Topic C: Biological psychology AS

The central nervous system (CNS) consists of the brain and spinal cord. It receives information from sensory systems, integrates it and sends signals that coordinate responses. Neurons carry information within this system; neurotransmitters carry a chemical signal across the tiny gap between neurons.

When an impulse reaches a terminal, vesicles release neurotransmitter into the synaptic cleft. Molecules diffuse across, bind to matching receptors and can excite or inhibit the postsynaptic neuron. The transmitter is then removed, for example by reuptake or enzymatic breakdown, so the signal is controlled rather than remaining permanently active.

Aggression is linked to coordinated brain systems for threat, emotion and control. The prefrontal cortex helps evaluate consequences and inhibit impulsive responses; limbic structures help detect emotionally significant events and organise defensive responses.

Brain scans and lesion cases can show that activity or damage is associated with aggression. Raine et al. found group differences across several regions in murderers who pleaded not guilty by reason of insanity, including reduced prefrontal activity. The pattern supports a network account rather than a single 'aggression centre'.

Hormones and genes can influence systems involved in arousal, threat and impulse control, but they do not make aggression inevitable. Their effects vary with development, situation and learning.

A useful model is gene-environment interaction: a biological variant may change sensitivity to provocation, while the environment supplies the trigger and the learned response options. McDermott et al. found the clearest MAOA group difference under high monetary provocation, illustrating this conditional effect.

The sleep-wake cycle is circadian: it repeats roughly every 24 hours. An internal pacemaker produces the rhythm, while external zeitgebers provide time cues that synchronise it to the environmental day.

After night work or rapid travel, the internal clock can remain aligned with the previous light schedule. Morning light may suppress melatonin and raise alertness just when a night worker is trying to sleep. Timed light and regular routines can gradually shift the rhythm.

An infradian rhythm has a period longer than 24 hours. The menstrual cycle and the seasonal pattern of seasonal affective disorder (SAD) are examples, but each involves different biological processes.

Bright-light therapy aims to replace a missing seasonal light cue. A person typically uses a suitable light box in the morning on a regular schedule; light shifts circadian timing and can reduce excessive daytime melatonin-related sleepiness. Treatment strength, timing, eye or medication risks and professional advice matter.

Research on bodily rhythms must separate an internally generated cycle from the environmental cues that reset it. Different methods provide complementary evidence, but each leaves a different alternative explanation.

Judge a claim by design: an experiment can strengthen causal inference through manipulation and control; a case study provides depth; a correlation or longitudinal study shows association and change over time. Replication across methods is stronger than one dramatic finding.

A correlation measures whether two co-variables vary together. Neither co-variable is manipulated, so the method describes a relationship rather than an experimental effect.

Correlations are useful when variables occur naturally or cannot ethically be manipulated, such as age, hormone level or sleep habits. Operational definitions, a suitable sample and a consistent procedure make the measurements replicable. A scatter diagram and correlation coefficient then show direction and strength.

A scatter diagram plots one paired score as one point. The overall pattern shows the direction and approximate strength of a relationship; the axes do not decide which variable causes the other.

Give the graph an informative title, label both axes with the operationalised co-variable and unit, choose a scale that uses the plotting area, and plot every paired score accurately. Inspect possible outliers because one unusual case can change the apparent pattern and the coefficient.

A correlation cannot establish cause and effect because its design does not manipulate one variable while controlling alternatives. Two main uncertainties remain even when the coefficient is strong.

Strengthen interpretation by measuring plausible third variables, using validated or objective measures, sampling a wider relevant population and following participants over time. A controlled experiment can test a causal hypothesis when manipulation is ethical, but it answers a narrower question than the original natural correlation.

Spearman's rank correlation coefficient, $r_s$, tests the strength and direction of a monotonic relationship between paired scores measured at least at the ordinal level. It is appropriate when the research question is correlational and the scores can be ranked.

$d$ is the difference between a case's two ranks and $n$ is the number of paired cases. Rank both co-variables in the same direction, give tied scores their mean rank, calculate each $d$ and $d^2$, sum $d^2$, then substitute and sense-check that $-1\le r_s\le1$. The sign gives direction; closeness to $1$ or $-1$ gives strength.

