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Gyri and Sulci of the Brain
By Olivia Guy-Evans, published June 09, 2021
The surface of the brain, known as the cerebral cortex, is very uneven, characterized by a distinctive pattern of folds or bumps, known as gyri (singular: gyrus), and grooves, known as sulci (singular: sulcus). These gyri and sulci form important landmarks that allow us to separate the brain into functional centers.
What is a gyrus?
The brain has an overall wrinkled appearance, consisting of many ridges and indentations. A gyrus (plural: gyri) is the name given to the bumps ridges on the cerebral cortex (the outermost layer of the brain).
Gyri are found on the surface of the cerebral cortex and are made up of grey matter, consisting of nerve cell bodies and dendrites.
They are unique structures that are important as they increase the surface area of the brain. A larger surface area means that more neurons can be packed into the cortex so that it can process more information. Ultimately, cognitive functions will be better with gyri without having to increase the actual brain size, which would not fit into a skull.
The layout and the size of gyri vary from person to person, although there are certain types of gyri which are found in everyone. Although, these types of gyri can vary in size and location between individuals.
There are specific types of gyri which are necessary to the brain’s function. For instance, the precentral gyrus is important as being the primary motor center of the brain.
Another important area is the superior temporal gyrus which holds Wernicke’s area an area vital for language development and the comprehension of speech.
As gyri are important to the structure of the brain, they have clinical significance. For example, some abnormalities with gyri can result in disorders such as epilepsy.
What is a sulcus?
A sulcus (plural: sulci) is another name for a groove in the cerebral cortex. Each gyrus is surrounded by sulci and together, the gyri and sulci help to increase the surface area of the cerebral cortex and form brain divisions.
They form brain divisions by creating boundaries between the lobes, so these are easily identifiable, as well as serving to divide the brain into two hemispheres.
A sulcus is a shallow groove that surrounds a gyrus, whereas sulci that are larger or deeper are given the term fissures.
The longitudinal fissure is the large furrow which divides the two hemispheres into left and right. A smooth-surfaced cortex would only be able to increase to a certain extent, therefore sulci in the surface area allows for continued growth, overall increasing brain function.
There are two types of sulci which are formed at different times. The primary sulci (e.g. the central sulcus) are formed independently before birth. Secondary sulci, however, are those formed by other factors other than the growth in adjoining areas of the cortex (e.g. the parieto-occipital sulci).
Sulci can also be defined in terms of their depth. A complete sulcus is a sulcus where the groove is very deep (e.g. the collateral sulcus), whereas an incomplete sulcus are not very deep (e.g. the paracentral sulcus).
Brain Sulci or Fissures
Listed below are a number of important sulci/fissures of the cerebrum.
Longitudinal fissure
The longitudinal fissure is a deep furrow located within the center of the brain, separating the left and right hemispheres. Within this fissure is the corpus callosum, which is a bundle of nerve fiberes that connects the left and right hemispheres of the brain in order to send visual, auditory, and somatosensory information between each half.
Central sulcus
The central sulcus, also known as the sulcus of Rolando, separates the parietal and frontal lobes. This is an essential sulcus because it defines the boundary between primary motor cortex and primary somatosensory cortex as well as between the parietal and frontal lobes.
It is believed that as motor functions develop, the shape of the central sulcus will also change, due to the role of this sulcus in separating the motor and sensory cortices.
It has also been suggested that the surface area of the central sulcus can affect the handedness of an individual. A larger central sulcus in the left hemisphere has been found in those who are right-handed, whereas in left-handed people, this sulcus is larger in the right hemisphere.
Parieto-occipital sulcus
The parieto-occipital sulcus is a deep groove which separates the parietal and occipital lobes of the brain.
This sulcus formed a notch on the external surface of the cortex, which serves as an indicator of where the parietal and occipital lobes lie. This sulcus is also a secondary sulcus as it forms after birth.
Lateral sulcus
The lateral sulcus is a deep groove which separates the parietal and temporal lobes. This is also known as the Sylvian sulcus and begins near the forebrain, extending to the lateral surface of the brain, with the insular cortex being located immediately deep within this sulcus.
Brain Gyri
Below is a listing of several key gyri in the brain and the divisions they create.
Cingulate gyrus
The cingulate gyrus is a component of the limbic system, consisting of a curved fold which covers the corpus callosum (a bundle of nerve fiberes which connects the right and left cerebral hemispheres).
The cingulate gyrus has a role in the processing of emotions and the regulation of behavior. As a result, damage to this area can result in emotional and behavioral disorders. This region is also involved in regulating autonomic motor function.
The cingulate gyrus is often referred to in terms of its divisions: anterior and posterior. The anterior cingulate gyrus is responsible for emotional processing and the vocalisation of emotions, as well as being involved in emotional bonding and attachment, especially between the primary caregiver and child.
This may be due to the fact that this structure has connections to the amygdala, a structure which processes emotions. This gyrus also has connections with areas in the frontal lobes which are important for speech and motor functions involved with speech production, such as Broca’s Area.
