Aim: Show brain of murders who plead guilty by reasons of insanity (GBRI) were different from brains of non-murders.
Especially relatively localised brain dysfunctions in pre-frontal cortex, amygdala and thalamus.
Sample: 41 murders pleading NGRI matched to 41 controls. (39 men & 2 women) matched on Sex, Age, Schizophrenic traits. Controls had 6 Schizophrenics. Rest with no trace of mental illness
Procedure: Experimental group in custody, went medication free for 2 weeks so it stops effecting the brain.
Murders with schizophrenia matched with controls with Schizophrenia
Tests of culture 14 non-white tested with 14 white murders, Test of left & right hand seeing if affected brain behaviour
Injected with FDG (flurodeoxyglucose) which traced brain metabolism. 10 mins before injection they did cpt practice task to activate brain lobes.
Continuous performance task to make frontal lobes, temporal lobes, parietal lobes work hard, spotting targets on screen, pressing button. Lasted 32 mins.
10 pet scans, at 10mm intervals done to pick up glucose readings in cerebral cortex. & sub cortical levels
Results: -Amygdala lower glucose in left (0.94) than controls (97), higher in right (0.88) than controls (0.83).
Thalamus higher glucose in right (1.15) than controls (1.09)
Parietal lobes had lower glucose than controls, same with Cerebral Cortex & Frontal Cortex.
Frontal lobe – lower glucose to controls in R & L. Corpus Callosum – lower glucose than controls
No S.D in performance task but S.D in brain metabolism of glucose in number of areas showing NGRS murders have different brain functions
Conclusion: Evidence confirms brains of murders pleading NGRI are different to non-murders. Deficits in Pre-frontal cortex & amygdala leads to violent behaviour.
Reduced Glucose in parietal lobes correlated with cog dysfunctions, reduce verbal ability and educational difficulties & violent opportunities.
PFC & AMYGDALA DAMAGE LEADS TO aggression.
| Strengths | Weaknesses |
| Reliability- carried out in lab using pet scans meaning high control over EV (culture, right handed, left handed, SZ) – standardized easier to test for consistencies
Reliability – pet scans considered objective as produce images of brain which only interpreted one way – makes study reliable & higher Scientific Application – brain activity in certain areas may act as predispotion for violence – violent criminals may be less accountable for their actions & important for sentencing Internal Validity – matched murders (41) to control of 41 with same age, sex & SZ – reduce effects of ppt variables comparison meaningful |
Generalisability – 41 ngri criminals used who aren’t mentally stable don’t qualify for results of entire world. Only used 3 females – can only apply to this group.
Validity – unable to conclude that violence is caused by bio differences – a cause and effect relationship cannot be established as environmental factors may play a part. Ethics – experimental group went medication free for 2 weeks before pet scan – psychological harm could be put on ppts as they aren’t taking meds Task validity – CPT was to look for targets & pressing a button which has no bearing on violent behaviour – not a task suitable for what is studying as doesn’t intent to create violent behaviour so lacks validity |