Psychology - Brain scanning techniques

Brain scans such as PET and MRI

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MRI - Magnetic Resonance Imaging
MRI allows us to see the structure of the brain and therefore whether there is damage or tumours that need to be treated. During an MRI the patient is placed in a large scanner which passes a very strong magnetic field through their head. The nuclei of some atoms in certain molecules spin a particular way when they are placed in the magnet; this allowed the image to appear on the screen. In the scanner, electromagnetic waves are passed through the body by the magnet, and the nuclei in hydrogen molecules emit their own radio wave at a frequency that the scanner picks up. Hydrogen concentrations differ in different parts of the brain, these results in a very detailed image.

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PET - Positron Emission Tomography
This is a way of seeing a picture of a working brain. It also shows any malfunction, therefore helping to identify damage or tumours. Patients are injected with glucose or water that has been labelled with a radioactive tracer while they lie with their head inside a scanner. Once the substance reaches the brain, the brain cells start to uptake the oxygen in the water or glucose and the tracer begins to decay. When the tracer decays it emits positrons, and the more glucose or oxygen the cells in the brain use up, the more positrons there will be emitted in that area of the brain. When the positrons are emitted, they collide with electrons and form gamma rays which are detected by the scanner to produce an image of the activity in areas of the brain.

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Brain scanning study - Raine et al 1997

Name - Raine et al
Aim - to investigate whether murders who pled insanity have brain abnormalities
Method - 41 murders had pleaded not guilty by reason of insanity and they were compared to a control group of 41 normal participants (matched pairs design). The murderers had histories of SX (Schizophrenia), drug abuse, epilepsy and brain damage.
39 men are used and 2 women, and they were of all different ages and ethnicity, they were all referred to brain scanning to test for evidence of insanity or incompetence for their defence. All were medication free for two weeks prior to the scan. They also had a urine screening to double check. A PET scan was used to examine cortical and sub cortical functioning. They completed target recognition for 32 minutes.

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Results cortical - murderers had:


  •  Low activity in frontal lobe - associated with the ability to control behaviour.

  • Low activity in parietal lobe - associated with verbal ability.

  •  Temporal lobe activity was the same in murderers and non murderers.

  •  higher activity in the occipital lobe

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Results sub cortical - murderers had:

  • low activity in the amygdala
  • low activity in the hypothalamus
  • High levels of activity in the thalamus on the right side leading to fearlessness and inability to comprehend consequences.

Conclusion - Murderers do have abnormal brain activity and biology does determine criminality.

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