Abstract
The previously-described differences in CAR and CER acquisition during the neonatal period related to mode of delivery persist for at least 3 mo. thereafter providing the infant is first given the conditioning experience during the neonatal period. In the present study groups of rhesus monkeys, half delivered by cesarean section and half delivered vaginally, were tested at monthly intervals starting on Day 1 or Day 31. The striking differences characteristic of the conditioning performances at birth were greatly reduced at Day 31 in those groups first observed at that age. Although the age-at-introduction × mode-of-delivery interaction was impressive, a convincing basis for interpretation is not apparent. Activity and vocalization levels could not be related to these conditioning performances.