The next time you and your spouse decide to engage in a debate after the baby has been put to bed, just remember to keep your tones friendly. According to research conducted by Alice Graham, a doctoral student at the University of Oregon, infants respond to their parents’ angry tone of voice, even when they’re sleeping.

“We were interested in whether a common source of early stress in children’s lives—conflict between parents—is associated with how infants’ brains function,” Graham said. Babies’ brains are highly plastic, allowing them to develop in response to the environments and encounters they experience. But this plasticity comes with a certain degree of vulnerability—research shows that severe stress, such as maltreatment or institutionalization, can have a significant, negative impact on child development.

The study, published in the journal Psychological Science, show that babies are not oblivious to parental conflicts, and exposure to them may influence the way babies’ brains process emotion and stress.

Read more: Naturally Moi