There's a simple reason why we need rat robots to depress live rats. We need depressed rats to be able to test drugs that treat depression. Before trying drugs out on humans, they get tested on animals.
If a drug 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 ways to make a normal rat depressed. For example, forcing it to swim for long periods, or putting it into a box and give it electric shocks. However, they aren't the cause of most depression in humans.
This robot, called WR-3, is basically an attack robot with three modes, including 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 continuous attacking with aggressive body motions and physical contact. Interactive attacking only attacks the rat whenever it moves at set distance.