Many primates including monkeys live in highly developed social environments and interact via communication with one another in social groups. These social behaviors displayed are shown through both friendly affiliative and aggressive/submissive agonistic ways. Yet at the same time, individual monkey behavior can vary tremendously from group behavior based on the environment in which the individuals are raised and the interactions that they have with other individuals in that particular raised environment. In particular, the interactions between mother and child during a critical developmental period when the C-tactile (CT) nerve fibers are developing have been linked to the social development of the child based on greater activity and connectivity strength in social brain regions, and increases in the child’s attention to and learning of faces. Researchers such as Elizabeth A Simpson and her colleagues theorized that CT touch may prime children for social interactions and set them on a path towards healthy social cognitive development. CT nerves are triggered by the slow and gentle stroking of an infant and prime the brain in a way that reduces the stress and increases the eye contact, smiling, and positive vocalizations of infants. However, little is known about the effects of touch on young infants’ psychological development in the newborn period (a highly sensitive period of transition with rapid growth in sensory and social processing) and it remains untested whether newborns can distinguish CT-targeted touch from other types of touch, or whether there are benefits of touch for newborns’ social, emotional, or cognitive development. 

Elizabeth’s team seeks to answer these questions with the experimentation of infant Rhesus macaques monkeys which share complex mother-infant interactions similar to humans and have frequent body contact from their mothers during the first weeks of life. They took 27 infant monkeys (16 males and 11 females) between the age of 7 to 15 days old for the experiment, in which all monkeys were separated from their mothers at their birth and stayed in nursing homes till the experiment occurred in order for standardization to take place. The 27 infants participated in three 5-minute counter-balanced caregiver interactions (each on a different day from one another), all with mutual gaze between the monkey and the researcher: stroking head and shoulders (CT-targeted touch), stroking palms of hands and soles of feet (Non-CT touch), or no stroking (No-touch). After the stroking interactions, infants watched social and nonsocial videos and picture arrays including faces and objects, while researchers tracked their visual attention with remote eye tracking. This was repeated 3 times total, one for each day to see the difference in targeted touch and infant behavior towards the presented stimulus afterward. Researchers were interested in infant behavior such as stress-related behavior, the orientation of the infants towards a stimulus: in this case the videos and picture arrays (attentional orienting system), and the specific stimulus in which the infant orientated itself towards (positive or negative stimulus).

Using the data of the 27 infant monkeys over the three days of experimentation researchers were able to collect enough to make a conclusion about infant interaction in relation to cognitive and behavioral development of infant monkeys. During the caregiver interactions, infants behaved differently while being touched compared to the no-touch condition, regardless if it was CT touch or a non-CT touch of the body parts. In both touch conditions, infants exhibited fewer stress-related behaviors such as self-scratching, locomotion (agitated movement), and contact time with a comfort object vs when they were not touched. Researchers concluded that these stress-related behaviors were a cause of anxiety due to the lack of interaction (touch) between the caregiver towards the infant. Another result was that following CT-targeted touch, infants were faster to orient to the picture arrays compared to the other interaction conditions which suggest that CT-targeted touch activates/primes infants’ attentional orienting system better than non-CT-targeted touch and no-touch treatments. In regards to the videos and pictures in which the infants associated themselves with and focused on, the no-touch condition infants attended longer to the nonsocial compared to the social video which correlates to a reflecting baseline preference for nonsocial stimuli when placed in a nonsocial condition (lack of touch). Meanwhile, in both touch conditions (CT and Non-CT touch), infants’ looked equally to the social and nonsocial videos. These results to the types of videos watched suggest that touch influences the types of visual stimuli that hold infants’ attention (and more strongly in regardless of the nonsocial lack of touch condition vs the social touch condition), where lack of touch is highly associated with nonsocial videos while touch is associated with both social and nonsocial videos. 

These results drive the conclusion that social interaction at infancy, leads to the development of infant’s behavioral as well cognitive conditioning and priming which influences their individualistic perception and interaction with the world around them and themselves on the basis of how they were raised and treated during their development phase. Specifically in regards to newborn touch promoting infants’ psychological development, and highlighting that touch positively affects the emotional and attentional development as early as the newborn period for primates.

References

Elizabeth, A., Sarah, E., Robert, J. et al. Social touch alters newborn monkey behavior. Elsevier (2019).

https://doi.org/10.1016/j.infbeh.2019.101368