The longitudinal fissure (or cerebral fissure, great longitudinal fissure, median longitudinal fissure, interhemispheric fissure) is the deep groove that separates the two
cerebral hemispheres
The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...
of the
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
. Lying within it is a continuation of the
dura mater
In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. ...
(one of the
meninges
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
) called the
falx cerebri
The falx cerebri (also known as the cerebral falx) is a large, crescent-shaped fold of dura mater that descends vertically into the longitudinal fissure between the cerebral hemispheres of the human brain,Saladin K. "Anatomy & Physiology: The Uni ...
. The inner surfaces of the two hemispheres are convoluted by
gyri
In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other ma ...
and
sulci
Sulci or Sulki (in Greek , Steph. B., Ptol.; , Strabo; , Paus.), was one of the most considerable cities of ancient Sardinia, situated in the southwest corner of the island, on a small island, now called Isola di Sant'Antioco, which is, howev ...
just as is the outer surface of the brain.
Structure
Falx cerebri
All three
meninges
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
of the cortex (
dura mater
In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. ...
,
arachnoid mater
The arachnoid mater (or simply arachnoid) is one of the three meninges, the protective membranes that cover the brain and spinal cord. It is so named because of its resemblance to a spider web. The arachnoid mater is a derivative of the neural c ...
,
pia mater
Pia mater ( or ),[Entry "pia mater"](_blank)
in
Falx cerebri
The falx cerebri (also known as the cerebral falx) is a large, crescent-shaped fold of dura mater that descends vertically into the longitudinal fissure between the cerebral hemispheres of the human brain,Saladin K. "Anatomy & Physiology: The Uni ...
is the name given to the dura mater in-between the two hemispheres, whose significance arises from the fact that it is the outermost layer of the meninges. These layers prevent any direct connectivity between the bilateral lobes of the cortex, thus requiring any tracts to pass through the corpus callosum. The vasculature of falx cerebri supplies blood to the innermost surfaces of the cortex, neighboring the midsagittal plane.
Cerebral asymmetry
Though this fissure divides the brain, the two hemispheres of the human cortex are not perfectly symmetrical, both in structure and in function. For example, the
planum temporale
The planum temporale is the cortical area just posterior to the auditory cortex (Heschl's gyrus) within the Sylvian fissure. It is a triangular region which forms the heart of Wernicke's area, one of the most important functional areas for languag ...
, roughly corresponding to the
Wernicke’s area, was found to be 10 times larger in the left than the right hemisphere. In contrast, the
caudate nucleus
The caudate nucleus is one of the structures that make up the corpus striatum, which is a component of the basal ganglia in the human brain. While the caudate nucleus has long been associated with motor processes due to its role in Parkinson's di ...
, within the
basal ganglia
The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...
, was found to be larger in the right hemisphere.
Corpus callosum
The
corpus callosum
The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental mam ...
connects the two halves of the brain at the bottom of its structure and delivers visual, auditory, and somatosensory messages between each half. Here, billions of neurons and glia can be found working together to send messages that form what is known as the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
. The corpus callosum is responsible for eye movement and visual perception, maintaining a balance between arousal and attention, and the ability to identify locations of sensory stimulation. In a clinical setting, those with epilepsy may benefit from the division of the corpus callosum.
Development
Phylogenetically
It is thought that a majority of existing animals, including
Homo sapiens
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
, have evolved from a common wormlike ancestor that lived around 600 million years ago, called the
urbilaterian
The urbilaterian (from German ur- 'original') is the hypothetical last common ancestor of the bilaterian clade, i.e., all animals having a bilateral symmetry.
Appearance
Its appearance is a matter of debate, for no representative has been (o ...
. A
bilateria
The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...
n animal is one that has symmetrical left and right body halves. While it is still debated whether this species had a complex brain or not, development of similar species support the hypothesis that it had at least a simple anterior collection of nerve cells, called a
cephalon. Furthermore, studies have shown that this cephalon was bilateral, consisting of two or more connected sub-collections that are separated by the
mid-sagittal plane, suggesting the first example of such a division.
Ontogenetically
A neural crest appears in the
mammalian embryo as soon as the 20th day of development. It is during embryonic development that a neural tube appears and is folded into a hollow structure, as shown in
Figure 1
Figure 1 is a Toronto, Ontario-based online social networking service for healthcare professionals to post and comment on medical images.
