``The aim is to identify brain-based markers that can detect early signs of depression,'' the project's chief investigator, Lea Williams, said.

``The earlier we can detect risks of depression, the earlier we can provide help.''

Scientists involved in the project are also inviting parents, children and siblings of people with depression to join the study.

Participants will take part in examinations of brain function and symptoms of depression.

These include MRI scans of brain behaviour while participants view facial expressions and identify the emotions being expressed.

Professor Williams said people at risk of depression were more likely to see negative emotions in people's faces.

Study co-ordinator Anna Watters said that at present, there were no agreed neuro-biological tests for detecting early signs of depression.

To volunteer for the study, phone 98458195.