Biological factors as potential causes of schizophrenia

Schizophrenia is a complex mental disorder, and biological factors play a significant role in its potential causes. These factors include genetic predisposition, biochemical imbalances, and neurological abnormalities, each supported by various research findings.

Studies on genetic influences on schizophrenia

• Family and twin studies - Research shows that having a close relative with schizophrenia increases the likelihood of developing the condition. Concordance rates, which indicate the probability that both individuals in a pair share the disorder if one does, are higher in identical (monozygotic, MZ) twins compared to non-identical (dizygotic, DZ) twins.
• Concordance rates in twins - Studies, such as those reviewed by Gottesman (1991), found a concordance rate of approximately 48% for MZ twins (who share 100% of their genes) and around 17% for DZ twins (who share 50% of their genes). This suggests a strong genetic component, as MZ twins are more likely to both have schizophrenia if one does.
• Adoption studies - Evidence from adoption research indicates that children adopted away from biological parents with schizophrenia still show a similar risk of developing the disorder, pointing to genetics over environmental influence.
• Limitations of genetic evidence - No study shows a 100% concordance rate even in MZ twins, implying that genetics alone cannot explain schizophrenia. Environmental factors or shared upbringing might also contribute to higher rates in family studies, as children may mimic observed behaviours.

Biochemical factors and the dopamine hypothesis

• The dopamine hypothesis suggests that overactive dopamine synapses in the brain are linked to schizophrenia. High levels of this neurotransmitter have been observed in post-mortem examinations and PET scans of affected individuals.
• Supporting evidence for dopamine involvement:
  • Antipsychotic medications, which block dopamine receptors, effectively reduce symptoms like hallucinations, supporting the idea that excess dopamine contributes to these experiences.
  • Drugs that boost dopamine activity, such as certain stimulants, can induce schizophrenia-like symptoms in unaffected individuals.
• Challenges to the dopamine hypothesis:
  • Antipsychotics primarily alleviate positive symptoms (e.g., delusions) but have little effect on negative symptoms (e.g., social withdrawal), indicating dopamine may not explain all aspects of schizophrenia.
  • The relationship between dopamine and schizophrenia is correlational, meaning it's unclear whether high dopamine levels cause the disorder or result from it.

Neurological factors and brain structure

• Neural correlates and abnormalities - Neural correlates refer to brain features linked to specific behaviours or conditions. Studies have identified structural differences in the brains of people with schizophrenia, such as enlarged ventricles (hollow spaces) and abnormalities in areas like the prefrontal cortex.
• Evidence from brain imaging - Research by Johnstone et al. (1976) revealed that individuals with schizophrenia often have larger ventricles, suggesting a loss of brain tissue in the temporal and frontal lobes. Similarly, MRI scans by Buchsbaum (1990) identified irregularities in the prefrontal cortex.
• Limitations of neurological findings - Enlarged ventricles are not exclusive to schizophrenia, as they can appear in individuals without the disorder. Additionally, these observations are correlational, so it's uncertain whether brain abnormalities cause schizophrenia or are a consequence of it.

Psychological factors contributing to schizophrenia

Beyond biological explanations, psychological theories focus on how family dynamics and cognitive processes might contribute to the development of schizophrenia. These perspectives highlight the role of environment and thought patterns in mental health.

Family dysfunction and its impact

• Some psychologists propose that dysfunctional family environments can lead to schizophrenia. Ideas include the concept of a 'schizophrenogenic' mother who is cold and controlling, creating conflict, and Bateson's (1956) Double Bind Theory, which suggests that contradictory family communication confuses children and may trigger the disorder.
• High levels of hostility and criticism in family settings, termed high expressed emotion (EE), are linked to increased relapse rates in individuals with schizophrenia. Research by Vaughn and Leff (1976) showed that patients returning to high EE environments after hospital discharge were more prone to relapse.
• Evidence supporting family disfunction theories:
  • Studies like Lidz et al. (1958) found that emotionally distant parents and unbalanced family dynamics could influence the onset of schizophrenia in children.
• Criticisms of family dysfunction theories:
  • These ideas often overlook biological evidence and unfairly blame families.
  • Many studies are retrospective, conducted after schizophrenia develops, so it's possible the disorder itself disrupts family life rather than the reverse.
  • Poor methodology in this research area has led to its general discredit.

Cognitive explanations for schizophrenia

• Dysfunctional thought processing - Cognitive theories suggest that schizophrenia arises from faulty information processing, leading to issues like delusions, thought interference, language difficulties, and memory impairments.
• Evidence supporting cognitive issues:
  • Neufeld (1978) demonstrated that individuals with schizophrenia took longer to process information and struggled with short-term memory compared to a control group.
  • Meyer-Lindenberg et al. (2002) also found reduced brain activity in areas tied to memory and reasoning during related tasks.
• Challenges to cognitive explanations:
  • Biochemical research indicates that cognitive deficits might result from increased dopamine levels rather than being the primary cause.
  • Cognitive theories alone cannot fully explain schizophrenia and may need integration with biological factors.

Socio-cultural influences on schizophrenia

Socio-cultural factors explore how societal conditions and status impact the likelihood of developing schizophrenia. These explanations consider the broader environment beyond individual biology or family dynamics.

Social causation hypothesis

• Impact of social status - The social causation hypothesis argues that individuals with lower social status are more prone to schizophrenia due to stressors like poverty and discrimination, which elevate stress levels and may trigger the disorder.
• Supporting evidence - Harrison et al. (2001) found a higher incidence of schizophrenia among people born in deprived areas, suggesting that factors such as unemployment and overcrowding play a role.
• Counterarguments and social drift - The evidence is correlational, so cause and effect are unclear. The social drift hypothesis counters that schizophrenia itself may lead to lower social status, as affected individuals often face challenges like unemployment, causing them to 'drift' into deprived areas rather than deprivation causing the disorder.

The diathesis-stress model combining biological and psychological factors

Rather than focusing solely on one type of explanation, the diathesis-stress model offers an interactionist approach, combining biological vulnerabilities with environmental stressors to explain the onset of schizophrenia.

Understanding the diathesis-stress model

• Biological vulnerability (diathesis) - This includes genetic predispositions and biochemical imbalances, such as those related to dopamine, which make an individual more susceptible to developing schizophrenia.
• Environmental stressors - These are external pressures, such as family conflicts, financial difficulties, or workplace stress, that can act as triggers for the disorder in vulnerable individuals.
• Interactionist perspective - Unlike reductionist biological theories that break schizophrenia down to simple components like genes or neurotransmitters, the diathesis-stress model takes a holistic view, suggesting that biological and psychological factors interact to produce the condition.
• Supporting evidence from twin studies - The fact that concordance rates in MZ twin studies are not 100% indicates a genetic link but also highlights the necessity of other factors, such as environmental stressors, in the development of schizophrenia.
• Implications of the model - This approach suggests that while some individuals may have a genetic or biological predisposition to schizophrenia, the disorder may only manifest under specific stressful conditions, providing a more comprehensive understanding of its causes.