Evidence of Physiological Comodulation During Human-Animal Interaction: A Systematic Review

This review examines the evidence in the literature for physiological co-modulation during human-animal interaction, identifying studies that assessed comodulation via simultaneous measurement of physiological signals in both species, performing quantitative comparisons. We searched (last search: August 5, 2025) PubMed, EMBASE, Scopus, Google Scholar, Animal Studies Repository, Cochrane, and the Consensus App academic search engine. Risk of bias was assessed using an adapted version of the ROBINS-I V2 tool. The results, grouped by data analysis method, interaction context, and physiological parameter, were synthesized narratively in structured tables. Thirty-seven studies were included, focusing on dogs (n = 22) and horses (n = 15), framed primarily within the interaction contexts of animal-assisted therapy/intervention and companionship. Cardiac and hormonal measures were most frequently assessed. Most studies (n = 20) performed correlation analyses. Sample sizes ranged from $\le$ 10 to $\ge$ 130 dyads. Comodulation was significant in 16 studies, partial in 16, and absent in 5. Time-series coupling methods yielded more consistent evidence than discrete-time correlations. Evidence, while not conclusive, supports physiological comodulation during human-animal interactions. However, the studies' heterogeneity limits generalizability; findings suggest comodulation may emerge under specific biological and methodological conditions, and future research should explicitly test its presence across contexts.