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 () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. Lying within it is a continuation of the dura mater (one of the

meninges In anatomy, the meninges (; meninx ; ) 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 the subarachnoid spac ...

) called the falx cerebri. The inner surfaces of the two hemispheres are convoluted by

gyri In neuroanatomy, a gyrus (: gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulcus (neuroanatomy), sulci (depressions or furrows; : sulcus). Gyri and sulci create the folded appearance of the brain in huma ...

and

sulci Sulci or Sulki (in Greek , Stephanus of Byzantium, Steph. B., Ptolemy, Ptol.; , Strabo; , Pausanias (geographer), Paus.), was one of the most considerable cities of ancient Sardinia, situated in the southwest corner of the island, on a small isla ...

just as is the outer surface of the brain.

Structure

Falx cerebri

All three

of the cortex ( dura mater,

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 cr ...

pia mater Pia mater ( or ),Entry "pia mater"
in
Falx cerebri 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 lang ...

, 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 part of the basal ganglia in the human brain. Although the caudate nucleus has long been associated with motor processes because of its relation to Parkinso ...

, within the

basal ganglia The basal ganglia (BG) or basal nuclei are a group of subcortical Nucleus (neuroanatomy), nuclei found in the brains of vertebrates. In humans and other primates, differences exist, primarily in the division of the globus pallidus into externa ...

, 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 ...

connects the two halves of the brain below the fissure and conveys visual, auditory, and somatosensory messages between each half. 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'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

, have evolved from a common wormlike ancestor that lived around 600 million years ago, called the urbilaterian. A

bilateria Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left� ...

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 Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino Jr., Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont ...

. 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. 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. EmbryonicBrain

Function

Essentially, the fissure's purpose is to separate the brain into two

hemispheres Hemisphere may refer to: In geometry * Hemisphere (geometry), a half of a sphere As half of Earth or any spherical astronomical object * A hemispheres of Earth, hemisphere of Earth ** Northern Hemisphere ** Southern Hemisphere ** Eastern Hemisphe ...

, left and right. Through case studies of brain damage or

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

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 Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

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 of storage, procedural and

cognitive function Cognitive skills are skills of the mind, as opposed to other types of skills such as motor skills, social skills or life skills. Some examples of cognitive skills are literacy, self-reflection, logical reasoning, abstract thinking, critical th ...

. 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 vertebrates, ...

, 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 Binocular vision is seeing with two eyes, which increases the size of the Visual field, visual field. If the visual fields of the two eyes overlap, binocular #Depth, depth can be seen. This allows objects to be recognized more quickly, camouflage ...

, (depth and three-dimensional vision), as well as a development of

binocular vision Binocular vision is seeing with two eyes. The Field_of_view, field of view that can be surveyed with two eyes is greater than with one eye. To the extent that the visual fields of the two eyes overlap, #Depth, binocular depth can be perceived. Th ...

. 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 A corpus callosotomy () is a palliative surgical procedure for the treatment of medically refractory epilepsy. The procedure was first performed in 1940 by William P. van Wagenen. In this procedure, the corpus callosum is cut through, in an e ...

, 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 disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

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 (I ...

(FFA) is in the right hemisphere, while language centers are predominantly in the left hemisphere. The diffusion tensor tractographies of neural tracts for language fnhum-07-00749-g001

The diffusion tensor tractographies of neural tracts for language fnhum-07-00749-g001

Repetitive transcranial magnetic stimulation

In studies, low-frequency repetitive transcranial magnetic stimulation (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 syste ...

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

As the corpus callosum is substantially smaller in surface area relative to the longitudinal fissure ( Figure 3), 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

References

External links

*
Diagram at nih.gov
{{DEFAULTSORT:Median Longitudinal Fissure Cerebrum Sulci (neuroanatomy) Medial surface of cerebral hemisphere