One of the two rats in the above picture isn't really a rat. One of the two rats in the above picture is, in fact, a robot. Look closely and you can just barely figure it out. Meanwhile, the rat that isn't a robot is seriously depressed, because that's what this robot specializes in: rat depression.
I should hope that you're wondering right now just why the heck someone would design a robot that exists only to instill depression in rats, since that seems kind of terrifying, to be honest. Fortunately, there's a simple answer: We need depressed rats to be able to test drugs that treat depression. Before trying drugs out on humans, they get tested on animals, and if you think you've got a drug that can safely make depressed people less depressed, it first needs to be able to safely make depressed rats less depressed, and that requires a bunch of depressed rats.
There are already some accepted ways to make a normal rat into a depressed rat. For example, you can force it to swim for long periods, or you can put it into a box and give it electric shocks. Do these things often enough, and you'll be left with one seriously unhappy rat. However, the problem with these methods is that humans don't usually experience depression like this: With some exceptions that nobody likes to talk about, prolonged swimming and shocks aren't the cause of most depression in humans, and researchers at Waseda University in Tokyo are trying to come up with a more accurate model by causing depression in rats with other (robotic) rats.
This robot, called WR-3, is basically an attack robot. It has three modes, or "behavior generation algorithms," which include chasing, continuous attacking, and interactive attacking. Chasing means that WR-3 will attempt to maintain a minimum distance from the rat but not actually attack it. Continuous attacking is, well, continuous attacking with aggressive body motions and physical contact. Interactive attacking only attacks the rat whenever it moves at set distance, which (to me) is the most sinister mode of all.
Experiments on different groups of rats of different ages showed that the most effective means of instilling depression (measured by overall listlessness) was to constantly harass young rats, and then intermittently harass them again when they got older, and that doing this is likely a better overall model for depression than other methods. So that's good news for drug testing, and bad news for lab rats.
On a personal note, as a rat owner I have to say that I'm a little bit sorry to see robots being used in this manner. I know it's medically important, and I have some friends who would likely be dead if it wasn't for animal testing of drugs, but still, developing a robot for the express purpose of instilling depression in animals and nothing else just seems like it somehow sets a bad precedent. But I suppose as far as the rats are concerned, if it's possible to use robots to depress them without causing undue amounts of fear or pain, that's a better route to take.
"A Novel Method to Develop an Animal Model of Depression Using a Small Mobile Robot" was published online today in Advanced Robotics, and you can read the whole thing at the link below.