The results of a commonly used test for learning and memory in mice may be inaccurate. A group of Finnish researchers report that the mice develop severe hypothermia, which impairs their performance on the test.

The Morris water maze (MWM) is the most commonly used test for measuring learning and memory in rodents. An investigator places the animal in a pool of water that contains a hidden escape platform. The animal's ability to find the platform depends on a number of variables, including memory, cognitive ability, motor coordination, and vision. Although the MWM was originally developed for use with rats, it is now in general use to assess learning and memory in mice, however, mice do poorly at this task in comparison with rats.

A group led by Jukka Puoliväli of the University of Kuopio (Kuopio, Finland) tested transgenic mice that carry Alzheimer's disease-associated mutations and their wild-type littermates. They found that five swims of 45 s each in 20 °C water with 30 s between trials caused a drop of as much as 9 °C in the animal's body temperature and an associated slowing of swimming speed (Behav. Brain Res., published online, doi: 10.1016/S0166-4328(02)00369-8). Females were more susceptible to hypothermia than males, and the transgenic animals were more vulnerable than the controls. Using 24 °C water lessened the drop in body temperature but resulted in an increase in the number of mice that floated rather than actively searching for the platform. However, by increasing the inter-interval time from 30 s to 13 min, Puoliväli's group was able to prevent hypothermia and the slowing of swimming speed.