2. dopamine

Dopamine = a neurotransmitter that generally has an excitatory effect and is linked to pleasure. Unusually high levels are associated with schizophrenia, in cortex and subcortex.

Low levels are associated with Parkinson’s

The dopamine hypothesis

  • excess of dopamine is associated with positive symptoms

  • Also found an increase in D2 receptors in postsynaptic receptors, so receive more dopamine

  • Subcortical areas of the brain

  • Original hypothesis was based on the discovery that antipsychotics (that reduce dopamine) improved schizophrenics condition

Updated dopamine hypothesis

  • both high and low levels of dopamine in different brain regions are part of schizophrenia

  • Low levels in the prefrontal cortex (decision making, memory, problem solving) explains cognitive problems (negative symptoms)

  • Also includes the origins of abnormal dopamine e.g genetic variations

  • Hyper = too much, hypo = too little

Evaluation

Strength — evidence

  • Parkinson’s patients. They have low dopamine and when they take medication that increases dopamine they can experience hallucinations

  • Medication for schizophrenia. Reduces dopamine which reduces symptoms

Limitation — glutamate

  • post mortem and live scanning studies have consistently found raised levels of the neurotransmitter glutamate, so other neurotransmitters rather than just dopamine may have a role

Strength —- amphetamine psychosis

  • Catherine tenn induced schizophrenia like symptoms in rats using amphetamines and then relieved symptoms using drugs that reduce dopamine. However other drugs that also increase dopamine levels do not cause schizophrenia-like symptoms

Limitation — other factors

  • Lloyd, believe that dopamine is a causative factor, it may be an indirect factor mediated through environmental factors.

Neural correlates

  • abnormalities within specific brain areas may be associated with the development of schizophrenia

  • Study the correlation with positive and negative symptoms

  • Originally used postmortems, now use fMRI

  • Cortex/ grey matter, lower volume over time. Greater reduction each time a person relapses

  • Enlarged ventricles suggest a loss of brain tissue in surrounding areas. Central brain areas = memory and emotion (positive symptoms). Prefrontal cortex = attention, memory, logic, decision making (Negative symptoms)

  • Allen et al scanned brains of patients experiencing hallucinations (fMRI), they listened to a recording and were asked if the voice was there’s or someone else’s. Schizophrenics couldn’t tell the difference and they had lower activation in the part of the brain responsible for processing sounds (positive symptoms)

  • Also reduced activity in the ventral striatum, involved in motivation/ reward (avolition, negative symptoms)