Theory-based research in schizophrenia.

TOPIC. Theoretical models to guide research into schizophrenia. PURPOSE. To review the most commonly used biological and environmental models of schizophrenia. SOURCES. Published literature and research conducted by the author. CONCLUSIONS. The vulnerability model includes both biological and environmental variables that impact the course of schizophrenia and treatment RESPONSES. Thus, it may be a useful framework for nursing research examining responses to various psychosocial treatments in schizophrenia. Search terms: Schizophrenia theory research ********** Schizophrenia is considered the most chronic and disabling of the severe mental disorders. Even with treatment, most people diagnosed with schizophrenia suffer lifelong symptoms. As a result of deinstitutionalization, the majority of people with schizophrenia reside in community settings. Unfortunately, service limitations and poorly coordinated care continue in many communities. The complexity of the disease of schizophrenia and the multitude of factors influencing the course of the illness and treatment responses have resulted in numerous models being proposed to describe and explain the disease. This article briefly reviews the most commonly used biological and environmental models of schizophrenia. The stress-diathesis model of vulnerability is described in detail. The vulnerability model is discussed in relation to research conducted by the author and compared to the Neuman Systems Model. The article concludes with the practical implications of the use of the vulnerability model. Biological Models The biological models of schizophrenia emphasize neurochemical dysregulation or anatomical changes in the brain. The most widely disseminated and thoroughly developed biological models include the neurotransmitter model (Carfagno, Hoskins, Pinto, Yeh, & Raffa, 2000; Stober et al., 1998) and the executive function model (Fucetola et al., 2000; Velligan & Bow-Thomas, 1999). The neurotransmitter model focuses on chemical transmission in the prefrontal cortex, hippocampus, and temporal lobes of the brain, postulating that increased dopamine receptor activity in these areas results in hallucinations and delusions (Turner, Fedtsova, & Jeste, 1997). The so-called typical antipsychotic medications (e.g., Haldol, Prolixin, Mellaril, Navane) act primarily to block dopamine receptors and increase dopamine destruction, while the atypical medications (e.g., Zyprexa, Risperidone) have an antagonist function against dopamine in addition to serotonin. This dopamine antagonism is thought to explain the effectiveness of these medications in reducing the positive symptoms of schizophrenia. In contrast, the executive function model explains schizophrenic symptoms in terms of neurocognitive deficits associated with dysfunction in prefrontal brain systems (McGrath, Scheldt, Welham, & Clair, 1997). The processes involved in cognitive control of action and thought operate on two levels. The routine level includes activities where learned responses are used. The supervisory level operates when learned responses are inadequate, for example when the solution to a task is unknown or when extraneous stimuli must be inhibited in order to perform some task (Robert et al., 1997). People with schizophrenia exhibit difficulties with supervisory level functions, including difficulties in ordering sequential behaviors, establishing goal-directed plans, maintaining task when interrupted, monitoring personal behavior, and associating knowledge with required responses. Difficulties with daily activities are especially evident when nonautomatic actions are involved. Environmental Models Environmental models of schizophrenia focus on interpersonal relationships (King & Dixon, 1999; Furukawa, Harai, Hirai, Kitamura, & Takahashi, 1999) or adaptation processes (Provencher, Foumier, Perreault, & Vezina, 2000). …