Latest research shows that a single socially stressful situation can contribute to depression by killing new nerve cells in the hippocampus, the area of the brain involved in learning, memory, and emotion. Anxiety disorders, autism, and attention-deficit disorders were previously thought to be primarily learned from poor parenting, but now appear to have biological causes. Stressors place adaptive demands on a person known as stress, while anxiety disorders involve unrealistic, unfounded fears or anxieties of disabling intensity as shown through phobic, panic, and obsessive-compulsive behaviors.