The neuron and synaptic transmission

The central nervous system is the brain and spinal cord. Its cells are neurons.

• Structure: dendrites receive signals; the cell body integrates them; the axon (often myelinated) carries the action potential; the terminal buttons release chemicals.
• Synaptic transmission: the action potential reaches the terminal button and vesicles release neurotransmitters into the synaptic cleft. These bind to receptors on the post-synaptic membrane. Excitatory neurotransmitters make the next neuron more likely to fire; inhibitory ones make it less likely. Leftover transmitter is broken down or taken back up (reuptake).
• Relevance to aggression: low serotonin activity is associated with impulsive aggression (serotonin normally inhibits impulsive responses), and dopamine is implicated in reward and reactivity.

How recreational drugs change transmission

Recreational drugs work by interfering with synaptic transmission. You must be able to explain a mode of action.

• Agonists mimic or boost a neurotransmitter's effect at the receptor. Antagonists block it.
• Reuptake inhibitors stop the transmitter being cleared from the cleft, so it keeps stimulating the receptors — this is how cocaine raises dopamine activity.
• Heroin acts as an agonist at opioid receptors; alcohol enhances the inhibitory transmitter GABA, which is why it is a depressant and reduces inhibition.

Link it up: if drugs can change behaviour by changing chemistry, that is strong evidence for the biological approach — and for a determinist, reductionist account of behaviour.

Mode of action

Brain structure and aggression

Edexcel uses aggression as the behaviour through which biological explanations are tested.

• The prefrontal cortex is involved in impulse control, planning and inhibiting responses. Reduced prefrontal functioning is linked with impulsive, poorly controlled aggression.
• The limbic system — especially the amygdala — is involved in processing threat and generating emotional responses including anger and fear. The hippocampus supports the memory of context, so damage may mean an aggressive response is triggered inappropriately.
• Case evidence: patients with damage to the prefrontal cortex (the classic example is Phineas Gage) may show major personality change and disinhibited behaviour — but a case study cannot establish cause and effect for everyone.

Which explanation of aggression?

Tap a statement, then tap the explanation it belongs to.

Classic study: Raine et al. (1997)

Aim: to see whether murderers pleading not guilty by reason of insanity (NGRI) show different brain functioning from controls.

• Sample: 41 people charged with murder or manslaughter and pleading NGRI, compared with 41 controls matched on age and sex (and, for the six with schizophrenia, matched with schizophrenic controls).
• Method: a quasi-experiment — the IV (being an NGRI murderer) is not manipulated. Participants did a continuous performance task while being injected with a glucose tracer and then scanned with PET.
• Findings: the NGRI group showed reduced glucose metabolism in the prefrontal cortex and in the corpus callosum, and abnormal asymmetries in the amygdala, hippocampus and thalamus (reduced activity on the left, higher on the right).
• Conclusion: violent offending pleading NGRI is associated with brain dysfunction — but Raine explicitly warned this does not show brain damage causes murder, nor that these findings apply to all violent offenders.

Evaluate it: objective, scientific measurement with a matched control group — but it is correlational in nature (no cause and effect), the sample is a very specific subgroup, and it raises socially sensitive questions about responsibility and social control.

What Raine can and cannot claim

Evolution, natural selection and testosterone

Evolutionary explanation: behaviours that increased survival and reproductive success in ancestral environments were naturally selected. Aggression could have secured resources, status, mates and the protection of offspring, so a predisposition to it may be adaptive.

• Support: aggression is found across cultures and species, and male-male aggression peaks in young adulthood — when mate competition is highest.
• Problems: the explanation is hard to falsify (it is a post-hoc story), it struggles to explain aggression that is clearly maladaptive, and it risks being used to excuse violence.

Hormones: testosterone is linked with aggression and dominance. Evidence includes higher testosterone in violent offenders in some prison samples and animal studies where castration reduces, and testosterone replacement restores, aggression. But in humans the relationship is correlational and modest — and aggression can itself raise testosterone, so the direction of causality is unclear.

Evolutionary reasoning

Freud's psychodynamic explanation of aggression

Edexcel requires the biological explanation to be compared with Freud's psychodynamic account.

• Structure of personality: the id (unconscious, pleasure principle, present from birth), the ego (reality principle, mediates) and the superego (morality, formed around age five).
• Freud proposed Thanatos, a death instinct: aggressive energy builds up and must be discharged. If it is not turned outwards it may be turned inwards.
• Catharsis — releasing aggressive energy safely (e.g. through sport) — should reduce aggression. If the ego is weak or the superego is over-harsh, aggression is more likely.

Comparison: both explanations are determinist and see aggression as coming from within, but the biological account is testable and scientific (scans, hormone assays) while Freud's rests on unconscious forces that cannot be directly measured or falsified. Evidence for catharsis is weak — venting aggression often increases it.

Match the method to what it does

Tap a method on the left, then its correct description on the right.

Scans, twin studies and adoption studies

• CAT — X-rays build a structural image. Cheap and quick, but no information about function and it uses ionising radiation.
• PET — a radioactive tracer shows metabolic activity while the person does a task (as in Raine). It is functional, but it is invasive and has poor temporal resolution.
• fMRI — measures blood oxygenation, giving good spatial resolution and functional information with no radiation, but it is expensive and the person must lie still.
• Twin studies compare MZ (100% shared genes) with DZ (50%) concordance — e.g. Gottesman and Shields (1966) on schizophrenia. Higher MZ concordance suggests a genetic component, but MZ twins are also treated more similarly, confounding nature with nurture.
• Adoption studies separate the two: if a child resembles the biological parents more than the adoptive ones, that supports a genetic influence.

Choosing a scan

Correlational research and Spearman's rho

The Topic 3 method is correlation — measuring two co-variables and testing the relationship between them.

• A positive correlation: as one rises, so does the other. A negative correlation: as one rises, the other falls. Plot the data on a scatter diagram.
• Edexcel names Spearman's rho for correlation with ordinal data. Compare the observed value with the critical value for the N, the level of significance (p ≤ 0.05) and one- or two-tailed. For Spearman's, the observed value must be equal to or greater than the critical value to be significant.
• The key limitation: a correlation cannot establish cause and effect. Testosterone and aggression may correlate, but aggression may raise testosterone, or a third variable (such as status) may drive both.

Interpreting a correlation

Contemporary study

How Topic 3 is assessed

Biological psychology is examined in Paper 1: Foundations in psychology and is compulsory.

• You will be asked to compare the biological explanation of aggression with Freud's psychodynamic explanation — a comparison built into the specification, so prepare it in advance.
• Expect data-response on a correlation: read a scatter diagram, describe the relationship, justify Spearman's rho, compare observed with critical values, and state why cause and effect cannot be inferred.
• Know Raine et al. (1997) in detail — sample, matching, PET method, three findings, and the fact that Raine himself warned against a causal reading.

Vocabulary counts here. Say agonist, antagonist, reuptake, synaptic cleft, prefrontal cortex — precise terminology is what separates a top band answer from a vague one.

The big ideas to know

That is the whole of Topic 3 — a compulsory topic on Paper 1. Press Finish to see your score.