@Njinte posted a link regarding "Mommy Brain" in a now closed thread. It didn't seem like a complete picture to me of what happens to the brains of new mothers. It doesn't make sense to me that a woman would lose her ability to think at the outset of the long, demanding role of raising long-dependent offspring. The article posted mentioned that sleep deprivation couldn't be ruled out as a likely cause of any degradation in cognitive abilities.
Still, seemed like a simplistic analysis. I wondered if mothers' brains were tasked with something else. (e.g. I feel more "primal", as in, don't ever fuck with my child or I will have you hunted down and hurt. *not joking* I never even used to support the death penalty).
Further to Njinte's link, here are some more articles discussing research that show a mother's brain likely actually grows. It's selective growth. Gray matter apparently increases in small but significant amounts. Though the ability to multitask may be affected. (That makes sense to me in that it's advantageous to mother, child and society for a child to take priority and form a strong emotional bond with her/his mother). It's about having different priorities and ensuring the survival of offspring, one's genes.
"From an evolutionary standpoint, a mother is faced with a really significant challenge," Kinsley said. "She had to do everything she did before, plus a whole new suite of behaviors to keep her offspring alive. How females evolved in nature is to have their brains adapt in pregnancy, so that their young enhance their behaviors.". From this article, also linked below.