A simple and rapid test of sensorimotor function in the aged rat.

A total of 107 Fischer 344 rats (male and female, 2 to 29 months old) were tested on three tasks designed to measure sensorimotor function. In the first task, a new test of sensorimotor function, animals were required to maintain their balance on a stationary inclined Plexiglas plane for 5 s. Performance was evaluated with a series of increasing angles ranging from 25 degrees to 50 degrees in 1 degree increments (four trials/angle). The animals were also evaluated on two common tests of sensorimotor function: suspension from a wire by the forepaws and traversing a narrow, horizontal bar (three trials each). Age effects were significant (p < .043 to p < .0001) for each of the 11 dependent measures (first fall angle, threshold angle, and total falls for the inclined plane, and first, best, mean, and median latencies to fall for the remaining two tests). No relationship was observed between performance, sex, and body weight. Coefficients of variation differed between tests, with the inclined plane being the least variable and the horizontal bar the most. Importantly, the inclined plane was least likely to violate the ANOVA assumption of homogeneity of variance, a problem often encountered when measuring age-related variables. Since the inclined plane test has a relatively low degree of variability, and since the between-group variation is homogeneous, it should serve as both a useful and robust test for sensorimotor function in the aged rat.