Nervous and mental diseases . the optic radiationsstreaming from the basal ganglia to the occipital cortex, hemianopsia is 176 DISEASES OF THE BRAIN PROPER. added. A lesion in the optic radiation within the white matter of theoccipital lobe may involve the connecting tracts between the half-visioncenters in the apex and the higher visual centers in the angular gyre,producing both hemianopsia and word-blindness. It thus appears thatword-blindness is due to disturbance of the angular gyre alone, and thatassociated hemianopsia is present only when the lesion implicates theoptic radiation (see Fig
Nervous and mental diseases . the optic radiationsstreaming from the basal ganglia to the occipital cortex, hemianopsia is 176 DISEASES OF THE BRAIN PROPER. added. A lesion in the optic radiation within the white matter of theoccipital lobe may involve the connecting tracts between the half-visioncenters in the apex and the higher visual centers in the angular gyre,producing both hemianopsia and word-blindness. It thus appears thatword-blindness is due to disturbance of the angular gyre alone, and thatassociated hemianopsia is present only when the lesion implicates theoptic radiation (see Fig. 75). The visual aphasic can see perfectly anything put before him, butwritten symbols, figures, and other conventional signs have entirely losttheir significance. That he sees them clearly is shown by the fact thathe can copy or draw them with as much precision as ever. Spontaneouswriting, however, is lacking. Not being able to call up the visualimages of written speech, he is unable to exteriorize them through the Fig. 75.—A lesion (X) divides the optic radiations within the occipital lobe, producing hemianopsia andword-blindness at once (Dejerine). motor writing apparatus, excepting in the case of some automatic com-binations, such as his signature. For similar reasons he can not writefrom dictation. The hemianopsic cases, however, write spontaneously andfrom dictation with ordinary facility, as in these cases the visual wordmemories are not necessarily destroyed, but only cut off from the lowerhalf-vision cortex in the occipital apex. They are unable, however, toread what they have written. Spoken language is both understood andexpressed with complete readiness. When familiar objects are not rec-ognized, mind-blindness is present and the lesion is probably appears that ordinary visual sensations, as sensation in general, aresymmetrically represented. The educated faculty of visual word mem-ories is represented in the left angular gyre alone. Graphic
Size: 1711px × 1460px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., booka, bookcentury1900, bookdecade1900, bookidnervousmentald00chu
