The diathesis-stress model proposes that schizophrenia develops through an interaction between a person’s vulnerability (diathesis) and an environmental stress trigger. This means that both nature and nurture contribute to the development of schizophrenia. A vulnerability alone is not usually enough to cause schizophrenia, and neither is stress on its own.
Meehl’s (1962) Original/Old Diathesis-Stress Model
The first person to put forward a diathesis theory was Meehl. Meehl proposed that some individuals inherit a single genetic vulnerability called the schizogene. According to Meehl, people who possess the schizogene are biologically vulnerable to schizophrenia, but the disorder will only develop if they also experience chronic stress.
One source of stress identified by Meehl was the schizophrenogenic mother, who was believed to be cold, rejecting and controlling. Meehl argued that individuals who did not possess the schizogene would not develop schizophrenia, regardless of the amount of stress they experienced.
Simply put – Genetic vulnerability (schizogene) + chronic stress (schizophrenic mother) = schizophrenia
The Modern Diathesis-Stress Model
Meehl’s explanation is now considered too simplistic. Research has shown that schizophrenia is polygenic, meaning that many genes contribute to an individual’s vulnerability rather than a single schizogene.
The modern diathesis-stress model also recognises that vulnerability is not purely genetic. For example, early brain trauma, neurodevelopmental abnormalities and other biological factors may increase vulnerability.
Similarly, modern definitions of stress have expanded beyond dysfunctional family relationships. Environmental triggers/stressors may include:
- Childhood trauma e.g. abuse, neglect or parental loss
- Family conflict e.g. EE families
- Urban living i.e. growing up or living in a densely populated city environment e.g. Increased social stress, Overcrowding, Greater exposure to crime & Noise and environmental stress
- Social adversity i.e. difficult or challenging social circumstances that create long-term stress e.g. Poverty, Unemployment, Social exclusion, Discrimination & Homelessness
- Cannabis use
Simply put – Biological vulnerability + environmental stress = schizophrenia. As you can see, biological vulnerability and environmental stress becomes much broader.
Relevant Research:
Read et al. (2001) reviewed a large body of research and concluded that around 69% of female patients and 59% of male patients with schizophrenia had experienced physical or sexual abuse during childhood. They argued that childhood trauma is an important risk factor for the disorder.
Much of the recent research into factors triggering an episode of schizophrenia has concerned cannabis use. Cannabis increases the risk of schizophrenia by up to seven times. However, this is when cannabis is smoked in high doses, and in people with a pre-existing, genetic vulnerability to schizophrenia. This may act as a particular risk factor, because cannabis interferes with the dopamine system.
Tienari et al. (2004) studied Finnish adoptees to investigate the interaction between genetics and environment. They found that adoptees with a genetic vulnerability to schizophrenia were more likely to develop the disorder when raised in stressful family environments characterised by criticism and low empathy. This supports the modern diathesis-stress model, which argues that schizophrenia develops through an interaction between biological vulnerability and environmental stressors.
Evaluation
- Point: There is research to support the interactionist explanation. Evidence: Read et al. reviewed a large body of research and concluded that around 69% of female patients and 59% of male patients with schizophrenia had experienced physical or sexual abuse during childhood. They argued that childhood trauma is an important risk factor for the disorder. Explain: These findings support the interactionist explanation because they demonstrate how severe environmental experiences may act as stressors that trigger schizophrenia in individuals who already possess a biological vulnerability. Consequence: As a result, the explanation gains credibility because it not only shows a link between stress and genes, it also explains why not everyone with a genetic vulnerability develops the disorder.
- Point: There is research support for the modern interactionist explanation of schizophrenia. Evidence: Tienari et al. investigated Finnish adoptees whose biological mothers had schizophrenia. They found that a critical and unsympathetic parenting style was associated with schizophrenia, but only in children who had a genetic vulnerability. Explain: This supports the interactionist view that schizophrenia develops through an interaction between biological vulnerability and environmental stressors rather than either factor acting alone. Consequence: This increases the explanatory validity of the interactionist approach because it is supported by evidence demonstrating that neither genetic factors nor environmental factors alone are sufficient to explain schizophrenia.
- Point: A strength of the interactionist explanation is that it has important practical applications to interactionist treatments. Evidence: Research by Tarrier et al. found that patients receiving a combination of antipsychotic medication and cognitive behavioural therapy (CBT) showed greater improvement than patients receiving medication alone. Explain: This supports the interactionist explanation because when biological issues and environmental stressors are targeted, there is greater success in treatment. Therefore, suggesting their contribution to schizophrenia. Consequence: This increases the explanatory power of the interactionist explanation because it can account for why treatments that target multiple factors are more effective than those focusing solely on biological influences. Therefore, the interactionist approach may provide a more complete account of schizophrenia than reductionist explanations.
- Point: A limitation of the interactionist explanation is that it remains largely deterministic in its account of schizophrenia. Evidence: The model proposes that inherited vulnerabilities interact with environmental stressors to increase the likelihood of developing the disorder. Explain: This reflects both biological and environmental determinism because the factors influencing schizophrenia are assumed to operate outside an individual’s conscious control. Consequence: As a result, the explanation may oversimplify the development of schizophrenia by underestimating the role of individual agency and resilience. This reduces its completeness as an explanation because it cannot fully account for why some people exposed to significant vulnerabilities and stressors do not develop the disorder.