The posterior cingulate gyrus has a role in spatial memory, including the ability to process information relating to the spatial orientation of objects in the environment.
This part of the cingulate gyrus has connections to the parietal and temporal lobes, which allows it to coordinate functions in the areas of movement, orientation, and navigation.
Precentral gyrus
The precentral gyrus is a part of the brain’s cortex responsible for executing voluntary movements, located in the most posterior position of the frontal lobe, outlining the temporal lobes.
The precentral gyrus is the anatomical location of the primary motor cortex, which is what this gyrus is commonly known as. This gyrus works by creating and organizing a map of the body, known as the homunculus or ‘little man’.
The precentral gyrus is believed to contain the motor control for the torso, arms, hands, fingers, and head. This gyrus also works by controlling the motor movements on the body’s contralateral side, meaning the opposite side to which it is located within the brain.
Superior temporal gyrus
The superior temporal gyrus is an area which contains the auditory cortex, which is responsible for the processing of sounds.
Specific sound frequencies are mapped precisely onto the auditory cortex, forming an auditory map, which is similar to the homunculus map of the primary motor cortex.
Some areas of the superior temporal gyrus are responsible for processing combinations of frequencies, whilst others are specialized for processing changes in amplitude or frequency. This gyrus also contains Wernicke’s area, discovered by Karl Wernicke in 1871.
Wernicke’s area is a region important in the comprehension of language as well as having a major role in the ability to produce spoken words.
Cingulate gyrus
The cingulate gyrus is a component of the limbic system, consisting of a curved fold which covers the corpus callosum (a bundle of nerve fibers which connects the right and left cerebral hemispheres).
The cingulate gyrus has a role in the processing of emotions and the regulation of behavior. As a result, damage to this area can result in emotional and behavioral disorders.
This region is also involved in regulating autonomic motor function. The cingulate gyrus is often referred to in terms of its divisions: anterior and posterior.
The anterior cingulate gyrus is responsible for emotional processing and the vocalization of emotions, as well as being involved in emotional bonding and attachment, especially between the primary caregiver and child.
This may be due to the fact that this structure has connections to the amygdala, a structure which processes emotions. This gyrus also has connections with areas in the frontal lobes which are important for speech and motor functions involved with speech production, such as Broca’s area.
The posterior cingulate gyrus has a role in spatial memory, including the ability to process information relating to the spatial orientation of objects in the environment.
This part of the cingulate gyrus has connections to the parietal and temporal lobes, which allows it to coordinate functions in the areas of movement, orientation, and navigation.
Abnormal Gyri and Sulci
Within the early stages of development, there can be an abnormal pattern of gyri and sulci which can lead to complications. Abnormal patterns are sometimes caused by disorders of cell migration in the developing cortex.
If gyri do not form properly during development, the cerebral cortex will be smoother than it should be, a condition called lissencephaly. Issues with smooth cerebral cortices can be a factor in the development of epilepsy.
Abnormally large gyri can form, leading to pachygyria, and abnormally small gyri can lead to microgyria. These abnormalities can affect the cerebral cortex as a whole, but they may also be localized to one area and the conditions can coexist which each other.
For instance, an individual’s brain may have an unusually small gyrus and an unusually large gyrus. Polymicrogyria is a condition which is characterized by an excessive number of gyri in the brain which develops before birth.
With this condition, the sulci will be abnormally shallow in comparison to typically developed brains. This results in an irregular surface to the cortex and can be localized to a single gyrus or can involve many gyri.
The most common symptom of polymicrogyria is the development of epileptic seizures, with the incidence rate of epilepsy reported to range from between 60-85% of those with polymicrogyria between the ages of 4 and 12 years of age.
Other symptoms of polymicrogyria can include a delay in development, problems with speech and swallowing, muscle weakness, or paralysis. Severe cases of polymicrogyria, named bilateral generalised polymicrogyria, can affect the brain as a whole.
Damage or developmental irregularities with specific gyri or sulci can affect specific functions. Perisylvian syndrome is a rare neurological disease which results from damage to the lateral sulcus (or Sylvian sulcus), resulting in language and speech problems.
Finally, abnormalities of the superior temporal gyrus have been associated with some of the symptoms of schizophrenia (Barta et al., 1990). It has been suggested that in individuals with one of the positive symptoms of schizophrenia, auditory hallucinations, their superior temporal gyrus had structural and functional deficits.
About the Author
Olivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master’s degree in Psychology of Education from the University of Bristol in 2019. Olivia has been working as a support worker for adults with learning disabilities in Bristol for the last four years.
How to reference this article:
How to reference this article:
Guy-Evans, O. (2021, June 09). Gyri and sulci of the brain. Simply Psychology. www.simplypsychology.org/gyri-and-sulci-of-the-brain.html
APA Style References
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Baxter, R. (2020, October 29). What is a gyrus? Kenhub. https://www.kenhub.com/en/library/anatomy/what-is-a-gyrus
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