Sulcus (neuroanatomy)





In neuroanatomy, a sulcus (Latin: "furrow", pl. sulci) is a depression or fissure in the surface of the brain. It surrounds the gyri, creating the characteristic appearance of the brain in humans and other large mammals.

Large furrows (sulci) that divide the brain into lobes are often called fissures. The large furrow that divides the two hemispheres—the interhemispheric fissure—is very rarely called a "sulcus".

Individual variation
The sulcal pattern varies between human individuals, and the most elaborate overview on this variation is probably an atlas by Ono, Kubick and Abernathey: Atlas of the Cerebral Sulci. Some of the larger sulci are, however, seen across individuals - and even species - so it is possible to establish a nomenclature.

Gyrification across species
The variation in the amount of fissures in the brain (gyrification) between species is related to the size of the animal and the size of the brain. Mammals that have smooth-surfaced or nonconvoluted brains are called lissencephalics and those that have folded or convoluted brains gyrencephalics. The division between the two groups occurs when cortical surface area is about 10 cm2 and the brain has a volume of 3–4 cm3. Large rodents such as beavers (40 lb) and capybaras (150 lb) are gyrencephalic and smaller rodents such as rats and mice lissencephalic.

Brain development
In humans, cerebral convolutions appear at about 5 months and take at least into the first year after birth to fully develop. It has been found that the width of cortical sulci not only increases with age, but also with cognitive decline in the elderly.

Notable sulci

 * Calcarine sulcus
 * Central sulcus
 * Central sulcus of insula
 * Cingulate sulcus
 * Circular sulcus of insula
 * Collateral sulcus
 * Fimbrodentate sulcus
 * Hippocampal sulcus
 * Inferior frontal sulcus
 * Inferior temporal sulcus
 * Intermammary sulcus
 * Intraparietal sulcus
 * Lateral sulcus
 * Lunate sulcus
 * Occipitotemporal sulcus
 * Olfactory sulcus
 * Paracentral sulcus
 * Parieto-occipital sulcus
 * Postcentral sulcus
 * Precentral sulcus
 * Rhinal sulcus
 * Subparietal sulcus
 * Sulcus of corpus callosum
 * Superior frontal sulcus
 * Superior temporal sulcus
 * Transverse occipital sulcus
 * Transverse temporal sulcus

Macaque
A macaque has a more simple sulcal pattern. In a monograph Bonin and Bailey list the following as the primary sulci :
 * Calcarine fissure (ca)
 * Central sulcus (ce)
 * Sulcus cinguli (ci)
 * Hippocampal fissure (h)
 * Sulcus intraparitalis (ip)
 * Lateral fissure (or Sylvian fissure) (la)
 * Sulcus olfactorius (olf)
 * Medial parieto-occipital fissure (pom)
 * fissura rhinalis (rh)
 * Sulcus temporalis superior (ts) - this sulcus runs parallel to the lateral fissure and extends to the temporal pole and often superficially merges with it.