The main object of this study is to evaluate the efficacy of equine assisted therapy on substantial and so far unsatisfactorily treatable symptom complexes in patients with schizophrenia.

The clinical picture in schizophrenia involves changes in perception, cognition, and affect such as delusions, hallucinations, and disorganized thinking and disorders of attention, memory, and executive thinking. A clinical differentiation, which is widespread in practice, divides the psychopathological disorders of schizophrenic patients in the clinical core areas into positive and negative symptoms.

The term negative symptoms was introduced by Hughlings-Jackson, who made the distinction between florid-psychotic or positive symptoms and "defect" or negative symptoms. The term "positive symptoms" usually includes delusions, hallucinations and formal thinking disorders. The latter are often explained in recent research tradition as a separate "disorganization syndrome". Negative symptoms also appear in the context of other psychiatric and neurological disorders, for example in patients with depression, Parkinson's and craniocerebral traumas.

Negative symptoms, according to Frith and Done, essentially signify a "deficit of willed action" or, more generally, a pathological deficit of activity and reactivity. To establish a border between idiopathic, i.e. primarily due to schizophrenia, outlasting ("trait") negative symptoms and secondary, temporary ("state") negative symptoms Carpenter and colleagues introduced the concept of the deficit vs. non-deficit form of schizophrenia. Negative symptoms constituting the deficit syndrome include affective flattening, limited emotional range, loss of interest, speech depletion, diminished purposefulness, and social listlessness. These symptoms are considered to be primary negative symptoms if they persist beyond the onset of an acute psychotic episode and have been established by differential diagnosis that they are not or at least not entirely secondary to the presence of depression, the side effects of antipsychotic treatment or other circumstances. While primary negative symptoms are currently largely immune to any type of treatment, secondary negative symptoms may remit spontaneously or after appropriate treatment.

Men are more frequently and stronger affected by negative symptoms than women. Also, the negative symptoms manifest themselves earlier in the course of the disease and are associated with stronger cognitive impairments than in women. However, the extent of men's deficits varies little during further psychotic episodes, while women tend to have a progressive profile. Recruitment for the current study will take into account the prevalence.

The positive symptoms can be treated very effectively with medication and stabilization can usually be achieved within a few weeks. On the other hand, the negative symptoms are very difficult to influence with medication. Ideally, modern integrative psychiatric treatment concepts therefore incorporate a combination of pharmacological, psychotherapeutic and psychosocial treatment strategies adapted to the specific symptom constellation and the particular needs and deficiencies of the individual patient.

In recent years, a wide variety of treatments (e.g. transcranial magnetic stimulation or psychosocial treatment options) have been used to improve the negative symptoms in schizophrenic patients, but treatment success has remained low. Thus, the results of existing studies on TMS and rTMS are also controversial. There are some studies in which positive effects were found on the psychpathology for example, whereas other studies could not find any significant positive effects of rTMS in schizophrenia patients.

Another applied intervention that has been established for many years in a wide variety of mental illnesses is animal assisted therapy. This is used for example in children with autism, patients with anxiety disorders or depression, but also in schizophrenic patients. The effects of animal assisted therapy are versatile. For example, improvements in autistic symptoms, emotional well-being, self-esteem, self-determination, depressive symptoms, positive and negative symptoms in schizophrenics or improvement in quality of life were found.

In studies that explicitly examined the effects of animal assisted therapy on schizophrenic patients, several positive outcomes have been reported. Maujean and colleagues found in their meta-analysis positive effects of animal assisted therapy on social contact, positive and negative symptoms, and the quality of life in terms of interpersonal relationships. Barak and colleagues investigated in their study how animal assisted therapy affects older schizophrenic patients and found a significant improvement on the Social Adaptive Functioning (SAFE) scale with a focus on the social function subscale. Furthermore, positive effects on the activities of everyday life and general well-being were found. There were several studies which assessed the PANSS (Positive and Negative Syndrome Scale) and found a significant improvement in the negative symptoms due to animal assisted therapy. In addition, a reduction of the cortisol level was noted and the adherence in the therapy group compared to the control group was significantly higher. Furthermore, a constant remission of the disease as well as a lower hospitalization of the patients were reported. One study, in addition to the PANSS, the Living Skills Profile (LSP) and the World Health Organization Quality of Life Assessment (WHOQOL-BREF) letter were included and a significant effects on both scales was found as well. In another meta-analysis conducted by Jormfeldt and Carlsson in 2018, six months after the last intervention, positive effects continued to be found at follow-up. Participants in animal assisted therapy reported benefits at the psychosocial level, such as increased self-efficacy and self-esteem, social stimulation, and new skills that could be transferred to other areas of life. In summary, there is already evidence for the efficacy of animal assisted therapy on the negative symptoms, psychosocial functioning and quality of life of schizophrenic patients, which should be further supported in the controlled setting as part of the planned study.

Appropriate conceptualization is essential for the development of suitable treatment methods for the negative symptoms of schizophrenic patients. However, the concept of negative symptoms has changed significantly since the development of the standard instruments SANS and PANSS, and for a long time there was no clear consensus on the construct of negative symptoms.

