Other Biological Methods (Edexcel A-Level Psychology): Revision Notes
Other Biological Methods
Brain-scanning techniques
Brain-scanning techniques allow psychologists and medical professionals to examine the structure and function of the brain. These methods have become increasingly important in understanding the biological basis of behaviour and diagnosing neurological conditions. The main techniques include CAT scans, PET scans, and fMRI scans, each with distinct purposes and methodologies.
CAT (computerised axial tomography) scans
CAT scans (also known as CT scans) use X-ray technology to create detailed images of brain structure. Unlike a standard X-ray that focuses on a single area, CAT scanning involves multiple X-ray beams passing through the head from different angles. A computer processes this information to generate a three-dimensional image of the brain's structure.
The primary use of CAT scans is to detect structural abnormalities such as tumours, areas of damage following head injury, or broken bones. However, these scans only reveal the physical structure of the brain and provide no information about brain function or activity levels.
Procedure: The patient lies on a bed that moves through the scanner whilst X-ray beams pass through the head. The scan duration ranges from a few seconds to approximately 10 minutes, depending on the area being examined. A computer processes the data, which a radiologist then interprets.
Advantages:
- Quick to conduct
- Provides accurate structural detail of the brain
- Assists clinicians in treatment planning and surgical decisions
- May reduce surgery duration and associated anaesthetic risks by allowing surgeons to plan procedures more precisely
Disadvantages:
- Exposes patients to radiation, creating potential health risks
- Risk-benefit analysis required before use (especially avoiding unnecessary scans)
- Pregnant women should avoid CAT scans where possible due to potential harm to the developing foetus
- Provides no functional information about brain activity
CAT scans only show the physical structure of the brain, not its function or activity. They expose patients to radiation, making risk-benefit analysis essential before use, particularly for vulnerable populations such as pregnant women.
PET (positron emission tomography) scans
PET scans are a form of nuclear medicine that measures brain activity by tracking glucose metabolism. Patients receive an injection of a radioactive tracer substance called fluorodeoxyglucose (FDG). This tracer consists of a radioactive atom attached to glucose molecules.
Procedure: Once injected, the tracer enters the bloodstream and is absorbed by active brain regions. Active areas of the brain consume more glucose for energy. As the brain uses the glucose, the radioactive atoms break down and emit positrons. These positrons produce gamma rays, which the scanner detects. Areas of high activity emit more gamma rays (appearing as warm colours like red), whilst areas of low activity emit fewer gamma rays (appearing as cooler colours like blue).
PET scans can identify abnormal brain activity patterns and detect regions not functioning normally, which may indicate damage or tumours. The technique is particularly useful for investigating psychological conditions.
Research Example: Raine et al. (1997) - PET Scans and Aggression
Raine et al. used PET scans to examine the brain activity of convicted murderers, comparing them to a matched control group of non-murderers.
Findings: The researchers identified abnormal activity in brain regions associated with impulsivity and risk-taking behaviour, potentially explaining increased aggressive tendencies in the murderer group.
Significance: This study demonstrated how PET scans can reveal functional differences in brain activity that may be linked to specific behaviours like aggression.
Advantages:
- Provides functional information about brain activity
- Helps researchers identify which brain areas are involved in specific behaviours
- Can predict potential issues related to abnormal brain activity patterns
Disadvantages:
- More invasive than other techniques due to radioactive substance injection
- Carries low but uncertain long-term health risks from radiation exposure
- Not advisable for patients to undergo multiple scans unless absolutely necessary
- Risk associated with radioactive material, though exposure levels are very low
fMRI (functional magnetic resonance imaging)
fMRI scans represent a relatively recent development (introduced in the 1990s) that enables measurement of brain activity without radiation exposure. This technique works by detecting changes in blood flow associated with neural activity.
Procedure: The patient's head is placed inside a powerful electromagnet. Brain activity is associated with increased blood flow to active regions, which deliver oxygen to neurons. Oxygen is carried by haemoglobin in red blood cells. When haemoglobin carries oxygen, it behaves as diamagnetic (repelled by magnetic fields), but when deoxygenated, it becomes paramagnetic (follows the magnetic field direction). The scanner detects these changes and uses them to create images showing which brain areas are active during different tasks. A computer processes this information to produce activation maps showing changing neural activity levels across brain regions.
