In 1949, Eddy de Wind, a Dutch psychiatrist and survivor of Auschwitz concentration camp introduced the term "concentration camp syndrome" regarding the psychological consequences of persecution, describing the "pathological after-effects" unique to former prisoners of Nazi concentration and extermination camps. The subsequently well-documented syndrome among Holocaust survivors includes anxiety and depression, intellectual impairment, social withdrawal, sleep disturbance and nightmares, physical complaints and mood swings with loss of drive. Several studies have examined the "chronic and progressive" nature of the condition, with symptoms increasing in intensity as survivors age.