A new research indicates that we are pre-programmed as social organisms very early on, weeks prior to our expected age of engaging in social encounters. The role of the deeper brain structures in social engagement has been recently shown in phylogenetic ancestral organisms, such as larval fish, but no direct evidence for the involvement of the brainstem in social engagement has yet been presented in humans.
To further understand the evolutionary pathway of humans as social beings, in this study, Dr. Ronny Geva and colleagues at The Gonda Brain Research Center, Department of Psychology, Bar Ilan University, Israel investigated the role of brainstem functioning on social engagement in human infants. The brainstem is the lower part of the brain where it connects to the spinal cord and to higher brain networks.
"It is fascinating to realize that our social engagement skills are enabled by structures that we share with so many organisms on the planet, and that each fetus carries a pre-program endowed to us through phylogeny to take an active role in the community," said Dr Geva.
The results of the study were recently published in the Journal of Social Cognitive and Affective Neuroscience.
In this longitudinal study, the researchers evaluated the efficiency of neonatal brainstem functioning in 125 healthy neonates that were born preterm, by using an electrophysiological test that measures the auditory brainstem evoked responses. This test was conducted before 35 weeks gestational age. The infants were followed up at four months of age, at which time they were tested in a set of structured vignettes that required varying levels of social engagement. At the time of the social engagement assessment, the infants' cardiac responses and their gaze behavior were recorded.
Time to disengagement as a function of social load and brainstem integrity.
NBSF, Normal brainstem functions; CBSF, Compromised brainstem functions. Image credit: Dr Ronny Geva,Soc Cogn Affect Neurosci
The data show that neonates who were diagnosed with a disrupted brainstem evoked response, evidenced by a delay in signal transmission rate through the brainstem, have a harder time engaging in a typical face to face interaction with an adult. They exhibit shorter latencies to avert their gaze in episodes involving direct face-to-face interactions, but they engage their gaze as effectively as the control group when interacting with masked agents or agents whose faces are partly veiled by toys.
Further analysis showed that their difficulty is related to the effect of the abnormality detected early on in the brainstem and that the effect was particularly strong in infant's whose weight-at-birth was less than expected for their age. The effect was not related to maternal stress levels or the infant's pattern of cardiac rate regulation.
These data support the notion that the integrity of brainstem transmission of sensory information during the final weeks of gestation may scaffold the development of social disengagement in humans, thereby attesting to the brainstem's preserved evolutionary role in developing humans. The results indicate that we are pre-programmed as social organisms very early on, weeks prior to our expected age of engaging in social encounters.
"This study is my long-awaited answer to the wise Sir Isaiah Berlin who asked me the question in 1989: "How can the social- role of the brainstem be studied in humans?" Well, Sir Berlin, we may have found a way," Dr Geva added.
The study offers a possible avenue to allow for targeting of infants who are at risk for social gaze aversion using neonatal auditory brainstem evoked responses at 35 weeks gestation. This particular age, which is earlier than routine auditory screens, may be a sensitive period for brainstem scaffolding of the social engagement network.
This research was funded by the Israel Science Foundation grant #1518 awarded to Ronny Geva.
Neonatal brainstem dysfunction risks infant social engagement. Geva R, Sopher K, Kurtzman L, Galili G, Feldman R, Kuint J. Soc Cogn Affect Neurosci. 2011 Dec 5. doi:10.1093/scan/nsr082 [Free Access]