Vasopressin enhances human preemptive strike in both males and females

Abstract

The neuropeptide arginine vasopressin (AVP), which is known to modulate a wide range of social behaviors in animals, has been identified as a modulator of various negative responses to social stimuli in humans. However, behavioral evidence directly supporting its involvement in human defensive aggression has been rare. We investigated the effect of intranasal AVP on defensive aggression in a laboratory experiment, using an incentivized economic game called the “preemptive strike game” (PSG). Participants played PSG individually (1 on 1) as well as in pairs (2 on 2) under either AVP or saline. We observed that exogenous but not basal AVP modulated the attack rate in PSG for both male and female participants. A model-based analysis of the aggregation of individual attack preferences into pair decisions revealed that the AVP effect on defensive aggression occurred mainly at the individual level and was not amplified at the pair level. Overall, these results present the first evidence that intranasal AVP promotes human defensive aggression for both males and females in a bilateral situation where each party can potentially damage the resources of the other party. These findings also parallel accumulating evidence from non-human animals concerning AVP’s involvement in territorial defense against potential intruders.

Conjecturing harmful intent and preemptive strike in paranoia

“…The reason why we could only detect a weak effect might be because of the relatively smaller baseline of attacking in comparison to those outlined in the previous studies (e.g., Halevy, 2017;Jind et al, 2017;Mifune et al, 2016, Simunovic et al, 2013. However, the rate of attack in this study was similar to those reported in several works (e.g., Kawada et al, 2019;Mifune et al, 2017). The diversity of experimental settings in these studies, such as stake sizes, experimental interface (i.e., laboratory or online), samples (i.e., university students or MTurk), sample sizes, and experimental manipulations, may have generated differences in the attack rate.…”

“…Participants might retroactively specify the reason behind their action as the action they had already performed. Third, as described in the introduction, previous studies have consistently provided empirical evidence that attacking in the PSG occurs as fear-based defensive aggression rather than an offensive one (Halevy, 2017;Kawada et al, 2019;Simunovic et al, 2013). For instance, Simunovic et al (2013) compared the rate of attack in the PSG between a condition wherein both players had an option to attack (i.e., "bilateral condition") and another wherein only one could attack their opponent unilaterally (i.e., "unilateral condition").…”

“…This research also proposes evidence that paranoia functions as self-defense against a perceived social threat. There is room for the present study to be enhanced; for instance, the PSG should be implemented in intergroup or individual versus group conflict situations (Jing et al, 2017;Kawada et al, 2019;Mifune et al, 2016). Further experimental studies with nonclinical groups would bolster understanding about normal psychological mechanisms of paranoia as an adaptive response to external threats.…”

“…Others exemplify that subjective perception of threats posed by outgroups (Jing et al, 2017) and the risk of being attacked (Halevy, 2017) facilitate attacks more in the PSG. An interconnection between attacking in the PSG and arginine vasopressin, a hormone in animals known for defensive aggression against intruders, has also been reported (Kawada et al, 2019).…”

“…Nonetheless, people presuming the irrationality or harmful intent of the opponent may engage in the attack preemptively. Previous studies provide empirical evidence to support this prediction as a substantial proportion of participants chose to attack in the PSG (Halevy, 2017;Jing et al, 2017;Kawada et al, 2019;Mifune, Hizen, Kamijo, & Okano, 2016;Mifune, Simunovic, & Yamagishi, 2017;Simunovic et al, 2013). Several papers indicate that the attacks in the PSG are primally triggered by fear rather than spite (i.e., preference for reducing the other's payoffs even though it is costly).…”