Changes in tactile discrimination and in visual reaching after successive and simultaneous bilateral posterior parietal ablations in the monkey

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Abstract
Behavorial changes were studied in eight monkeys that experienced successive unilateral posterior parietal ablations and in 3 animals that received bilateral parietal ablations. In all cases, at least 2 systematic neurological examinations were given after each operation. One examination was a test of tactile discrimination and the other a test of visual reaching. Test reactions were absent or diminished in contralateral limbs following unilateral removals. Both tests were more impaired following contralateral than after ipsilateral removals. Test impairment following one-stage bilateral removals was no greater than that following unilateral right-sided removals. The findings show that defects of tactile shape discrimination and visual reaching associated with posterior parietal ablations in the monkey are predominantly crossed and a certain amount of independence exists between the hemispheres in controlling these activities. The disorder of reaching may also be related to a central loss of position sense.