Love and Bonding

Prairie voles, oxytocin and vasopressin, the reward circuitry of romantic love, parental bonding and heartbreak: what neuroscience has learned about attachment — and where the 'love hormone' story goes too far.

The faithful vole

Prairie voles are small rodents that typically form lasting pair bonds, share nest-building and raise young together. Their close relatives, montane voles, are promiscuous and less parental. Research by Thomas Insel, Larry Young, Sue Carter and others found a key difference: prairie voles have many more receptors for oxytocin and vasopressin in reward-related regions, such as the nucleus accumbens and ventral pallidum. Blocking these receptors prevents pair bonds forming; in one 2004 study, increasing vasopressin receptors in the ventral pallidum of male meadow voles (another promiscuous species) made them prefer a single partner. Bonding seems to emerge when social hormones and dopamine reward signals coincide.

Romantic love in human brains

In 2000 Andreas Bartels and Semir Zeki in London scanned people looking at photos of partners they were deeply in love with, and in 2005 Helen Fisher, Arthur Aron, Lucy Brown and colleagues scanned people in the early stages of intense romantic love. Both found activation in dopamine-rich reward regions, including the ventral tegmental area and caudate nucleus, and reduced activity in some areas tied to critical social judgement. Romantic love, they argued, behaves like a powerful motivation system. Studies of people recently rejected found activity in reward and craving regions too — consistent with heartbreak feeling like withdrawal.

Parental bonding

Oxytocin is released during childbirth and breastfeeding, and parenting changes the brain: studies of new mothers and fathers show increased responsiveness to infant cues. Caregiving fathers also show brain and hormonal changes.

The "love hormone" myth

Oxytocin was widely marketed as the "love" or "trust hormone" after a 2005 study found that nasal oxytocin increased trust in an economic game. Later, larger studies often failed to replicate effects of nasal oxytocin, and oxytocin can also increase favouritism toward one's own group and defensive aggression. It seems to increase the salience of social information, for better or worse — not to make people simply nicer.