How Flies Maintain Vision in Varying Light

When light conditions shift quickly, our eyes must respond almost instantly to ensure stable visual processing, particularly in situations like driving through forests with alternating shadows and sunlight. Professor Marion Silies from Johannes Gutenberg University Mainz (JGU) points out that simply adapting the photoreceptors is not enough; an additional corrective mechanism is essential. Her previous research has already shown that such a "gain control" mechanism exists in the fruit fly Drosophila melanogaster.

Silies's team has now identified the algorithms, mechanisms, and neural networks that enable flies to maintain stable visual processing despite rapid changes in light levels. Their findings were published in Nature Communications, contributing valuable insights into how these organisms adapt to fluctuating luminance.

Rapid changes in luminance challenge stable visual perception for both humans and many animal species that depend on vision for navigation. These fluctuations also impact technology, such as camera-based navigation systems in self-driving cars, which often rely on radar or lidar to accurately assess object contrast against their backgrounds.

The researchers used a combination of theoretical and experimental methods to study the compound eyes of Drosophila, consisting of 800 individual units called ommatidia. They found that changes in luminance can disrupt contrast responses, necessitating effective gain control to maintain consistent visual processing.

Led by Dr. Burak Gür, the study utilized two-photon microscopy to pinpoint where stable contrast responses originate in the visual circuitry. They identified specific neuronal cell types located two synapses away from the photoreceptors that respond locally to visual information, highlighting the importance of spatial pooling in accurately computing contrast.

The team discovered a cell type named Dm12, which pools luminance signals over a specific radius to correct contrast responses in rapidly changing light. Silies concluded that they have unveiled the algorithms, circuits, and molecular mechanisms that stabilize vision during these changes. She believes that luminance gain control in mammals, including humans, likely operates in a similar manner due to shared neuronal structures.