Scientists are discovering a different kind of answer which has to do with the types of abnormalities in the brain and body that are characteristic of people with depression.

CNN: Enke death: What are the roots of depression?

Even more intriguingly, nerve cells in the colons of Parkinson's sufferers who are constipated contain structural abnormalities known as Lewy bodies, which are a hallmark of the affected brain tissue in people with Parkinson's.

ECONOMIST: Parkinson's disease: Movement difficulties | The

Research in autism has indicated abnormalities in spinal fluid and chemical signaling in the brain- anecdotal reports of children undergoing stem cell therapy have indicated some potentially encouraging results.

FORBES: Stem Cell Therapy To Treat Autism?

Many psychiatric disorders that are thought of as problems of adulthood actually often arise for the first time in adolescence and by examining the scans of his volunteers Prof Bullmore hopes to learn whether at their root these conditions are abnormalities in brain development.

BBC: Brain scan study to understand workings of teenage mind