How does the brain turn light waves into experiences of colour?

Researchers have discovered specific networks of neurons in fruit flies that respond selectively to various hues. Hue denotes the perceived colors associated with specific wavelengths, or combinations of wavelengths of light, which themselves are not inherently colourful. These hue-selective neurons lie within the optic lobe, the brain area responsible for vision. Scientists had previously reported finding neurons in animals’ brains that respond selectively to different colors or hues, say, red or green. But no one had been able to trace the neural mechanisms making this hue selectivity possible. Now, the researchers have been able to find the fly brain connections. The intricate map details how some 130,000 neurons and 50 million synapses in a fruit-fly’s poppy seed-sized brain are interconnected. With the connectome serving as a reference, the researchers used their observations of brain cells to develop a diagram they suspected represents the neuronal circuitry behind hue selectivity. These were then portrayed as mathematical models to simulate and probe the circuits’ activities and capabilities. The modeling helped reveal that these circuits can host activity required for hue selectivity and also pointed to a type of cell-to-cell interconnectivity, known as recurrence, without which hue-selectivity cannot happen.