Advantages:
- Non-invasive (no injections or radiation exposure)
- Safer than PET scans, with no associated radiation risks
- Preferred method for psychologists researching brain activity
- Can be used repeatedly on the same individual
- Provides detailed functional information
Disadvantages:
- Cannot be used on patients with cardiac pacemakers or recent metal surgical implants
- Unsuitable for claustrophobic individuals or those anxious about confined spaces or loud noises
- Requires patients to remain still in a large tube for the scan duration
- Some individuals may become stressed during the procedure, potentially affecting results
- Expensive equipment and procedure
Key Distinction: fMRI scans are the safest option for repeated brain activity measurements as they involve no radiation exposure, making them the preferred choice for psychological research. However, they cannot be used on patients with certain medical devices or those with claustrophobia.
Using brain scanning to study human behaviour
Psychologists increasingly employ brain-scanning methods to establish links between brain structures, activity patterns, and various human behaviours. Aggression has been a behaviour of particular research interest.
Research Example: Raine et al. (1997) - Brain Activity in Murderers
Method: Raine et al. used PET scans to investigate brain activity in murderers. The researchers examined prisoners convicted of murder and compared their brain activity to a matched control group of non-murderers.
Findings: The PET scans revealed abnormal activity in the murderers' group, particularly in brain regions associated with impulsivity and risk-taking behaviour.
Conclusion: This finding suggested a possible neurological basis for increased aggressive behaviour.
Research Example: Montag et al. (2011) - Video Games and Brain Activity
Research Focus: Investigated whether playing violent video games alters brain activity and potentially increases aggressive tendencies.
Method: Used fMRI scans to compare gamers with control participants.
Findings: Gamers showed reduced activity in response to negative emotional stimuli compared to control participants.
Interpretation: This dampening of emotional response to negative stimuli might explain a suggested link between extensive gaming and increased aggression, as gamers may not process aggressive actions as 'serious' due to altered brain processing patterns.
Evaluation of brain scanning research on behaviour:
Brain-scanning techniques provide objective measurements of brain structure and function, making the evidence highly reliable. Substantial evidence has accumulated linking specific brain regions (such as the limbic system and prefrontal cortex) to aggressive behaviour. However, several issues arise when interpreting this research:
Critical Limitation: Correlation vs. Causation
The evidence indicates an assumption that specific brain areas cause aggressive behaviour, but correlation does not prove causation. Being involved in violent behaviour may change brain functioning rather than brain differences causing the behaviour.
- Conclusive support for either position is difficult because it would require scanning brains before individuals show violent tendencies and comparing these with scans taken afterwards
- We cannot accurately predict who will become violent before aggressive behaviour occurs
- Sample sizes in brain-scanning studies can be limited, making generalisation problematic
- Recruitment of large, diverse groups of participants (particularly specific populations like murderers) presents practical challenges
Twin and adoption studies
Twin and adoption studies provide researchers with methods to investigate the relative contributions of nature (genetics) and nurture (environment) to human behaviour.
Twin studies
Twin studies offer a unique research design to examine genetic influences on behaviour. Monozygotic (MZ) twins (identical twins) share 100% of their genetic material, whilst dizygotic (DZ) twins (fraternal twins) share only 50% of their genes, similar to any two siblings. By comparing behaviour between identical twin groups and fraternal twin groups, psychologists can determine which group shows greater behavioural similarity.
The degree to which behaviour matches between twins is termed the concordance rate. If behaviour shows similar concordance rates in both MZ and DZ twins, researchers might conclude that genetic factors play a minimal role, as environmental factors (shared upbringing) could explain the similarity. However, if MZ twins show significantly higher concordance than DZ twins, this suggests a genetic component to the behaviour.
Research Example: Gottesman and Shields (1966) - Twin Study of Schizophrenia
Method: Studied twins over a 16-year period, focusing on schizophrenia diagnosis.
