Mens brains shrink after birth of first child: Researchers

The scans showed that men lost on average 1 - 2% of their cortical brain, as well as the visual system’s volume, after the birth of their first-born. The cortical part of the brain is believed to be responsible for parental acceptance and warmth.
The reduction in gray matter, however, does not necessarily means that men become incapable of using either of the two parts. This process, dubbed as "synaptic pruning", suggests deconstruction of some of the existing neural connections in favor of the active creation of new ones that are acutely needed – such as some basic parenting skills and attachment to the first-born.
Such changes to the brain explain some previous studies, including ones suggesting that males may also suffer from postpartum depression to some extent, just as many women do. The findings also correlate with the 2020 study that showed fathers performing better in visual memory tasks than childless men – presumably due to sustaining changes to their brain's visual system.
Women also undergo changes to their brains upon conception and not all of them are related to the hormonal changes in their bodies. The studies into grey matter shifts suggest that some of the postpartum phenomenon often experienced by women, such as depression, mood swings, and forgetfulness, may be explained by the changes to their brain structure.
The changes to men's brains are more subtle but also are far less studied than those experienced by females.

Men's brains shrink after birth of first child: Researchers