Parietal lobe
Encyclopedia
The parietal lobe is a part of the Brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 positioned above (superior to) the occipital lobe
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...

 and behind (posterior to) the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...

.

The parietal lobe integrates sensory
Sensory
Sensory may refer to:relating to senses or smellIn biology:* Sensory preference* Sensory system, part of the nervous system of organisms* Sensory neuron, nerve cell responsible for transmitting information about external stimuli...

 information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the dorsal stream of the visual system
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...

. This enables regions of the parietal cortex to map objects perceived visually into body coordinate positions.

The name derives from the overlying parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....

, which is named from the Latin pariet-, wall.

Anatomy

The parietal lobe is defined by three anatomical boundaries: the central sulcus
Central sulcus
-External links:* via the Neuroscience Information Framework...

 separates the parietal lobe from the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...

; the parieto-occipital sulcus separates the parietal and occipital lobe
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...

s; the lateral sulcus
Lateral sulcus
-External links:* * * http://www.uams.edu/radiology/education/residency/diagnostic/pdf/sylvian_cistern_RSNA2003.pdf...

 (sylvian fissure) is the most lateral boundary separating it from the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....

; and the medial longitudinal fissure
Medial longitudinal fissure
The great longitudinal fissure is the deep groove which separates the two hemispheres of the vertebrate brain....

 divides the two hemispheres.

Immediately posterior to the central sulcus, and the most anterior part of the parietal lobe, is the postcentral gyrus
Postcentral gyrus
The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. It is the location of primary somatosensory cortex, the main sensory receptive area for the sense of touch...

 (Brodmann area
Brodmann area
A Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells.-History:...

 3), the secondary somatosensory cortical area. Dividing this and the posterior parietal cortex
Posterior parietal cortex
The posterior parietal cortex plays an important role in producing planned movements. Before an effective movement can be initiated, the nervous system must know the original positions of the body parts that are to be moved, and the positions of any external objects with which the body is going to...

 is the postcentral sulcus
Postcentral sulcus
The postcentral sulcus of the parietal lobe lies parallel to, and behind, the central sulcus in the human brain....

.

The posterior parietal cortex can be subdivided into the superior parietal lobule
Superior parietal lobule
The superior parietal lobule is bounded in front by the upper part of the postcentral sulcus, but is usually connected with the postcentral gyrus above the end of the sulcus....

 (Brodmann areas 5
Brodmann area 5
Brodmann area 5 is one of Brodmann's cytologically defined regions of the brain. It is involved in somatosensory processing and association.-Human:Brodmann area 5 is part of the parietal cortex in the human brain...

 + 7
Brodmann area 7
Brodmann area 7 is one of Brodmann's cytologically defined regions of the brain. It is involved in locating objects in space. It serves as a point of convergence between vision and proprioception to determine where objects are in relation to parts of the body....

) and the inferior parietal lobule (39
Brodmann area 39
Brodmann area 39, or BA39, is part of the parietal cortex in the human brain. BA39 encompasses the angular gyrus, lying near to the junction of temporal, occipital and parietal lobes....

 + 40
Brodmann area 40
Brodmann area 40, or BA40, is part of the parietal cortex in the human brain. The inferior part of BA40 is in the area of the supramarginal gyrus, which lies at the posterior end of the lateral fissure, in the inferior lateral part of the parietal lobe....

), separated by the intraparietal sulcus
Intraparietal sulcus
The intraparietal sulcus is located on the lateral surface of the parietal lobe, and consists of an oblique and a horizontal portion. The IPS contains a series of functionally distinct subregions that have been intensively investigated using both single cell neurophysiology in primates and human...

 (IPS). The intraparietal sulcus and adjacent gyri
Gyrus
A gyrus is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci .-Notable gyri:* Superior frontal gyrus, lat. gyrus frontalis superior* Middle frontal gyrus, lat. gyrus frontalis medius...

 are essential in guidance of limb and eye movement
Saccade
A saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...

, and based on cytoarchitectural and functional differences is further divided into medial (MIP), lateral (LIP), ventral (VIP), and anterior (AIP) areas.

