Beliefs that are in stark contrast to reality, often having to do with persecution or an exaggerated sense of importance or glory.
Delusions are generally experienced by people suffering from a severe psychotic disorder, usually schizophrenia, although delusional thinking can occur in other types of patients (as the result of drug or alcohol abuse, for instance). Typical delusional ideas are categorized into delusions of grandeur, in which a person imagines for him or herself some God-given purpose or, in some cases, believe they are in fact historical personalities of great importance. Another type of delusion are delusions of persecution, in which a patient will believe that some person or group is out to harm him. Still another set of delusions involve what are referred to as "command hallucinations," in which a person hears voices telling him or her to commit an act. These delusional thoughts can lead people to acts of self-mutilation or to violent criminal acts.
Many psychological disorders feature aspects of delusional thought. People suffering from depression often experience delusions such as beliefs that they are worthless, sinful, or too unlikable to engage productively in society. Other forms of delusional thinking occur in people with somatoform and dissociative identity disorders. These include body dysmorphic disorder, obsessive-compulsive disorder, and multiple personality disorder.
John Junginger, a clinical scientist at Indiana University, studied 138 patients who exhibited delusional beliefs and developed a scale of "bizarreness." Junginger identified the 12 types of delusional beliefs (including those mentioned above) as well as several others, such as "insertion" and "control." After categorizing delusional thoughts as such, Junginger conducted another study, attempting to discern how well his categories could predict violent behavior. Describing the study in Omni magazine, Steve Nadis wrote that "Junginger suspects psychotics are more likely to act out their false beliefs if they have involved, highly 'systematized' delusions." That is, elaborate delusional beliefs correlate more highly with violent behavior than vague delusional beliefs; so that someone who believes that some unidentified person is out to hurt them is less likely to act violently than someone who believes that a specific neighbor has been sending him messages to kill himself through the walls.
While researchers such as Junginger have sought out methods to predict violence as a result of delusions, other psychologists have been attempting to explain the occurrence of delusional thoughts. One intriguing idea, proposed by G.A. Roberts in the British Journal of Psychiatry in 1991, is that delusions actually help psychotic and schizophrenic patients by providing them with a detailed sense of purpose for their lives. Roberts found that people currently exhibiting delusional behavior were less depressed than those who had been delusional but were recovering.
Nadis, Steve. "Dangerous Delusions: Making Sense of Senseless Behavior." Omni (December 1994): 32.
Starr, Cynthia. "A 'Secret Disorder'Yields to Serotonin Reuptake Inhibitors." Drug Topics (5 July 1993): 20.