor coordination and midline crossing
- Short attention span and hyperactivity
- Shows signs of OCD and tics
Interesting Facts About The Corpus Callosum
- The word Corpus Callosum means 'tough body' in Latin.
- Only placental mammals or eutherians possess a corpus callosum. Marsupials and vertebrates like reptiles and birds don't have one.
- Information passes through the corpus callosum between 5m/sec or 10m/sec, depending on the brain size.
- Compared to their large brains, the corpus callosum in whales and elephants are similar in size to humans.
Conclusion
In the vast communication hub of the brain, where many critical functions are determined, the corpus callosum is a super highway that makes them possible. Life without a corpus callosum is not impossible, but it is highly challenging. The next time you look at a beautiful landscape, painting, or picture, thank your faithful corpus callosum for making it possible!
