Influence of dorsal rhizotomy on a sustained avoidance response in rats

Abstract

Sustained avoidance responding was studied in each hind limb of rats before and after unilateral dorsal rhizotomy (T13 through L6, left). The subjects were required to make a change in the resting posture of the unseen hind limb, and to maintain the change, to avoid shock to a sensate area of the trunk. Two dichotomous training variables were manipulated: the presence or absence of preoperative training and the order of training of the two hind limbs. Although the animals rapidly reached criterion with sensate limbs before and after surgery, acquisition with dorsal rhizotomized (DR) limbs failed to occur except when the order of postoperative training was sensate limb:DR limb. Even then, acquisition was significantly slower with DR than intact limbs, and the topography of the avoidance response differed in the two cases. It appeared that response-related changes in body parts immediately surrounding the DR limb were not critical for successful performance, and when there was failure of acquisition, the number of training sessions was not a relevant variable. It was concluded that tonic movements cannot be acquired in the absence of peripheral topographic feedback from the responding body part, unless information concerning the general response requirement is first provided to the rat via training with a sensate limb.