浦飯　幽子

rats have feelings too

In 2019, neuroscientist Kelly Lambert and her team at the University of Richmond in the United States built something unusual: tiny cars for rats. Each car was made from a clear plastic food container on wheels. Inside, there were three small copper bars. When a rat touched a bar with its paws, the car moved, and by choosing which bar to touch, the rat could steer left, right or straight. The rats were rewarded with pieces of sweet cereal when they drove to a target. They learned to drive. Over time, the researchers moved the treats farther away, and the rats learned to navigate the car across the enclosure to reach them. Rats that had lived in more interesting, enriched environments learned faster. And when researchers measured hormones related to stress, they found signs that learning to drive may actually have helped the rats feel calmer.

In 2016, scientists at Humboldt University in Berlin confirmed that rats laugh when they're tickled. The laughter is ultrasonic (too high for human ears) but recordings show rats actively seek out the researcher's hand to be tickled again, and even jump for joy. The study changed how science views emotion in small animals.