**1. Introduction**

Psychotic disorders such as schizophrenia may feature frightening hallucinations as well as bizarre beliefs and behaviors that not only arouse anxiety in the general public and the media

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

but also amongst doctors [1]. But, even after more than 100 years of research, they remain some of the most mysterious and costliest mental disorders [2] that can only be detected and treated once the symptoms are manifest. More recently, psychosis research has increasingly shifted its focus to the non-clinical part of the general population.

Importantly, it has been shown that PLE and psychotic disorders share etiological risk factors, cognitive correlates, demographic characteristics, and diminished well-being, which supports a continuum of psychotic symptoms and associated factors across the general population [20–22]. However, while it is generally agreed upon that a psychosis continuum exists, there is no consensus even on the most basic dimensions of the psychosis phenotype and involved constructs lack clear definitions [23–25]. While PLE are generally seen as indicators of psychosis proneness, studies suggest that they are frequently reported in the general population and are not necessarily associated with distress, help-seeking, or the onset of psychotic disorders [20, 26, 27]. More specifically, there is some evidence indicating they might be differentially implicated in mental health and the formation of mental disorders [28–32]. However, as psychosis research has tended not to differentiate between different PLE and to categorize them homogeneously, only little is known about their individual psychopathological significance and their role in the formation of different psychosis spectrum disorders [32, 33]. Similarly, only little attention has been given to comparing the phenotypical similarity of psychotic experiences between healthy and clinical individuals [19, 34]. Therefore, new instruments have been called for in order to allow accurate mapping out of the psychosis continuum [35]. Further complicating the study of PLE, a variety of terms and self-report instruments with different conceptualizations of psychosis and PLE are being used, which may entail inconsistent results and blur the sources of these inconsistencies [24, 34, 36]. However, these limitations are rarely addressed or regarded in the study of PLE although they might ultimately impede progress

Subtypes of Psychotic-Like Experiences and Their Significance for Mental Health

http://dx.doi.org/10.5772/intechopen.78691

5

Importantly, attaining a clearer picture of PLE and associated factors might contribute to elucidating psychosis formation, improving risk screening, as well as facilitating new therapeutic approaches. Understanding the specific meaning of different subtypes of PLE for mental health might have become even more important since recent approaches aim at studying the subclinical interplay of symptoms leading to mental illness or the retention of mental health [37, 38]. In this context, an empirically established and generally agreed upon categorization of PLE regarding their psychopathological significance may be of fundamental importance. Although similar categorizations have been proposed [30, 39], it has not yet been clarified to

This chapter presents empirical findings that necessitate a more differentiated investigation of PLE and points out limitations in their current assessment. Further, it advocates a more differentiated view on PLE and clearer use of the associated terminology, concepts, and instruments. Aiming to stimulate further research in this area, a tentative categorization of PLE is

Research into subclinical psychosis is marked by a rather general view on psychotic-like experiences (PLE) and the interchangeable use of various instruments and terms with different underlying conceptualizations of psychosis [24, 25, 32, 34]. This section presents evidence necessitating a more differentiated view on PLE and points to pitfalls in their assessment that

in all areas of psychosis research.

which categories certain PLE should be assigned.

provided, and possible future research directions are indicated.

need to be considered when researching subclinical psychosis.

