Biological explanations; Dopamine hypothesis

Question 1

History; previous DH

Answer 1

• The DH was developed out of successful treatment for schizophrenia.
• Evidence is correlational; lacks causality
• Inconsistent findings; drug treatment does not help all patients

Question 2

Studies identifying causality

Answer 2

Two lines of evidence suggest a genuine causal role for dopamine in schizophrenia:

• Experimental: L-dopa, a drug which increases dopamine levels, leads to schizophrenic like symptoms in previously unaffected (Parkinson’s) patients.
• Prospective: Recreational use of amphetamines, which also increase dopamine activity, also induce schizophrenic like symptoms.

Question 3

Inconsistency of findings

Answer 3

DH does not apply to all people with schizophrenia

• Drug treatment doesn’t help everyone
• Not all uses of L-dope or amphetamines develop s. symptoms
• Dopamine is not involved in Type 2/ Negative symptoms of S.

Question 4

Recent developments: New DH

Answer 4

• About 6,000 papers have been published since 1990 alone.
• Howes & Kapur claim that dopamine is the common mechanism that produces psychotic symptoms of S.
• All those with S who have psychotic symptoms have pre-synaptic dopamine dysfunction.

Question 5

Initial causes

Answer 5

• Multiple factors both genetic and environmental result in dopamine dysregulation; genes, stressful life events, obstetric complications, family factors, drug use.
• This addresses the second problem of causality; dopamine dysfunction results from multiple factors.
• These can then combine to give unique symptoms which results in unique pathways from the initial cause to the presynaptic dopamine dysfunction.

Question 6

Locus of dysfunction

Answer 6

• The locus of dopamine dysregulation is presynaptic, involving increased synthesis and tendency to release the transmitter
• So excess dopamine is produced and released, but the dysfunction is presynaptic rather than at the dopamine receptor.
• Current drugs act ‘downstream’ rather than ‘upstream’ so they are not treating the primary cause of abnormality.

Question 7

Effect of psychotic symptoms

Answer 7

-Dopamine dysregulation is linked specifically to the dimensions of positive psychotic symptoms and ‘psychosis proneness’ regardless of diagnosis.

Question 8

Psychological effects

Answer 8

• Dopamine dysregulation alters the appraisal of stimuli through the process of aberrant salience (mistaken relevance)
• People with schizophrenia have difficulty telling the difference between relevant and irrelevant info. They do not filter out the irrelevant info and become confused in their thoughts.

Question 9

Nature-nuture

Answer 9

Howes & Kapur see dopamine dysregulation as the common mechanism in schizophrenia. The precise causes are a mix of genetic and environmental factors, including EE and stressful life events.

Question 10

Howes & Kapur: Review of evidence - Initial causes

Answer 10

• Genes: The genes that raise most risk are those associated with the dopaminergic pathways
• Environment: Factors are associated with unemployment, lack of close friends and subordination (hierarchies) Animal studies have shown these factors lead to dopamine dysfunction.
• Interaction: these factors interact e.g. early experiences lead to extreme reactions later due to dopamine dysfunction.

Question 11

Howes & Kapur: Review of evidence - Locus of dysfunction

Answer 11

-A meta-analysis of brain scanning studies by Howes et al. found that high rates of presynaptic dopaminergic function in s patients, while other dopamine dysfunction seems to be less pronounced.

Question 12

Howes & Kapur: Review of evidence - Effect on psychotic symptoms

Answer 12

• Schizophrenic patients with psychotic symptoms display dopamine dysfunction, while those without do not.
• Non-schizophrenics who experience psychotic symptoms also have dopamine dysfunction
• Drugs that reduce positive symptoms all work on the dopamine system.

Question 13

Howes & Kapur: Review of evidence - Psychological effects

Answer 13

-Some studies have linked dopamine systems to motivational salience

Question 14

Key study: Howes et al. (2012)

Answer 14

Aim: Investigating the nature of dopaminergic dysfunction in schizophrenia using meta-analysis of in vivo studies.
Method: 44 studies, with 618 patients with sz, and 608 controls. They used a variety of scans, computed tomography and pet scans to measure dopamine function. Studies were grouped into those of presynaptic function and those of dopamine transporter and receptor availability.
Results: Showed significant elevation (d=0.79) of dopaminergic function in sz patients. And so the conclusion is that the largest dopaminergic abnormality in sz is presynaptic.