In their 2014 review, Marder & Kirkpatrick juxtaposed the standard instruments SANS and PANSS with newer gauges designed to assess negative symptoms. As one of the first scales designed exclusively for the detection of negative symptoms in schizophrenic patients, the SANS has played a key role in the holistic study of schizophrenia. However, Marder & Kirkpatrick argue that the SANS contains items that are unlikely to be part of the negative symptoms (inappropriate affect & impaired attention). These items have also often been omitted by researchers in recent years when using the SANS. Furthermore, more recent studies suggest that it would be useful to distinguish between the anticipatory and the consumptive aspect of anhedonia, as the patients do have some limitations in the first, but this does not seem to be the case with the latter. At a National Consensus Meeting held by the NIMH (National Institut for Mental Health), negative symptom domains were identified that are inconsistent with the five subscales of the SANS or the five factors of the PANSS. The fixed domains are dulled affect, alogy, asociality, anhedonia, and avolition. A scale used to record the negative symptoms should accordingly only contain items that belong to the above-mentioned areas. Another issue is that the meter should be able to detect changes in the symptoms. In addition, it should be short and internationally applicable (easy to translate and transferable to different cultures). Finally, a measurement tool should have psychometric properties such as inter-rater reliability, internal consistency, test-retest reliability, and content, convergence, and discriminant validity.

Under these conditions, the BNSS emerged. This short scale for detecting negative symptoms in schizophrenic patients consists of 13 items and can be collected within 15 minutes. It was important to the authors of the scale to distinguish between the anticipatory and consumptive aspects of anhedonia, as well as between experience and behavior. The BNSS showed excellent inter-rater and test-retest reliability, as well as good vailidity in comparison with other scales, as shown in psychometric studies. Furthermore, it could be shown that the scale has an inverse correlation with a measure of the functional level and the MATRICS Consensus Battery. An additional important point is that the BNSS correlates only marginally with masses of positive symptoms, anxiety, and depression. For these reasons, the BNSS should also be used in the planned study. In addition, the further development of objective measuring instruments for the collection of negative symptoms in the study by examining the application of acoustic analysis and the concept of the voice should explain changes in schizophrenia as a correlate of negative symptoms.

Other target variables of the study will be the PSP scale (Personal and Social Performance Scale) and the S-QoL (Quality of Life Questionnaire in Schizophrenia). The PSP was designed out of the DSM-IV Social and Occupational Functioning Assessment Scale (SOFAS) with the goal to develop a scale that can quickly and validly capture the personal and psychosocial functioning of patients. Among the advantages of the PSP over other scales such as the SOFAS or the GAF (Global Assessment of Functioning), is the fact that the professional, social and personal functioning are operationalized in more detail, since there is no mixing of psychopathological symptoms and psychosocial aspects. Furthermore, the four subscales of the PSP, which are initially collected in order to then form a total score, give a higher information value than is the case with the SOFAS or the GAF . In addition, initial studies on the PSP have shown that the scale has high validity and reliability values. The PSP is a third-party assessment and, as already mentioned, contains four subscales whose items are queried on a 6 point scale. From the assessments of the four subscales, an overall score is then formed, ranging from 0-100 and subdivided into 10 intervals. To simplify the survey, Schaub and Juckel have developed an interview guide for the German version of the PSP.

As mentioned above, the recovery and improvement of psychosocial functioning have become increasingly the focus of treatment efforts in recent years. In this context, the quality of life of patients was often examined. As a secondary target variable, therefore, an instrument for assessing the subjective quality of life should also be used in the planned study. Despite the large number of life-quality assessment tools validated or specifically developed for schizophrenic patients in recent years, there is no clear consensus on which survey instrument to use. The selection should therefore focus on the concrete conceptualization of the instrument, the question and the applicability of the population to be examined in the existing setting. In the present study, the Quality of Life Questionnaire is to be applied in schizophrenia (S-QoL). It uses 41 items to record 8 subscales of the quality of life such as well-being, self-esteem, resilience and autonomy. The S-QoL is a self-assessment tool and its application takes 15 minutes.

The present study STABLE is planned with inpatients at the Psychiatric University Clinic, Department of Forensic Psychiatry, Center for Inpatient Forensic Therapy Rheinau. In the active control phase, a WHO-recommended psychosocial intervention for the treatment of schizophrenia, the training of everyday activities and self-employment (board games, everyday skills, etc.) is used. In terms of content, the training of everyday activities is based on the sub-program "Social Skills" of the IPT (Integrated Psychological Therapy Program).

The study complies with the European Mental Health Action Plan 2013-2020.

Inclusion Criteria:

• Diagnosis of schizophrenia (ICD-10: F20.0-20.3, F20.5)
• men or female patients (older than 18 years of age)
• written informed consent

Exclusion Criteria:

• acute risk of harming oneself or others
• severe manifest allergies
• medically uncontrolled epilepsy
• Significant side effects of medication (blood pressure fluctuations with dizziness, movement-limiting Parkinson's disease, etc.).