physiology and social tolerancE
Increasingly we hear calls in the United States and across the world for greater expression of kindness and understanding in the face of diversity and difference. But over phylogeny, social difference has predominately triggered fight or flight. Indeed, like other primates, humans are aggressively territorial and conspecific violence has been a basic threat to fitness up to the present. Who, then, successfully meets the call for social tolerance? We study one answer to this question, appealing to the concept of cardiovascular control: Some primates including humans possess a vagal system that provides uniquely sensitive parasympathetic regulation of arousal. When the social environment is deemed safe, vagal activation “brakes” the influence of the sympathetic nervous system on the heart and reduces activity of the hypothalamic-pituitary-adrenal axis. This fosters a state of calm that is necessary for engaging in social interaction. The brake is lifted when the social environment is deemed threatening. This produces mobilization of the metabolic resources required to take action such as fight or flight. The human cardiovascular may therefore support humans’ ultrasociality. But there are individual differences: Degree of vagal control is indicated by heart rate variability, a measure of beat-to-beat temporal changes in the heart rate. High frequency heart-rate variability (HF-HRV) in particular represents a rhythmic fluctuation of the heart rate in the respiratory frequency band.
Our work tests the possibility that HF-HRV is an index of social tolerance. We use social challenges such as direct eye contact and physical contact, to test the prediction that compared to those with low HF-HRV, individuals with high HF-HRV maintain lower arousal when faced with such challenges in safe environments. We also test the culture-level prediction that individuals who live in societies with high ancestral diversity on average have higher HF-HRV and examine why this might be so.
REPRESENTATIVE PUBLICATIONS
Harrod, E. G., Shrira, I., Martin, J. D., & Niedenthal, P. M. (2023). Living in ancestrally diverse states of the United States is associated with greater vagal tone. Frontiers in Psychology, 13, 1068456.
Harrod, E. G., Coe, C. L., & Niedenthal, P. M. (2020). Social structure predicts eye contact tolerance in nonhuman primates: evidence from a crowd-sourcing approach. Scientific Reports, 10(1), 1-9.
Martin, J. D., Abercrombie, H. C., Gilboa-Schechtman, E., & Niedenthal, P. M. (2018). Functionally distinct smiles elicit different physiological responses in an evaluative context. Scientific Reports, 8(1), 3558.