CAT/CT (Computerised Axial Tomography) Scans (AO1)
- Structural scan - uses X-rays
- Creates slices of the brain built into a 3D image
- Specialists identify any areas of brain damage or tumours
- Lie on the moving platform to be passed through a scanner
- Psychologists use them to establish the size of brain regions (amygdala linked to aggression) or to identify lesions in the brain leading to loss of neurons and connections (pre-frontal cortex linked to aggression)
CAT/CT (Computerised Axial Tomography) Scans (AO3 - Strengths)
AO3 ‹+› non-invasive, painless way to produce 3D images of the brain, can reveal abnormal structures in the brain (tumours, structural damage), responsible for changes in behaviour (aggression)
AO3 ‹+› objective data of brain structures, viewed by multiple researchers, check for consistency, increases reliability, interpretation is not subjective
CAT/CT (Computerised Axial Tomography) Scans (AO3 - Weaknesses)
AO3 ‹-› only provide structural information through still images, limited use in research looking for links between areas of brain activity and specific behaviours
AO3 ‹-› emits radiation, increases exposure (more radiation) to patient if the scan is more detailed and and complex, can be harmful to cells (person more at risk), use in psychological research is limited
PET (Positron Emission Tomography) Scans (AO1)
- Functional scan
- Establish levels of activity in brain areas
- Radioactive glucose tracer injected into the arm, travels around the body until it reaches the brain
- Brain metabolises glucose, more active areas of the brain will metabolise more glucose relative to other areas
- Tracer will decay and emit positrons, collide with electrons in the body to form gamma rays
- Gamma rays are detected by the scanner and these are displayed as images
- Hotspots (red/orange) show higher levels of relative activity
- Studies -> take a resting brain activity measurement before exposure to stimulus to establish a baseline
PET (Positron Emission Tomography) Scans (AO3 - Strengths)
AO3 ‹+› produce images of the brain that can be checked by other researchers, able to interpret the images to check the consistency of the results, increases reliability
AO3 ‹+› sensitive enough to detect neurotransmitter activity and activity of receptors on neurons (e.g. dopamine activity during drug use), able to link brain activity to behaviour and the participant’s experiences
PET (Positron Emission Tomography) Scans (AO3 - Weaknesses)
AO3 ‹-› more invasive than other scans due to radioactive tracer being injected, lead to cell damage and higher risk of DNA mutations -> ethical issues, can only be carried out every 6 months, limiting use in psychological research
AO3 ‹-› only show generalised areas of brain activity, not specific locations, areas of brain activity can differ between participants -> hard to pinpoint exact area of brain activity, difficulty drawing conclusions about which areas of the brain are linked to specific behaviours
fMRI Scans (Functional Magnetic Resonance Imaging)
- Functional and structural
- No radiation
- Placed in a scanner which produces a strong magnetic field -> causes the nuclei in H atoms to align with the direction of the magnetic field
- As neural activity increases, blood flow increases, delivers more oxygen to those parts of the brain
- O₂ binds to haemoglobin and is carried to the brain
- Oxyhaemoglobin repels the magnetic field (diamagnetic)
- Deoxyhaemoglobin aligns with the direction of the magnetic field (paramagnetic)
- Changes picked up by the scanner, maps levels of neural activity in the brain
- Used by psychologists to measure emotional responses (aggression) to tasks done whilst in the scanner (measure neural activity in response to a series of faces displaying emotions)
fMRI (Functional Magnetic Resonance Imaging) Scans (AO3 - Strengths)
AO3 ‹+› non invasive, no radiation, safer for use in psychological research, participants can have multiple scans, check for consistency, increase reliability
AO3 ‹+› produce higher resolution images than PET scans (can show brain activity to the mm), more precise in pinpointing activity in specific brain areas
fMRI (Functional Magnetic Resonance Imaging) Scans (AO3 - Weakness)
AO3 ‹-› 5-sec time lag between brain activity and image appearing on the screen, interpretation of information more difficult, reduces reliability if errors are made
AO3 ‹-› cannot look at the activity of neurotransmitters (PET scans can), cannot fully replace PET scans if we want to understand human behaviour linked to neurotransmitter activity in the brain
Brain Functioning as an Explanation for Aggression (P1) - Pre-frontal Cortex, Corpus Callosum
- Cerebral Cortex divided into 4 lobes
- Pre-frontal cortex is associated with deferred gratification and decision making,
