In 1989, an experimental psychologist named Willard Stanton Small analyzed rats' response to fear. He found that rats freeze when faced with fear. Today, Northeastern University's psychology assistant professor Rebecca Shansky challenged the long-held belief.

A team led by Shansky found that female rats "dart" in response to fear. The animals run around in a harried frenzy as though they are attempting an escape.

Shansky's team found that female darting rats are better in incorporating a process that blocks the fear response. These darting rats display a type of cognitive flexibility that male rats lack when they freeze in fear.

The research was published in the journal eLife and it challenged all past studies that focused on freezing to specify a fear response. The latest study was done on rats and not humans; however, it could help the scientific community to better understand fear reactions in humans. Moreover, it could pave the way for the development of better therapies for post-traumatic stress disorder (PTSD) that, according to the U.S. Department of Veterans Affairs' National Center for PTSD, affects about eight million Americans in any year.

The researchers conducted tests that involved teaching 120 rats to connect a particular tone with a foot shock. A video camera recorded the rats' length of reaction during the training.

The team found that female rats didn't freeze at the sound but they darted back and forth, as if they are trying to find an escape. Shansky said that the ones who displayed low levels of freezing are commonly interpreted as fearless or not learning. However, further behavioral analysis showed that darting is not a sign of being fearless or failure to learn. Rather, darting among the female rats was similar to freezing in the male rats - a learned response.

"The learning curve for darting was the same as the learning curve for freezing," said Shansky, stressing that they saw darting exclusively in the female rats, over 40 percent of the ones involved in the study.

The team then blocked the rats' fear response by playing the tone but leaving out the foot shock. When the rats seem to conquer their fear, the process of a "good" memory replacing a "bad" one takes place, which is called extinction. The team found that female darters are better in conquering the fear response compared to the male freezers.

Photo: Vladimir Pustovit | Flickr