Sulcus (neuroanatomy)

In neuroanatomy, a sulcus (Latin: "furrow", pl. sulci) is a depression or groove in the cerebral cortex. It surrounds a gyrus (pl. gyri), creating the characteristic folded appearance of the brain in humans and other mammals. The larger sulci are usually called fissures.

Sulcus
Sulcus and gyrus.
Identifiers
NeuroNames1208
TA98A14.1.09.006
TA25433
FMA75759
Anatomical terminology
Gray's Fig. 726 – Lateral surface of left cerebral hemisphere, viewed from the side.
Gray's Fig. 727 – Medial surface of left cerebral hemisphere.
Rotating image of human brain, illustrating the lateral sulcus
Illustration depicting general brain structures including sulci

Structure

Sulci, the grooves, and gyri, the folds or ridges, make up the folded surface of the cerebral cortex. Larger or deeper sulci are termed fissures, and in many cases the two terms are interchangeable. The folded cortex creates a larger surface area for the brain in humans and other mammals. When looking at the human brain, two-thirds of the surface are hidden in the grooves. The sulci and fissures are both grooves in the cortex, but they are differentiated by size. A sulcus is a shallower groove that surrounds a gyrus. A fissure is a large furrow that divides the brain into lobes and also into the two hemispheres as the longitudinal fissure.[1]

Importance of expanded surface area

As the surface area of the brain increases more functions are made possible. A smooth-surfaced brain is only able to grow to a certain extent. A depression, sulcus, in the surface area allows for continued growth. This in turn allows for the functions of the brain to continue growing.[2]

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.[3] Some of the more prominent sulci are, however, seen across individuals – and even species – making a common nomenclature across individuals and species possible.

Development
Main article: Gyrification

In humans, cerebral convolutions appear at about 5 months and take at least into the first year after birth to fully develop.[4][5][6] Development varies greatly between individuals. The potential influences of genetic, epigenetic and environmental factors are not fully understood.[7] It has been found that the width of cortical sulci increases not only with age,[8] but also with cognitive decline in the elderly.[9]

Types

Sulci are divided into following categories:

On the basis of function:

  1. A limiting sulcus separates at its floor into two areas which are different functionally and structurally e.g. central sulcus between the motor and sensory areas.[10]
  2. Axial sulcus develops in the long axis of a rapidly growing homogeneous area e.g. postcalcarine sulcus in the long axis of the striate area.
  3. Operculated sulcus separates by its lips into two areas and contains a third area in the walls of the sulcus e.g. lunate sulcus is an operculated sulcus, separating the striate and parastriate areas.

On the basis of formation:

  1. Primary sulci: formed before birth, independently. Example: central sulcus.
  2. Secondary sulcus: produced by factors other than the exuberant growth in the adjoining areas of the cortex Examples are the lateral and parieto-occipital sulci.

On the basis of depth:

  1. Complete sulcus is very deep so as to cause elevation in the walls of the lateral ventricle. Examples are the collateral and calcarine sulci.
  2. Incomplete sulci are superficially situated and are not very deep, E.g. paracentral sulcus.

Notable sulci

Other animals

The variation in the number 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.[4][5] 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 pounds (18 kg)) and capybaras (150 pounds (68 kg)) are gyrencephalic and smaller rodents such as rats and mice lissencephalic.[11]

Macaque

A macaque has a more simple sulcal pattern. In a monograph Bonin and Bailey list the following as the primary sulci:[12]

See also
This article uses anatomical terminology.

References
  1. Carlson, N. R. (2013). Physiology of Behavior. Upper Saddle River, NJ: Pearson Education Inc.
  2. Cusack, R. (2005). The intraparietal sulcus and perceptual organization. Journal of Cognitive Neuroscience, 17(4), 641–651. doi: 10.1162/0898929053467541
  3. Ono, Kubick, Abernathey, Atlas of the Cerebral Sulci, Thieme Medical Publishers, 1990. ISBN 0-86577-362-9. ISBN 3-13-732101-8.
  4. Hofman MA. (1985). Size and shape of the cerebral cortex in mammals. I. The cortical surface. Brain Behav Evol. 27(1):28–40. PMID 3836731
  5. Hofman MA. (1989).On the evolution and geometry of the brain in mammals. Prog Neurobiol.32(2):137–58. PMID 2645619
  6. Caviness VS Jr. (1975). Mechanical model of brain convolutional development. Science. 189(4196):18–21. PMID 1135626
  7. Dubois, J., & Benders, M. (2007). Mapping the early cortical folding process in preterm newborn brain. Oxford Journals, 18, 1444–1454. dpi: 10.1093/cercor/bhm180
  8. Tao Liu, Wei Wen, Wanlin Zhu, Julian Trollor, Simone Reppermund, John Crawford, Jesse S Jin, Suhuai Luo, Henry Brodaty, Perminder Sachdev (2010) The effects of age and sex on cortical sulci in the elderly. NeuroImage 51:1. 19–27 May. PMID 20156569
  9. Tao Liu, Wei Wen, Wanlin Zhu, Nicole A Kochan, Julian N Trollor, Simone Reppermund, Jesse S Jin, Suhuai Luo, Henry Brodaty, Perminder S Sachdev (2011) The relationship between cortical sulcal variability and cognitive performance in the elderly. NeuroImage 56:3. 865–873 Jun. PMID 21397704
  10. Ribas, Guilherme Carvalhal (February 2010). "The cerebral sulci and gyri". Neurosurgical Focus. 28 (2): E2. doi:10.3171/2009.11.focus09245. PMID 20121437.
  11. Martin I. Sereno, Roger B. H. Tootell, "From Monkeys to humans: what do we now know about brain homologies," Current Opinion in Neurobiology 15:135–144, (2005).
  12. Gerhardt von Bonin, Percival Bailey, The Neocortex of Macaca Mulatta, The University of Illinois Press, Urbana, Illinois, 1947
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