Details matter for mice and men

A good researcher tries to account for all variables when designing experiments. Unfortunately, it’s difficult to think of all the criteria that could affect results. Case in point: Brianna Gaskill of Purdue University and her colleagues have found that the temperature at which laboratory mice are housed can play a role in their behavior.

Typically, mice are kept at about 20–24°C, well below their body temperature of about 30°C. The animals are usually provided with nesting materials that they can use to keep warm while they’re inactive. The researchers hypothesized that mice would build more elaborate nests when provided with more building materials and when being placed in colder cages.

The researchers floated two polycarbonate mouse cages in heated water tanks, one of which was maintained at 20°C (nesting, or N cage) and the other of which varied in temperature from 20–35°C (temperature, or T cage).  Mice could pass freely between the two cages via a tube. The N cage contained varying amounts of nesting material.

As predicted, the mice showed temperature-dependent preferences for spending time in the two cages. Mice preferred the T cage when it was 22-30°C, but spent most of their time in the N cage when the T cage was set at either 20°C or 35°C. The mice also spent more time in the N cage as more nesting material was provided there. This suggests that researchers doing cognitive studies on mice, and nest-building is a common parameter in such studies, would do well to consider temperature and nesting supplies in their experimental designs. For example, are mice building more complex nests because that drug you gave them made them smarter or simply because their cages happened to be a few degrees cooler?

This study has an even bigger lesson about unforeseen consequences though. A behavior that the researchers did not predict but which could definitely skew results was that the mice frequently transferred the bedding material from the N cage to the T cage, particularly at the very temperature ranges where they preferred to spend time in the T cages. In other words, rather than building warmer nests in the N cage to make it as comfortable as the T cage, they just moved their ‘belongings’ into the T cage.