Biological Explanations: Dopamine Hypothesis

Dopamine hypothesis

The theory that schizophrenia is caused by abnormal dopamine activity in the brain.

Hyperdopaminergia

Excess dopamine activity in subcortical areas such as the mesolimbic pathway.

Mesolimbic pathway

Associated with emotion and reward; excess dopamine linked to positive symptoms.

Positive symptoms link

Hyperdopaminergia can lead to hallucinations and delusions.

Hypodopaminergia

Low dopamine activity in cortical areas, particularly the prefrontal cortex.

Prefrontal cortex role

Responsible for decision-making and executive functioning.

Negative symptoms link

Hypodopaminergia associated with speech poverty and avolition.

Revised dopamine hypothesis

Schizophrenia involves both dopamine excess and dopamine deficit in different brain regions.

Dopamine receptors

D2 receptor overactivity increases dopamine sensitivity.

Antipsychotic drug action

Dopamine antagonists block D2 receptors and reduce positive symptoms.

Evidence from drugs

Amphetamines increase dopamine and can induce psychosis-like symptoms.

Parkinson’s medication

Drugs that increase dopamine can trigger schizophrenia symptoms in some individuals.

Post-mortem evidence

Some studies show higher numbers of dopamine receptors in schizophrenia brains.

Neuroimaging evidence

Brain scans show dopamine dysregulation in schizophrenic patients.

Strength: drug treatment success

Effectiveness of antipsychotics supports dopamine involvement.

Strength: scientific and measurable

Dopamine levels, receptors and pathways can be objectively studied.

Limitation: not complete explanation

Not all patients respond to dopamine-blocking drugs.

Limitation: serotonin involvement

Other neurotransmitters (e.g. serotonin, glutamate) also linked to schizophrenia.

Glutamate hypothesis

Low glutamate activity may play a major role in cognitive and negative symptoms.

Limitation: causation issue

Dopamine abnormalities may be consequence, not cause.

Limitation: reductionist

Reduces complex disorder to a single neurotransmitter.

Best explanation

Neurochemical imbalance interacts with genetics and environment.