Direct observation and automated scoring of the activity of active and inactive inbred mouse strains

Inbred mouse strains previously found to be low (A/J) and high (C57BL/6J) in open-field activity were tested in a plastic oval runway while their runway activity was directly observed and also monitored by a contact switch recording device. The activity of active C57BL/6J mice was accurately monitored by the recording device, but scores of inactive A/J mice were inflated by a factor between 2 and 3 X. Activity differences between strains were consistently maintainedduring repeated tests under both high and very dim illumination if direct observational scores were used. Utilization of scores obtained by the automated recording device resulted in a failure to obtain group differences under the condition of dim illumination. These results were directly related to the mode of locomotion of the two mouse strains.