Depression is common, affecting an estimated 264 million people of all ages worldwide.

While the causes are varied and complex, genetics, changes in brain chemistry, and environmental factors (such as stress or traumatic events) all play a part.

Historically, depression was thought to result from a chemical imbalance in the brain. But researchers now think that this is actually a symptom of depression — not the cause.

Alongside a potential chemical imbalance, depressed people may also show changes in how their brain networks connect and alterations in their function and anatomy.