Dad bod & dad brain: How a man's brain changes when he becomes a father

The bonding experience is promoted by important neurological changes.

The male brain undergoes some surprising changes when he becomes a father...

Photo by Halfpoint on Shutterstock
  • In the first days and weeks of fatherhood, a man's testosterone and cortisol levels decrease and oxytocin, estrogen, and prolactin levels surge, promoting an important bonding experience between a father and his newborn child.
  • One of the most significant changes scientists have observed in the brain of new-dad mice is neurogenesis (the process of new neurons being formed in the brain), directly linked to the time spent with their newborn pup in close proximity.
  • Human males also "bulk" their brains, with areas linked to attachment, nurturing and empathy showing increased gray and white matter.


What happens in a man’s brain when he becomes a father…

high contrast photo of man holding newborn baby fatherhood

There is a clear physical connection between a mother and her newborn - but what about fathers?

Photo by Natalia Lebedinskaia on Shutterstock

A man's entry into fatherhood isn't accompanied by the same hormonal, physical, and emotional changes that a woman experiences throughout pregnancy, childbirth, and motherhood...but the changes that happen in the male brain due to fatherhood are no less important.

In fact, researchers have recently been looking into the connection between a father and his newborn child, and there have been several studies that reveal a man's brain undergoes several changes in the first weeks of fatherhood.

High functioning in the "emotional processing" networks in the brain.

In a 2014 study, researchers compared brain activity in 89 new parents as they watched videos of their children. This study would examine the mothers (who were, in this case, the primary caregivers), fathers who worked outside the home but frequently helped with childcare, and homosexual fathers who raised a child without the help of a female.

In all three groups, the brain networks that are linked to emotional processing and social understanding were highly active. One of the most important notes from this study is that the fathers who raised a child without a female's assistance showed almost identical emotional processing signals in the brain that caregiver mothers did.

Testosterone decreases, estrogen increases, causing a surprising effect...

Psychologist Elizabeth Gould (and her colleagues from Princeton University) have conducted a series of studies that show there is an increase in estrogen, oxytocin, prolactin, and glucocorticoids in both animal and human fathers.

Several studies (including this 2001 study by the Department of Biology at Queen's University in Ontario) have shown the male testosterone (known as the male sex hormone) and cortisol (a stressor hormone) levels to dip in the first weeks of fatherhood.

While estrogen has been considered the female sex hormone, estradiol (the predominant form of estrogen) plays a key role in nurturing behaviors and male sexual function. When this form of estrogen is present in the male system, it promotes more nurturing behaviors in the father.

Prolactin (referred to as the "mom hormone", as it is used in the female system to promote lactation) also spikes in new fathers. According to a 2002 study, lowered testosterone levels and heightened prolactin levels in the male brain are associated with emotional responses to infant cries in new fathers.

Oxytocin spikes in new mothers, fathers, and babies - promoting bonding and empathy within the whole family unit.

Oxytocin, commonly known as "the love hormone", also surges in the male system after the birth of a child. This hormone surge has proven to promote bonding, empathy, and altruism in the new father.

This 2012 study where fathers who inhaled oxytocin (subsequently spiking the oxytocin levels in their bloodstream) proved that new fathers who experienced these changes in hormone levels were more engaging with their newborns.

The researchers also concluded that this spike in oxytocin also had an impact on the newborn as well—their oxytocin levels also spiked.

The brains of new-dad mice develop new neurons that help improve their memory and navigation systems

Conceptual illustration of neuron cells with glowing link knots neurogenesis fatherhood

Neurogenesis (the process of forming new neurons) occurs in the male brain in the first days of fatherhood...

Image by Rost9 on Shutterstock

One of the most significant changes scientists have observed in the brain of a new-dad mouse is neurogenesis (the process of new neurons being formed in the brain). The new neurons that are formed have been proved to be directly linked to the time spent with their newborn pup in close proximity.

In this 2010 study, neurogenesis took place in male mice in the first few days following the birth of their pups. However, this extra boost of brain cells only happened in the mice that stayed in the nest. Other male mice, who were removed on the day of their pup's birth, showed no new neuron changes.

When the researchers allowed the father to be close to the pups without physical contact (placing a mesh barrier between them), no additional neurons appeared, proving the father had to be physically present in the nest and interacting with his pups to experience neurogenesis. You can read more about this interesting experiment in Scientific American.

One of the new sets of brain cells formed were located in the "olfactory bulb", which is responsible for how we process different smells and odors, and these new neurons were specifically tuned into the smell of the mice's new pups.

Another of the new sets of brain cells grew in the hippocampus, which is the part of the limbic system in our brain that plays a role in memory and navigation.

Fatherhood also adds more gray and white matter to the areas of the brain that affect attachment.

A 2014 study conducted at the University of Denver by developmental neuroscientist Dr. Pilyoung Kim examined 16 new dads, once between the first 2-4 weeks of becoming a father and again between weeks 12-16.

This study revealed not only hormone changes, but physical changes to the male brain during the first months as a father. Certain areas (the parts of the brain that are linked to attachment, nurturing and empathy) showed more gray and white matter in the later tests.

This "bulking" of the brain, according to Dr. Kim, reflects a ramping up of parental skills in new fathers. "This anatomical change in the brain may support the fathers' gradual learning experience over a period of many months," says Dr. Kim.

It's incredible to know that in each new, attentive father's brain there is a special set of neurons that are dedicated to fatherhood and exist solely because of his child.

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Reactive oxygen species (ROS) accumulate in the gut of sleep-deprived fruit flies, one (left), seven (center) and ten (right) days without sleep.

Image source: Vaccaro et al, 2020/Harvard Medical School
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The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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