Dopamine Hypothesis

• Dopamine Hypothesis


  Theory that an imbalance of neurotransmitters (dopamine) may account for schizophrenic symptoms
• Two nerve pathways associated with schizophrenia

  1. Mesolimbic

  2. Mesocortical
• Mesolimbic pathway


  • Carries signals from the ventral tegmental area to the
• Mesocortical pathway


  • Carries signals from the ventral tegmental area to the frontal lobe
• Too little DA in the Mesocortical pathway

  Found in those with negative symptoms like little emotion, hallucinations and delusions
• Too much DA in the Mesolimbic pathway

  Could produce positive symptoms
• J.J Griffiths tested the Dopamine Hypothesis

  1. Induced psychosis on non-schizophrenic patients with an administration of a drug that increases DA

  2. Individuals experienced hallucinations and a cold emotional response

  3. Then with the drug used to reduce DA, this had no effect on those showing negative symptoms
• Antipsychotics block D2 receptors which reduces the amount of DA released into the synapse
• The dopamine hypothesis is supported by evidence as it explains why antipsychotic drugs work.
• Dopamine hypothesis is supported by evidence as antipsychotic drugs are effective at treating schizophrenia.
• The dopamine hypothesis has been criticised because it doesn't explain all aspects of schizophrenia such as cognitive deficit and social withdrawal.
• Cognitive deficit - difficulty concentrating or remembering things
• However, there are limitations to the dopamine hypothesis such as not all schizophrenia patients respond well to antipsychotics and some people who don't have schizophrenia also experience high levels of DA.
• Therefore, other theories suggest that glutamate may be involved in schizophrenia rather than just DA.
• Glutamate is an excitatory neurotransmitter that stimulates neurons to fire action potentials.
• However, there are limitations to the dopamine hypothesis such as not all people respond well to antipsychotic medication.
• There are also other neurotransmitters involved in schizophrenia such as glutamate and GABA.
• Glutamate is thought to be overactive in schizophrenia leading to too many connections between neurons (hyperconnectivity). This can lead to excessive stimulation of the brain causing hallucinations and delusions.
• Social withdrawal - lack of interest in other people
• Serotonin (5HT) is involved in mood regulation and low levels have been linked to depression.
• There are alternative theories that suggest different neurotransmitters may be involved in schizophrenia such as serotonin and glutamate.
• Some people with schizophrenia do not show increased activity in the mesolimbic pathway.
• Dopamine receptor blockers (antipsychotics) only reduce positive symptoms of schizophrenia, leaving negative symptoms unchanged.