Function

The parietal lobe plays important roles in integrating sensory information from various parts of the body, knowledge of numbers and their relations, and in the manipulation of objects. Portions of the parietal lobe are involved with visuospatial processing. Although multisensory in nature, the posterior parietal cortex is often referred to by vision scientists as the dorsal stream of vision (as opposed to the ventral stream in the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....

). This dorsal stream has been called both the 'where' stream (as in spatial vision) and the 'how' stream (as in vision for action).

Various studies in the 1990s found that different regions of the posterior parietal cortex in Macaque
Macaque
The macaques constitute a genus of Old World monkeys of the subfamily Cercopithecinae. - Description :Aside from humans , the macaques are the most widespread primate genus, ranging from Japan to Afghanistan and, in the case of the barbary macaque, to North Africa...

s represent different parts of space.
  • The lateral intraparietal (LIP) contains a map of neurons (retinotopically-coded when the eyes are fixed) representing the saliency of spatial locations, and attention to these spatial locations. It can be used by the oculomotor system for targeting eye movements, when appropriate.

  • The ventral intraparietal (VIP) area receives input from a number of senses (visual, somatosensory, auditory, and vestibular
    Vestibular system
    The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...

    ). Neurons with tactile receptive fields represented space in a head-centered reference frame. The cells with visual receptive fields also fire with head-centered reference frames but possibly also with eye-centered coordinates

  • The medial intraparietal (MIP) area neurons encode the location of a reach target in nose-centered coordinates.

  • The anterior intraparietal (AIP) area contains neurons responsive to shape, size, and orientation of objects to be grasped as well as for manipulation of hands themselves, both to viewed and remembered stimuli.


More recent fMRI studies have shown that humans have similar functional regions in and around the intraparietal sulcus and parietal-occipital junction. The human 'parietal eye fields' and 'parietal reach region', equivalent to LIP and MIP in the monkey, also appear to be organized in gaze-centered coordinates so that their goal-related activity is 'remapped' when the eyes move. Both the left and right parietal systems play a determining role in self transcendence
Transcendence (philosophy)
In philosophy, the adjective transcendental and the noun transcendence convey the basic ground concept from the word's literal meaning , of climbing or going beyond, albeit with varying connotations in its different historical and cultural stages...

, the personality trait measuring predisposition to spirituality http://www.cell.com/neuron/abstract/S0896-6273%2810%2900052-8

This lobe is divided into two hemispheres- left and right. The left hemisphere plays a more prominent role for right handers and is involved in symbolic functions in language and mathematics. Meanwhile, the right hemisphere plays a more prominent role for left handers and is specialised to carry out images and understanding of maps i.e.spatial relationships. Damage to the right hemisphere of this lobe results in the loss of imagery, visualization of spacial relationships and neglect of left side space and left side of the body. Even drawing may be neglected from the left side. Damage to the left hemisphere of this lobe will result in problems in mathematics, long reading, writing and understanding symbols. The parietal association cortex enables individuals to read, write, and solve mathematical problems.The sensory inputs from the right side go to the left side and vice-versa.

Pathology

Gerstmann's syndrome is associated with lesion to the dominant (usually left) parietal lobe. Balint's syndrome
Balint's syndrome
Bálint's syndrome is an uncommon and incompletely understood triad of severe neuropsychological impairments: inability to perceive the visual field as a whole , difficulty in fixating the eyes , and inability to move the hand to a specific object by using vision...

 is associated with bilateral lesions. The syndrome of hemispatial neglect
Hemispatial neglect
Hemispatial neglect, also called hemiagnosia, hemineglect, unilateral neglect, spatial neglect, unilateral visual inattention, hemi-inattention or neglect syndrome is a neuropsychological condition in which, after damage to one hemisphere of the brain, a deficit in attention to and awareness of...

is usually associated with large deficits of attention of the non-dominant hemisphere. Optic ataxia is associated with difficulties reaching toward objects in the visual field opposite to the side of the parietal damage. Some aspects of optic ataxia have been explained in terms of the functional organization described above.
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