- Low levels of activity linked with aggression
- Corpus Callosum involved with the regulation and control of behaviour, linked to understanding the long-term implications of a situation
- Low levels of activity = high levels of aggression
- Leads to inappropriate emotional expression and an inability to grasp the long-term implications of a situation (act impulsively with no thought to consequences)
AO3 ‹+› Raine et al (S.E) conducted PET scan on 41 NGRIs and found aggressive behaviour to be associated with lower activity in the corpus callosum and pre-frontal cortex compared to non-violent offenders, supports link between specific brain activity and aggression
AO3 ‹-› cannot make cause and effect statements, differences in brain activity of violent offenders may be due to the brain developing differently in response to environmental factors (neglect, abuse), aggression = developmental factors that affect brain functioning
Brain Functioning as an Explanation for Aggression (P2) - Amygdala, Hypothalamus
- Limbic system includes the amygdala and hypothalamus
- Hypothalamus regulates behaviours (pain response, anger, aggression) and our autonomic nervous system (blood pressure, arousal levels)
- Amygdala responsible for self-preservation and identifying threats, linked to arousal, aggression and fight-or-flight response
- Smaller amygdala linked to aggression
- Reduced activity linked to a lack of fear (may be more aggressive if they are not scared of being violent)
AO3 ‹+› Swantje et al (S.E) found a negative correlation between the volume of the amygdala (measured by MRI) and self-reported lifetime aggression in humans (smaller size, more aggression), clear link between functioning and aggressive behaviour
AO3 ‹-› deterministic, suggests those with a smaller amygdala are destined to be aggressive and cannot control their own behaviour, gives people an excuse for their behaviour so less likely to take responsibility for their actions or be receptive to treatment programmes, could then have implications for others in society (family members including children)
Brain Functioning as an Explanation for Aggression (Conclusion)
AO3 ‹+› knowledge of the link between brain functioning and aggression can be supported by brain scans and used to understand aggression and deal with individuals appropriately - Donta Page (violent murderer) was saved from the death penalty, argued his behaviour was not in his control
AO3 ‹-› simplifies the complex human behaviour of aggression being due to neural activity in specific brain areas, ignores the impact of culture and social learning on aggression, reductionist
P1: Raine et al. (1997) - Aim, Sample
- Raine et al. (1997)
- Aimed to look at direct measures of both cortical and subcortical brain functioning using PET scans in a group of murderers pleading not guilty by reason of insanity (NGRIs) and compare these to controls
- Sample = 41 NGRIs (39m/2f), 41 controls, matched for sex, had a similar age (31.7 years) and medication free for 2 weeks before the study
AO3 ‹+› use of control group matched with the NGRIs for variables (sex, age), screened for physical and mental health (exclude those with a history of head trauma or substance misuse), important participant variables controlled, allows for reliable comparisons between both groups
AO3 ‹-› only represents a small group of violent offenders (NGRIs), not representative of all types of violent offenders, reduces generalisability to non-NGRIs and their behaviour
P2 - AO1: Raine et al. (1997) - Procedure, Results
- All participants injected with a radioactive glucose tracer and required to carry out a continuous performance task (CPT - shown to increase glucose metabolism in the frontal lobes)
- After 32 mins, participants given a PET scan
- Found that NGRIs had a lower activity in their prefrontal, parietal areas, corpus callosum and left amygdala compared to controls
- Concluded that his findings supported dysfunction in the prefrontal cortex being linked to impulsive behaviour
- Abnormal activity in subcortical structures linked to unusual emotional responses (lack of fear)
P2 - AO3: Raine et al. (1997)
AO3 ‹+› standardised procedure (CPT for 32 mins before PET scan, med free for 2 weeks), replication, check consistency, increase reliability
AO3 ‹-› took place in an artificial, controlled laboratory setting with participants completing a task not related to violent behaviour, may act differently when committing a crime in real-life, lack ecological validity
Conclusion: Raine et al. (1997)
AO3 ‹+› U.A. use findings as a diagnostic tool to identify individuals who match the NGRI population to predict violent behaviour, lead to earlier interventions
AO3 ‹-› May lead to people not being held accountable for their criminal behaviour, socially sensitive issue
