The EthoVision video tracking system--a tool for behavioral phenotyping of transgenic mice

Video tracking systems enable behavior to be studied in a reliable and consistent way, and over longer time periods than if they are manually recorded. The system takes an analog video signal, digitizes each frame, and analyses the resultant pixels to determine the location of the tracked animals (as well as other data). Calculations are performed on a series of frames to derive a set of quantitative descriptors of the animal's movement. EthoVision (from Noldus Information Technology) is a specific example of such a system, and its functionality that is particularly relevant to transgenic mice studies is described. Key practical aspects of using the EthoVision system are also outlined, including tips about lighting, marking animals, the arena size, and sample rate. Four case studies are presented, illustrating various aspects of the system: (1) The effects of disabling the Munc 18-1 gene were clearly shown using the straightforward measure of how long the mice took to enter a zone in an open field. (2) Differences in exploratory behavior between short and long attack latency mice strains were quantified by measuring the time spent in inner and outer zones of an open field. (3) Mice with hypomorphic CREB alleles were shown to perform less well in a water maze, but this was only clear when a range of different variables were calculated from their tracks. (4) Mice with the trkB receptor knocked out in the forebrain also performed poorly in a water maze, and it was immediately apparent from examining plots of the tracks that this was due to thigmotaxis. Some of the latest technological developments and possible future directions for video tracking systems are briefly discussed.