The Relationship Between Dissociation and Symptoms of Psychosis

A Meta-analysis

Eleanor Longden; Alison Branitsky; Andrew Moskowitz; Katherine Berry; Sandra Bucci; Filippo Varese

Disclosures

Schizophr Bull. 2020;46(5):1104-1113. 

In This Article

Discussion

This is the first meta-analysis to systematically summarize and evaluate the magnitude of the associations between dissociative experiences and all symptoms of psychosis, and the findings support the existence of a robust and well-replicated relationship. Indeed, while the majority of literature examining links between dissociation and psychosis has primarily focused on hallucinations, the current analyses suggest that dissociative phenomena are robustly related to multiple positive symptoms and appear to be related to higher disorganization. Conversely, associations with negative symptoms were of considerably smaller magnitude and, in some cases, were nonsignificant. Furthermore, the effects considered in our review were observed across both clinical and nonclinical samples (although with differences in overall magnitude), indicating that dissociation may be an important factor underlying vulnerability to psychotic experiences across the continuum of psychosis.

Firstly, our review replicates and expands previous meta-analytic findings suggesting significant links between dissociation and auditory hallucinations.[14] It also indicates that dissociation is linked to hallucinations across multiple sensory modalities and that the association with visual hallucinations is of comparable strength to that of auditory. The link between dissociation and hallucinatory experiences was additionally of similar size in both clinical and nonclinical studies. Some authors have argued that this association calls for a radical shift in the way such symptoms are conceptualized by researchers and clinicians, in that hallucinations amongst psychosis patients may be better conceived as "traumatic in origin and dissociative in kind."[4] (p521) However, others have backed more cognitive perspectives; for example, that dissociation could make individuals more prone to hallucinations by increasing confusion between inner and outer experiences,[28] or that heightened states of dissociation may interact with preexisting cognitive vulnerabilities (such as source monitoring biases affecting the capacity to correctly identify the source of internally and externally generated events[29]).

This review also indicates that dissociative experiences present large associations with paranoia and delusions. Similarly, it identified significant links with symptoms of disorganization, although these were of a somewhat smaller magnitude relative to positive symptoms. One possible explanation for these associations is trauma-related, in that paranoia and delusions may arise from flashbacks which are not recognized as such.[30] These experiences, which are consistent with models of traumatic memory,[31] would typically be associated with powerful feelings of depersonalization/derealization that could subsequently drive the development of delusions and other psychotic symptoms.[32] In this regard, future primary and secondary research could usefully elucidate such links by examining the relationship between psychotic and dissociative phenomena in those with a history of trauma exposure relative to those without.

Our analyses also corroborate findings from previous empirical studies that suggest the magnitude of associations between dissociative phenomena and negative symptoms is less robust than for positive symptoms. When focusing on specific groups of negative symptoms (cognitive symptoms, reduced emotional experience/expressiveness, and lack of motivation, asociality, and withdrawal), we observed small but statistically significant relationships. We note, however, that the number of studies considering negative symptoms is relatively sparse and characterized by high heterogeneity in the specific symptoms examined. Although our grouping of negative symptoms is consistent with existing proposals regarding their underlying dimensional structure (eg, in terms of diminished motivation and expression[33]), we were limited by the small number of diverse symptoms examined in the primary studies. There is an ongoing debate around the exact underlying structure of negative symptoms,[34] and concerns remain regarding the risk of conflating their assessment with extraneous complaints such as depression or medication side effects. This has the potential of biasing the accurate estimation of the relationship between negative symptoms and dissociation (as well as other psychological and neurocognitive constructs), highlighting the need for further assessment innovation and future research to corroborate these findings. There are no clear models that posit a mechanism linking dissociation to negative symptoms, and indeed patients with dissociative identity disorder are often clinically distinguished from psychotic patients by an absence of negative symptoms.

Overall, our findings support proposals that certain psychotic symptoms might be better conceptualized as dissociative in nature.[4] They are also consistent with evidence suggesting common etiological underpinnings between dissociation and symptoms of psychosis. In this respect, dissociation is common in individuals who have endured potentially traumatizing events[35] and the risk for, and severity of, psychotic symptoms has been overwhelmingly linked to similar traumatic exposures.[36,37] Furthermore, meta-analytic evidence suggests that dissociation in people with mental health difficulties, including psychosis, is associated with histories of childhood trauma,[38] while multiple studies suggest dissociation is a well-replicated mediator of the link between childhood adversity and psychotic symptoms.[39] However, it should be noted that our meta-analysis did not consider the potential role played by peritraumatic dissociation in the etiology of psychotic experiences. This remains an under-researched topic that could be addressed in future investigations.

