The parietal lobe is strategically located between other lobes and has a greater variety of clinical manifestations than other parts of the brain. It is involved in somatosensory processing, spatial awareness, language, praxis, and more. Damage can cause syndromes like Gerstmann syndrome, apraxia, agraphia, acalculia, hemispatial neglect, and others, depending on whether the left or right lobe is affected. The parietal lobe works in conjunction with other brain regions to carry out its diverse functions.

1. PARIETAL LOBE DR ARUN S

2. IntroductionNo independent existence as anatomical / physiological unitOperates in conjunction with brain as a wholeStrategically situated b/w other lobesGreater variety of clinical manifestations than rest of the hemisphereDysfunction likely to be overlooked unless special techniques used

3. HistoryIn 1874 Bartholow recorded odd sensation from legs on stimulating post central gyrus through skull woundsCushing in 1909 --- Electrical stimulation in conscious human beings under LA –– mainly tactile hallucinations

4. Critchley(1953) – monograph on “ The Parietal Lobes” Djerine– alexia , agraphia -- angular gyrus lesion Liepmann--- ideomotor & ideational apraxia in (L) sided lesion

5. NeuroanatomyOccupies middle third of cerebral hemispheresSituated b/w frontal ,temporal ,occipital lobes with anatomical & functional continuity

6. BoundariesAnterior –Central sulcus & its imaginary continuation over inner paracentral lobule medially Posterior- parieto occipital sulcus on mesial aspect & its continuation (imaginary) to join pre occipital notch inferolaterallyLower- Sylvian fissure & its imaginary extension backwards

8. Lateral surface 2 well defined sulciPost central sulcus –parellel to Fissure of RolandoInter parietal sulcus- runs AP from post central sulcus to occipital lobe

9. Lateral surfaceGyri Post central gyrus- primary sensory area(3,1,2) Superior parietal lobule(5,7) Inferior parietal lobule ( Ecker’s lobule )Supramarginalgyrus (area 40) arches over Sylvian fissure Angular gyrus (area 39 ) - arches over the superior temporal sulcus

10. Mesial surfaceParacentral lobule- mesial part of post central gyrusPrecuneus- behind post central gyrusSubjacent part of cingulategyrus- below sub parietal sulcus

12. Vascular supplyLateral - MCA Artery of Rolandic fissureArtery of inter parietal fissure Artery of post parietal fissureInter opercular parietal arteryArtery to angular gyrusMesial - ACA mainly & PCA to a slight extent

14. Venous drainage Superficial middle cerebral vein –lies in lateral fissure Vein of Trolard (superior anastomotic vein) - connects sup middle cerebral vein to SSSVein of Labbe’ ( inferior anastomotic vein ) - connects sup middle cerebral vein to Transverse sinus

15. Post central gyrusGranular cortexReceives most of its afferents from VPL nucleus of thalamusProjects to somatosensory association cortex (area 5)Some parts (except hand & foot ) connected to opposite somatosensory cortex via corpus callosumRepresentation of C/L side of body

17. Postcentral gyrusSuperior part represent the LL Middle part -- the trunk & UL and Lower part --the faceAmount of cortex devoted to any particular body area – proportional to sensory acuity Tips of fingers & lips larger area of representation

18. Posterior parietal regionSuperior & inferior Parietal lobuleConnections Post central gyrus

19. Superior parietal areaArea 5b- occupies large portion of Sup parietal lobule Extends over medial surface to include pre cuneusNo large pyramidal cells in layer VGranular layer – great depth & density

20. Inferior parietal areaSupra marginal & angular gyrus No pyramidal cells Granular cortex well developedClose proximity to occipital & temporal lobe

21. Parietal lobe functionsDifficult to describe due to bewildering range of symptoms Simple functional division Anterior region- post central gyrus / sensory stripPosterior region – lies behind post central gyrus & is composed of tertiary cortex

22. Functions of anterior regionSomato sensory perceptionTactile perception Body senseVisual object recognition

23. Functions of posterior regionLanguage Reception of spoken language Reading Spatial orientation & attentionRoute following L- R discrimination Calculation

24. Intentional movement

25. Praxis

26. Constructional ability DrawingShort term auditory memoryOptic radiation passes to Occipital Lobe via deep region . Lesion ---VF defectsAngular & supramarginal gyri of dominant hemisphere – imp in language & related functions

27. APRAXIA Definition Difficulty in performing skilled motor acts which can not be explained by an elementary sensory or motor deficit or language comprehension disorder

28. ApraxiaLimb apraxia–Limb kinetic / melokineticIdeomotorIdeationalDisassociation ConductionConceptual Constructional & dressing –often associated with neglect & visual perceptual disorders

29. Scattered , fragmentedLoss of spatial relationsFaulty orientation Energetic drawing Addition of lines to make drawing correct

30. Coherent , simplifiedPreservation of spatial relationsCorrect orientation Slow & laborious Gross lack of details

31. TestsPressure sensitivityTwo point discriminationPoint localisation Position senseTactual object recognition

32. Two point discriminationUse a compass / calibrated 2 point esthesiometer1mm tip of tongue 2-4 mm finger tips 4-6 mm dorsum of fingers 8-12 mm on palm20-30 mm on dorsum of palm

33. AmorphosynthesisInability to synthesize separate tactile sensations into perception of form Lack of recognition of C/L body & of spaceAstereognosisLoss of ability to recognize object by touch Unable to name objects, describe or demonstrate their usePrimary sensations intact

34. Asomatognosia Agnosia relates to patient’s own body TypesAnosognosiaAutotopagnosia

35. AnosognosiaIgnorance of existence of disease More with (R ) PL lesions U/L neglect may co existDeny weakness /sensory loss of affected limbExtreme cases- disowns limb

36. AutotopagnosiaImpairment in localization / naming of parts of own bodyPatient unable to point to body parts named by examiner / move them May not be able to identify them on examiner’s body / on diagram

37. Finger agnosiaInability to recognize , name & point to individualized fingers on self & others – usually middle 3 fingersForm of autotopagnosia B/L lesionCentral feature of Gerstmann syndrome

38. Language dysfunctionDominant PL lesionDefect in reception of spoken language & readingConduction aphasia

39. AgraphiaSpontaneous writing & writing on command more affected than copy rightingIrregular & tremulous script, misspelling , semantic & syntactial errorsSite – inferior parietal lobule

40. Apractic agraphia- agraphia despite normal sensory, motor & visual feed back, word & letter knowledgeLesion- Dom sup parietal lobuleVisuo spatial agraphia-neglect of (U) side of paper in writingLesion -- (R) temp- parietal junction

43. Effects of unilateral disease of the parietal lobe, right or leftA. Corticosensory syndrome and sensory extinction B. Mild hemiparesis (variable), unilateral muscular atrophyin children, hypotonia, poverty of movement, hemiataxiaC. Homonymous hemianopia or inferior quadrantanopia(incongruent or congruent) or visual inattentionD. Abolition of optokineticnystagmus with target movingtoward side of the lesionE. Neglect of the opposite side of external space

44. Effects of unilateral disease of the dominant (left) parietallobeA. Disorders of language (especially alexia)B. Gerstmann syndrome (dysgraphia, dyscalculia, finger agnosia, right-left confusion)C. Tactile agnosia (bimanual astereognosis)D. Bilateral ideomotor and ideational apraxia

45. Effects of unilateral disease of the nondominant (right) parietal lobeA. Visuospatial disordersB. Topographic memory lossC. Anosognosia, dressing and constructional apraxiasD. ConfusionE. Tendency to keep the eyes closed, resist lid opening,and blepharospasm