Depression has been associated with reduced volume of the hippocampus in magnetic resonance imaging studies in humans. A new study now clarifies the cellular basis of these volumetric changes, which have been unclear until now. Beginning in the 1980s, a series of studies in rodents suggested that an area of the hippocampus, a brain region implicated in mood and memory, was particularly vulnerable to stress. When analyzing the brain tissue in detail, they reported loss of nerve cells called neurons with stress.