In terms of different dissociation subtypes, our analyses found no striking differences in their respective associations with symptoms of psychosis, although in some analyses absorption appeared to be more linked to psychotic-like experiences in nonclinical samples. However, an important caveat should be noted: our evidence synthesis only considered the bivariate associations between dissociative and psychotic symptoms. It is, therefore, not possible to establish with high confidence whether symptom-specific associations might exist between psychotic experiences and dissociation, or between psychotic experiences and specific dissociative subtypes. Multivariate analyses accounting for covariation between different psychotic and dissociative experiences might be better placed to answer such questions. When these analyses have been conducted in primary research studies, some have reported alleged symptom-specific effects (eg, in the case of auditory hallucinations) whilst others have found no strong support for dissociation exclusively impacting individual symptoms.[40]

The difference observed in multiple analyses regarding the relatively larger association between dissociative and psychotic symptoms in nonclinical rather than clinical samples might be explained by several factors. Notably, as patients are likely to be more symptomatic than nonclinical participants, it is possible that studies conducted on clinical samples present restricted variance which might impact the magnitude of effects extracted from these studies. However, a further complication that should be considered when appraising our findings is the comparability of assessment measures typically used in clinical investigations, such as the PANSS, and the various schizotypy measures employed by nonclinical studies (many of which are highly heterogeneous in terms of the experiences they intend to capture). Whilst it is widely accepted that psychosis exists on a continuum with non-pathological experiences and traits, it could be argued that certain phenomena considered in the nonclinical literature (eg, paranoid ideation) may not be fully comparable with their clinical counterparts (eg, persecutory delusions). It, therefore, remains a possibility that the larger effects observed in our nonclinical analyses might reflect fundamental differences in the constructs assessed by different measures.

Another potential limitation of the literature considered in this review relates to the possible comorbidity between psychotic and dissociative disorders. Few studies formally assessed the presence of comorbid dissociative diagnoses when investigating the association between psychotic experiences and dissociation, yet there is some suggestion that undiagnosed dissociative disorders are not uncommon in psychotic populations.[41] Future investigations may attempt to clarify the impact of comorbidity by applying diagnostic interviews such as the Structured Clinical Interview for DSM-5 Dissociative Disorders.[42] It should also be noted that medication status may have confounded results via patients exhibiting antipsychotic side effects (eg, memory problems, detachment, affective flattening) that could be mistaken for dissociation during the assessment.[43] We were additionally unable to conduct dissociation subtype analyses within groups (clinical vs nonclinical) yet some studies have suggested, for example, that different subtypes of dissociation were related to hallucinations in clinical vs nonclinical voice hearers.[44]

Several other caveats should also be considered when interpreting our findings. Although the analyses found no substantial evidence of publication or other forms of selection bias, our search strategy was limited to peer-reviewed English-language studies and it is possible that certain relevant studies might have been overlooked. As mentioned previously, the bivariate approach may also have masked more subtle differences in the relationship between dissociation and specific psychotic symptoms. Furthermore, our meta-analysis could not directly contrast the effects between dissociation and specific symptoms as the same studies often examined multiple psychotic experiences within the same sample. Additional methodological and statistical developments in meta-analysis and aggregate analysis of individual participant datasets (eg, network analysis, meta-analytic structural equation modeling, and independent patient data meta-analysis) might enable future evidence syntheses to estimate such effects with greater precision. Although subgroup analyses were conducted to account for the most important methodological and clinical variances between the studies included in this review, the summary effects reported should still be interpreted cautiously in light of the statistical heterogeneity detected in most of our analyses.

Finally, the findings bear several implications for clinical practice. Research into the development of psychological interventions for psychosis has recently moved toward devising and evaluating more targeted treatments in order to improve the effect sizes of generic cognitive-behavioral therapies (which traditionally focused on a range of different psychotic symptoms simultaneously). Future meta-analyses may help refine the issue of whether the relationship between dissociation and psychotic experience varies across different diagnostic groups. However, the current review suggests that the role played by dissociation in the maintenance of presenting difficulties should be carefully evaluated in the context of targeted therapies for voices, delusional beliefs, and other psychotic symptoms for which a strong link with dissociation was observed. As dissociation often represents a consequence of adversity exposure, trauma-focused therapies could also represent a meaningful treatment option for many people with psychotic and dissociative experiences. The adaptation of protocols used to treat dissociation likewise represents a promising area of intervention development for psychosis. For example, reconceptualizing voices as dissociated parts of the self and using dialogical approaches to improve relationships between hearer and voice is one instance of applying techniques developed in the dissociation field amongst psychosis populations.[45] Such an intervention is currently undergoing controlled evaluation amongst patients with schizophrenia spectrum diagnoses (ISRCTN45308981), and if effective could represent a treatment advance that encapsulates the considerable clinical and conceptual overlap between dissociation and psychosis. In this respect, therapeutic approaches derived from dialogical principles may also have applicability beyond auditory hallucinations; a tradition notably begun by Laing's[46] characterization of schizophrenia as the "divided self," and expanded by the work of theorists such as Lysaker et al[47] who posit that issues of self-diminishment in psychosis can be addressed via psychotherapy that focuses on developing a coherent internal narrative.

Ultimately, our findings raise the issue of whether different psychotic symptoms do in fact have distinct etiologies. The strong association between dissociation and different types of positive symptoms suggests that they may have similar causal factors. Evidence suggests that substantial overlaps exist in biological and socio-environmental risks across diagnostic categories and specific symptoms[48] and accordingly there has been a move toward transdiagnostic therapies.[49–51] Nonetheless, there are likely to be a myriad of risk and resilience factors for each symptom and the relative importance of each is liable to vary from person to person, highlighting the importance of developing individualized formulations to help understand the development of distressing symptoms within the context of psychological therapies.

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