Some rats, like some people, are more adventurous than others--and some are more prone to anxiety. These traits can remain stable over time for an individual rat, according to a study in the June issue of Behavioral Neuroscience (Vol. 118, No. 3). The researchers also found that female rats were, on average, more "novelty-seeking" than their male counterparts, and that female rats in estrus were particularly adventurous.
These findings, says researcher Jeremy Ray, a doctoral student in psychology, support the idea of a stable "personality" in rats.
"Just 20 years ago," he says, "the idea of a rat having a personality would have been preposterous. But now people are looking at [many animals] to see whether they might have some sort of sum of emotional responses to events that equals a personality."
Ray and Stefan Hansen, PhD, both of Göteborg University in Sweden, tested 32 male and 32 female rats twice a week for three consecutive weeks. Each time they ran two tests. The first was a "hole board" test measuring novelty-seeking. The researchers placed each rat on a large platform with 16 small round holes and recorded how many times the rat poked its nose into the holes.
Next, the researchers put the rats through a "canopy" test to measure harm-avoidance, or anxiety. This time they placed the rats on a different platform, part of which was covered with a canopy to make it darker and safer-feeling. Then, the researchers measured how many times and for how long the animals ventured into the non-covered area. They found that the rats had strong and persistent individual differences in how they reacted to the tests: one-third of the rats never came out from under the canopy, while others spent up to a minute, on average, outside it. In the hole board test, the minimum and maximum nose-poking rats differed by a factor of eight.
In general, females varied more than males in how long they spent outside the canopy--individual females were more likely than males to show significant changes in their behavior over time--and females in estrus spent the most time of all outside. Females also sought more novelty, as measured by the hole board test: They were much more active and nose-poked more than males.
One complicating factor, Ray says, is that there is no perfect test for either harm-avoidance or novelty-seeking. The canopy test, for example, is designed to elicit anxiety, but it might reflect some novelty-seeking behavior as well. "It's a tricky thing to connect a particular behavior to a personality," Ray says.
--L. WINERMAN