Figure 1 was founded in Toronto by Dr. Joshua Landy, Richard Penner and Gregory Levey. The platform launched ...
. This process is also known as neurulation. The neural tube is where the central nervous system forms, which later on in development will be subdivided and differentiated into distinct sections of the brain and spinal cord. These subdivisions occur by signaling molecules that direct differentiated cells to their correct location of the organism. The bilateral sides of this structure then give rise to the two hemispheres of the Homo sapiens cortex but do not merge at any point besides the corpus callosum. As a result, the longitudinal fissure is formed. The longitudinal fissure can appear as early as the eighth week of development, and distinctly separates the two hemispheres by around the tenth gestational week.
Function
Essentially, the fissure's purpose is to separate the brain into two
hemispheres, left and right. Through case studies of brain damage or
stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
to either side of each hemisphere, there is evidence that the left side of the brain controls the right side of the body, and the right side controlling the left side of the body.
Stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
patients have been found to unilateral impairment following damage to either the left or right hemisphere, this effecting the opposite side of the body. Separating each hemisphere allows for
specialization
Specialization or Specialized may refer to:
Academia
* Academic specialization, may be a course of study or major at an academic institution or may refer to the field in which a specialist practices
* Specialty (medicine), a branch of medical ...
of storage, procedural and
cognitive function
Cognitive skills, also called cognitive functions, cognitive abilities or cognitive capacities, are brain-based skills which are needed in acquisition of knowledge, manipulation of information and reasoning. They have more to do with the mechanisms ...
. Through "split-brain experiments", the left hemisphere is shown to specialize in mathematics, language and general logistics. The right hemisphere is further specialized, generally, in music, art, facial recognition and in most
spatial events.
The longitudinal fissure also pays a role in the
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
tract. This is shown in (figure 4.) with the
optic chiasm
In neuroanatomy, the optic chiasm, or optic chiasma (; , ), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrate ...
, which takes the nerve from the right eye to the left hemisphere and the left eye to the right hemisphere. The longitudinal fissure allows for this misdirection and crossover of nerves. The crossover seems to be counterintuitive, however it does serve an adaptive purpose. This purpose is to give us
stereopsis
Stereopsis () is the component of depth perception retrieved through binocular vision.
Stereopsis is not the only contributor to depth perception, but it is a major one. Binocular vision happens because each eye receives a different image becaus ...
, (depth and three-dimensional vision), as well as a development of
binocular vision
In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...
. These two components combined give the ability to have a larger perceived visual field, which coincides with the hypothesis that this is an adaptive function given by the fissures placement and structure. Damage to the nerve past the optic chiasm, will cause loss or impairment to the corresponding eye. If the right side of the brain is damaged and the nerve is damaged or destroyed, then the left eye will also follow the severity of damage.
Clinical significance
The longitudinal fissure plays a key role in
corpus callosotomy
Corpus callosotomy is a palliative surgical procedure for the treatment of medically refractory epilepsy. In this procedure the corpus callosum is cut through in an effort to limit the spread of epileptic activity between the two halves of the ...
, neurosurgery resulting in
split brain, as it provides unobstructed access to the corpus callosum. Corpus callosotomy is one of the procedures used for
pharmacologically treating intractable
epilepsy
Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...
cases, and it consists of the division of the nerve fibers running between the two hemispheres through the corpus callosum. A neurosurgeon separates the two hemispheres physically by pulling them apart with special tools, and cuts through either approximately two thirds of the fibers in the case of partial callosotomy, or the entirety in the case of complete callosotomy. Without the presence of longitudinal fissure, the corpus callosotomy procedure would be significantly more challenging and dangerous, as it would require the surgeon to navigate through densely connected cortical areas. Following the procedure, the two hemispheres are no longer able to communicate with each other as before.
While patients’ brains usually adapt and allow for uninterrupted daily life, cognitive tests can easily determine whether a patient has split-brain. In an experiment involving a chimeric figure, with a woman’s face on the left half and a man’s face on the right half, a patient with split-brain focusing on the middle point will point to the woman’s face when prompted to point to the face in the picture, and will answer “a man” if asked what the picture is depicting. This is because the
Fusiform Face Area
The fusiform face area (FFA, meaning spindle-shaped face area) is a part of the human visual system (while also activated in people blind from birth) that is specialized for facial recognition. It is located in the inferior temporal cortex ( ...
