Parietal Lobes

Subdivisions

• postcentral gyrus (broadmann’s areas 1-3)

• Superior parietal lobule (broadmann’s areas 5 and 7)

• Parietal operculum (broadmann’s area 43)

• Supramarginal gyrus (broadmann’s area 40) (inferior parietal lobule)

• Angular gyrus (broadmann’s area 39) (inferior parietal lobule)

Function zones

• anterior zone is areas 1-3, 43 (somatosensory cortex)

• Posterior zone is areas 5, 7, 39, 40 (posterior parietal cortex)

von Economo maps

posterior parietal areas, E (5, 7), F (40, 43), G (39)

Somatosensory strip

• areas 5, 7 is tactile perception

• To motor regions about limb position and movement

4 principles of the connections

1. area 5, 7 are somatosensory

2. Areas 40, 43 motor system

3. Area 39 is more complex connections (parieto-temporo-occipital crossroads)

4. Close relation between posterior parietal connections and prefrontal cortex and controlling spatially guided behaviour

3 pathways leave the posterior parietal region

1. Parieto-premotor (how pathway)

2. Parieto-prefrontal (Visuospatial functions)

3. Parieto-medial temporal (spatial navigation)

Anterior zones

Process somatic sensations and perceptions

posterior zones

• integrate info from vision with somatosensory info for movement and spatial function

• Significant role in mental imagery

Double dissociation

Function A can be preserved but impaired function B in one patient and impaired function A but preserved function B in another patient

Somatoperceptual disorders

• lesions to the post central gyrus

• Abnormally high somatosensory thresholds

• Impaired position sense

• Deficits in tactile perception

• Clumsy finger movements (afferent paresis)

Astereognosis

• disorder of tactile perception

• Inability to recognize objects by touch

Simultaneous extinction

• failure to report a stimulus one one side (extinction)

• Damage to areas 5, 7, 40, 43

Numb touch (blind touch)

• cannot feel stimuli/touch but can report location of touch

• Large lesions in areas 5, 7, 39, 40, 43

• Could burn/cut themselves without feeling it

Asomatognosia

Loss of sense of one’s own body; commonly affects left side of body

Balint’s sydrome

• Damage to 5, 7

• Could not fixate on a visual stimulus, directed gaze 40 degrees when shown stimuli

• When paying attention toward one object, cannot see others

• Can have optic ataxia

Optic ataxia

• severe deficits in reaching under visual guidance

• Movements not requiring visual guidance is okay (eg. Buttoning)

• Visuomotor problem- integrating visual info with motor system

Allesthesia

patients begin to respond to a stimulus on the neglected side as if the stimulus was on non neglected side of the body

Contralateral neglect

• lesion in the right inferior parietal lobe

• Caused by defective sensation, perception, attention or orientation

Gerstmann syndrome

• finger agnosia

• Inability to write (a graphic)

• Inability to do simple math problems (acalculia)

• Disrobed language function

• Left parietal lobe lesion (area 39)

Ideational apraxia

Difficulty in conceiving the overall goal of the movements (eg. Pouring water in a glass)

Ideomotor apraxia

problems in forming the subgoals (eg. Getting food from the fridge)

Motor apraxia

problems in executing actual movements (eg. Making pouring motion)

Constructional apraxia

difficulties in making a series of movements in order to assemble components together to form an object (eg. Building a puzzle)

Common themes in apraxia

• damage to left inferior parietal cortex (area 40); damage to right inferior parietal region (constructional)

• Special role in left hemisphere, impaired movement if impaired

• Parietal connection to frontal lobe structures involved in movement control

• Difficulties copying

Movement type in apraxia

left parietal lesions impaired hand/arm but not facial movements but left frontal lesions impaired facial but not hand/arm movements

Complexity in apraxia

left anterior and posterior lesions impaired copying a series of facial and hand/air movements

Spatial attention

• Selectively attend to different stimuli

• Inferior parietal lobes play an important role for this

Posner task

• test difficulties with disengaging attention

• Press a key as fast as possible every time you see a target (left/right)

• Cue is presented before each trial

• Patients are slow to control invalid cue trials, cannot disengage their attention from originally cued location

Disorders of spatial cognition

inability to use topographic information (eg. Map reading) and is associated with right hemisphere damage

Mental rotation

• requires mental imaging and manipulation of the stimulus

• Left hemisphere deficit may result from inability to generate appropriate mental image

• Right hemisphere deficit may result from inability to manipulate image