Animal Models in Neuroscience

Why neuroscience studies worms, flies, fish, mice, rats, songbirds and monkeys; what each species offers; the limits of translating animal findings to humans; brain organoids; and the ethics of the 3Rs.

Much of what we know about neurons, synapses, development and behaviour comes from animals, chosen because each makes some question easier to answer.

The menagerie

C. elegans, a millimetre-long roundworm, has exactly 302 neurons in the hermaphrodite, with a fully mapped wiring diagram (published 1986). Its transparency, short life and genetics make it ideal for studying how genes shape circuits and behaviour; work in worms helped uncover programmed cell death and ageing genes.

The fruit fly Drosophila has about 140,000 neurons and powerful genetic tools. Flies revealed the clock genes behind circadian rhythms, genes for learning, and, in 2024, the first complete wiring diagram of an adult brain.

Zebrafish larvae are transparent, so researchers can image activity across nearly the whole brain while the fish behaves. Songbirds such as zebra finches learn their songs from tutors during a sensitive period — a model for vocal learning and speech. The sea slug Aplysia and the squid offered giant, accessible neurons.

Mice are the workhorse mammal: genetically modifiable, with brains organised like ours in many basic respects, used for optogenetics, disease models and behaviour. Rats are favoured for complex learning and navigation. Non-human primates, especially macaques, have a visual system, prefrontal cortex and motor system closest to ours, and have been central to research on vision, decision-making, movement and brain-computer interfaces.

The translation problem

Many treatments that worked in animals have failed in human trials — for example, numerous drugs that protected the brain after stroke in rodents, and many Alzheimer's drugs. Reasons include differences in brain anatomy and lifespan, models that capture only part of a human disease, and young, genetically uniform animals versus diverse older patients.

Organoids and alternatives

Brain organoids grown from human stem cells, computer models, human tissue removed during surgery, and large human imaging and genetic datasets complement animal work.

Ethics

Animal research is regulated by law and ethics committees in most countries, guided by the 3Rs — Replace animals where possible, Reduce numbers, and Refine procedures to minimise suffering — formulated by William Russell and Rex Burch in 1959. Research on primates is especially restricted and debated.