The Grid Walking task is used to assess deficits in descending motor control.
A mouse is placed on top of a grid floor with the holes measuring 1 cm across. The grid is enclosed by clear plexiglass walls and elevated on a clear plexiglass platform. Mirrors are placed perpendicular to each other on two of the sides of the apparatus at an angle so that a camera view from above can visualize the grid floor as a line from both sides.
The mouse is allowed to explore the enclosure for a set amount of time and the behavior is recorded. The video can then be analyzed to count the number of foot slips through the grid. The two angles of the mirror allow the experimenter to asses which foot had slipped.