NEUROLOGICAL AND BEHAVIORAL-EFFECTS OF A UNILATERAL FRONTAL CORTICAL LESION IN FETAL KITTENS .2. VISUAL-SYSTEM TESTS, AND PROPOSING AN OPTIMAL DEVELOPMENTAL PERIOD FOR LESION EFFECTS

Nine fetal kittens sustained removal of the left frontal cortex during the last third of gestation (E 43-55) and were compared to animals su staining a similar lesion postnatally (P 8-14) as well as to intact li ttermates. Beginning after 6 months of age, the animals' visual field and depth perception were assessed. In addition, pupil size as well as eye alignment were measured. On two visual field tests the fetal-lesi oned cats showed test dependent decrements for some angles of vision. In terms of depth perception, only the prenatal-lesioned animals showe d a higher binocular threshold; they also showed ocular misalignment w hich may have contributed to their depth perception impairment. Moreov er,these animals had a larger ipsilateral pupil. The neonatal-lesioned animals were like normal cats for all tests and measurements. We conc lude that, as for the tests reported in the preceding paper, the outco me for visual related behaviors of a prenatal frontal cortical lesion in the cat is also worse than that of a similar lesion sustained neona tally. Dysgenetic anatomical changes of the visual system induced indi rectly by the frontal lesion are proposed as a possible explanation fo r these age-at-lesion differences. Based on the present work as well a s on the literature, we propose the existence of an ''optimal developm ental period'' for the best behavioral and anatomical outcome of perin atal brain lesions. We argue that this concept fits contemporary data and can better explain the different age-at-lesion effects of brain in jury across animals species than the ''Kennard Principle'' (or ''infan t-lesion effect'').