**2. Psychotic-like experiences: they are probably not all the same**

Delusions and hallucinations are the core features of psychosis. They are also referred to as "positive symptoms," as it appears that they have been added to the experience of affected individuals. While they are the hallmark feature of different psychotic disorders, it is their combination with other psychological difficulties as well as their relative expression that defines a specific diagnostic categorization of an affected individual [3, 4]. Research on the symptoms of schizophrenic patients has suggested the presence of two additional basic symptom clusters associated with psychosis, namely disorganized and negative symptoms [5]. Disorganized speech and disorganized behavior refer to loose associations in speech and physical actions that do not appear to be goal-directed (e.g., catatonia, which is maintaining peculiar and often uncomfortable postures) [6]. As opposed to positive and disorganized symptoms, the term "negative" symptoms refers to the impression that something has been taken away from the patient's behavior and experience. Negative symptoms manifest in flat or blunted affect (a reduced range of expression of emotions, reduced amount or fluency of speech) and avolition (the loss of will to do things). According to a more recently suggested model, psychosis exists as a transdiagnostic phenotype including affective symptoms as additional factors, i.e. depression and mania [7, 8]. The notion of transdiagnostic associations between psychotic and affective symptoms has recently been adopted in the fifth and latest edition of the standard diagnostic manual in the United States (DSM5, see [4]) in that bipolar disorders were separated from depressive disorders and relocated between depressive disorders and schizophrenia spectrum disorders [9]. Hence, if affective difficulties are not the predominant symptoms, but positive, disorganized, and negative symptoms are prominent, an affected individual might be diagnosed with schizophrenia (or "non-affective psychosis") [7]. In contrast, individuals with fewer negative symptoms but with a high prevalence of affective symptoms (manic and depressive symptoms) might be diagnosed with psychotic depression or bipolar disorder. Lastly, if affective and psychotic symptoms are similarly present, an individual might be diagnosed with schizoaffective disorder.

In contrast to the categorical, "Kraepelinian" approach, the Swiss psychiatrist Eugen Bleuler thought already 100 years ago that psychosis was just an extreme expression of thoughts and behaviors that could be found in varying degrees throughout the general population [10]. This was seminal for different models considering psychosis as a series of symptoms that are aligned along a continuum between clinical and non-clinical populations, such as schizotypy, psychosis proneness, subclinical psychosis, or at-risk mental states [11–14]. More recently, it has been suggested that psychosis exists as an extended *and* transdiagnostic phenotype that can be conceptualized at subclinical levels as a measurable behavioral expression of risk for psychosis [15, 16]. Psychotic experiences in the absence of a diagnosis are generally referred to as psychotic-like experiences (PLE), irrespective of their apparent severity. Research has mostly focused on them since they are the best indicators of early stages, although negativelike symptoms might present themselves earlier on the temporal trajectory leading to mental illness [17, 18]. There has been growing interest in the study of PLE, as it promises to provide new insights into factors and mechanisms involved in both the emergence of mental disorders and the maintenance of mental health [19].

Importantly, it has been shown that PLE and psychotic disorders share etiological risk factors, cognitive correlates, demographic characteristics, and diminished well-being, which supports a continuum of psychotic symptoms and associated factors across the general population [20–22]. However, while it is generally agreed upon that a psychosis continuum exists, there is no consensus even on the most basic dimensions of the psychosis phenotype and involved constructs lack clear definitions [23–25]. While PLE are generally seen as indicators of psychosis proneness, studies suggest that they are frequently reported in the general population and are not necessarily associated with distress, help-seeking, or the onset of psychotic disorders [20, 26, 27]. More specifically, there is some evidence indicating they might be differentially implicated in mental health and the formation of mental disorders [28–32]. However, as psychosis research has tended not to differentiate between different PLE and to categorize them homogeneously, only little is known about their individual psychopathological significance and their role in the formation of different psychosis spectrum disorders [32, 33]. Similarly, only little attention has been given to comparing the phenotypical similarity of psychotic experiences between healthy and clinical individuals [19, 34]. Therefore, new instruments have been called for in order to allow accurate mapping out of the psychosis continuum [35]. Further complicating the study of PLE, a variety of terms and self-report instruments with different conceptualizations of psychosis and PLE are being used, which may entail inconsistent results and blur the sources of these inconsistencies [24, 34, 36]. However, these limitations are rarely addressed or regarded in the study of PLE although they might ultimately impede progress in all areas of psychosis research.

but also amongst doctors [1]. But, even after more than 100 years of research, they remain some of the most mysterious and costliest mental disorders [2] that can only be detected and treated once the symptoms are manifest. More recently, psychosis research has increasingly

