On Instagram, Dr. Sermed Mezher claims that becoming a father physically changes the brain. The idea is correct if we formulate it carefully: MRI studies suggest measurable changes in some new fathers, especially during first fatherhood.
What MRI observes in some new fathers
The English doctor influencer recalls that we often talk about the brain changes observed during and after pregnancy in mothers, but that fathers are not necessarily outside of this biological history. He explains in particular that the cortex, presented as a sort of processing unit of the brain, can decrease in volume in new fathers, but less markedly.
This is indeed one of the points found in recent work. A study published in Cerebral Cortex in 2024 suggests that the transition to fatherhood may be accompanied by
modest decreases in cortical volume in men becoming fathers for the first time. Another longitudinal study, published in 2023, goes in the same direction in two international samples.
But we must avoid the shortcut: fathers’ brains do not “shrink” in the sense of a global or worrying loss. Researchers talk about variations measured in brain imaging, in certain cortical areas, in specific groups. These changes are interpreted as indices of neuroplasticity, that is to say the brain’s ability to change with experience.
Another important nuance: this does not mean no overall loss of intellectual abilities. These studies describe average trends, not a test to tell what’s going on in a particular father’s brain.
The bond with the baby before birth: an association, not proof
The video also emphasizes a more surprising point: certain changes observed after birth seemed linked to a measurement collected before the baby’s arrival, namely the degree of prenatal bond felt with the fetus. This is an interesting result, but it should be read with caution.
In the 2024 study, stronger prenatal bonding was associated with greater cortical decreases. However,
association does not constitute causation : we cannot conclude that feeling very connected to the baby directly “causes” these brain changes. Other factors may be involved.
Dr Mezher also mentions the very concrete complications of the arrival of a newborn: lack of sleep, stress, change of pace… This reserve is essential. In the study, greater cortical decreases were also associated with more sleep disturbances, anxiety or depressive symptoms, and psychological distress.
In other words, these changes should not be presented as only positive, nor as proof that one father would be more invested than another. They could reflect both parental commitment, adaptation to a new role and a period of vulnerability. To extend this relational dimension without reducing it to the brain, we can also focus on one-on-one moments between a father and his baby.
Hormones, fatigue, commitment: what that doesn’t say about a father
The doctor also mentions hormonal changes, notably a drop in testosterone. Here again, careful formulation is required: the transition to fatherhood can also be accompanied of hormonal variations, observed in certain longitudinal studies, but their magnitude and temporality vary according to men and contexts.
What neuroscience shows above all is that fatherhood is not just a change in schedule. It can occur in the body and in the brain, like other major life transitions. The comparison with the transformation of the brain during pregnancy helps to understand this idea, provided that the mechanisms of mothers are not exactly copied from those of fathers.
The most useful point to remember is therefore simple:
no MRI says if a father is a “good parent”. Current studies mainly focus on first-time fathers, with modest numbers, and they do not make it possible to establish a rule valid for all.
Talking about fathers’ brains can help us recognize that the arrival of a baby also transforms men, sometimes profoundly. But this transformation is not only measured in cortical volume: it is also built in daily care, attention to the baby’s signals, the possible rest, the support received and the place left to the father in the first months.