Biological Explanations for Schizophrenia

THE DOPAMINE HYPOTHESIS

Dopamine Hypothesis

The original Dopamine Hypothesis states that the brain of schizophrenic patients produces more dopamine than the brain of a “normal” person.

Through further research, it is now thought that schizophrenics have an abnormally high number of D2 receptors.

Normal Level of Dopamine In The

Human Brain

Elevated Level of Dopamine In The Brain of a Schizophrenic Patient

(specifically the D2 receptor)

Neurons that use the transmitter ‘dopamine’ fire too often and transmit too many messages.

There is an excess of D2 receptors at the synapse in schizophrenics Lowering DA activity helps remove the symptoms of schizophrenia

Research Support

• In your groups/pairs you have a piece of evidence to support the dopamine hypothesis

• Summarise this research and write it in the appropriate section in your booklet.

• You must then outline the study to the rest of the class.

Randrup et al (1966) – Amphetamines

• Amphetamines are a stimulant drug which increase levels of dopamine.

• They injected rats with 1-20mg of amphetamines (also other animals)

• They caused schizophrenic-like symptoms such as hyperactivity

• Effects were reversed with anti-psychotics which reduce dopamine

Seidman (1990) – Post-mortems

• Post-mortems are examinations done on people after death.

• Compared schizophrenics brains with normal brains and found schizophrenic brains had higher numbers of dopamine receptors (D2 receptors)

Kessler et al (2003) – PET scans

• PET scans are scans which show brain functioning

• Injected people with a drug which binds to dopamine receptors – this drug is then highlighted by the PET scan so the receptors can be counted

• They found that schizophrenic patients had higher levels of dopamine receptors compared to non-schizophrenics

Patients with Parkinson’s disease

• Parkinson’s disease is a loss of nerve cells in the part of the brain responsible for controlling voluntary movement. This part of the brain also produces dopamine therefore people with Parkinson’s have lower than normal levels of dopamine.

• This is treated with a drug called L-Dopa which increases dopamine in the brain. With prolonged use of drug, they can develop schizophrenic symptoms

Evaluation of the dopamine hypothesis

• Has allowed for a successful treatment of schizophrenia to be developed

- What could this be?

Antipsychotic drugs block dopamine receptors, preventing dopamine having an effect on the brain – this reduces symptoms

BUT – only reduce positive symptoms – have no effect on negative symptoms - so dopamine probably only causes pos symptoms

Which came first - Schizophrenia or Excess dopamine?

Does excess dopamine cause schizophrenia or does schizophrenia cause excess dopamine???

DIFFICULT TO TEST!

The Chicken or the Egg?

Which Came First?

PROBLEMS WITH CAUSE AND EFFECT

Evaluation of the dopamine hypothesis

• This explanation is considered to be reductionist – why?

• Reducing a complex disorder to simply having problems in brain chemical levels. Ignores other factors such as their environment.

Evaluation of the dopamine hypothesis

• This explanation is considered to be deterministic – why?

• Taking away free will. This explanation claims that if you have raised dopamine levels you will develop schizophrenia when actually you could create a healthy environment for yourself and not.