This issue contains two papers which concern the occurrence of hallucinations in Parkinson's disease. This is a matter of great importance in the management of the disease. Hallucinations and related phenomena are of wider interest because they may provide clues to the brain mechanisms involved in their production.

Almost 65 years have passed since the publication of the now classic work of Wolff and Curran1: Nature of delerium and allied states. Their study reported that “no evidence was found that there was any specific relationship between a particular noxious agent and the form and content of the accompanying psychobiologic disturbances.” These findings suggest that a range of events may provoke a reaction in the functioning of the brain but …