Laughing Lab Rats – New Study Reveals How Brain Creates Joy

A day in the life of a lab rat is usually pretty miserable, as one could imagine. You’re likely poked, produced, bothered, or even starved – all in the name of science.

A recent study highlights some rats that were part of a fun-filled study that yielded some important results. The study, published November 11th in Science showed that nerve cells in the brain process glee in a specific way.

Image Credit: Shimpei Ishiyama & Michael Brecht

For centuries, scientists have tried to solve the mystery of tickling. Many studies have been done on the subject, as the mysterious reaction is often associated with some of the most pleasant human emotions. Scientists knew rats responded to a tickle, but how the brain created that reaction and emotion was unknown.

When tickled, the rats laughed and jumped for joy, an acrobatic feat called “Freudensprünge” or joy jumps. By documenting the levels of laughter, study coauthor Shimpei Ishiyama of Humboldt University of Berlin found that the belly of the rat is the most ticklish.

The response, scientists believe, is created partially by nerve cells in the somatosensory cortex. In humans, this part of the brain is usually associated with touch perception. When tickled, many of the rat’s nerve cells in this part of the brain became active.

But additional experiments found active nerve cells when the rats were chasing a tickling hand without being touched. This suggests the cells are responding to something specific about a tickle, not just touch in general. Also, when the researchers used electrodes to stimulate the somatosensory cortex in untouched rats, the rats laughed.

The study also found that mood can affect how the rats react to being tickled, much like a person who doesn’t want to be tickled might appear stressed. Nerve cells in the somatosensory cortex were less likely to show activity when the rats were anxious. They also released less laugh-like noises.

Not only did this study make progress for scientists to understand human emotion, but it certainly seemed like a lot of fun.

“Science has been obsessed with bad things,” Ishiyama said in a PopSci article. “It’s important to also study positive motivations like happiness or fun.”

He also noted that he hopes to continue studying other mysterious aspects of ticklishness, including trying to figure out why people can’t tickle themselves successfully.