A new study from brain scientists at the University of California, Irvine highlights a warning for new mothers: Put away the cellphone when dealing with the baby. The study found links between chaotic and interrupted interactions between baby and mother and depression, drug use and other risky behaviors among adolescents. To develop properly, the brain seems to need predictable, complete patterns of interactions with parents — and not sessions haphazardly or repeatedly cut off by parents’ distractions. Because we’re programmed to respond instantly to cellphone calls and texts, researchers warn parents that allowing devices to disrupt contact with an infant can be dangerous.