The peripheral unconditioned stimulus pathway in a model learning system involving defensively conditioned heart rate...

The peripheral pathway transmitting the unconditioned stimulus information is described in a vertebrate model system for studying learning-visually conditioned heart rate change in the pigeon. In this system footshock serves as the unconditioned stimulus, and it is shown that the effective stimulation field of this stimulus, defined with respect to the unconditioned cardioacceleratory response, includes cutaneous dermatomes 21-25 (L1-Sl). The stimulus information is then transmitted by Group III and IV fibers in portions of the femoral and sciatic nerves which enter the spinal cord over segments 21-25. Further, it is shown that interrupting this pathway by section of dorsal roots 21-25 precludes establishing conditioned heart rate change with footshock as the unconditioned stimulus.