A team of Japanese researchers has come up with a new method of making rats depressed: A robotic rat that chases and attacks them at all hours. But it isn't just wanton cruelty — the researchers need sad rats in order to test anti-depression treatments.

Naturally, the process of systematically depressing rats is not a pleasant one, but beyond that there are good ways and bad ways to do it. Surgery and chemical treatments can make rats appear listless and reject food, but is that really a good analog to human depression? If people get depressed by being caught up in the rat race, then why not create a literal rat race? That's what researchers at Waseda University did.

Enter the abusive cagemate, a robot rat that constantly follows its target around, running into it constantly when the rat is young, then more intermittently when the rat reaches adulthood.

The result is a profoundly downtrodden rat, as judged primarily by its lack of activity. And because there is no chemical or physiological damage (as drug treatment or surgery could do), it's possible these "naturally depressed" rats could be more reliable for tests of anti-depression drugs.

Needless to say, the rats are, in all other ways, treated humanely. It's not pretty, but it is innovative, and medical science may benefit.

The paper describing the researchers' methods can be downloaded here.

Devin Coldewey is a contributing writer for NBC News Digital. His personal website is coldewey.cc.