There are a lot of reasons why paid parental leave is a good idea. It takes financial stress off new parents, makes breastfeeding easier, helps dads bond with babies, and makes moms more likely to return to the workforce. There’s a lot to be said for the way paid parental leave impacts a family’s work-life balance, but there’s also a lot of science behind how it impacts a baby’s brain.

Society tends to focus on how parental leave benefits parents, but we should be talking about how much it benefits babies. According to Scientific American, paid parental leave isn’t just a convenience: It’s crucial for baby’s brain development.

Baby brains are growing at at a rapid pace in those early weeks of life. To parents of newborns, it can seem like the dirty onesies are multiplying before their eyes, but that’s nothing compared to how quickly the synapses (or connections) in a newborn’s brain are multiplying. Research shows baby brains form up to a thousand new connections per second. It’s amazing, but it doesn’t happen in a vacuum.

Studies have proven that babies who are exposed to the kind of stimulation parents on leave can provide get a brain boost, and the synapses that are frequently used in the first months of life get stronger, while those that aren’t used disappear.

“Brain development is why the parent-child relationship is so important—you can keep an infant warm and nourished without it, but their brain won’t develop properly,” says Daniel Barron, a new dad and resident psychiatrist at Yale University, in Scientific American.

We know that the “serve and return” game parents play with babies plays a huge role in the developmental process. When babies don’t get a response to their babbling or gesturing—or if the responses of the adults around them are unreliable—the brain doesn’t form connections in the way that it should, according to Harvard University’s Center on the Developing Child.

It’s not just the serve and return that build the brain connections, but, as Barron notes, the feel of a parent’s touch, the sound of their voice and even the scent on their skin that help baby brains make sense of the world.

Studies have shown that exposure to supportive touch in infancy impacts how newborn brains processes touch, which is necessary for learning and social-emotional connections. Skin-to-skin contact is also a building block for cognition and communication, and babies can get more of it when parents have paid parental leave.

Unfortunately, the United States is the only country among 41 nations that does not mandate any paid leave for new parents, according to the Organization for Economic Cooperation and Development (OECD), but some employers are picking up the slack and implementing paid parental leave policies for moms—and dads—at their companies.

As they should. The science proves how important such policies are. An investment in parental leave isn’t just an investment in families—it’s an investment in the future.