Drosophila nervous system

Drosophila is the tiny fruit fly that hovers around ripe bananas, and its nervous system is one of the most powerful tools scientists have for understanding how brains work. The fly brain is about the size of a poppy seed and holds roughly a hundred thousand neurons, far fewer than the billions in a human brain, yet it lets the insect see, smell, walk, fly, court a mate, and even learn from experience. Because it is small enough to study in full but rich enough to produce real behavior, it sits in a sweet spot between a simple worm and a complicated mouse.

What makes the fruit fly especially useful is genetics. Scientists can switch single genes on or off in chosen neurons, light up particular cells with glowing markers, and use light or heat to turn specific neurons on and watch the behavior change, all in an animal that breeds quickly and cheaply. Many genes that build the fly's brain have close cousins in our own, so a discovery in the fly often points to how the same machinery works in people. Researchers have now traced complete wiring maps, called connectomes, of fly brains, drawing every neuron and the connections between them. This combination of a fully mapped circuit and precise genetic control is why the humble fruit fly has become a model for studying memory, sleep, navigation, and even diseases like Parkinson's.