The brain is unique in appearance with indentations and depressions. Just 3 pounds in weight, the adult brain is 60 percent fat; the rest’s water, protein, carbohydrates, and salts. We know about the brain’s gray and white matter but much less about the folds. So what is the brain's surface called a sulcus?
Sulcus is the patterned grooves or furrows on the brain’s cerebral cortex that increase the brain's size and separate the lobes and irregular-shaped ridges of the gyri. Sulci are the folds between the brain’s lobes and the cell-carrying tissue that connects to the rest of the body.
Whether we're marveling at a sunset, reading a book, resolving a mathematical equation, or fine-tuning a drawing, we're wired to the brain’s working. The sulcus is a mysterious anatomical receptor, not just the fissures separating the brain's lobes and the gyri. The role of sulci in the processing and interpreting of messages on the brain’s surface is worth looking at.
All About Sulcus
The brain's surface, the cerebral cortex, is uneven and has characteristic folds and bumps: the sulci (singular sulcus) and the gyri (singular: gyrus). Both landmarks allow us to separate the brain into functional centers – a left and a right. The sulci form the boundaries inside and in between the brain's two hemispheres.
The sulci are the folds that stand out as grooves or furrows between the brain’s different lobes and the irregular ridges or gyri on the brain’s surface. The folds are essential as these increase the brain’s size, and allow for a greater gray area and more neurons. The sulci are visible on the brain's cortex, which fascinates one when looking at a plastic brain model.
Looked at from our level, the sulcus is how we are hotwired by the brain to think, act and respond. The neurons in the gray matter on the brain’s outer layer receive and interpret information sent to the white matter in the brain and then along the central nervous system to the body.
How we learn, remember, and reason depends on the thin gray matter layer of neurons on the brain’s surface. This is the cerebral cortex region consisting of different lobes, the sulci folds, and the gyri.
Sulcus And Brain Lobes
Sulci (singular sulcus) in the brain’s cerebral cortex connect to the central nervous system. The sulci are part of the brain's outer lobes. The folds like crevices stand out between adjacent gyri on the brain's surface.
The brain’s cerebrum has four lobes with different lobes functions:
- The frontal lobe – the brain's most prominent lobe at the front of the head.
- Parietal lobe – this lobe is in the middle of the brain
- Occipital lobe – a lobe at the back of the brain
- Temporal lobe – the sides of the brain
Frontal Lobe
The neuro-physical and psychological aspects of the frontal lobe are how it defines our personality – this is what influences us how to decide, do things and move. Our sense of smell is here. It’s also the region for our ability to speak (the Broca’s area).
Parietal Lobe
The parietal lobe sits in the middle of the brain, and an essential function is identifying objects. Our level of understanding of what others say resides in this region, also known as the Wernicke area. This part of the brain affects our spatial relations, and it's also from here that we experience physical pain.
Occipital Lobe
The occipital lobe governs our sight and all aspects of vision.
Temporal Lobe
If you wondered how we remember, this happens in the temporal lobes. Our short-term memory and speech start here. Another function of the temporal lobes is signaling to us who we are.
In the lobes of the brain, the sulcus and the gyrus are closely connected, and these differ from each other. More than one sulcus covers the depressions or furrows between the gyri. The sulci and gyri function together to increase the brain’s cerebral cortex and increase the richness of information that can be processed. The sulci also are in the grooves between the lobes.
Difference Between Sulci And Gyrus
As the command center, the brain controls our senses, emotions, and movements. And yet, we only use only 10 percent of our brains. There’s so much more to discover, like the role and functions of the sulci. One can't, however, speak of the sulci and not the gyri best known through their physical appearance on the brain's surface.
The sulci and gyri have differences :
- Sulcus – inward fold or depression on the brain’s surface
- Gyrus – outward or raised ridge on the brain’s surface
The sulcus or sulci (plural), as the furrows or fissures are differentiated from the gyrus or gyri, the raised coils, and twists. The sulcus appears in various regions, of which the three most prominent are:
- Lateral sulcus - a deep fissure that separates the frontal and parietal lobes from the temporal lobe
- Central Sulcus - a cortical surface that separates the frontal and parietal lobes
- Parieto-occipital Sulcus - a posterior position
The sulcus has functions like:
- Divides the brain’s two hemispheres into a left and a right side
There are also two types of sulci, which differ in terms of the different times these were formed. These are:
- Primary sulci (e.g., the central sulcus) formed independently before birth
- Secondary sulci are formed by the growth in adjoining areas of the cortex (e.g., the parieto-occipital sulci)
What stands out in neurobiological research is the depth of the sulci folds, which form the boundaries between lobes and over the gyri.
The sulci folds' depth (and, in this case, the shallowness) is used as a diagnostic tool in some cases relating to the incidence rate of epileptic seizures. These are also indicators of schizophrenia and auditory hallucinations associated with structural deficits that are directly related to the shallowness of the sulci. A smooth cerebral cortex is a medical aberration.
Nothing about the brain is simple. From a neuro-psychological perspective, the role of sulci stretches from social cognition and cognitive empathy to the ability to take a perspective. This includes behaviors like being altruistic and prosocial and the above clinical diagnoses where the sulci are linked to abnormal brain functions.
