Effects of manipulating stimulation intensity and duration on fixation of a peripherally-induced spinal reflex...

Two studies were conducted to examine the effects of manipulating stimulation intensity and duration on post-spinal-section retention of a peripherally induced postural asymmetry. In the first experiment, two groups of rats received 1-3 mA of hindlimb stimulation for 60 or 90 min followed by a spinal cord section. Even though all animals demonstrated postsection persistence of asymmetry, significant differences between the two groups of animals were not discerned. Experiment 2 was conducted to more systematically evaluate intensity and duration manipulations. Twelve groups of rats that received 1, 3, or 5 mA of stimulation for either 30, 45, 60, or 90 min were used. Significant differences were found between intensity groups when presection asymmetry, postsection asymmetry, and percentage retention measures were analyzed. Significant differences between duration groups were found only when the 90 min groups were compared with animals that were given shorter periods of stimulation and when 60 min groups were compared to 30 min groups. From these data we have concluded that the intensity of the fixating stimulus is a major determinant of the magnitude of asymmetry persistence observed after spinal section.