Dopamine Hypothesis: Schizophrenia is caused by excess amounts of the neurotransmitter dopamine. It is suggested that there are excess D2 receptors at the synapse. An increase in dopamine in the mesolimbic pathway is suggested to contribute to the positive symptoms, and an increase of dopamine in the mesocortical pathway is linked to the negative symptoms. Sensitivity to dopamine could occur through genetics or brain lesioning; or damage to the prefrontal cortex
Strengths
PET scan evidence supports biological differences in the prefrontal cortex, this evidence is objective
Amphetamines increase dopamine production and produce psychotic symptoms similar to the positive symptoms, suggesting dopamine is the cause
Antipsychotics are successful in treating schizophrenia, they work by blocking receptors and reducing dopamine, suggesting this is the cause
LDopa which is given to Parkinsons patients increases dopamine and can produce symptoms similar to schizophrenia
Weaknesses
Animal studies are often used to see the effects of dopamine. This is not how the disorder occurs naturally and therefore the findings may not be generalised to humans due to the biological differences
It is difficult to establish cause and effect. It may be that schizophrenia causes excess dopamine rather than excess dopamine being the cause
Amphetamines only mimic positive symptoms of schizophrenia, and do not account for the negative symptoms – this suggests it is something other than dopamine
PET scans show blocking dopamine receptors do not always remove symptoms of schizophrenia. Antipsychotics work by blocking receptors but many patients still suffer
Blocking dopamine receptors take time to work. The drug works immediately but the symptoms do not immediately leave, suggesting something other than dopamine is responsible
Strengths
PET scan evidence supports biological differences in the prefrontal cortex, this evidence is objective
Amphetamines increase dopamine production and produce psychotic symptoms similar to the positive symptoms, suggesting dopamine is the cause
Antipsychotics are successful in treating schizophrenia, they work by blocking receptors and reducing dopamine, suggesting this is the cause
LDopa which is given to Parkinsons patients increases dopamine and can produce symptoms similar to schizophrenia
Weaknesses
Animal studies are often used to see the effects of dopamine. This is not how the disorder occurs naturally and therefore the findings may not be generalised to humans due to the biological differences
It is difficult to establish cause and effect. It may be that schizophrenia causes excess dopamine rather than excess dopamine being the cause
Amphetamines only mimic positive symptoms of schizophrenia, and do not account for the negative symptoms – this suggests it is something other than dopamine
PET scans show blocking dopamine receptors do not always remove symptoms of schizophrenia. Antipsychotics work by blocking receptors but many patients still suffer
Blocking dopamine receptors take time to work. The drug works immediately but the symptoms do not immediately leave, suggesting something other than dopamine is responsible