The term 'delusion' signifies a complex edifice of ideas in which 'delusional ideas' are linked with other ('normal') thoughts. Delusions are communicated to others in the form of judgements. In this context, the term 'delusional idea' customarily refers to pathologically falsified judgements for which three criteria have been proposed: the unrivalled conviction with which they are held, their lack of amenability to experiences or compelling counterarguments, and the impossibility of their content. (49 The last criterion must be discarded for two reasons. Firstly, collective beliefs derived from the sociocultural setting of a person can be considered, in other surroundings, as false or impossible. Taking this into account, delusion is often defined as a 'false unshakable belief which is out of keeping with the patient's social and cultural background'. (38> Secondly, in certain delusions (e.g. delusional jealousy) the content does not go beyond the possible. Thus delusions are best defined as overriding rigid convictions which create a self-evident, private, and isolating reality requiring no proof. (41)
Delusions can occur for various reasons. Jaspers (4°) introduced the distinction between primary and secondary delusions. He supposed that the first, called true delusional ideas, are characterized by their 'psychological irreductibility', whereas the second, called delusion-like ideas, emerge understandably from disturbing life experiences or from other morbid phenomena, such as pathological mood states or misperceptions. This led to the assumption that primary delusions are the direct expression of specific somatic dysfunctions which are frequently considered to be the basis of schizophrenia. Four types of primary delusions have been distinguished in this perspective.
1. Delusional intuitions (autochthonous delusions), occurring spontaneously, 'out of the blue'.
2. Delusional percepts, in which a normal perception acquires a delusional significance. Schneider(42) assumed that the 'psychological irreductibility' was clearly evident in this process, and included delusional percepts among his 'first rank symptoms' of schizophrenia.
3. Delusional memories can be distorted or false memories coming spontaneously into the mind like delusional intuitions. In other cases they occur, like delusional percepts, in two stages which means that normal memories are interpreted with delusional meaning.
4. Delusional atmosphere refers to an ensemble of minuscule and almost unnoticed experiences which impart a new and bewildering aspect to a situation. The world seems to have been subtly altered; something uncanny seems to be going on in which the subject feels personally involved, but without knowing how. From this uncertainty evolves first certainty of self-reference and then the formation of fully structured and specific delusional meanings. The apparent change in the surrounding situation is accompanied by tension, depression, or suspicion, and by anxious or even exciting expectations, so that it is often called 'delusional mood'.
The primary-secondary distinction assumes that the delusional atmosphere is part of the process underlying all primary delusional phenomena. If this preliminary perturbation is not perceived clearly or is not communicated by the patient as a general change in the situation, it may be manifested only as single delusional percepts, intuitions, or memories. In cases in which the initial change in the whole atmosphere is experienced clearly, a subsequent restriction on a perceived detail of the environment, or on a fully formed delusional idea, can lead to a release from the preceding perplexity. The origin of primary delusions is then commonly attributed to a basic cognitive anomaly perturbing information-processing, which reduces the influence of past experiences on current perception. This is considered to entail a heightened awareness of irrelevant stimuli and an ambiguous unstructured sensory input allowing the intrusion of unexpected and unintended material from long-term memory.(43)
The assumption of a purely cognitive origin for some delusional phenomena is called into question by the hypothesis that delusions only occur if they are preceded by affective disturbances. This standpoint is thrown into relief in Janzarik's concept of the 'structural-dynamic coherence'. Janzarik (7) designates as 'dynamic' a fundamental realm including affectivity and drive which he contrasts with the 'psychic structure' containing inborn recognition patterns and acquired representations. The inborn recognition patterns as well as some of the acquired representations are dynamically invested, i.e. linked with positive, negative, or ambivalent feelings. Normally, these dynamically loaded elements ('values') are kept permanently in the background by neutral representations based on learned experiences which assure a realistic critical evaluation of the situation. In addition to the feelings tied to structural elements, everybody has a certain amount of 'free floating dynamic' which may develop into a depressive, anxious, euphoric, or irritable state.
If these dynamic fluctuations reach a morbid level, reality testing becomes distorted by the exagerated influence of values. Stable modifications of the dynamic background make the corresponding values powerful. Dynamic restriction, for example in depression, activates solely negative values which can no longer be conterbalanced by a critical evaluation of possible positive aspects of the situation. Dynamic expansion, as in mania, produces the opposite effect. In states of dynamic instability, rapid changes occur in the activation of different values, causing the puzzling uncertainity of the delusional atmosphere. In the case of schizophrenia the dynamic instability is hypothetically attributed to 'irritation' provoked by perturbed information-processing (44) or to an increased state of arousal produced by the neurochemical changes underlying the basic cognitive disturbance. (45,> Similar fluctuations of affectivity and drive may occur in other conditions, for instance in temperamentally hyper-reactive personalities or rapidly alternating manic-depressive mixed states. This casts doubt on the assumption that delusional atmosphere is specific for schizophrenia.
The content of delusions is determined by the mood in which they emerge and evolve, by the patient's personality and sociocultural background, and by previous life experiences. In principle, the content can embrace all kinds of presumptions which have been placed in separate categories based on certain characteristics. The following six main delusional themes are usually distinguished:
• delusions of persecution based on the assumption that the patient is pursued, spied upon, or harassed
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