Last May, I took a trip to San Diego for my brother-in-law’s graduation from college, and to meet his 4-month old son, Landon, for the first time. Throughout the weekend, I couldn’t suppress my inner science nerd, and often found myself probing my nephew’s foot reflexes. Pressured from my wife’s disapproving looks and the blank stares I received from her family as I explained why his toes curled this way or that, I dropped the shop-talk in favor of baby-talk.

Having spent my postdoctoral career in neuroscience, brain development is particularly fascinating to me. But on this family visit, more striking than the baby’s neurodevelopment was the re-development of my 26-year-old brother-in-law.

In just a few months’ time, Jack went from my wife’s little brother to a hands-on, first-time father. When I first met Jack, he was a tall, lanky, wet-behind-the-ears nineteen-year-old kid, who enlisted in the U.S. Navy right after graduating high school. As a two-tour Iraq war veteran, Jack saw more of the world in six years than most of us ever will, and had a large repertoire of crazy sailor stories to boot.

Still, raising Landon will no doubt be the biggest challenge Jack’s ever faced. Whether he knows it or not, and whether he likes it or not, things are about to drastically change for him. By the end of the weekend trip, I saw glimpses that Jack had come to terms (well, sort of) with the fact that his life will never be the same: After struggling with securing Landon’s car seat in the back of his souped-up Mazda RX-8 for several weeks, Jack finally broke down and traded it in for a more sensible car that will make it easier to transport the little guy.

The birth of a child is arguably the most important event in parents’ lives. It’s fairly easy to wrap our heads around the notion of the mother-child bond. The two are intimately connected during the nine months of pregnancy. Hormones, such as oxytocin, that course through a mother’s body biologically link her to the baby. Their heartbeats can even synchronize. Following birth, a mother provides a natural food source for the newborn. In stark contrast, we know very little about the biology of the father-child bond.

After conception, men aren't exactly needed to keep their child alive. They don't gestate or lactate. Yet research shows that the father-child bond is crucial to a kid’s future success. If a father leaves his offspring to be raised solely by their mother, the children are more likely to suffer emotional troubles, be aggressive, experience addiction issues, or have run-ins with the law.

Since there's no clear physical connection between a father and his child -- at least not like the one seen with mom and baby -- researchers are starting to look deep in the brain for better clues to understand the power of this relationship. A recent wave of studies are starting to bear fruit: We are now learning that in the first few days after birth, changes occur in the brains of both the dad and the baby, depending on whether the father is around or not. Perhaps neuroscientists have finally cornered the elusive father-child bond, and found the b iological hook that makes sure a father sticks around after birth.

Brains are not static, and neurons constantly rewire themselves throughout life. Not only do brain cells alter their connections, but additional neurons can also spontaneously form, a process called neurogenesis. While the mechanism of neurogenesis is not fully understood, extra brain cell growth is strongly correlated to learning new things.

A recent study has shown that neurogenesis took place in male mice in the days following the birth of their pups. But the extra boost of brain cells only occurred if the mouse father stayed in the nest. In other words, if he was removed on the day of their birth, nothing happened. One new set of brain cells formed in the olfactory bulb, and were specifically tuned to the smells of his pups. Another set of neurons grew in the hippocampus, a crucial memory center in the brain, which helped to consolidate the smell of his pups into a long-term memory.

In mammals, neurons located in the nose detect scents using special odor receptors, and shuttle the information to the olfactory bulb, which is the integration center for smell. Yet smelling his pups alone was not enough to cause new neurons to form. When the researchers separated the father from his pups by placing a mesh screen between them in the cage, no additional brain cells appeared. The father had to be physically present in the nest in the early postnatal days to get another dose of neurons. The physical contact he had with his pups in the nest coupled with the smells of his young are what made the neurons grow.

The brain cells that formed when a father interacted with his offspring were also regulated by a hormone called prolactin. This means that the same hormone responsible for milk production in the breasts of new mothers also seems to be involved in fostering the postnatal connection between a father and his offspring. Mouse fathers that had the prolactin gene turned off did not form any offspring-specific brain cells.

Being separated for a few weeks time is usually long enough for adult mice to forget their cage mate pals. But these new neurons helped to form long-term memories and bonds, as the mouse fathers easily recognized their offspring by smell even after they had been separated for a long period of time.

While it appears the seed of the father-child bond is planted by supplemental neurons in a new dad, it seems a child, on the other hand, may be born with a brain that expects this bond to form in the first place.

To prove this, a few recent studies turned to a rodent that employs a remarkably familiar nest structure. Degu rats are biparental animals, which means parenting duties are split between the mothers and father. Degu fathers behave just like human fathers. They spend the early days of their pups’ lives helping with basic care, like warming and grooming. And as the pups get older, the degu fathers begin actively playing with their toddler offspring.

Researchers reasoned that absent fathers in the degu nests would create a true social and emotional void for the offspring, just as a missing dad would impact the dynamic of a human family. They found that if a rodent father remained in the nest with his pups – presumably due to the newfound bond with his offspring – his babies’ brains developed normally. But if the father was removed from the nest shortly after the birth of his pups, his newborns’ brains started to break down at the level of synapses, which are short chemical junctions in the brain that allow brain cells to communicate with each other.

Specifically, the degu pups raised without fathers had fewer synapses in both the orbitofrontal cortex and the somatosensory cortex. Having fewer synapses can alter the way information is processed in the young animals, and would make these brain areas perform abnormally.

The orbitofrontal cortex is a part of the prefrontal cortex that regulates decision-making, reward, and emotion. Extrapolating from the degu rat experiments, faulty synapses and processing problems in this locale may ultimately explain why we see some kids who grow up without a father in their life wrestle with (sometimes very serious) behavior problems.

These rat studies square with what we already know about the role of touch in neurological development. Having spent the prior weeks with the senses deprived while afloat in amniotic fluid, a newborn animal's somatosensory cortex is ripe for change. But instead of flourishing in the early postnatal days, the synapses of the somatosensory cortex wither away when degus are raised without a father. As a consequence, the newborns may not process touch as well as they should, which could lead to a number of other developmental problems, like metabolism issues or irregular hormone production.

These animal studies show that a father's brain is significantly and beautifully intertwined with his offspring's. For whatever reasons, be they biological, evolutional, or societal, the onus of human parenthood has traditionally fallen on the mother. But the evidence is showing that a father has direct influence on his child's neurodevelopment – and indeed, his brain can benefit as well.

Perhaps my nephew, bolstered by a healthy set of brain connections, formed in response to something as simple as Jack's touch, may already have the required tools to meet with behavioral and emotional challenges as he gets older. And while I can't exactly probe Jack's brain to see if he's sprouting neurons, I noticed an undeniable change in his focus, as his new bond took hold. Small movements and sounds from Landon that went unnoticed by most mysteriously caught Jack’s attention. It’s comforting to think that, in some way, there’s a small set of neurons tucked away in Jack’s head solely dedicated to his son.

Are you a scientist? Have you recently read a peer-reviewed paper that you want to write about? Then contact Mind Matters co-editor Gareth Cook, a Pulitzer prize–winning journalist at the Boston Globe, where he edits the Sunday Ideas section. He can be reached at garethideas AT gmail.com