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Parietal lobe

parietal lobe, parietal lobe tumor
The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals The parietal lobe is positioned above the occipital lobe and behind the frontal lobe and central sulcus

The parietal lobe integrates sensory information among various modalities, including spacial sense and navigation proprioception, the main sensory receptive area for the sense of touch mechanoreception in the somatosensory cortex which is just posterior to the central sulcus in the postcentral gyrus,1 and the dorsal stream of the visual system The major sensory inputs from the skin touch, temperature, and pain receptors, relay through the thalamus to the parietal lobe

Several areas of the parietal lobe are important in language processing The somatosensory cortex can be illustrated as a distorted figure – the homunculus Latin: "little man", in which the body parts are rendered according to how much of the somatosensory cortex is devoted to them2 The superior parietal lobule and inferior parietal lobule are the primary areas of body or spacial awareness A lesion commonly in the right superior or inferior parietal lobule leads to hemineglect

The name comes from the overlying parietal bone, which is named from the Latin paries-, meaning "wall"

Contents

  • 1 Structure
  • 2 Function
  • 3 Clinical significance
  • 4 Additional images
  • 5 See also
  • 6 References

Structureedit

Animation Parietal lobe red of left cerebral hemisphere

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 body2

Immediately posterior to the central sulcus, and the most anterior part of the parietal lobe, is the postcentral gyrus Brodmann area 3, the primary 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

Functionedit

Cortical functions of the parietal lobe are:

  • Two point discrimination

through touch alone without other sensory input ie, visual

  • Graphesthesia – recognizing writing on skin by touch alone
  • Touch localization bilateral simultaneous stimulation

The parietal lobe plays important roles in integrating sensory information from various parts of the body, knowledge of numbers and their relations,3 and in the manipulation of objects Its function also includes processing information relating to the sense of touch4 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 vision5 and the "how" stream as in vision for action6 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 movements7

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 fixed8 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 appropriate9
  • The ventral intraparietal VIP area receives input from a number of senses visual, somatosensory, auditory, and vestibular10 Neurons with tactile receptive fields represent space in a head-centered reference frame10 The cells with visual receptive fields also fire with head-centered reference frames11 but possibly also with eye-centered coordinates10
  • The medial intraparietal MIP area neurons encode the location of a reach target in nose-centered coordinates12
  • The anterior intraparietal AIP area contains neurons responsive to shape, size, and orientation of objects to be grasped13 as well as for manipulation of hands themselves, both to viewed13 and remembered stimuli14 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 hand7

More recent fMRI studies have shown that humans have similar functional regions in and around the intraparietal sulcus and parietal-occipital junction15 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 move16 Both the left and right parietal systems play a determining role in self transcendence, the personality trait measuring predisposition to spirituality17

Clinical significanceedit

Features of parietal lobe lesions are as follows:

  • Unilateral parietal lobe
    • Contralateral hemisensory loss
    • Astereognosis – inability to determine 3-D shape by touch
    • Agraphaesthesia – inability to read numbers or letters drawn on hand, with eyes shut
    • Contralateral homonymous Lower quadrantanopia
    • Asymmetry of optokinetic Nystagmus OKN
    • Sensory Seizures
    • Extinction phenomenon contralateral
  • Dominant hemisphere
    • Dysphasia/Aphasia
    • Dyscalculia
    • Dyslexia –a general term for disorders that can involve difficulty in learning to read or interpret words, letters, and other symbols
    • Apraxia – inability to perform complex movements in the presence of normal motor, sensory and cerebellar function
    • Agnosia tactile agnosia – inability to recognize or discriminate
    • Gerstmann syndrome – Characterized by acalculia, agraphia, finger anomia and difficulty in differentiation of right and left
  • Non dominant hemisphere
    • Spatial disorientation
    • Constructional apraxia
    • Dressing apraxia
    • Anosognosia – a condition in which a person suffering disability seems to be unaware of the existence of his or her disability

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 problemsThe sensory inputs from the right side of the body go to the left side of the brain and vice versa

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 ago1819 Apraxia is predominantly a symptom of left brain damage, but some symptoms of apraxia can also occur after right brain damage20

Amorphosynthesis is a loss of perception on one side of the body caused by a lesion in the parietal lobe Usually, left-sided lesions cause agnosia, a full-body loss of perception, while right-sided lesions cause lack of recognition of the person's left side and extrapersonal space The term amorphosynthesis was coined by D Denny-Brown to describe patients he studied in the 1950s21

Can also result in sensory impairment where one of the affected person's senses sight, hearing, smell, touch, taste and spatial awareness is no longer normal 22 23

Additional imagesedit

See alsoedit

  • Lobes of the brain

Referencesedit

  1. ^ http://wwwrufriceedu/~lngbrain/cglidden/parietalhtml
  2. ^ a b Schacter, D L, Gilbert, D L & Wegner, D M 2009 Psychology 2nd ed New York NY: Worth Publishers
  3. ^ Blakemore & Frith 2005 The Learning Brain Blackwell Publishing ISBN 1-4051-2401-6
  4. ^ Penfield, W, & Rasmussen, T 1950 The cerebral cortex of a man: A clinical study of localization of function New York: Macmillan
  5. ^ Mishkin M, Ungerleider LG 1982 Contribution of striate inputs to the visuospatial functions of parieto-preoccipital cortex in monkeys Behav Brain Res 1982 Sep;61:57-77
  6. ^ Goodale MA, Milner AD Separate visual pathways for perception and action Trends Neurosci 1992 Jan;151:20-5
  7. ^ a b Fogassi L, Luppino G 2005Motor functions of the parietal lobe Current Opinion in Neurobiology, 15:626-631
  8. ^ 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:101152/jn005192002 PMID 12612015 
  9. ^ 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:101016/S0079-61230655010-1 ISBN 9780444519276 PMC 3615538  PMID 17027387 
  10. ^ a b c 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:101038/nn1480 PMID 15951810 
  11. ^ 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:101016/jneuron200406008 PMID 15207243 
  12. ^ Pesaran B, Nelson MJ, Andersen RA 2006 "Dorsal premotor neurons encode the relative position of the foot, eye, and goal during reach planning" Neuron 51 1: 125–34 doi:101016/jneuron200605025 PMC 3066049  PMID 16815337 
  13. ^ a b 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 
  14. ^ 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 
  15. ^ Culham JC, Valyear KF 2006 "Human parietal cortex in action" Curr Opin Neurobiol 16 2: 205–12 doi:101016/jconb200603005 PMID 16563735 
  16. ^ Medendorp WP, Goltz HC, Vilis T, Crawford JD 2003 Gaze-centered updating of visual space in human parietal cortex J Neurosci 16;2315:6209-14
  17. ^ 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:101016/jneuron201001026 Retrieved 2012-05-19 
  18. ^ Goldenberg, George 2009 "Apraxia and the Parietal Lobes" Neuropsychologia 47 6: 1449–1459 doi:101016/jneuropsychologia200807014 PMID 18692079 
  19. ^ Liepmann, 1900 clarification needed
  20. ^ 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:101038/nn1425 PMID 15768034 
  21. ^ Denny-Brown, D, and Betty Q Banker "Amorphosynthesis from Left Parietal Lesion" AMA Archives of Neurology and Psychiatry 71, no 3 March 1954: 302-13
  22. ^ http://alzheimersaboutcom/library/blparietalhtm
  23. ^ Murat Yildiz et al "Parietal Lobes in Schizophrenia: Do They Matter", Schizophrenia Research and Treatment Volume 2011 2011

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