Findings:
- When one MZ twin was diagnosed with schizophrenia, 42% of their co-twins also received the diagnosis
- In contrast, only 9% of DZ co-twins were diagnosed with schizophrenia when their twin had the condition
Conclusion: The higher concordance rate in MZ twins compared to DZ twins suggested a genetic element contributing to schizophrenia development.
Research Example: Coccaro et al. (1997) - Aggressive Traits in Twins
Method: Investigated aggressive traits in male twins (182 MZ pairs and 118 DZ pairs). Participants completed the Buss-Durkee Hostility Inventory, a 75-item questionnaire assessing various emotional traits associated with aggression.
Findings: The study found high concordance rates between twins for measures such as indirect assault, suggesting heritability in some features of aggression.
Conclusion: This research indicated that impulsive aggression could be at least partly attributable to genetic factors.
Adoption studies
Adoption studies provide the most effective method for separating nature from nurture influences on behaviour. Researchers study adopted individuals and correlate their behaviour with both their adopted families and their biological families.
Adoptees share no genetic material with their adopted families but experience the same environmental upbringing. Conversely, adoptees share 50% of their genes with each biological parent but typically have not lived with them for most of their life. If adoptee behaviour shows greater similarity to the adopted family, researchers might conclude that environmental factors are more influential. However, if behaviour correlates more strongly with the biological family and shows no association with the adoptive family, this suggests the behaviour has a biological cause.
Research Example: Cadoret and Stewart (1991) - Adoption Study of Aggression
Method: Researched adopted boys and examined relationships between their behaviour and both biological and adoptive families.
Findings:
- Boys faced an increased risk of attention deficit/hyperactivity and aggression if they had a biological parent convicted of a crime in adulthood
- Boys were more likely to be aggressive or receive an attention deficit/hyperactivity diagnosis if psychiatric problems existed in members of the adoptive family
Conclusion: This research demonstrates that complex behaviours like aggression can have multiple causes and cannot be attributed solely to nature or nurture.
Evaluation
Twin and adoption studies face several methodological challenges that affect the validity and interpretation of findings.
The Nature vs. Nurture Problem
The primary aim of these research methods is to investigate biological causes of behaviour, but completely separating nature from nurture proves virtually impossible. For example, children are rarely adopted immediately from birth. Adoptees may have spent time living with their biological family before adoption or in foster care, meaning confounding variables may affect the findings.
Similarly, almost all twins are raised together in the same environment, making it problematic to assume that higher concordance in MZ twins compared to DZ twins must be genetic. MZ twins may be treated more similarly than DZ twins due to their identical appearance, potentially explaining their more concordant behaviour through similar life experiences rather than shared genetics.
Sample Size Limitations
Recruiting large, diverse groups of MZ and DZ twins, or adoptees and their parents, proves challenging. Consequently, psychologists may find generalisation from their samples problematic.
Adoption studies face a specific problem: children placed for adoption tend to be placed with families that closely reflect their family background. Any similarities between adoptees and their biological families may result from experiencing similar life events rather than genetic factors.
Ethical Considerations
Gathering accurate and reliable information about people's life experiences, particularly regarding sensitive topics like adoption, can be difficult. Participants may be reluctant to participate in research examining their biological and adoptive families, as involvement could be uncomfortable, or access to both families may be limited, restricting available information.
Additional ethical implications emerge when using such methods to investigate behaviours like aggression, as psychologists might be perceived as labelling people as 'bad apples' based on their family history.
Key Points to Remember:
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CAT scans use X-rays to image brain structure but not function; they expose patients to radiation and are useful for detecting damage or tumours.
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PET scans involve injecting a radioactive tracer to measure brain activity through glucose metabolism; they show functional activity but carry low radiation risks.
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fMRI scans detect blood flow changes using magnetic fields to map brain activity without radiation; they are non-invasive but unsuitable for some patients (e.g., those with pacemakers or claustrophobia).
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Twin studies compare concordance rates between MZ twins (100% shared genes) and DZ twins (50% shared genes) to determine genetic influences on behaviour; higher MZ concordance suggests genetic factors.
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Adoption studies examine whether adoptee behaviour correlates more with biological or adoptive families to separate nature from nurture; however, complete separation is difficult due to confounding variables and ethical limitations.