Self-consciousness impairments in schizophrenia with and without first rank symptoms using the moving rubber hand illusion

Sense of agency in schizophrenia: A reconciliation of conflicting findings through a theory-driven literature review

The sense of agency is the experience of being the author of self-generated actions and their outcomes. Both clinical manifestations and experimental evidence suggest that the agency experience and the mechanisms underlying agency attribution may be dysfunctional in schizophrenia. Yet, studies investigating the sense of agency in these patients show seemingly conflicting results: some indicated under-attribution of self-agency (coherently with certain positive symptoms), while others suggested over-attribution of self-agency. In this review, we assess whether recent theoretical frameworks can reconcile these divergent results. We examine whether the identification of agency abnormalities in schizophrenia might depend on the measure of self-agency considered (depending on the specific task requirements) and the available agency-related cues. We conclude that all these aspects are relevant to predict and characterize the type of agency misattribution that schizophrenia patients might show. We argue that one particular model, based on the predictive coding theory, can reconcile the interpretation of the multifarious phenomenology of agency manifestations in schizophrenia, paving the way for testing agency disorders in novel ways.

The bodily self from psychosis to psychedelics

The sense of self is a foundational element of neurotypical human consciousness. We normally experience the world as embodied agents, with the unified sensation of our selfhood being nested in our body. Critically, the sense of self can be altered in psychiatric conditions such as psychosis and altered states of consciousness induced by psychedelic compounds. The similarity of phenomenological effects across psychosis and psychedelic experiences has given rise to the "psychotomimetic" theory suggesting that psychedelics simulate psychosis-like states. Moreover, psychedelic-induced changes in the sense of self have been related to reported improvements in mental health. Here we investigated the bodily self in psychedelic, psychiatric, and control populations. Using the Moving Rubber Hand Illusion, we tested (N = 75) patients with psychosis, participants with a history of substantial psychedelic experiences, and control participants to see how psychedelic and psychiatric experience impacts the bodily self. Results revealed that psychosis patients had reduced Body Ownership and Sense of Agency during volitional action. The psychedelic group reported subjective long-lasting changes to the sense of self, but no differences between control and psychedelic participants were found. Our results suggest that while psychedelics induce both acute and enduring subjective changes in the sense of self, these are not manifested at the level of the bodily self. Furthermore, our data show that bodily self-processing, related to volitional action, is disrupted in psychosis patients. We discuss these findings in relation to anomalous self-processing across psychedelic and psychotic experiences.

Body transfer illusions in the schizophrenia spectrum: a systematic review

Schizophrenia has been viewed as a disorder of the self. Accordingly, the question arises if and how senses of ownership and agency are impaired in schizophrenia. To address this question, several body transfer illusions (BTIs) have been investigated in schizophrenia patients and other schizophrenia spectrum (SCZ-S) populations. The objective of the study was to systematically review the current evidence from BTIs in the SCZ-S. A systematic literature search in PubMed and CENTRAL (search date: February 12, 2022) was conducted on BTI studies carried out in SCZ-S populations. Studies were included if they were published in English after peer review, reported original research data, related to the SCZ-S, and used a BTI as its study method. Conference papers, study protocols, and reviews were excluded. For each included BTI study, various study characteristics and outcomes were retrieved, and a risk-of-bias score was calculated based on six study quality criteria. K = 40 studies were identified, of which k = 20 studies met the eligibility criteria. For BTI paradigms using visuotactile stimulation, most studies found elevated sense of ownership ratings in SCZ-S populations compared to healthy controls (HC). Implicit illusion measures (e.g., proprioceptive drift), in turn, did not generally indicate elevated embodiment levels in SCZ-S populations. Likewise, no consistent group differences emerged between SCZ-S populations and HC with respect to BTI paradigms using visuomotor stimulation. Furthermore, BTI vividness was found to correlate significantly with core symptoms of schizophrenia and various subclinical characteristics related to the SCZ-S. In line with the self-disturbance hypothesis, SCZ-S populations appear to be affected by aberrations in bodily self-awareness. Review registration: PROSPERO (identifier: CRD42022287960).

Sense of body ownership and body agency in schizophrenia

Recent research suggests that embodiment sensations (sense of body ownership and sense of body agency) are altered in schizophrenia. Using a mirror box illusion setup, we tested if the anomalous embodiment experience depends on deficient processing of visuomotor synchrony, disrupted processing of movement mode, or both. The task required participants to press a lever with their index while looking at the image of the experimenter's hand moving on a similar lever. The illusion of embodiment could arise because looking toward the direction of their own hand the participant saw the reflection of the experimenter's hand visually superimposed to his own one through a mirror. During the illusion induction, we systematically varied visuomotor asynchrony (4 delays were imposed on the movement of the experimenter's hand) and the mode of movement (the participant could perform active vs. passive movements). The strength of the illusion of embodiment of the external hand was assessed with explicit judgments of ownership and agency. Patients' data showed an anomalous modulation of ownership with respect to visuomotor synchrony manipulation and an altered modulation of agency with respect to both visuomotor synchrony and movement mode manipulations. Results from the present study suggest that impairments affecting both the processing of temporal aspects of visuomotor signals and the processing of type of movement underlie anomalous embodiment sensations in schizophrenia. Hypotheses about potential deficits accounting for our results are proposed.