love hormone

By Robyn McQuaid, Department of Neuroscience, Carleton University

You’ve heard of oxytocin, the ‘love hormone’, right? You know, it’s that chemical (hormone) released in our brain that makes us want to cuddle, and is released during sex? Maybe you’ve heard of it as the hormone that is released during breast feeding that helps enhance mother-infant bonding? In fact, this is what was first discovered about oxytocin – it is released in large quantities during suckling and labor (Carter, 1998; Van Tol, 1988). Recently, there has been a surge of interest in this hormone, making it particularly popular in research related to prosocial behaviors. This may be because it was discovered that oxytocin can be manipulated by administering it through a nasal spray, causing individuals to become more socially accommodating. For instance, just one administration of intranasal oxytocin causes individuals to display enhanced generosity (Zak et al., 2007), trust (Kosfeld et al., 2005) and empathy towards others (Domes et al., 2007; Shamay-Tsoory et al., 2013).

So then it’s settled, oxytocin really is a lovable ‘cuddle chemical’. Well, that would be just too simple! As it turns out there seems to be a darker side to this hormone. In fact, intranasal oxytocin administration also increased aggressive behaviors towards competing members from other groups (De Dreu et al., 2010). In a subgroup of individuals it was associated with aggression and violent behaviors towards a romantic partner (DeWall et al., 2014). And it has even been linked to increased lying to benefit one’s in-group members (De Deru et al., 2014). Rodent studies also support this notion as intranasal oxytocin promoted maternal aggression in response to an intruder (Jia et al., 2008). Furthermore, mice with increased oxytocin receptors (receptors are the place where oxytocin binds to have its effects) displayed elevated fear and anxiety in response to a negative social stressor (Guzmán et al., 2013).

rejectionThis is where our research comes in. Instead of manipulating oxytocin through nasal spray, we were interested in examining genetic variants of the oxytocin receptor gene (the gene that codes for oxytocin receptors). It had been suggested that having a particular oxytocin receptor genotype was associated with greater prosociality. We examined whether having this ‘prosocial’ oxytocin genotype would be beneficial to individuals who experienced adversity, such as childhood maltreatment. We had university students come into the lab where we collected their saliva and had them answer questionnaires. We determined oxytocin genotypes from their saliva samples and associated them to experiences of early-life maltreatment and depression scores. What we found was surprising! Individuals with the oxytocin genotype that had typically been viewed as ‘prosocial’ were more likely to experience higher depressive symptoms following childhood maltreatment. Once again, the oxytocin story is not so simple! Could it be that individuals carrying the more ‘prosocial’ genotype were more hurt and affected by the maltreatment? We suggested that individuals carrying the more prosocial oxytocin genotype might actually be more sensitive to their environments, and for better or worse, be affected by early-life experiences. In essence, these individuals may thrive in a positive environment. But, this same genotype may encourage susceptibility to poor outcomes in a negative environment (McQuaid et al., 2013).

We asked ourselves, is this effect specific to early-life adversity, or would it be found in other contexts/environments? Once again we had university students come into the lab and provide saliva samples, but this time we had them play an on-line computer game called Cyberball. Cyberball is a simulated ball-throwing game that induces social ostracism (Williams, 2000). Participants played a game of catch with two other co-players that they believed to be real, but were actually simulated. They either received the ball an equal number of times (they were in the included condition) or received the ball twice and then no longer (the excluded/ostracized condition). What we found was that individuals with that ‘prosocial’ oxytocin genotype, were more affected by ostracism, displaying lower levels of self-esteem and elevated blood pressure and cortisol (a stress hormone) levels following exclusion (McQuaid et al., 2015).

What does this all mean? Well for starters, calling oxytocin the ‘love hormone’ or the ‘cuddle chemical’ is a huge oversimplification! In fact, oxytocin may just be increasing the salience of social cues. So, yes, oxytocin can facilitate cuddling in the right circumstance, but if you are feeling socially rejected, oxytocin might only make this hurtful experience more painful. Given this, what good is oxytocin? Can or should it be offered as a potential treatment in clinical populations? Well, among healthy individuals, who presumably do not display social processing deficits, oxytocin administration could actually have adverse consequences rendering individuals overly sensitive within social situations (Cardoso et al., 2014). But for people with social deficits, such as individuals with autism spectrum disorders, intranasal oxytocin has been effective at improving social cognition (Hollander, 2007). So for now, let’s just say, the popular ‘cuddle chemical’ would be more accurately referred to as the ‘contextual-sensitive mood chemical’, but that doesn’t make for a sexy headline.

Based on:

McQuaid, R.J., McInnis, O.A., Stead, J.D., Matheson K., & Anisman, H. (2013). A paradoxical associated of an oxytocin receptor gene polymorphism: Early-life adversity and vulnerability to depression. Frontiers in Neuroscience, 7: 128.

McQuaid, R.J., McInnis, O.A., Matheson K., & Anisman, H. (2015). Distress of ostracism: Oxytocin receptor gene polymorphism confers sensitivity to social exclusion. Social Cognitive and Affective Neuroscience. [Epub ahead of print].

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