The parietal lobe is located at the top of the brain and is involved in processing somatosensory information, spatial awareness, and language comprehension. It contains the primary somatosensory cortex and association areas important for functions like tactile perception, discrimination, localization, and stereognosis. Injuries or lesions to different areas of the parietal lobe can cause syndromes like Gerstmann's syndrome involving acalculia, finger agnosia, and right-left disorientation if the angular gyrus is affected. The supramarginal gyrus is involved in tasks like praxis, repetition, and constructional abilities.

1. Parietal Lobe

2. Parietal lobe boundary Lateral surface Anterior - Central sulcus Inferio-Posterior – sylvian fissure. No sharp boundaries,merges with temporal & occipital lobe Medial sufface Posterior – parietooccipital sulci to line extending down to the preoccipital notch on the inferior border

3. Parietal lobe sulci and gyri Post central sulcus – posterior boundary of somatosensory cortex. Interparietal sulcus behind post central sulcus which divides the parietal lobe into sup. & inf. Parietal lobule Posterior end of sylvian fissure curves upwards to terminates into inf.parietal lobule – surrounding cortex supramarginal gyrus[SMG 40]

4. Parietal lobe sulci and gyri Posterior end of sup. Temporal sulcus – angular gyrus[AG 39] SMG & AG = Ecker’s Iinf Parietal Lobule Ecker’s IPL & post. Third of first temporal gyrus constitute the wernicke’language area 3,1,2-primary sensory areas 5- somatosensory association area 7-somatosensory or somatosensory/visual

5. Anatomy Histology Post central gyrus – homotypical granular cortex Rest – association cortex Development Sup and inf. Parietal lobule and adjacent temporal occipital lobe larger in human than primate develops 6-7 years of age

6. Partial lobe connections Affrents Post central gyrus VP thalamic nuclei Spindle affrent -> 3a Cutaneous affrent -> 3b + 1 Joint affrent -> 2 Association cortex To frontal, temporal and occipital cortex of both side Effrents Somatosensory cortex -> area 5 superior parietal lobule 1,3,5 (except hand and foot area) -> opp. somatosensory cortex

7. Electrical stimulation Somatosensory cortex Numb tingling sensation and sense of movements , rarely pain warmth and cold Sup and Inf. parietal lobule No sensory or motor response (silent area)

8. Functions Ant. Parietal cortex- tactile perception Post.secondary sensory area-tactile discrimination,position, t. localization, stereognosis, graphaesthesia Spatial orientation Constructional activity Language - Understanding the grammatical & syntactical aspects of language Arithmetic, calculation

9. Post Central Gyrus Eyes closed - patient is to position hand to match position of other. Passive finger detection. Two point threshold. Von Frey Hair threshold. Vibration sense. With lesion most severe changes are distal, coarse sensations return first Height discrimination Pinpoint vs. head. Touch area on skin, have patient point to area on contralateral side. Fasten a button. Tie a shoelace. Localized lesion by deficit interactions.

10. Post Central Gyrus Test s Eyes closed - match one hand to position set by examiner. Passive finger detection two point threshold two point finger test matchbox test finger-tip number writing. Vibration sense - tuning fork Weight discrimination. Pinpoint vs. head - use a pin. Touch area and have patient point to contralateral area Fine motor tasks unusual speech. Consonant substitutions (especially of similar sounds), without broken or jerky speech typical of Broca's Aphasia. May see writing errors due to role of articulatory movements in analysis of words.

11. Inferior Parietal Lobule 1. Apraxia for dressing. 2. Constructional apraxia (spatial apraxagnosia) - problems in motor integration in constructional tasks. 3. Spatial orientation deficit (more severe for right hemisphere lesions than left:). 4. Right-left disorientation. 5. Planto-pokinesia (disorganization of discriminations in spatial Judgment). 6. Visuospatial agnosia . Difficulty in performing reversible operations in extrapersonal space (difficulty in taking different perspectives) (more severe for right hemisphere lesions than left). Inability to maintain visual image of patterned and verbal material. Visuographic defects. Unilateral neglect. General intellectual impairment (lesions in left hemisphere). Problems with writing and defective comprehension in reading.

