The brain opioid theory of social attachment: a review of the evidence

Abstract

The psychology of close human relationships is increasingly well understood and our understanding of the neurobiology of the onset of pairbonding behaviour in a range of species has benefited from the use of rodent-based models. However, the human literature has suffered from a lack of focus upon the unique nature of primate social bonds and has so far failed to adequately identify the neurobiological and behavioural mechanisms which maintain these complex, diverse and enduring social networks. One neurobiological mechanism that has been overlooked is the endogenous opioid system. Though less explicitly researched than the more familiar oxytocin/vasopressin system, there is considerable evidence that the opioids play a fundamental role in sociality, especially in the primates. This review summarises our current understanding of the evidence for the role of this system in prosocial behaviour in non-primate mammals, nonhuman primates and humans. An important conclusion is that the opioid system may play a more central role in sociality in primates (including humans) than in other mammalian taxa.

Breaking Bread: the Functions of Social Eating

“…Both laughter (Manninen et al, submitted) and alcohol (Gianoulakis and Barcomb 1987;Gianoulakis 2004) are known to trigger the endorphin system, the principal psychopharmacological mechanism that underpins primate and human social bonding (Dunbar 2010;Machin and Dunbar 2011). Although the potential role of eating was not directly tested here other than in respect of chocolate consumption, endorphin activation is known to be associated with feeding behavior (Bakshi and Kelley 1993;Zhang and Kelley 2000;Fig.…”

“…In respect of the evening meal, they were also asked to say how many people were present (2, 3, 4 or 5+, including themselves) and, on a simple binary choice, whether or not any of the following had occurred during the meal: laughter, reminiscences, jokes, singing, dancing, party games, drinking alcohol or eating chocolate. Laughter, singing, dancing and storytellling are all known to trigger the endorphin system Pearce et al 2015;Tarr et al 2016;Dunbar et al 2016), the main pharmacological factor underpinning social bonding in primates and humans (Curley and Keverne 2005;Depue and Morrone-Strupinsky 2005;Machin and Dunbar 2011). Alcohol is also a major trigger of the endorphin system (Naber et al 1981;Van Ree 1996;Hertz 1997;Gianoulakis 2004) -so much so that an endorphin antagonist such as naltrexone is now the treatment of choice for alcohol addiction (O'Brien et al 1996;Saland et al 2008).…”

“…There is now considerable evidence, for example, to suggest that the size and quality of one's social network has very significant consequences for one's health, susceptibility to illness (and even death), wellbeing and happiness (Holtzman et al 2004;Min et al 2007;Rodriguez-Laso et al 2007;Fowler and Christakis 2008;Dominguez and Arford 2010;Pinquart and Duberstein 2010;Holt-Lunstad et al 2010;Liu and Newschaffer 2011;Chou et al 2012;Tilvis et al 2012;Oesch and Dunbar 2015). We also know that activities such as laughter, singing and dancing all lead to an enhanced sense of bonding towards those with whom one does these activities Pearce et al 2015;Tarr et al 2015Tarr et al , 2016Manninen et al, submitted), mainly because they trigger the endorphin system in the brain that underpins primate social bonding (Panksepp et al 1997;Curley and Keverne 2005;Dunbar 2010;Machin and Dunbar 2011). Since endorphins are involved in the control of feeding (Bakshi and Kelley 1993;Zhang and Kelley 2000;DiFeliceantonio et al 2012), the very fact of eating might itself trigger the endorphin system and promote bonding, and doing so socially may lead to the same kind of enhanced endorphin effects from behavioural synchrony that have been noted in physical exercise (Cohen et al 2010).…”

Group size, vocal grooming and the origins of language

“…With the progressive evolution of hominin community size to around 150 in modern humans (Gowlett, Gamble, & Dunbar, 2012), some novel means were necessary to allow time to be used more efficiently for social bonding so that larger groups could be evolved. In effect, it was necessary to find a way of triggering the same neuroendocrine mechanism that underpins bonding in primates (the endorphin system; Keverne, Martensz, & Tuite, 1989;Dunbar, 2010;Machin & Dunbar, 2011) to more individuals simultaneously (in effect, increasing the grooming group size).…”

The Complexity of Jokes Is Limited by Cognitive Constraints on Mentalizing

“…Machin and Dunbar 2011). In order to cause laughter, the best jokes are thought to build up a set of expectations in a listener and then use a punchline to update their knowledge in an unexpected way (Canestrari and Bianchi 2012;Forabosco 2008;Hurley et al 2011;Ramachandran 1998;Suls 1972).…”