Higher visual integration abnormalities, illusions and visual hallucinations

The function of the occipital lobe is to provide visual perception and integration of images with the rest of the brain. There are two fundamental pathways by which our brain interprets and manipulates visual scenes. One is the parietal-occipital dorsal pathway where the visual-spatial information is analyzed. The lesions in this area may cause pictures of simultagnosia, optic ataxia, ocular apraxia and akinetopsia. On the other hand, the temporal-occipital ventral pathway is responsible for recognizing objects and faces. Thus, the lesions may produce prosopagnosia, associative and aperceptive visual agnosia. Alterations in the identification of persons may be classified in hypo identification processes as in the Capgras syndrome in which the subject recognized is not felt to be a family member for the patient or they may suffer a hyperidentification phenomenon such as the Fregoli syndrome in which a subject is felt to be a family member of the patient. At times, these phenomena may cause intermetamorphopsia pictures. Visual hallucinations may be due to many causes that include phenomena of deafferentation, stroke, drugs and medications, migraine and neuro degenerative diseases. A correct serniological analysis of the higher visual abnormalities and its topographic site may be key pieces to know the etiology of the clinical picture.