Pavlov explained simultaneous agnosiaby saying the cells were "so weakened" that one excited point exerts an inhibitory effect on the other excited point, thus making it apparently nonexistent (Pavlov IP, Pavlov's Wednesday Clinics, vols 1-3, Izd. Akad. Nauk SSSR, Moscow and Leningrad, 1949 (Russian) as cited p. 123. Cites Pribham as saying defect is due to corticofugal projections to inferior temporal lobe.
Luria then took a subject affected with a bullet wound, injected caffeine 0.05 ml of 1 % solution, , with the result that the patient could see two and sometimes three objects for 30-40 minutes (as long as the caffeine lasted) and the visual ataxia disappeared.
Examination of the patient:
cf p.117
Patients obscure pictures. May require tachistoscope to bring out changes with brief exposures if mild case. Defect involves not only perception but also drawing.
Tests-- cannot place a dot in the center of a circle or a cross/ cannot draw a triangle around a triangle.
The "secondary zones" of the left occipital cortex differ from the right insofar as they "retain their intimate connection with speech" unlike the right. Lesions of the left cause an agnosia for letters or reading (optic alexia). In right hemisphere agnosia for objects or faces is more common.
Monday, February 23, 2009
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