A form of mental confusion in which the patient is assailed with doubt and uncertainty about his own thoughts.Perplexity is one of the more transient disorders of thinking found primarily in schizophrenia. The patient “is at a loss when trying to understand why and how his thought processes are operating” (Landis and Mettler, 1964). These authors cite, as one example, the shifting explanations given by a paranoid patient to account for her ideas of persecution: “As far as I know they used an oscillograph on me, but I might be mistaken . . . Whether a dictaphone was actually in the apartment upstairs or not I don’t know, I wasn’t there … I did feel the effects of something. I couldn’t say what it was, gas or not. I really heard the gas stove move but I could be mistaken . . . People across the street appeared to be signaling. It is possible I was wrong . . . There might not have been a scandal in the papers about me. The psychiatrists told me there was, but I didn’tread the news … I was taking the psychiatrist’s word for granted that he was a criminologist. That is, so far as I know. I couldn’t swear he was.” (Milici, 1937)Another form of perplexity is observed in patients suffering from a diffuse impairment of brain functions, as in toxic, infectious, or head injury disorders. Since these cases involve a disturbance of consciousness rather than disordered thinking, the patients are not perplexed by the thoughts and ideas that pass through their minds, as in schizophrenia, but are bewildered by their inability to concentrate, understand questions, or grasp the situation. They therefore wear a puzzled, distressed, and at times surprised expression on their faces