All subjects will be screened with a standardized psychiatric examination using the mini international neuropsychiatric interview (MINI) to determine present psychiatric state. General psychological state will be assessed using the 17 item Hamilton depression rating scale (HAM-D17), the Dutch version of the symptom checklist (SCL-90) and the hospital anxiety and depression rating scale (HADS). The psychiatric evaluation will be carried out by a psychiatrist. Volunteers with deviating scores on any topic will be excluded from participation.