Parietal lobes

Parietal lobes

1. Subdivisions

   • Post central gyrus
     • Brodmann's area 1, 2, 3
   • Superior parietal lobule
     • Brodmann's area 5, 7
   • Parietal operculum
     • Brodmann's area 43
   • Inferior parietal lobule
     • Supramarginal gyrus
       • Brodmann's area 40
     • Angular gyrus
       • Brodmann's area 39
   • Functional zones
     • Anterior zone
       • Somatosensory cortex
         • 1, 2, 3, 43
       • Process somatic sensations and perceptions
     • Posterior zone
       • Posterior parietal cortex
         • Remaining areas
       • Integrate information from vision with somatosensory information for movement

2. A theory of parietal lobe function

   • Use of spatial information
     • Object recognition
       • Viewer centered object identification
       • Posterior parietal cortex
     • Guidance of movement
       • Sensitive to eye movements
       • Posterior parietal cortex
     • Cognitive spatial map
       • Route knowledge, unconscious knowledge of how to reach a destination
   • Three symptoms do not fit with the visuomotor view of the parietal lobe
     • Difficulties with arithmetic
       • Acalculia
         • Might result from the spatial properties of addition and subtraction
           • Two digit number occupy different spaces
           • "Borrowing" during subtraction
     • Difficulties with certain aspects of language
       • Words have spatial organization
         • Tap vs. pat
     • Difficulties with movement sequences
       • Individual elements of the movement have a spatial organization

3. Somatosensory symptoms of parietal lobe lesions

   • Lesions to the post central gyrus
     • Abnormally high sensory thresholds
     • Impaired position sense
     • Deficits in stereogenesis, also tactile perception
   • Somatoperceptual disorders
     • Astereognosis
       • Inability to recognize an object by touch
     • Simultaneous extinction
       • Two stimuli are applied simultaneously to opposite sides of the body
       • A failure to report a stimulus on one side is referred to as extinction

4. Symptoms of posterior parietal lobe damage

   • Contralateral neglect
     • Neglect for visual, auditory and somethetic stimulation on one side of the body or space
     • During recovery, patients go through allesthesia and then simultaneous extinction
       • Allesthesia - begins to respond to the neglected stimuli as if they were on the other side of the body
     • Lesion most often in the right inferior parietal lobe
       • Right intraparietal sulcus and the right angular gyrus
   • Object recognition
     • After right parietal lobe lesions, patients are poor at recognizing objects in unfamiliar views
   • Apraxia
     • Movement disorder in which the loss of movement is not caused by weakness, inability to move, abnormal muscle tone, intellectual deterioration, or other disorders of movement
     • Ideomotor apraxia
       • Cannot copy serial movements
         • More likely to be associated with left parietal lesions
     • Constructional apraxia
       • Cannot copy pictures, build puzzles, or copy a series of facial movements
         • Associated with right and left parietal lesions
   • Deficits in drawing appear after damage to the right parietal lobe
   • Spatial attention
     • Function of the parietal lobe to selectively attend to different stimuli
     • Disengagement
       • Shifting attention from one stimulus to the next
     • Disorders of spatial cognition
       • Mental rotation requires:
         • Mental imaging of the stimulus
         • Manipulation of the image
       • LH deficit may result from the inability to generate the image
       • RH deficit may result from the inability to manipulate the image