Neonatal neurobehavioral correlates of lateral bias and affect in infant chimpanzees (Pan troglodytes)

In this study, I extend previous findings of population-level asymmetries in lateral bias of multiple behavioral measures in infant chimpanzees. Moreover, I propose that different neurobehavioral mechanisms are associated with different behavioral measures. A longitudinal design was employed to assess neonatal neurobehavioral integrity,lateral bias at 3 months old, and lateral bias and affect at 9 to 10 months old. Approximately half of the sample was raised under standard nursery conditions (females, n = 9; males, n = 11), and the other half was raised in a "responsive care" nursery designed to promote species-typical chimpanzee development (females, n = 9; males, n = 8). Significant right biases were confirmed for hand-to-mouth self-calming behavior. Significant left biases were found in grasping of objects (at 9-10 months old). Hand-to-hand grasping, reflexive stepping, head posture while sleeping in a supine position, and defensive swipes were individually lateralized rather than population level biased. Neonatal neurobehavioral assessments were found to be significantly associated with lateral bias both at 3 months and at 9 to 10 months old. Arousal at 2 days of age was negatively correlated with hand-to-mouth bias, motor performance at 2 days old was positively correlated with hand-to-hand bias, and orientation performance at 30 days of age was positively correlated with head bias. The lateral bias in touching and grasping objects at 9 to 10 months of age was positively correlated with head bias by 3 months of age and with State Regulation at 2 days of age. Affective behavior at 9 to 10 months old was correlated with defensive bias at 3 months and with muscle tone at 2 days of age. Rearing environment, gender, and emotional reactivity were found to influence lateral bias. These findings support the hypothesis that different asymmetric behaviors, even if lateralized to the same direction, may reflect different biological processes and different functional mechanisms.