Chemical messengers
IB Psychology· Biological approach· 14 min read
1. Core concept
Chemical messengers carry the signals that shape behaviour. Neurotransmitters (e.g. serotonin, dopamine) act fast across synapses in the brain; hormones (e.g. cortisol, adrenaline) travel more slowly through the bloodstream to distant targets — and a few, like adrenaline, do both. Because changing their levels changes mood and behaviour, they are central to biological explanations and to drug treatments — but the evidence linking a messenger to a behaviour is usually correlational, and cause can run in either direction.
2. Key studies
IB Psychology answers must be supported by named studies. Learn these to cite as evidence:
Fisher, Aron & Brown (2005)
fMRI found dopamine-rich reward areas (VTA, caudate) active when participants viewed a beloved. — Anchors the NEUROTRANSMITTER class — dopamine linked to the experience of romantic love.
Weaver et al. (2004)
Early maternal care programmed the glucocorticoid (cortisol) stress-hormone receptor, changing adult stress behaviour. — Anchors the HORMONE class — the cortisol stress-hormone system shaping behaviour (each named class gets an example).
3. Evaluation (AO3)
Strength — measurable and manipulable — Levels can be measured and altered pharmacologically, enabling causal tests and treatments (e.g. SSRIs).
Limitation — correlation & direction — Does low serotonin cause low mood, or low mood lower serotonin? A single messenger rarely acts alone, so simple 'imbalance' claims are contested.
4. Scope
5. Common Pitfalls
Wrong move:
Treating hormones and neurotransmitters as interchangeable — answering a neurotransmitter question with a hormone (e.g. oxytocin, testosterone).
Why:
A frequently penalised misconception in IB Psychology exams.
Correct move:
Neurotransmitters act fast across a synapse; hormones travel slowly in the blood. A question about one is not satisfied by an example of the other — match the messenger to the question.
Going deeper
- Neurotransmissionhow neurotransmitters actually transmit signals is neurotransmission (BIO_9).
- Diathesis–stress modelthe cortisol/stress-hormone programming links to gene × environment (BIO_5).