CLINICAL HANDBOOK OF SCHIZOPHRENIA

86 I. CORE SCIENCE AND BACKGROUND INFORMATIONences.” A delusional belief involves four features: It is objectively false, it is idiosyncratic,it is illogical, and it is stubbornly maintained. Although DSM-IV-TR classifies delusionsbased on their content (e.g., persecutory, grandiose, erotomanic, self-referential, grandiose,somatic, or nihilistic), recent research suggests that delusions can be clustered intothree distinct entities: Delusions of influence (delusions of being controlled, thoughtinsertion or withdrawal), self-significance delusions (grandeur, reference, guilt/sin), anddelusions of persecution. It is hypothesized that each of these clusters may be linked tounderlying neurobiological processes.For the purpose of diagnosis, DSM-IV-TR acknowledges Schneider’s description of“bizarre” delusions as being especially characteristic of schizophrenia. Delusions aredeemed bizarre if they are clearly implausible and not understandable, and do not derivefrom ordinary life experiences or the person’s cultural system. Delusions that express aloss of control over mind or body are generally acknowledged as bizarre; these include aperson’s belief that his or her thoughts have been taken away by some outside force(“thought withdrawal”), that alien thoughts have been put into his or her mind(“thought insertion”), or that his or her body or actions are being acted on or manipulatedby some outside force (“delusions of control”). If the delusions are judged to be bizarre,this single symptom is considered as adequate evidence to make the diagnosis ofschizophrenia.HALLUCINATIONSAccording to DSM-IV-TR, hallucinations may occur in any sensory modality (e.g., auditory,visual, olfactory, gustatory, and tactile), but auditory hallucinations are by farthe most common. Auditory hallucinations are usually experienced as voices (thoughoccasionally they may be limited to just sounds). Sometimes they are of the “command”type—a voice commanding the person to perform some action. The experienceof hallucination is distinct from the person’s own thoughts. DSM-IV-TR specifies thatthe hallucinations must be experienced in the context of a clear sensorium. It is importantto keep in mind, however, that some hallucinations may fall within the context ofnormal experience (e.g., voices heard either at the time of falling asleep (hypnagogic)or waking up (hypnapompic), or an isolated experience of hearing one’s name calledout). They may also be considered normal in the context of certain religious rites andcultures.The term “Schneiderian hallucinations” refers to a specific forms of auditory hallucinations(e.g., two voices having a dialogue independent of the person experiencing thehallucination, or hearing multiple voices commenting on the person’s action). DSM-IV-TR identifies these as being sufficient by themselves to diagnose schizophrenia.Disorganization DimensionDISORGANIZATION OF THOUGHTDisorganized thinking or formal thought disorder has been argued by some to be the singlemost important feature of schizophrenia. It refers to abnormalities in the form, structure,or processing of speech rather than its content. Because of the difficulty inherent indeveloping an objective definition of a thought disorder, and because in a clinical settinginferences about thought are based primarily on the individual’s speech, the concept ofdisorganized speech has been emphasized in the definition for schizophrenia used inDSM-IV-TR. The speech of individuals with schizophrenia may be disorganized in a varietyof ways. The person may “slip off the track” from one topic to another (“derailment”