SENSE OF AGENCY IN SCHIZOPHRENIA

Keywords: schizophrenia, schizotypy, sense of agency, rubber hand illusion, hand

In our normally daily life we all perform goal-directed actions on which we even do not reflect upon. But we normally experience these actions as self-initiated (Werner et al. 2014). Abnormally self-experiences have been related to disorders of the schizophrenia spectrum (Ferri et al., 2013). Deficits of Sense of Agency (SoA) have been associated with sensory-motor integration in schizophrenia (Werner et al. 2014). In the study of Ferri et al. (2014) it was hypothesized that the higher susceptability to the rubber hand illusion would be related to the positive symptoms of schizophrenia. It was investigated whether patients with schizophrenia was associated with visuo-tactile integration with the rubber hand illusion. Patiens seemed to have a different experience to the rubber hand than control participants. The negative symptoms od schizophrenia were suggested to be the result of a disturbed body ownership which manifests itself when the actual sensory stimuli are absent as related to the rubber hand illusion, and according to the authors this would be especially related to anhedonia (Ferri et al., 2013). A limitation of their study is that they only got subjective reports of the participants. In their study, Werner et al. (2014) developped an experiment where subjects had to report subjective agency  episodes while they were controlling a virtual pen. Participants with schizophrenia differed from healthy control participants in the duration of false negative agency judgments which was to be found prolonged in patients. Errors in external agency judgments happened while there were no differences among motor signals and sensory feedback when they did not differ. The authors argue that their findings are in agreement with the hypothesis that changes seen in schizophrenia patients are the result of a deficient and stronger integration mechanism that is more vulnerable to errors because of the strong dependence on extenal, but not internal cues (Werner et al., 2014).

In the study of Thakkar, Nichols, McIntosh, and Park (2011) the rubber hand illusion was also stronger in patients with schizophrenia than in healthy control participants. The patients reported this illusion as more vivid on a questionnaire. They also exhibited mislocation of their own hand, which is indicative of a deficit in body ownership in schizophrenia (Thakkar et al. 2011). Asai, Sugamori, and Tanno (2008) found that in healthy participants scoring high on schizotypal traits, passivity phenomena might be due to the anomalous prediction of one's own movements or actions. In another study by Asai and Tanno (2008) participants scoring eighter low or high on schizotypal traits had to press a button, whereafter a tone followed. The participants had to indicate whether they had the feeling that they themselves or someone else had elicited the tone. It was concluded that participants high on schizotypal traits show impairments in their sense of agency. 

Subjective feeling of control can be saparated from motor performance. Prospective internal signals are evident in the prefrontal cortex in patients with schizophrenia, but they are not doing well in communicating and monitoring by the parietal cortex (Voss et al. 2017).

Garbani et al. (2016) aimed to study the integrety of body representation in patients with schizophrenia and also the pattern of performance concerning the passivity symptoms on a body illusion task and a hand laterality task. The results show that patients with schizophrenia exhibited deficient performance on both of those two tasks. The patients with schizophrenia showed enhanced disembodiment of their own hand. In addition, they showed a decreased sense of agency over their own hand as compared to healthy control participants (Garbani et al., 2016). The suggestion of these authors is that symptoms of passivity are associated to impairments in body representations, including body schema, alternations in the sense of agency, as well as internal timing deficits that lead to overwhelming associability with external sensory stimuli, such that the sensation becomes that someone's actions are produced by another (external) agent (Garbani et al., 2016).

Bulot, Thomas, and Delevoye-Turrell (2007) designed an easy motor task to measure as an implicit indicator of how a pre-reflective  sense of agency in schizophrenia patients works. The actually wanted to know the immediate sense of agency. The experiment consisted of a fall of a pendulum either caused by the experimenter or the participant. Patients with schizophrenia experienced self- and -other initiated action as the same. They did not improve the force of the grip when they were themselves the agent of the pendulum release. According to the authors, these findings are suggestive of an impairment in pre-reflective sense of agency in patients (Bulot et al., 2007). Patients with schizophrenia performed a prime-based agency inference assignment in which they learned that it was about evaluating their experiences of personal effects and how they come and go (Prikken et al. 2017). In every trial, one place was gently primed shortly before the subjects did press the stop button and saw the outcome location. Patients with schizophrenia who had positive symptoms had a reduced agency. furthermore, schizophrenia patients exhibited a diminished capacity to use implicit cues for self-agency that were available to them. This finding was still evident after taken into consideration the disease state and is therefore suggested to be a stable trait (Prikken et al. 2017).

Surprise has an influence on sense of agency (Moore et al., 2011). In schizotypy, training with more surprising results was related to an enhanced sense of agency. individual differences in associative learning might be associated to higher level experiences of their world (Moore et al., 2011).

Renes et al. (2013) examined implicit and explicit ways to inferences about self agency. In the explicit condition (matching goal to outcome), both healthy controls and patients with schizophrenia exhibited enhanced self agency. In the implicit condition (priming) only the healthy control subjecs exhibited enhanced self agency whereas patients with schizophrenia did not. It has been suggested that implicit causes are the result of a disturbance in self agency in schizophrenia (Renes et al. 2013).

I think that the positive symptoms, such as delusions and hallucinations can be explained by a reduced sense of agency. The patient has in these instances not the ability to attribute states to their own, rather they think these experiences are generated from the outside. Delusions in which the patient thinks that the police task force is after him or her might be explained by defective sense of agency. Auditory hallucinations might be explained by voices that the patients hears which might be their own thought and associated with not from themselves.