The ladder rung walking task assesses skilled walking and measures both for limb and hind limb. Placing, stepping and inter limb coordination. The apparatus consists of two clear plexiglass walls, one meter in length and 20 centimeters high, one centimeter from the base.
Small holes have been drilled at one centimeter intervals. Metal rungs 13 centimeters long, and three millimeters in diameter are placed at regular or irregular intervals along the base of the walls. The walls of the apparatus can be adjusted to suit the size of the rat being tested.
The wall spacing should be narrow enough to prevent the rat from turning around while in the apparatus, but not so narrow as to impede the rat's natural walking movement. One centimeter of clearance on either side of the rat should be sufficient. Each end of the rung ladder apparatus is placed on a transport tub.
At one end is a neutral starting tub, and on the other end is the rat's familiar home tub. It may take some time for the test subject to begin and finish a crossing to keep stress levels. At a minimum, the rat should not be pushed or prodded.
It is best to let the animal cross at its own leisure. If the rat continually turns around in the apparatus, the walls may be spaced too widely. If narrowing the ladder walls does not prevent the behavior, the tester may place a hand in the crossing channel just behind the rat to score the wrong walking task.
A seven point system was devised where each paw placement on a rung receives a score ranging from zero to six. They are total miss deep slip, slight slip, replacement, correction, partial placement, and six correct Placement. A total miss Receives a score of zero and occurs when the rat's paw fails to touch a rung during an attempted placement causing the animal to fall.
A fall being defined as when a limb passes between the rungs causing body posture and balance to be disrupted. Total misses with the four Paw are rare. A deep slip occurs When a limb is placed on a rung, but slips off when weightbearing causing fall.
Deep slips of the four Paw are also rare. A slight slip occurs when a paw slips off a rung after placement, but does not result in a fall That disrupts walking. Replacement occurs when a paw is placed on a rung, but is quickly moved to another rung before bearing any weight.
A correction is when a paw aims at one rung, but is placed on another rung without touching the first rung. A correction also Occurs if a paw is placed on a rung and is quickly repositioned before bearing weight. This type of correction is rare In the hind paws.
Partial placement occurs when a paw Is placed on a rung with just the wrist or digits of a front limb or the heel and digits of a Hind limb. A correct Placement of a paw requires the midpoint of the palm to be positioned directly on top of a rung. While Fully bearing weight, a stepping cycle is Considered to have occurred when one four paw and one hind paw, typically the contralateral hind paw has contacted the rungs and fully supported the rat's weight.
These are effectively four individual steps, a four paw and a hind paw, followed by a four paw and a hind paw. This allows the rat to establish a stepping rhythm as only consecutive steps are scored. When the rat makes a stop on the ladder, the last cycle before the stop, and the first cycle after the Stop are not scored.
The last cycle before a rat reaches the end of the ladder is also not scored. Resulting errors by the other paws are not recorded. Scoring should not resume until the faulting paw Has completed one successful cycle.
