A ubiquitous model for monogamy and promiscuity is the vole model that compares the closely related montane voles, which do not form pair bonds and mate freely with many partners, and prairie voles which are innately monogamous. Research comparing the montane and prairie voles has identified both oxytocin (OT) and vasopressin (AVP) as playing a key role in these behaviors with prairie voles having more OT and AVP as well as increased receptor density for these hormones (Insel & Shapiro, 1992).  Vasopressin seems to play more of a role for male pair-bonding, while oxytocin is critical for female pair bonding (Carter et al., 1995).  Specific brain areas, such as the ventral pallidum, nucleus accumbens, medial amygdala, medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST) have been identified as critical areas that are differentiated between montane and prairie voles.  The most robust difference is seen in the large number of V1aR receptors in the ventral pallidum in prairie voles, while montane voles do not have these receptors. Researchers have also found that prairie voles have a much higher density of D2 dopamine receptors in the nucleus accumbens and other areas in the dopamine reward pathway (Edwards & Self, 2006).  Many of the areas identified as key dopamine receptor areas involved in bonding are also key areas for vasopressin receptor areas involved in bonding. Thus, in male prairie voles, there seems to be great overlap between reward and bonding.

We (Hamilton & Meston, 2017) examined whether it is possible that similar neural substrates underlie monogamy and non-monogamy in human males. In our study, we looked at differences in neural activation in response to sexual and romantic stimuli in monogamous and non-monogamous men. We found that monogamous men showed more reward-related neural activity when viewing romantic pictures compared to nonmonogamous men. There were no significant differences between groups in activation to sexual stimuli. Our findings demonstrate that the neural processing of romantic images is different for monogamous and non-monogamous men. There is some overlap in the neural areas showing increased activation in monogamous men in the present study and the neural areas that show differences in the vole models of monogamy and affiliation. 

Recommend paper: 

Hamilton, L. D., & Meston, C. M. (2017). Differences in neural response to romantic stimuli in monogamous and non-monogamous men. Archives of Sexual Behavior, 46(8), 2289-2299. PDF (749 KB)