Jaak Panksepp, a neuroscientist who helped reveal the emotional lives of animals by tickling rats and listening to their ultrasonic laughter in experiments that upended his field and opened new possibilities for the treatment of depression and other forms of mental illness, died April 18 at his home in Bowling Green, Ohio. He was 73.

The cause was cancer, said his wife, Anesa Miller.

For much of his career, Dr. Panksepp was brushed aside by colleagues who accepted the prevailing notion that emotions were uniquely human experiences. Panksepp – along with many pet owners – suspected otherwise, and he sought to prove his intuition through the rigors of science.

“People don’t have a monopoly on emotion,” he once said. “Rather, despair, joy and love are ancient, elemental responses that have helped all sorts of creatures survive and thrive in the natural world.”

At Bowling Green State University in the late 1990s, he conducted the experiments that would vault him to national renown. He recalled walking into the laboratory one day and remarking to an assistant, “Let’s go tickle some rats.”

He credited a graduate student with repurposing a bat detector capable of recording high-pitched sounds to listen to the rats’ laughterlike chirps. “Lo and behold,” he told the Toledo Blade in 1998, “it sounded like a playground!”