Still, other moms might flag in supportiveness because their jobs are too demanding or because they have postpartum depression. Garner says he’s even seen the reverse of poverty turn harmful: Two uber-successful parents spending their free time twiddling on their phones rather than attending to their newborn.

About 10 years ago, Joan Luby, a psychiatry professor at the Washington University School of Medicine, invited 92 children between the ages of four and seven to a lab in St. Louis. The kids took a test that measured whether they were depressed—some were, and some weren’t. One by one, the children and their primary caregivers (in most cases, the mom) were invited into a room that contained a brightly wrapped gift with a bow on top. A research assistant told the children they could have the gift if they waited patiently for eight minutes. In the meantime, the mother was told to fill out a daunting stack of complicated forms. Annnd ... go!

As expected, the kids went bonkers. They begged. They whined. They stretched their tiny hands toward the box. They, being kids, yearned for nothing more than to rip it open.

But the researchers’ eyes were on the parents. Some of the moms were supportive, telling their little eager beavers “that they knew it was hard to wait. Or they touched them or said something reassuring, might have even given them positive feedback for being patient,” Luby told me.

The other moms were too overwhelmed by the forms to be comforting. They were unresponsive to their child’s pleas and they didn’t reassure them. Some snapped at or hit their children for being annoying.

Proceedings of the National Academy of Sciences

When Luby and her colleagues conducted an MRI four years later, they found that the non-depressed children whose mothers had not been nurturing had smaller hippocampuses than the kids who were depressed but had levels of high maternal support. In other words, it was better for the kids to be depressed with supportive moms, than not depressed with unsupportive ones. Since the hippocampus governs things like memory, cognitive function, and emotion, the smaller hippocampal volume suggested to Luby that the children with the non-supportive moms were doing worse both cognitively and emotionally.

“What was exciting about this finding is that it showed that early nurturance was having a material effect on tangible brain outcomes,” Luby said.

It’s this type of evidence that led the American Academy of Pediatrics to announce this week that all parents should read aloud to their children from birth—the first time the group has ever weighed in on early literacy. The recommendation was based on findings that wealthier people hear millions more words than low-income people do as children, and that this verbal difference translates to a big gap in school test scores.