The eerie opening shot of the slow drive of a bomb-carrying car in Orson Welles’ 1958 Touch of Evil prompts strong reactions in film watchers. Now reactions in the brains of an unusual audience — mice — offer a major twist in our understanding of how brain cells parse visual scenes.
Scientists used to think that each of the many cells in the brain’s visual system primarily handles a single job, such as responding to a black and white contrast. But a study published December 16 in Nature Neuroscience does away with that simplicity.
Researchers including Saskia de Vries, a neuroscientist at the Allen Institute for Brain Science in Seattle, used a powerful microscope to study 59,610 brain cells in the visual systems of live mice, through openings in their skulls. The researchers then watched whether these cells responded to (or ignored) a lineup of visual input, including clips from Touch of Evil and simpler images, such as drifting black stripes and a still picture of a butterfly.
The way that the nerve cells, or neurons, behaved was a surprise. Overall, only about 10 percent of the neurons studied responded as the researchers expected, based on data from earlier studies. “The remaining neurons don’t look like what’s going on in the textbook,” de Vries says.
Across the trials, many cells responded to several kinds of visual scenes, such as drifting lines and movies, but unreliably. Some cells responded to all of the images. And a large group of cells — about a third of all tested — responded to none of the visual scenes, the researchers found.
“What, then, do these neurons do?” the researchers ask in their paper. More experiments may offer clues, but for now, these mystery neurons’ roles are still in the dark.