Delusions and hallucinations are the core features of psychosis. They are also referred to as "positive symptoms," as it appears that they have been added to the experience of affected individuals. While they are the hallmark feature of different psychotic disorders, it is their combination with other psychological difficulties as well as their relative expression that defines a specific diagnostic categorization of an affected individual [3, 4]. Research on the symptoms of schizophrenic patients has suggested the presence of two additional basic symptom clusters associated with psychosis, namely disorganized and negative symptoms [5]. Disorganized speech and disorganized behavior refer to loose associations in speech and physical actions that do not appear to be goal-directed (e.g., catatonia, which is maintaining peculiar and often uncomfortable postures) [6]. As opposed to positive and disorganized symptoms, the term "negative" symptoms refers to the impression that something has been taken away from the patient's behavior and experience. Negative symptoms manifest in flat or blunted affect (a reduced range of expression of emotions, reduced amount or fluency of speech) and avolition (the loss of will to do things). According to a more recently suggested model, psychosis exists as a transdiagnostic phenotype including affective symptoms as additional factors, i.e. depression and mania [7, 8]. The notion of transdiagnostic associations between psychotic and affective symptoms has recently been adopted in the fifth and latest edition of the standard diagnostic manual in the United States (DSM5, see [4]) in that bipolar disorders were separated from depressive disorders and relocated between depressive disorders and schizophrenia spectrum disorders [9]. Hence, if affective difficulties are not the predominant symptoms, but positive, disorganized, and negative symptoms are prominent, an affected individual might be diagnosed with schizophrenia (or "non-affective psychosis") [7]. In contrast, individuals with fewer negative symptoms but with a high prevalence of affective symptoms (manic and depressive symptoms) might be diagnosed with psychotic depression or bipolar disorder. Lastly, if affective and psychotic symptoms are

similarly present, an individual might be diagnosed with schizoaffective disorder.

and the maintenance of mental health [19].

In contrast to the categorical, "Kraepelinian" approach, the Swiss psychiatrist Eugen Bleuler thought already 100 years ago that psychosis was just an extreme expression of thoughts and behaviors that could be found in varying degrees throughout the general population [10]. This was seminal for different models considering psychosis as a series of symptoms that are aligned along a continuum between clinical and non-clinical populations, such as schizotypy, psychosis proneness, subclinical psychosis, or at-risk mental states [11–14]. More recently, it has been suggested that psychosis exists as an extended *and* transdiagnostic phenotype that can be conceptualized at subclinical levels as a measurable behavioral expression of risk for psychosis [15, 16]. Psychotic experiences in the absence of a diagnosis are generally referred to as psychotic-like experiences (PLE), irrespective of their apparent severity. Research has mostly focused on them since they are the best indicators of early stages, although negativelike symptoms might present themselves earlier on the temporal trajectory leading to mental illness [17, 18]. There has been growing interest in the study of PLE, as it promises to provide new insights into factors and mechanisms involved in both the emergence of mental disorders

shifted its focus to the non-clinical part of the general population.

4 Psychosis - Biopsychosocial and Relational Perspectives

Importantly, attaining a clearer picture of PLE and associated factors might contribute to elucidating psychosis formation, improving risk screening, as well as facilitating new therapeutic approaches. Understanding the specific meaning of different subtypes of PLE for mental health might have become even more important since recent approaches aim at studying the subclinical interplay of symptoms leading to mental illness or the retention of mental health [37, 38]. In this context, an empirically established and generally agreed upon categorization of PLE regarding their psychopathological significance may be of fundamental importance. Although similar categorizations have been proposed [30, 39], it has not yet been clarified to which categories certain PLE should be assigned.

This chapter presents empirical findings that necessitate a more differentiated investigation of PLE and points out limitations in their current assessment. Further, it advocates a more differentiated view on PLE and clearer use of the associated terminology, concepts, and instruments. Aiming to stimulate further research in this area, a tentative categorization of PLE is provided, and possible future research directions are indicated.