12. IPL Assessment 1. Inability to analyze positions of hands on a clock. 2. Confuses symmetrically arranged symbols (e.g., d & b). 3. Difficulty making rotations on a 2-D stick test. 4. Difficulty changing perspectives on a village scene test. 5. Difficulty with transformations on pool reflections test. 6. Problems on both visual and tactile route finding tests. 7. Difficulty in maze learning. 8. Inability to follow habitual routes. 9. Difficulty designating body parts on examiner. 10. Difficulty drawing common objects to demand. 11. Problems in visual memory for patterns and verbal matter. 12. Errors on the Bender. 13. Poor performance on Unknown Faces Test 14. Difficulty with simple addition, subtraction, multiplication, and division, both presented orally and written. 15. WAIS arithmetic subtest scores lowered. 16. Low test scores on Army General Classification Test.

13. Supramarginal Gyrus Ideomotor apraxia: disruption of organization of complex acts Results from left hemisphere lesion Usually affects both sides, may be worse on right side Can affect the face (buccofacial) and/or the limbs Conduction aphasia: results from left hemisphere lesion if the underlying arcuate fasciculus is cut Severely defective repetition Paraphasia in repetition and in spontaneous speech Normal comprehension Impaired writing, spontaneous and to dictation, errors in spelling, word choice, syntax

14. Supramarginal Gyrus Astereognosis: impairment of somatosensory discrimination Left hemisphere lesion: both hands affected Right hemisphere lesion: deficit - left hand Finger agnosia: inability to recognize, name, and point to individual fingers on self and others (left hemisphere lesion). Right-left disorientation Can't distinguish right from left on self or env. More common with left hemisphere lesion

15. Supramarginal Gyrus (SMG) Acalculia Loss of ability to understand & order numbers More severe with left hemisphere lesion Tactile perceptual disability: results from contralateral lesion Gerstmann's syndrome: : Right-left disorientation Finger agnosia Agraphia Acalculia R ight hemisphere C onstructional apraxia Mild left side neglect and/or denial Inability to interpret maps

16. Tests for SMG Ideomotor apraxia Carrying out motor acts to command: buccofacial (blow out a match, protrude tongue, drink through a straw) Carrying out motor acts to command: limb (salute, use a toothbrush, flip a coin, hammer a nail, comb hair, snap fingers, kick a ball, crush out a cigarette) Conduction aphasia Repetition of words, phrases, & sentences Write to dictation (letters, words, sentences) Ask patient to write sentences describing a Job, the weather, or a picture Confrontation naming of objects, clothing, body parts, parts of objects

17. Tests for SMG Astereognosis (with eyes closed) Patient identifies by touch such common objects as a coin, paperclip, pencil, or key (each hand tested separately) Patient judges the relative size of a series of coins Patient judges the texture of a series of objects, such as cloth, wire, sandpaper Finger agnosia In-between test, Two-Point Finger Test, and Match Box Test Identifying named fingers on examiner's hands and naming fingers on self

18. Test for SMG Right-left disorientation Identification of right and left limbs on self and examiner Crossed commands on self and examiner Acalculia Written addition, subtraction, multiplication, and division problems Verbal complex problems Fingertip number writing Gerstmann's syndrome Right-left disorientation Finger agnosia Agraphia: writing to dictation and writing sentences describing scenes in pictures Acalculia

19. Test for Left SMG Constructional apraxia copying designs match stick tests block construction test Left-side neglect glove test: ask the patient to put on a pair of gloves drawing to command: clock, bicycle, flower in pot behavioral observations Have patient locate cities on a map

21. Clinical syndromes Either hemisphere Cortical sensory syndrome& sensory extinction Total hemi anesthesia with large acute lesion of white matter Mild hemi paresis, unilateral muscular atrophy in children, hypotonia, poverty of movements, hemiataxia Homonymous hemianopia [incongruent or congruent], visual inattention sometime anosognosia, neglect of one half of body and extrapersonal space (with right than left lesion) Abolition of optokinetic nystagmus with target moving towards the side of lesion

22. Right hemisphere Topographic disorientation Topographic memory loss Anosognosia /dressing apraxia Constructional apraxia Hemi-inattention Apraxia of eye opening Confusion

23. Left Hemisphere Disorder of language Fluent aphasia, alexia Gerstman’s syndrome (Angular gyrus) acalculia, finger agnosia, left/right disorientation, agraphia Tactile agnosia (bimanual asteriognosis) Bilateral Ideomotor & ideational apraxia

24. Bilateral Parietal Syndrome Visual spatial imperceptions Optic ataxia Spatial disorientation Simultagnosia Visual Agnosia Constructional apraxia

25. Misellaneous Blunted emotionality. apathy. Inattentiveness Confusion, allocheiria Optic ataxia depersonalisation

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