INSTRUMENTAL LEARNING WITHIN THE SPINAL CORD: EXPOSURE TO NONCONTINGENT SHOCK DISRUPTS LEARNING FOR AT LEAST 20 HOURS. E. D. Crown*, R. L. Joynes, A. R. Ferguson, & J. W. Grau, Department of Psychology, Texas A&M University
We have shown that spinal cord neurons are capable of supporting a simple form of instrumental learning using a variation of Horridge's (1962) Master/Yoke paradigm (Grau, Barstow, & Joynes, in press). In this paradigm, spinal rats learn to maintain their hindleg in a flexed position if they are given shock for extending their leg. These subjects, known as master rats, receive contingent shock while the yoked subjects receive shock whenever the master rat is shocked. Master rats display their learning by exhibiting an increase in the duration of the flexion response. Yoked controls that receive noncontingent shock irrespective of leg position do not exhibit a prolonged flexion response. Moreover, they later fail to learn (learning deficit) when tested with contingent shock applied to either the same, or contralateral, leg.
In Experiment 1, we attempted to take experimental control over the onset and offset of the shock stimuli, effectively emulating the noncontingent shock schedule produced by a typical master subject. We found that presenting 180, 0.08-s legshocks on a variable schedule (averaging 1 shock per 2-s) for 6 minutes disrupted learning when response contingent shock was later applied to the contralateral leg. Experiment 2 examined whether its necessary to apply noncontingent shock to the leg or whether shock to a different location (the tail) would be equally effective. We found that 180, 0.08-s tailshocks (1.5 mA, delivered via extracutaneous electrodes) also induced the learning deficit. Experiment 3 demonstrated that this deficit lasted 20 hours.
Symposium on Spinal Cord Plasticity, November 1998, Los Angeles CA.