|Brain: Parietal lobe|
|Principal fissures and lobes of the cerebrum viewed laterally. (Parietal lobe is shown in yellow)|
|Lateral surface of left cerebral hemisphere, viewed from the side. (Parietal lobe is shown in orange.)|
|Gray's||subject #189 822|
|Vein||Superior sagittal sinus|
The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the dorsal stream of the visual system. This enables regions of the parietal cortex to map objects perceived visually into body coordinate positions. Several portions of the parietal lobe are important in language processing. Just posterior to the central sulcus lies the Postcentral Gyrus. This area of the cortex is responsible for somatosensation. Somatosensory cortex can be illustrated as a distorted figure - the homunculus (little man), in which the body parts are rendered according to how much of the somatosensory cortex is devoted to them.
The name comes from the overlying parietal bone, which is named from the Latin paries-, wall.
The parietal lobe is defined by three anatomical boundaries: The central sulcus separates the parietal lobe from the frontal lobe; the parieto-occipital sulcus separates the parietal and occipital lobes; the lateral sulcus (sylvian fissure) is the most lateral boundary, separating it from the temporal lobe; and the medial longitudinal fissure divides the two hemispheres. Within each hemisphere, the somatosensory cortex represents the skin area on the contralateral surface of the body.
Immediately posterior to the central sulcus, and the most anterior part of the parietal lobe, is the postcentral gyrus (Brodmann area 3), the secondary somatosensory cortical area. Dividing this and the posterior parietal cortex is the postcentral sulcus.
The posterior parietal cortex can be subdivided into the superior parietal lobule (Brodmann areas 5 + 7) and the inferior parietal lobule (39 + 40), separated by the intraparietal sulcus (IPS). The intraparietal sulcus and adjacent gyri are essential in guidance of limb and eye movement, and based on cytoarchitectural and functional differences is further divided into medial (MIP), lateral (LIP), ventral (VIP), and anterior (AIP) areas.
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. Its function also includes processing information relating to the sense of touch. 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). This dorsal stream has been called both the 'where' stream (as in spatial vision) and the 'how' stream (as in vision for action). The posterior parietal cortex (PPC) receives somatosensory and/or visual input, which then, through motor signals, controls movement of the arm, hand, as well as eye movements.
Various studies in the 1990s found that different regions of the posterior parietal cortex in Macaques 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). 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. The AIP has neurons that are responsible for grasping and manipulating objects through motor and visual inputs. The AIP and ventral premotor working together, are responsible for visuomotor transformations for actions of the hand.
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, the personality trait measuring predisposition to spirituality.
This lobe is divided into two hemispheres - left and right. The left hemisphere is involved in symbolic functions in language and mathematics, meanwhile, the right hemisphere 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 spatial relationships and neglect of left-side space and left side of the body. Even drawings may be neglected on 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 of the body go to the left side of the brain and vice-versa.
Gerstmann's syndrome is associated with lesion to the dominant (usually left) parietal lobe. Balint's syndrome is associated with bilateral lesions. The syndrome of hemispatial neglect 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.
Apraxia is a disorder of motor control which can be referred neither to “elemental” motor deficits nor to general cognitive impairment.The concept of apraxia was shaped by Hugo Liepmann about a hundred years ago. Apraxia is predominantly a symptom of left brain damage, but some symptoms of apraxia can also occur after right brain damage.
Can also result in sensory impairment,when one of your senses; sight, hearing, smell, touch, taste and spatial awareness, is no longer normal. 
Several studies have suggested that abnormal parietal function may be associated with schizophrenia. There is a possibility that grey matter abnormalities begin in parietal and occipital lobes, progress towards the frontal regions, causing schizophrenia structural and functional alterations.
Additional images 
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- Penfield, W., & Rasmussen, T. (1950). The cerebral cortex of a man: A clinical study of localization of function. New York: Macmillan.
- Mishkin M, Ungerleider LG. (1982) Contribution of striate inputs to the visuospatial functions of parieto-preoccipital cortex in monkeys. Behav Brain Res. 1982 Sep;6(1):57-77.
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- Fogassi L, Luppino G. (2005).Motor functions of the parietal lobe. Current Opinion in Neurobiology, 15:626-631.
- Kusunoki M, Goldberg ME (March 2003). "The time course of perisaccadic receptive field shifts in the lateral intraparietal area of the monkey". J. Neurophysiol. 89 (3): 1519–27. doi:10.1152/jn.00519.2002. PMID 12612015.
- Goldberg ME, Bisley JW, Powell KD, Gottlieb J (2006). "Saccades, salience and attention: the role of the lateral intraparietal area in visual behavior". Prog. Brain Res. Progress in Brain Research 155: 157–75. doi:10.1016/S0079-6123(06)55010-1. ISBN 9780444519276. PMC 3615538. PMID 17027387.
- Avillac M, Deneve S, Olivier E, Pouget A, Duhamel JR (2005). "Reference frames for representing visual and tactile locations in parietal cortex". Nat Neurosci 8 (7): 941–9. doi:10.1038/nn1480. PMID 15951810.
- Zhang T, Heuer HW, Britten KH (2004). "Parietal area VIP neuronal responses to heading stimuli are encoded in head-centered coordinates". Neuron 42 (6): 993–1001. doi:10.1016/j.neuron.2004.06.008. PMID 15207243.
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- Murata A, Gallese V, Luppino G, Kaseda M, Sakata H (May 2000). "Selectivity for the shape, size, and orientation of objects for grasping in neurons of monkey parietal area AIP". J. Neurophysiol. 83 (5): 2580–601. PMID 10805659.
- Murata A, Gallese V, Kaseda M, Sakata H (May 1996). "Parietal neurons related to memory-guided hand manipulation". J. Neurophysiol. 75 (5): 2180–6. PMID 8734616.
- Culham JC, Valyear KF (2006). "Human parietal cortex in action". Curr Opin Neurobiol 16 (2): 205–12. doi:10.1016/j.conb.2006.03.005. PMID 16563735.
- Medendorp WP, Goltz HC, Vilis T, Crawford JD. (2003) Gaze-centered updating of visual space in human parietal cortex. J Neurosci. 16;23(15):6209-14.
- Urgesi, Cosimo; S M Aglioti; M Skrap; F Fabbro (2010-02-11). "The Spiritual Brain: Selective Cortical Lesions Modulate Human Self-Transcendence". Neuron 65 (3): 309–319. doi:10.1016/j.neuron.2010.01.026. Retrieved 2012-05-19.
- Vallar G (2007). "Spatial neglect, Balint-Homes' and Gerstmann's syndrome, and other spatial disorders". CNS Spectr 12 (7): 527–36. PMID 17603404.
- Goldenberg, George (2009). "Apraxia and the Parietal Lobes". Neuropsychologia 47 (6): 1449–1459. doi:10.1016/j.neuropsychologia.2008.07.014. PMID 18692079. Retrieved 2012-05-19.
- Liepmann, 1900[clarification needed]
- Khan AZ, Pisella L, Vighetto A, Cotton F, Luauté J, Boisson D, Salemme R, Crawford JD, Rossetti Y. et al. (2011). "Optic ataxia errors depend on remapped, not viewed, target location". Nat Neurosci 8 (4): 418–20. doi:10.1038/nn1425. PMID 15768034.
- Murat Yildiz et al. "Parietal Lobes in Schizophrenia: Do They Matter?", Schizophrenia Research and Treatment Volume 2011 (2011)
See also 
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