Handling newborn monkeys alters later exploratory, cognitive, and social behaviors

Abstract

Touch is one of the first senses to develop and one of the earliest modalities for infant-caregiver communication. While studies have explored the benefits of infant touch in terms of physical health and growth, the effects of social touch on infant behavior are relatively unexplored. Here, we investigated the influence of neonatal handling on a variety of domains, including memory, novelty seeking, and social interest, in infant monkeys (Macaca mulatta; n=48) from 2 to 12 weeks of age. Neonates were randomly assigned to receive extra holding, with or without accompanying face-to-face interactions. Extra-handled infants, compared to standard-reared infants, exhibited less stress-related behavior and more locomotion around a novel environment, faster approach of novel objects, better working memory, and less fear towards a novel social partner. In sum, infants who received more tactile stimulation in the neonatal period subsequently demonstrated more advanced motor, social, and cognitive skills-particularly in contexts involving exploration of novelty-in the first three months of life. These data suggest that social touch may support behavioral development, offering promising possibilities for designing future early interventions, particularly for infants who are at heightened risk for social disorders.

Keywords: Communication; Development; Maternal sensitivity; Mother-infant; Neonate; Plasticity.

Fig. 1

The four tasks revealed effects of extra handling, with the extra handled infants exhibiting: (A) greater locomotion and (B) less self-mouthing in a novel environment at 2 weeks, (C) faster latencies to touch novel objects at 3 weeks, (D) better working memory at 6 weeks, and (E) less lipsmacking in response to a novel person at 12 weeks. Light gray bars reflect infants who received no additional handling (standard-reared). Blue bars reflect infants who received additional handling (handling only and face-to-face + handling groups combined). Across all tasks, standard-reared infants differed from each group of handled infants, *ps < 0.05, ^#p = 0.056. Error bars reflect standard error of the mean. Dashed line indicates chance (graph D). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)