The latest on daddy brains

From The Economist, Aug 24th 2006


Fatherhood alters the structure of your brain—if you are a marmoset


PARENTING has obvious effects on mothers, but fathers appear to be affected, too. A study published this week shows that fatherhood increases the nerve connections in the region of the brain that controls goal-driven behaviour—at least, it does in marmosets.

Pregnancy and motherhood have long been known to bring about changes—many of them positive—to the female brain. Pregnant and nursing rats have a greater number of neural connections, particularly in the region of the brain that controls hormones and maternal behaviour. The brain changes coincide with improvements in spatial memory and speedier foraging skills, which might help a mother rat protect and feed her young.




Just what effect parenting might have on the brains of fathers has remained an open question, however. Male rats sometimes eat their young rather than nurture them, which makes them a poor model for studying how fatherhood affects the brains of species that frown on infanticide. Marmoset fathers on the other hand are a model of paternal devotion. They carry their babies for more than half the time during the offspring's first three months, passing them to the mother only when the babies need to be fed.

Elizabeth Gould of Princeton University and her colleagues compared the brains of marmoset fathers with those of males that lived in mated pairs, but lacked offspring. They found substantial differences. The nerve cells in the prefrontal cortex of fathers had more tiny projections, known as dendritic spines, than those of non-fathers. Because dendritic spines are the sites of connection between neighbouring nerve cells, the increased number may mean more activity in the fathers' brains than in those of the non-fathers. The nerve cells in the prefrontal cortex of the fathers also contained more receptors for vasopressin, a small peptide that influences social behaviour and pair-bonding.

The researchers also showed that, as the offspring aged and fathers became detached from them, the abundance of vasopressin receptors fell. This suggests that the parental behaviour is associated with the changes in the brain. The work is published this week in Nature Neuroscience.

What does this mean for human fathers? It is hard to tell. The attention of marmoset fathers makes them an extreme example of fatherhood. Human fathers do not usually get involved to anything like the same extent. That said, the scientists looked at the marmoset's prefrontal cortex because earlier studies had shown that activity in the prefrontal cortex of human parents—male and female alike—increases when they see their own offspring. Thus the same brain region is active in parenting in both species.

Craig Kinsley of the University of Richmond, Virginia, who did the work with rat mothers, speculates that Dr Gould's new findings may reflect human behaviour quite closely. “There is a lot of interest in the idea that having children forces responsibility on males in many respects. If you consider that the prefrontal cortex plays a major role in planning, judgment and the anticipation of the consequences of behaviour, you could make a clear argument that the changes in that part of the brain would be involved with judicious attention toward offspring.”