Lisa Feldman Barrett, a neuroscientist at Northeastern University, points to evidence that mood disorders can stem from metabolic problems—which in turn can have roots in stressors that affect the brain, such as early childhood trauma and neglect or sleep deprivation. Such experiences can also shape how we interpret internal sensations. Rather than passively receiving information, the brain is constantly constructing a model of its sensory conditions and guessing what caused them in order to direct the correct response, Barrett says. “You feel a tug in your chest, and your brain has to decide if it’s because you ate too much for dinner or if it’s the early sign of a heart attack.”