Ask most people about the neurochemical origins of depression and you’ll likely hear how low serotonin levels are the cause. But today’s scientists know depression’s roots are more tangled and complex. One area of interest to them is the brain’s prefrontal cortex, a region responsible for motivational and goal-directed behavior. For those with depression, this region’s neurons are unhealthy, their connections, called synapses, withering like rotten roots.