Sulci Are Landmarks On the Brain’s Cortex
Researchers are intrigued by the brain's cortex and the depth of the sulcus folds. From studies done on the brain cortex, there's no doubt that these extraordinary folds, the sulci, stand out as landmark features with the gyri. Neuroscientists realized they needed to consider the relationship between the folds and their depths and what's regarded as developmental pathologies.
Amongst the many findings, it's known that the patterns of these folds carry the insignia of a person’s genetic makeup. But the patterns are also influenced by environmental factors.
Though there’s variation in the cortex between individuals, some consistent patterns exist in the sulci folds, which is also why subtle abnormalities become visible. The folds indicate cognitive disorders such as schizophrenia, bipolar disorder, ADHD, and autism.
Some research has looked at the age-related deviances in sulci depths and even the prevalence of hallucinations.
Sulcus And Early Childhood Abnormalities
Neuroscientific research has seen that the brain's development of the central sulcus changes in early childhood, and sometimes these changes can indicate abnormalities. In the first three years of life, neurodevelopmental disorders surface, as this is also when the brain cortex grows rapidly. Diagnosing and treating clinical disorders is possible by zooming in on sulci.
Interestingly, the human brain grows rapidly from birth to childhood, and at six years old, the brain is 95% of its final volume. The cortical folding starts in the gestational stage of the brain and at around 16 weeks. Neuroscientists can scan the depth of sulci and use these to diagnose functional and developmental pathologies.
Scientists have seen that the patterns of these folds (sulci) are influenced by one's genetic makeup and environmental factors. Some abnormalities associated with the folding patterning (sulci) are cognitive disorders like schizophrenia, bipolar disorder, ADHD, Williams' syndrome, and autism.
Neuroscientists have seen that in autism, the brain's morphology changes. The changes are visible in the sulci in the central, intraparietal and frontal lobes. In these instances, it's the length and depth of the sulcus that stands out. Scientists have also seen how healthy cortical folding in early childhood is a baseline for normal cortical maturation.
Not much research has been done, and it's primarily early. Cortical sulcal development is poorly understood. Besides the cerebrum being the brain's largest part, the frontal cerebral cortex has gray matter, and the brain's white matter is at the center. The cerebrum influences our movement, speech, judgment, and thinking.
Furthermore, the cerebrum's sulci folds and gyrus ridges are spread across the two halves of the cerebral cortex. The sulci stretch between the lobes from the front to the back of the head. Neuroscientists have seen that the right controls the body's left side and have found the left brain hemisphere controls the right side.
The appearance of the sulci has been studied to seek out abnormalities. The anatomical functions of the sulci remain a world to be discovered. Especially in as much as the sulci contribute to who we are.
Sulcus And The Aging Brain
Neuroscientists maintain that as we age, our brains atrophy. This neuronal death shows up as wider and shallower sulci.
The changes in the brain have been looked at in middle-aged persons. What happens with age is that the sulcus changes as the adjacent gyri shrink, which affects the brain's global shape. And the research specifically looked at how adjacent gyri's atrophy influenced the sulci's width or depth.
The areas that were looked at were: the frontal sulcus, central sulcus, lateral sulcus, temporal sulcus, and intra-parietal sulcus. And what researchers found was that age brought about:
- Wider sulci
- Shallower sulci
The width and flattening out of sulci are caused by changes in the brain that are directly related to age.
On another level, sulci changes also impact people's emotional well-being. The region in the brain that brings about the changes is the limbic node. This is also where the lateral sulcus is – an area associated with the conscious experience of emotion and knowing contexts.
Our emotions, moods, and even our proneness to addiction come from the limbic region. This is also the area that's associated with our primitive Lizard brain. The lizard brain refers to limbic responses – flight, fight, and more.
Sulcus And Hallucinations
Ever wondered why we hallucinate? Well, research shows that the voice we hear that tells us we’re no good or even seeing a poisonous snake come our way, if it's not, are hallucinations. The terror we experience is linked to folds in our brains, the paracingulate sulcus. This means that the inability to tell actual events from those created by our imagination lies in this fold.
Researchers use electromagnetic imaging to look at the brain's imagination center. The center in our brain’s frontal lobe shows that the brain cortex around the paracingulate sulcus activates when we imagine what others think or feel. So too, patients with brain damage to their frontal lobe cannot plan, and their sense of self is impaired.
Research has shown that the paracingulate sulcus in the brain’s imagination region influences how we perceive reality. Some people have virtually no paracingulate sulcus. Researchers found that the lengths of the folds or sulci can indicate reactions like hallucinations.
The shorter sulci are associated with hallucinations like hearing voices and seeing things. These experiences are hallucinatory rather than visual or aural perceptions. Researchers could tell that some patients with schizophrenia might experience hallucinations while others might not.
The hallucinatory neural processes are part of the brain's anatomy. The research that looks at the depth of the sulcus folds in the cortical brain areas is a start for treating hallucination sufferers.
Conclusion
Possibly the least known fact is that the folds on the brain's cortex expand the neural field of the central nervous system because of their shape. It's one of the marvels of the brain to have the depressions of the sulci count for more area for gray matter. And so too the raized gyri increases the active neuron count on the brain’s surface.
In addition, scans as diagnostic tools have been able to diagnose and even treat patients because of information on the depth of the sulci, comparing the furrow’s to what's closest to the norm.
