Does your smartphone take great pictures? Here’s something that might surprise you. Engineers who want to design the optimum low-energy light-detecting device for a camera should take their cues from the mammalian retina. Recent research by Duke University neurobiologists has shown that natural selection and evolution have made our retinas function far beyond anything engineering currently can achieve. Researchers used efficient coding theory, a theoretical model of sensory coding in the brain and examination of monkey retinas, nearly identical to human retinas, to determine that retinal cells are arranged in highly organized “mosaics” to maximize sensitivity and efficiency.
The retina has approximately one million ganglion cells, a type of neuron near the inner retinal surface, and they are the only retinal neurons to communicate directly with the brain. Dendrites extend from the ganglion cell body to receive and transmit information. The dendrites form a thick and complex layer in which the mosaics are laid out. Each mosaic receives and conveys a particular type of information. Different retinal neurons are sensitive to specific stimuli that combine to form an image. For example, cones are sensitive to light and color, while rods are sensitive to low light, but not to color. Other neurons detect motion, contrast and shape. Researchers found that the neural mosaics are stacked, with each layer responding to a different characteristic of the visual field. In this way, the retina identifies 40 different visual features. The mosaics also adapt to changing visual conditions.
As for energy efficiency, retinal cells conserve energy by not responding to certain visual “noise,” optimizing their function to detect things that are hard to see, as happens in low lighting.
Researchers estimated that with this cell selectivity, the retina avoids redundancy and consumes about 6 percent of the energy used by a typical smartphone image sensor, yet it can respond to a single photon, which the smartphone cannot. The Duke University team next wants to investigate the differences in neural cell response times and the speed at which the neurons fire that provide a sense of motion. This research provides important information for the development of artificial retinas, still in early stages, that can restore sight.
It seems that new (and more expensive) smartphones come out every year. But when you consider that with the rapid and expansive advances in technology, the natural self-assembled living tissue of the retina has yet to be duplicated or matched, you will understand how amazing our eyes are!
• Linda Conlin
Pro to Pro Managing Editor