Folds and Grooves of the Cerebrum: An Anatomical Explanation

The noggin's exterior ain't all smooth, it's covered in ridges and grooves, giving it a rough, wrinkled look. These aren't random occurrences, but rather made up of ridges called gyri and grooves called sulci. They're essential for how our brains are structured and work.

By understanding these features, scientists can map various brain regions linking them to specific functions like movement, memory, and language.

What Are Gyri and Sulci?

Thickened ridges on the brain's surface are gyri, while the grooves separating them are sulci.

The folding of the brain increases its surface area, thus packing more neurons inside without increasing the size of the brain. A larger surface area leads to a better ability to process complex information.

Why Is the Brain Folded?

Brain folding allows a large cortex to fit into the limited space of the skull—a necessary feature for higher-level functions like reasoning, memory, and language.

Although the layout of these folds differs between people, some key gyri and sulci appear consistently across human brains, making them valuable to brain research and understanding.

Gyri

Gyri consist mostly of grey matter—clusters of nerve cell bodies and dendrites responsible for thinking, sensing, and processing.

By increasing surface area, gyri provide more neural connections and higher cognitive capacity. Each gyrus focuses on a specific function.

Types of Gyri

Cingulate Gyrus

This gyrus is part of the limbic system, a collection of structures associated with emotions and behavior. It aids in emotional vocalization and bonding between caregiver and child, while also handling spatial memory and movement coordination through connections with the parietal and temporal lobes.

Precentral Gyrus

The precentral gyrus is located in the frontal lobe and contains the primary motor cortex. It creates a map of the body, controlling motor movements on the body's opposite side.

Superior Temporal Gyrus

The superior temporal gyrus hosts the auditory cortex, processing sounds through precisely mapped sound frequencies. Within this gyrus lies Wernicke's area, crucial for language comprehension and producing spoken words.

Improper formation of gyri can lead to brain malformations:

Schizophrenia—associated with structural abnormalities in the superior temporal gyrus, especially in patients who experience auditory hallucinations [Barta et al., 1990].
Lissencephaly—a condition where the brain appears smooth due to a lack of gyri.
Pachygyria—abnormally large gyri.
Polymicrogyria—excessively small and numerous gyri with shallow sulci, often resulting in developmental delays, seizures, and speech or motor difficulties.

Sulci

Sulci are the grooves that divide the brain's ridges. The deeper grooves are called fissures.

These structures:

Increase the surface area of the brain.
Divide the brain into lobes and functional areas.

Some sulci appear early in fetal development (primary sulci), while others emerge later in life (secondary and tertiary sulci), often shaped by experience and brain growth.

Types of Sulci

Longitudinal Fissure

The longitudinal fissure divides the left and right hemispheres of the brain. Inside this fissure lies the corpus callosum, which connects the hemispheres.

Central Sulcus

The central sulcus, also known as the sulcus of Rolando, separates the parietal and frontal lobes. It defines the boundary between the primary motor cortex and primary somatosensory cortex.

Parieto-Occipital Sulcus

The parieto-occipital sulcus forms a deep groove that separates the parietal and occipital lobes. Unlike primary sulci, this structure forms after birth as a secondary sulcus.

Lateral Sulcus

The lateral sulcus, also known as the Sylvian sulcus, separates the parietal and temporal lobes, with the insular cortex nestled deep within it.

Changes in sulci can reflect or contribute to neurological issues:

Perisylvian Syndrome—a rare condition involving the lateral sulcus, often resulting in speech and language impairments.
Abnormal Central Sulcus Development—can affect motor control and movement planning.

These structural variations can significantly impact brain function and behavior.

Table: Major Gyri and Sulci of the Brain

Brain Folding and Development

The brain begins forming folds during prenatal development. These folds reflect both genetics and environmental influences.

Primary sulci appear early and are mostly hardwired.
Secondary and tertiary sulci develop later and may be influenced by experience.
Regions involved in complex functions like language tend to have more intricate folds.

Evolutionary Perspective

Cortical folding is a vital marker of advanced brain function. Animals with more folds—such as humans, dolphins, and elephants—show greater cognitive abilities.

The gyrification index, which measures the degree of folding, is much higher in humans than in animals with smooth brains (like rodents). This, in turn, leads to:

More advanced problem-solving, language, and social skills.
More cortical surface area.
Denser neural networks

Summary

Gyrus and sulci are vital for brain organization, brain growth, and brain function. From emotions and memory to movement and speech, these folds help make us who we are.

Gyri, the thickened ridges on the brain's surface, consist mainly of grey matter, housing clusters of nerve cell bodies and dendrites responsible for thinking, sensing, and processing.
Sulci, the grooves separating gyri, increase the surface area of the brain, helping to pack more neurons inside without increasing the size of the brain.
Understanding gyri and sulci allows scientists to map various brain regions linked to specific functions like movement, memory, and language.
Improper formation of gyri can lead to brain malformations, such as Schizophrenia, Lissencephaly, Pachygyria, and Polymicrogyria.
Sulci divide the brain into lobes and functional areas, with changes in sulci reflecting or contributing to neurological issues like Perisylvian Syndrome and abnormal central sulcus development.
The brain's folding pattern develops during prenatal development, with primary sulci appearing early and being mostly hardwired, while secondary and tertiary sulci develop later and may be influenced by experience.
Cortical folding is a vital marker of advanced brain function, with animals with more folds showing greater cognitive abilities. The gyrification index, which measures the degree of folding, is much higher in humans than in animals with smooth brains like rodents.
A better understanding of gyri and sulci contributes to scientific fields like psychology, neuroscience, medicine, health and wellness, fitness and exercise, mental health, and nutrition, as well as the broader field of neurology and its disorders.
Proper development of gyri and sulci plays a crucial role in cognitive skills, behavior, and mental health, highlighting the importance of taking care of one's health and wellness for optimal brain function.

Folds and Grooves of the Cerebrum: An Anatomical Explanation