As the father of 12-week-old twins, I was intrigued to see a new paper has been published looking at the brain changes associated with fatherhood. Before now, nearly all human research on the neural effects of parenting has been focused on mothers.

When you become a dad, it's like a plate has been set spinning in your brain (or two in my case) - suddenly, no matter where you are, or what you're doing, you have this restless vigilance for your fragile offspring. And then there's the time spent playing and feeding, when you're alert to every flicker of emotion on their little face, every tiny hiccup or cry. It would be incredible if these new responsibilities and ways of interacting didn't have a profound effect on the brain.

A team led by Pilyoung Kim at the Universities of Denver and Yale twice scanned the brains of 16 new fathers (average age 36; 7 were first-time dads). The first scan took place between 2 and 4 weeks after their babies were born; the second scan 12 to 16 weeks later. Previous research has shown functional changes in the brains of fathers, in the way that they show heightened neural activity in response to the sight of their own infants. However, this is the first time that researchers have documented structural changes in the brains of human fathers.

Comparing the later scan with the first scan, Kim's team found increased grey matter volume in several regions of the fathers' brains. This included areas previously identified as showing growth in new mothers, including the striatum (involved in reward processing, among other functions), hypothalamus (hormonal control), amygdala and anterior cingulate cortex (ACC; involved in emotional processing), and the lateral pre-frontal cortex (PFC; involved in memory and decision making). The PFC is one of the areas that has been associated with heightened activity when fathers view their own infants. Prior monkey research has also shown an increase in branching between neurons in the PFC of fathers.

What do all these brain volume increases mean? It's hard to know, but Kim et al point out that animal research implicates many of these neural regions as important for attachment and nurturing behaviors. The changes may also reflect the new and powerful salience of babies to their fathers. But which comes first - the baby salience or the brain changes?

The new research also uncovered several brain regions that appeared to shrink in early fatherhood. The regions displaying reduced grey matter volume included medial pre-frontal cortex, post-central sulcus, precuneus, and inferior parietal cortex, all of which are considered part of the "default mode network". This group of brain regions tends to become collectively more active as we switch off from the outside world. Kim and her colleagues speculated that the shrinking of these brain regions could reflect a "shift of resources" away from the default-mode network, in line with fathers' new vigilance for their precious offspring.

Other regions that showed reduced grey matter included the orbitofrontal cortex (OFC) and the left insula - these regions have previously been implicated in anxiety, and the researchers speculated that their shrinkage could reflect a diminishing of fathers' anxiety over the first few months of their infants' lives. Supporting this interpretation, fathers who were bolder in their physical play with their babies (based on analysis of five-minute play sessions), tended to have more accentuated OFC volume reduction.

Another strand to this research was to compare the fathers' brain changes with their levels of depression. It's only recently that psychologists have fully recognized that fathers, like mothers, are at risk of depression after their children are born. The data showed that greater volume increases in the striatum and ACC were associated with lower depression scores. However, none of the fathers in this study showed serious signs of depression so this result is fairly meaningless.

Hopefully you can tell from my choice of words that this research is only preliminary. The sample size is small, there was no control group, and with only structural data to go on, the researchers were left to surmise about the meaning of their results. We also have little idea about the duration of the observed brain changes. Nonetheless, I was pleased to see that neuroscientists are beginning to take an interest in the neurology of fatherhood. Psychology studies are increasingly showing the importance to children of having early positive interactions with their fathers, so it makes sense for neuroscience to catch up.

Well, the scientist in me is pleased to see this development, but actually I have to say the researchers' discussion about the possible future applications of their research left me feeling a little uncomfortable. Their hope is that future research combining structural and functional data will give them a better idea of the brain changes typically seen in a well-adjusted father who has formed a healthy attachment with his offspring. This information, they explained, could then be used to identify "distinct changes in the parental brain among at-risk fathers in order to construct more specific and early interventions." This conjured for me a creepy image of fathers having their brains scanned to see if they have suitably bonded to their babies. Certainly any developments along these lines would require a lot more research and have to be handled with extreme care. Imagine the potential hurt if a neural "mis-diagnosis" were made.