How little we know about the neuroscience of fatherhood
Fathers caring for their children is the general rule across most vertebrates; almost all nonmammalian vertebrates use fathers as a prime caregiver. And yet, the world of neuroscience knows little about paternal care. This is partly because the males of our common laboratory species, the lab mouse and rat, are more likely to eat their young than show any special care for them. The resulting deficit in knowledge is obvious with any cursory look through a textbook on the neurobiology of parental behavior: after ten chapters detailing maternal behavior, there might be one perfunctory chapter detailing how little we know about paternal behavior. But here’s a cool fact I learned from one of those chapters: did you know that male Djungarian hamsters assist in delivering pups by tearing away the membranes just after birth. They play midwife!
It seems like the precise neural circuitry for maternal and paternal care are different; lesioning the amygdala decreases paternal care and increases maternal care. Likewise, many neurohormones that cause maternal behavior have little effect on males. But some of these pathways are likely to be the same. I’ll quickly discuss a paper which describes the influence of the neuropeptides prolactin and oxytocin on paternal care. Oxytocin is the ‘love hormone’ and strongly stimulates pair-bonding, influences social recognition, and has strong effects on general sociality. Although it is typically thought of as having a pro-social influence, the reality is a bit more complicated (of course!). Prolactin is a bit of a sex hormone, providing the body with sexual gratification after intercourse and counteracting the effects of testosterone, estrogen, and dopamine. It clearly has a stronger social effect as well or I wouldn’t be talking about it in relation to child-rearing!
In order to assess the relationship between these two neuropeptides and fatherhood, Gordon et al. first measured their concentration in fathers across time and found them to be fairly stable. When they compared the of these neuropeptides to the propensity of the fathers to play with their children, they found them to be strongly related. Each were associated with a specific paternal behavior: prolactin with facilitation of a child’s exploratory behavior and oxytocin with how much the fathers matched their facial emotions with that of their children. Since this is only a correlational study, we cannot say for sure whether or not these neuropeptides are directly causing these behaviors. However, these are similar to what are seen with maternal behaviors, allowing the researchers to compare their results to the richer maternal literature in the future. It will be interesting to see if future work can relate receptor variants for these neuropeptides to differences in paternal behavior. Perhaps we can get a genetics of daddyhood?
Gordon I, Zagoory-Sharon O, Leckman JF, & Feldman R (2010). Prolactin, Oxytocin, and the development of paternal behavior across the first six months of fatherhood. Hormones and behavior, 58 (3), 513-8 PMID: 20399783