Brain-scanning techniques differ in what they measure. CAT is mainly structural; PET and fMRI can index function. The technique must match the research question, safety constraints and required detail.

To study aggression, researchers can compare activity in specified regions during a standard task or compare groups with carefully matched controls. Operationalising the task, pre-registering regions and using blind, consistent analysis reduces selective interpretation.

Twin studies compare similarity in monozygotic (MZ) twins, who share virtually all their segregating genes, with dizygotic (DZ) twins, who share on average about half. If MZ aggression is more concordant than DZ aggression, genetic influence is plausible.

A higher MZ similarity supports heritability within the studied population and environment. Shared environmental influence makes twins alike; non-shared experiences and measurement error make them differ. Brendgen et al. used peer and teacher ratings to compare physical and social aggression in six-year-old twins.

List A provides the descriptive tools used across psychology. Choose a summary from the data type and distribution rather than calculating every statistic available.

Label tables and axes, retain units, check totals and denominators, and inspect unusual scores before choosing the mean or standard deviation. Descriptive statistics summarise the sample; they do not show whether a relationship or difference is statistically significant.

Raine et al. tested whether people charged with murder or manslaughter who pleaded not guilty by reason of insanity (NGRI) showed different brain functioning from matched controls.

The study compared 41 NGRI participants (39 men and 2 women) with 41 controls matched on sex and similar characteristics. Participants completed a 32-minute continuous performance task after receiving a glucose tracer, then underwent PET scanning. Regional glucose metabolism was compared with cortical-peel and region-of-interest methods.

PET provided objective physiological data and matching reduced several participant differences. However, the selected NGRI sample is not representative of all murderers, the CPT was not an aggressive task, medication history and diagnosis complicate interpretation, and the design cannot show that brain differences caused the offences.

Brendgen et al. asked whether genetic, shared-environment and non-shared-environment influences differ for physical aggression and social aggression in six-year-old twins.

The longitudinal Montreal sample included 234 twin pairs. Same-sex twins were classified for zygosity mainly from physical resemblance at 18 months, with a proportion checked using DNA. At age six, peers selected photographs matching behavioural descriptions, while teachers completed established social and physical aggression scales. Parents provided written consent.

Agreement across peer and teacher methods strengthens reliability, and the large twin sample permits genetic modelling. Yet appearance-based zygosity can be wrong, peers may nominate after recent conflict, ratings do not directly observe every act, and six-year-old mostly European-descent Montreal twins limit age and cultural generalisation.

McDermott et al. tested whether MAOA activity predicts costly aggressive punishment and whether its effect changes with environmental provocation.

Genetic samples from 78 male participants classified them as high-activity (MAOA-H) or low-activity (MAOA-L). In four rounds of a power-to-take game, a fictional opponent removed either 20% or 80% of money earned on a vocabulary task. Participants could pay to give that opponent unwanted hot sauce; whether and how much they allocated operationalised aggression.

High provocation increased aggression overall, and the low-activity group responded most strongly when 80% was taken. This supports a gene-environment interaction: genotype altered sensitivity to provocation rather than producing the same behaviour in every situation.

Hoefelmann et al. compared cross-sectional and prospective links between lifestyle behaviours and self-reported sleep quality and duration in Brazilian high-school students.

The secondary analysis used data from students aged 14-24 in 20 public schools. Of 2,000 initially selected, 989 completed baseline and nine-month assessments; 949 supplied longitudinal sleep-quality data and 950 sleep-duration data. Closed questionnaire items measured activity, screen use, food, soft drinks, alcohol, perceived sleep quality and daily sleep duration.

Poor perceived sleep and insufficient duration were common and stable, but an association measured at one time did not become a prospective prediction. This contrast demonstrates why cross-sectional correlation is weak evidence of causal direction.

A biological-psychology practical must test a relationship between two operationalised co-variables, gather paired quantitative data ethically and report association without claiming causation.

Suitable questions include the relationship between daily social-media time and average nightly sleep, or height in centimetres and a score from an established self-rated aggression scale. A diary or device can improve sleep-time validity; anonymous responses can reduce social-desirability pressure for aggression.