(FFA) is in the right hemisphere, while language centers are predominantly in the left hemisphere.
Repetitive transcranial magnetic stimulation
In studies, low-frequency
repetitive transcranial magnetic stimulation
Transcranial magnetic stimulation (TMS) is a noninvasive form of brain stimulation in which a changing magnetic field is used to induce an electric current at a specific area of the brain through electromagnetic induction. An electric pulse ge ...
(rTMS) applications have been tested with various cognitive processes during time
perception
Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...
tasks. Studies have analyzed the effects of the low-frequency rTMS on tests of time perception when the rTMS has been applied to the "parietal medial longitudinal fissure". Findings have shown evidence to support the hypothesis that participants in this study would underestimate their perception of time for short amounts of time and overestimate for longer periods of time. Specifically, the 20 participants underestimated 1 second time intervals and overestimated 4 second/9 second intervals after applying 1-Hz rTMS.
Neurosurgery
The longitudinal fissure can serve as an effective surgical passage in the frontal bone during central and pterional craniotomies, which is opening into the skull by surgery. While there are variations in the head shapes of many species, dogs have been found to have a high variation in terms of head shapes making it difficult to find a brain surgical procedure that will work effectively for them. One goal of the study was to distinguish the longitudinal cerebral fissure anatomy and their possible variations in brachy‐(B), dolicho‐(D) and mesaticephalic‐(M) dogs. Even though the lateral cerebral fissure morphology was uniform in the dog breeds. Mesaticephalic‐(M) dogs were found to have the greatest surgical passage resulting in access to more brain structures, while the dolicho‐(D) dogs had the smallest surgical passage.
Research
![201405 corpus callosum](https://upload.wikimedia.org/wikipedia/commons/9/91/201405_corpus_callosum.png)
As the corpus callosum is substantially smaller in surface area relative to the longitudinal fissure (
Figure 3
Figure may refer to:
General
*A shape, drawing, depiction, or geometric configuration
* Figure (wood), wood appearance
*Figure (music), distinguished from musical motif
*Noise figure, in telecommunication
* Dance figure, an elementary dance patte ...
), fiber bundles passing through are densely packed together, and precision tracking is essential to distinguish between the individual bundles that originate from and lead to the same cortical centers. Understanding such connections allows us to understand the contralateral concurrences and what diseases can result from lesions to them.
Diffusion tensor imaging
Diffusion-weighted magnetic resonance imaging (DWI or DW-MRI) is the use of specific MRI sequences as well as software that generates images from the resulting data that uses the diffusion of water molecules to generate contrast in MR images. It ...
(DTI or dMRI) along with fiber-tracking (FT) algorithms and
functional Magnetic Resonance Imaging
Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
(fMRI) is used to image these bundles.
[Rokem, A., Takemura, H., Bock, A. S., Scherf, K. S., Behrmann, M., Wandell, B. A., . . . Pestilli, F. (2017). The visual white matter: The application of diffusion MRI and fiber tractography to vision science. Journal of Vision, 17(2), 4. ] For instance, occipital-callosal fiber tracts were localized with 1–2 mm precision using DTI-TF techniques - which are very important for the cooperation of visual cortices, and any lesion to them can lead to
alexia, the inability to read.
Additional images
File:03 2 facies dorsalis cerebri gyri.jpg, facies dorsalis cerebri gyri
File:Slide4KLI.JPG, Cerebrum. Medial face. Dissection of corpus callosum etc.
File:Gehirn, basal - beschriftet lat.svg, Basal view of a human brain
File:Slide2STE.JPG, Cerebrum. Optic and olfactory nerves. Inferior view. Deep dissection.
File:Slide2Dsa.JPG, Cerebrum. Inferior view. Deep dissection.
File:Slide6Neo.JPG, Meninges and superficial cerebral veins. Deep dissection. Superior view.
File:Sheep Brain Dissection 2 - black background with labels.png, Sheep Brain Dissection with labels
File:Sobo 1909 645.png, An anatomical illustration from the 1908 edition of Sobotta's Anatomy Atlas
See also
*
Lateralization of brain function
The lateralization of brain function is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. The median longitudinal fissure separates the human brain into two distinct cerebra ...
References
External links
*
Diagram at nih.gov
{{DEFAULTSORT:Median Longitudinal Fissure
Cerebrum
Sulci (neuroanatomy)
Medial surface of cerebral hemisphere