Smell facilitates auditory contagious yawning in stranger rats

Abstract

Most vertebrates yawn in situations ranging from relaxation to tension, but only humans and other primate species that show mental state attribution skills have been convincingly shown to display yawn contagion. Whether complex forms of empathy are necessary for yawn contagion to occur is still unclear. As empathy is a phylogenetically continuous trait, simple forms of empathy, such as emotional contagion, might be sufficient for non-primate species to show contagious yawning. In this study, we exposed pairs of male rats, which were selected for high yawning, with each other through a perforated wall and found that olfactory cues stimulated yawning, whereas visual cues inhibited it. Unexpectedly, cage-mate rats failed to show yawn contagion, although they did show correlated emotional reactivity. In contrast, stranger rats showed auditory contagious yawning and greater rates of smell-facilitated auditory contagious yawning, although they did not show correlated emotional reactivity. Strikingly, they did not show contagious yawning to rats from a low-yawning strain. These findings indicate that contagious yawning may be a widespread trait amongst vertebrates and that mechanisms other than empathy may be involved. We suggest that a communicatory function of yawning may be the mechanism responsible for yawn contagion in rats, as contagiousness was strain-specific and increased with olfactory cues, which are involved in mutual recognition.

Insights from social transmission of information in rodents

“…This shows that emotional contagion of pain in rodents can occur both without the immediate presence of a pained conspecific and without the observer themselves undergoing pain at the time of observation. Interestingly, Kavaliers et al and Langford et al were both able to establish that the socially induced hyperalgesia occurring in their respective studies was at least partially moderated by visual input. These results show that the social transfer of heightened pain reactivity may be induced through multiple sensory channels, not just through olfactory cues (as described in the previous section).…”

The roots of empathy: Through the lens of rodent models

“…The effect was observed uniformly among mammals. It was reported in humans (Gallup and Church, 2015; Platek et al, 2003; Provine et al, 1987), non-human primates (Campbell and de Waal, 2011, 2010), canines (Romero et al, 2014) and rodents (Moyaho et al, 2015) alike. Contagious yawning has been shown to have no respiratory function (Provine et al, 1987).…”

Experimental evidence of contagious yawning in budgerigars (Melopsittacus undulatus)

“…To date, experimental evidence of contagious yawning is restricted to humans (Homo sapiens; e.g., Provine 1986;Platek et al 2003), chimpanzees (Pan troglodytes) in response to conspecifics (Amici et al 2014;Anderson et al 2004;Campbell et al 2009;Campbell and de Waal 2011;Massen et al 2012) and human yawns (Campbell and de Waal 2014;; but see Amici et al 2014), domesticated dogs (Canis familiaris) in response to human yawns (Joly-Mascheroni et al 2008;Romero et al 2013;Silva et al 2012; but see Harr et al 2009;O'Hara and Reeve 2011;Buttner and Strasser 2014), and, most recently, a subline of high-frequency yawning Sprague-Dawley rats (Rattus norvegicus; Moyaho et al 2014). Video-induced yawning has also been reported in stumptail macaques (Macaca arctoides; Paukner and Anderson 2006), but this response also cooccurred with heightened self-directed behaviors and thus appears to be due to social tension or stress rather than contagion.…”