Interactionist Treatment:
The interactionist approach to treating schizophrenia uses a combination of biological and psychological therapies. Typically, antipsychotic medication is used first to reduce the most severe symptoms, after which psychological therapies such as cognitive behavioural therapy (CBT) can be used alongside medication.
Antipsychotic Medication
Atypical antipsychotics, such as Clozapine, work by blocking dopamine receptors and serotonin receptors in the brain. This helps to reduce the activity of these neurotransmitters.
According to the dopamine hypothesis, schizophrenia is associated with abnormal dopamine activity, and atypical antipsychotics act on both dopamine and serotonin systems. By reducing dopamine activity, antipsychotic drugs can help alleviate symptoms such as hallucinations and delusions. The action on serotonin receptors may also help improve mood and tackle avolition symptoms.
Cognitive Behavioural Therapy (CBT)
CBT assumes that some symptoms of schizophrenia, particularly delusions and hallucinations, may be influenced by faulty interpretations of experiences.
The therapist works collaboratively with the patient to:
- Identify irrational beliefs.
- Examine the evidence for and against these beliefs.
- Develop alternative explanations.
- Reduce the distress associated with symptoms.
For example, a person who believes they are being monitored by the government may be encouraged to evaluate the evidence supporting this belief and consider alternative explanations.
CBT normally involves around 5–20 sessions, depending on the individual’s needs.
CBT helps individuals with schizophrenia identify and challenge irrational beliefs. For example, a therapist may use logical disputation to question whether a delusion is internally consistent and empirical disputation to examine the evidence supporting it. The therapist then helps the patient develop alternative explanations for their experiences, reducing the distress caused by symptoms such as hallucinations and delusions
Disputing irrational beliefs
Logical Dispute – (does it make sense?) Could there be other reasons for having side effects to the drugs? This line of questioning helps the person develop alternative explanations for their experiences.
Empirical Dispute – (is there evidence?) For example, the therapist may ask the patient to think of examples when the staff have protected them? This is an example of empirical dispute, as the therapist is encouraging the patient to look for evidence to disprove their beliefs.
This line of questioning can be carried out without causing distress, provided there is an atmosphere of trust between the patient and the therapist, who remains empathetic and non-judgmental.
Exchanged belief – This is the outcome in response to the cognitive therapy. The patient develops a new belief that is a more accurate reflection of reality, and this helps to alleviate the stress caused by hallucination’s and delusions.
Evaluation:
- Point: A strength of the interactionist approach to treatment is that research evidence demonstrates the effectiveness of combining biological and psychological therapies. Evidence: Tarrier et al. found that patients receiving a combination of antipsychotic medication and CBT experienced greater symptom reduction than those receiving medication alone. Explain: This suggests that targeting both the biological and psychological aspects of schizophrenia can lead to better treatment outcomes than focusing on only one aspect of the disorder. Consequence: Therefore, the interactionist treatment approach may be more effective at reducing symptoms and improving patient functioning because it addresses multiple factors associated with schizophrenia
- Point: A limitation of interactionist treatment is that it can be expensive and time-consuming to implement. Evidence: Patients typically require ongoing medication as well as regular CBT sessions delivered by specially trained therapists. Explain: This requires considerably more resources than prescribing medication alone. Consequence: As a result, access to interactionist treatment may be restricted in some healthcare settings, limiting its practical usefulness despite its potential effectiveness.
- Point: A strength of interactionist treatments is that they may produce long-term improvements in functioning. Evidence: Research by Turkington et al. found that CBT helped patients challenge delusional beliefs and develop coping strategies for managing symptoms. Explain: Unlike medication, which often works only while it is being taken, CBT teaches skills that can continue to be used after therapy ends. Consequence: This suggests that interactionist treatments may be more effective at preventing relapse and promoting long-term recovery than treatments that focus solely on symptom reduction.
- Point: A strength of interactionist treatments is that they can be tailored to the individual’s unique needs. Evidence: During CBT, therapists focus on an individual’s specific delusions, hallucinations and thought processes rather than applying exactly the same intervention to every patient. In addition, antipsychotic treatment can be personalised through adjustments to both the dosage and type of medication prescribed. Explain: This means that treatment can address the specific symptoms and circumstances experienced by each patient. Such an approach recognises that schizophrenia affects individuals differently and that the causes and manifestations of the disorder may vary from person to person. Consequence: As a result, interactionist treatments may be more effective than standardised approaches because they can target the particular difficulties experienced by an individual. This personalised approach may also improve patient engagement and increase the likelihood of positive treatment outcomes.
- Point A limitation of interactionist treatments is that they can be difficult to deliver on a large scale. Evidence Medication can be prescribed to thousands of patients relatively easily, whereas CBT requires trained therapists and regular face-to-face appointments. Explain Because therapist availability is often limited, not all individuals diagnosed with schizophrenia are able to access psychological treatment alongside medication. Consequence This reduces the practicality of the interactionist approach because many healthcare systems may struggle to provide combined treatment for all patients who could benefit from it.
