A new study published in Behavioral Neuroscience suggests that giving birth causes the brains of mothers to grow in certain areas. The study compared brain size soon after birth with brain size months later and concluded that the gray matter of the brain increased by a significant amount. The specific areas of the brain that were affected deal with maternal motivation, reward and emotion processing, sensory integration, and reasoning and judgment. All of these areas are relevant to child-rearing (although you could make a case that every area of the brain is related in some fashion to child-rearing).
It shouldn’t be surprising that the female brain reacts to giving birth and caring for a child. After birth, females are flooded with hormones like estrogen, oxytocin and prolactin, and first-time mothers are learning an entirely new set of skills, including surviving on little sleep, coming bolt awake at the first murmurings of a waking infant, and mastering the interpretation of baby cries to determine whether a child is starving, dealing with a poop-filled diaper, or just lonely for Mom’s smiling face.
Not surprisingly, the study did not include the impact of having a child on the brains of new fathers. My guess would be that any such study would conclude that the birth of a child does nothing to divert the male brain from its long, gradual slide to eventual senility. While maternal brains respond energetically to new stimuli, sluggish paternal brains just hope to get some sleep.