Classification
Disorders of higher cortical function are often grouped into two processing streams. The first stream, the inferior (ventral) or occipitotemporal pathway for object recognition, extends from below the calcarine fissure into the adjacent temporal lobe. It facilitates object recognition and color perception. Disorders here include achromatopsia, prosopagnosia, alexia, and topographagnosia.
The second stream, the superior (dorsal) or occipitoparietal pathway for object localization extends from the upper bank of the calcarine fissure into the adjacent parietal lobe. It processes visuospatial attributes, including location and motion. Disorders here include akinetopsia, Balint syndrome (simultagnosia, ocular apraxia, and optic ataxia), and hemineglect.
▶ Table 10.1 lists the clinical findings, recommended tests, associated clinical signs, and lesions associated with these higher cortical disorders.
Higher cortical disorder | Clinical finding | Test | Associated clinical signs | Brain lesion |
Alexia without agraphia | Patient able to write but not read | Reading a text and writing | Right homonymous hemianopia Left occipital lobe and splenium of corpus callosum | |
Hemiachromatopsia | Patient does not recognize colors in one hemifield |
| Ipsilateral homonymous superior quadrantanopia | Contralateral inferior occipitotemporal lobe |
Prosopagnosia | Patient cannot recognize famous people or identify familiar faces | Identify famous people in magazine |
| Bilateral inferior occipitotemporal lobes |
Visual object agnosia | Patient is unable to identify objects by sight but can give a verbal description or recognize by another sensory modality | Name objects presented visually |
| Bilateral occipitotemporal lobes |
Optic aphasia | Patient is unable to name visually presented objects or point to named objects (able to name and recognize what he or she hears or feels) | Name an object he or she sees | Right homonymous hemianopia | Left occipital lobe |
Hemineglect (left) | Patient draws only the right half | Clock drawing | Inattention Left sensorimotor hemiparesis | Right inferior parietal lobe |
Topographagnosia | Patient is unable to identify familiar landmarks and buildings |
