Look out Above: Experiment Explores Innate Visual Behavior in Mice

Oct. 10, 2013 — When you're a tiny mouse in the wild, spotting aerial predators -- like hawks and owls -- is essential to your survival. But once you see an owl, how is this visual cue processed into a behavior that helps you to avoid an attack? Using an experimental video technique, researchers at the California Institute of Technology (Caltech) have now developed a simple new stimulus with which they can spur the mouse's escape plans. This new stimulus allows the researchers to narrow down cell types in the retina that could aid in the detection of aerial predators.

"The mouse has recently become a very popular model for the study of vision," says biology graduate student Melis Yilmaz, who is also first author of the study, which will be published online in the journal Current Biology on October 10. "Our lab and other labs have done a lot of physiological, anatomical, and histological studies in the mouse retina" -- a layer of light-sensitive cells in the eye that relay image information to the brain -- "but the missing piece was mouse behavior: What do mice do with their vision?"

Yilmaz, under the supervision of Markus Meister, Lawrence A. Hanson, Jr. Professor of Biology, studied the behavior of 40 mice, placed one-by-one in a tiny room called a behavioral arena. After placing each mouse alone in the arena and letting it explore the new environment for a few minutes, Yilmaz played videos of different visual stimuli on a computer monitor mounted on the ceiling, the screen facing down onto the arena. The researchers then watched a video feed of the mouse's behavior, obtained with a camera located on one of the walls of the arena.

Surprisingly, all of the mice responded to one specific visual stimulus: an expanding black disk, which is meant to imitate the appearance of an approaching aerial predator.

A quarter of the mice responded to the looming disk by completely freezing in place, not moving a muscle or twitching a whisker or tail until the disk disappeared. "When I first saw this behavior, my first thought was that the video recording had stopped," Yilmaz says.

A far more common reaction to the looming disk -- seen in around 75 percent of the mice -- was to flee for the cover of a tent-like nest in one corner of the arena.

"For each mouse, this was the very first time that the animal was put into this arena, and it was the very first time that it saw that stimulus, and yet it has this sort of immediate reflex-like response…beginning to flee in less than a quarter of a second," Meister says. "What's attractive about this behavior is that it's incredibly robust, so we can rely on it, and it's quite specific to this particular visual stimulus. If the same disk was presented on a monitor at the bottom of the arena, the animals don't respond to that at all. And a looming white disk is also much less effective," he adds.

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